ZOO 4070 Study Guide - Final Guide: Siblicide, Inclusive Fitness, Satin Bowerbird
2 May 2018
School
Department
Course
Professor
Killing a brother or a sister may be a common adaptive
strategy among nestling birds, benefiting both the
surviving offspring and the parents
•
Involves the death of younger offspring by their older
sibling
•
Simple push out of the net
○
Daily barrage of pecks to the head
○
Methods of execution:
•
Aka are there certain environmental conditions
under which killing a close relative is an adaptive
behaviour?
○
Are there other behaviours or biological features
that distingush them from non-siblicidal species?
○
Does siblicide promote the fitness of the individuals that
practice it, or is such behaviours pathological ?
•
Nestling birds are easy to observe
○
Because birds tend to monogamous, siblicide is
likely to involve full sublings
○
Young birds require a lot of food during first few
weeks of development --> high competition
between nestlings
○
Some avian parents may not be expending their
max possible effort toward brood's survival
○
Factors:
•
Usually lay 2 eggs
○
Eaglets hatch 3 days apart, so older one is
significantly larger
○
Elder eaglet launches relentless attack upon sibling
the moment it hatches
○
Black Eagle:
•
Brood = 3 chicks
○
Arboreal
○
Osprey:
•
Generally ground-nesting birds
○
*predict direction of aggressive between
siblings
!
Two-three chicks hatch ~4 days apart -->
considerable size disparity
○
Blue-footed booby:
•
Best in trees or reed beds
○
3-4 nestlings hatch at 1-2 day intervals
○
Fighting starts as soon as second sibling has
hatched
○
Egret:
•
Species typically lay 2 eggs, and older (more
powerful) chick kills its nestmate
!
Ex. Black easle
!
Obligate
○
Fighting does not always lead to death
!
Osprey: fighting is present in some but not
others
!
Blue-footed booby: chick may hit its sibling a
few times per day and then rapidly escalate to
a lethal rate of attach
!
Egrets: have frequency sibling fights, but
birds do not always kill each other
!
Facultative:
○
Obligate and Facultative Siblicide:
•
Most fundamental
!
*provision of additional food diminishes
nestling mortality
!
Resource competition
○
Size of food and sibling aggression link lies
in relation between intimidation and
monopolization
!
Position of bird to obtain small amount of
food from parents can be enhanced through
physical aggression or threat
!
*Ex. Great Blue Heron: birds only
express siblicidal aggression when food
is small enough to be taken directly
from parent
□
When food units are large, sublethla fishting
may be less effective
!
Provision of food to the nestlings in small units
○
Most siblicidal birds are predatory and have
hooked or pointed breaks
!
Weaponry
○
No escape
!
Spatial confinement
○
Asynchonous hatching is a behavioural
adaptations that allows for secondary
adjustment in brood size to match resource
levels
!
Competitive disparities between siblings
○
*first 4 are considered essential preconditions for
evolution of sibling aggression
Traits:
•
Natural selection should always reward the
most selfish act
!
**trouble with this is that it implies that all
organisms should be as selfish as possible
(not the case)
!
Elimination a competitor improves one's own
chance of survival, and thereby increases the
likelihood that genes promoting such behaviour will
be represented in the next generation
○
A gene's fitness also depends on the way it
influences the reproductive prospects of close
genetic relatives = inclusive fitness
!
In all siblicidal species, there is a tendency
for the victim to be the youngest in the brood
!
*usually when resources are high
in a "good" season
!
If marginal individual survives with
siblings, it represents an extra unit or
parental success (or extra reproductive
value)
□
Marginal offspring may serve as a
replacement for an elder sibling that
dies prematurely --> insurance
□
The youngest sibling is marginal in the sense
that its reproductive value can be assessed in
terms of what it adds to or subtracts from the
success of other family members
!
If the senior chick is alive but weakening and
incapable of killing the younger chick, the
younger one may be able to kill the senior
chick
!
Removing the "insurance" eggs results in a
reduction I the mean number of fledglings per
nest
!
Marginal offspring provides a greater
total reproductive value to the parents
when the brood size is smaller
□
Magnitude of the total reproductive values
depend on the size of the brood
!
Hamilton: fitness of a gene is more than its
contribution to the reproduction of the individual
○
Siblicide as an adpatation:
•
Senior sibling's own viability seems secure
!
Resources are inadequate for the survival of
both siblings
!
Two conditions must be met:
○
Average food supply is in adequate for
supporting two chicks at reasonable levels of
parental effort
!
As a result, the second chick is dispatched as
soon as possible
!
In obligate siblicide species:
○
Mean longevity of the victim is usually
greater
!
In facultative siblicide species:
○
Timing of Siblicide:
•
Evolutionary difference between obligate and
facultative forms may be function of the risk that a
junior chick poses to the welfare of its senior
sibling
○
Risk = resource consumption and potential for
bodily harm
○
If there is enough food for both chicks and if
the younger sibling can be subjugated so it
does not pose a threat, the survival of the
younger one is beneficial by increases their
inclusive fitness
!
If resources are adequate only for survival of one
chick, or if a young chick poses a significant
physical threat, the senior sibling may be expected
to destroy the younger one
○
Not a direct relationship between immediate
availability of food and level of sibling
aggression
!
Favoured in order to obviate any future
competition
!
*usually less food is delivered to nest vs.
facultative
!
Obligate siblicide --> when resources are routinely
limited and siblings tend to pose a threat to each
other
○
Increase in amount of aggressive
pecking in boobys was delayed by a
day --> aggression is controlled by a
factor that changes over time
(hunger/growth status_)
□
Once tape was removed, aggressive
pecking rate returned to normal -->
reversible response in facultative
species is sensitive to the weight level
of the senior chick
□
Tested for food supply and aggression (senior
chick's neck was taped to prevent it from
swallowing food --> pecks nest mates more
frequently)
!
Therefore, aggression is based on food
delivery rate as well
□
Junior siblings are lost from the nest at higher
rates following prolonged periods of bad
weather, when parental foraging is reduced
!
Facultative siblicide --> in circumstances in which
resources are not always limited
○
Causes of Siblicide:
•
Avian Siblicide:
Sexual-strategies theory holds that patterns in mating
behaviour exist because they are evolutionary
advantageous
•
Greater strength, size, agility,
confidence/cunning
□
Intrasexual -competition between members
of the same sex to gain preferential access to
mating partners
!
Intersexual -preferential mate choice of
opposite sexes
!
Sexual selection -evolution of characteristics that
confer a reproductive advantage to an organism
○
Darwin: showed that mate preference could affect human
evolution
•
The sex that invests more in offspring is selected to
be more discriminating in choosing a mate
○
Sex that invests less in offspring is more
competitive with members of the same sex for
sexual access to the high-investing sex
○
Trivers: parental investment of the sexes influences the
two processes of sexual selection
•
After internal fertilization, the gestation period lasts
~9 months and is usually followed by lactation
○
Consider necessary minimum parental investment by a
female:
•
Contribution of sperm
○
Consider necessary minimum parental investment by
male:
•
Disparity in parental investment means that the
replacement of a child typically cost more to females than
males
•
Where men can provide resources, women should
desire those who are able and willing to commit
those resources to her and her children
○
Parental-investment theory predicts that women will be
more choosy and selective about their mating partners
•
Hypothesis 1: short-term mating is more important
for men than women
○
Hypothesis 2: men seeking a short-term mate will
solve the problem of identifying women who are
sexually accessible
○
Hypothesis 3: men seeking a short-term mate will
minimize commitment and investment
○
Hypotheses 4-5: men seeking a short-term mate
will solve the problem of identifying fertile women,
whereas men seeking a long-term mate will solve
the problem of identifying reproductively valuable
women
○
Hypothesis 6: men seeking a long-term mate will
solve problem of paternity confidence
○
Hypothesis 7: women seeking a short-term mate
will prefer men willing to impart immediate
resources
○
Hypothesis 8: women will be more selective than
men in choosing a short-term mate
○
Hypothesis 9: women seeking a long-term mate
will prefer men who can provide resources for their
offspring
○
Sexual Strategies:
•
A women's physical appearance is the most
powerful predictor of the occupational status of the
man she marries
○
Similarities among cultures and between sexes
implies a degree of psychological unity or species
typicality that transcends geographic, racial,
political, ethnic, and sexual diversity
○
Identifying mates who show a proclivity to
cooperate and mates who show evidence of
having good parenting skills
!
Adaptive problems men and women face equally:
○
Conclusion:
•
Strategies of Human Mating:
Type of
Mating
Men's Reproductive
Challenges
Women's Reproductive
Challenges
Short-
term
Partner number
•
Identifying
women that are
sexually
accessible
•
Minimizing
cost/risk/commit
ment
•
Identifying
women who are
fertile
•
Immediate resource
extraction
•
Evaluation short-
term mates as
possible long-term
mates
•
Attaining men with
high-quality genes
•
Cultivating potential
back up mates
•
Long-
term
Paternity
confidence
•
Assessing a
woman's
reproductive value
•
Commitment
•
Identifying
women with good
parenting skills
•
Attaining women
with high-quality
genes
•
Identifying men who
are able and willing
to invest
•
Physical protection
from aggressive men
•
Identifying men who
will commit
•
Identifying men with
good parenting skills
•
Attaining men with
high-quality genes
•
The developmental trade-offs involved shape two
brain phenotypes
○
Male plainfin midshipman fish exercise alternative
reproductive tactics
•
To acquire these abilities, type I males take
longer to reach sexual maturity
!
Type I males build the nests in which females
deposit their eggs and attract the females with their
almost indefatigable humming
○
Reproductive strategy is to sneak into the
type I's nest or lie perched outside the nest's
entrance and deposit their sperm there -->
"sneaker" or "satellite" males
!
Type II males may become sexually mature earlier,
but they are smaller and do not build nests/attract
females
○
For midshipman, type I males are the largest and the only
morph capable to attracting females
•
Behavioural differences translate into differences in
the structure and function of the nervous system
○
Having two distinct male forms (each exhibiting distinct
behaviours)presents an opportunity to study a brain-
behaviour relationship
•
Behavioural trade-off exhibited reflect sexual phenotype
of the nervous system, which in tem directs the
expression of an adult individual's sexual behaviour
•
Type I males "hum" and wait the arrival of females
in nests they have built under rocks in intertidal and
tidal zones
○
Females deposit their eggs and leave the male to
guard the nest soon after spawning
○
*type II male also releases sperm while
fanning water towards the nest's opening
!
Type II males lie perched outside of or sneak into
type I male's nest and shed sperm in competition
with the type I male for the eggs
○
Type II males have the advantage in gonad
size (9x greater gonad:body weight vs. type I)
!
Type II males may therefore invest up to 15%
of their weights in testes (vs. 1% in type I)
!
On average, type I males are ~2x longer than 8x
heavier than type II males at the time of sexual
maturity
○
Similar colouration and size to type II males
!
Females only select one type I male to mate
with each season
!
Number of eggs per female increases with
body size
!
Males will mate with numerous
females
□
Each female leaves her entire clutch in the
nest of the chosen male
!
Gravid females resemble type II males in having a
large gonad:body
○
Short grunts -threat to any potential intruder
males
!
Helps females select the best male
□
Mating hums -last from minutes-hours
!
Contracting muscle causes
swimbladder to act like a drum
□
Higher vocal muscle:body weight
□
More muscle fibers with larger
diameter
□
Wider Z lines (actin overlap)
□
SR (with Ca2+) is more highly
branched
□
Muscles contain more mitochondria
□
--> better equipped to sustain
continuous singing
□
*have specializations in sonic musculature
!
Nesting type I male vocalization:
○
Nests and Songfests:
•
Apply biocytin crystals to the cut ends of the
motorneurons (that innervate and stimulate the
sonic muscles) and the biocytin would be carried
backwards from the nerve ending along an axon to
its parent cell body
○
Each pacemaker neuron connects to
motorneurons on both sides of the brain and
fire in a constant rhythm
!
Sonic motorneurons in midshipman receive direct
input from a set of pacemaker cells
○
Ventral medullary neurons form the major route
connecting the two sides of the pacemaker-
motorneuron circuit and likely make a major
contribution to coordinating the activities of both
sides of the brain --> simultaneous contraction of
both sonic muscles
○
Same ratio of nerve cells:body weight
□
Male morphs and females possess identical
circuitry
!
--> frequency of vocalizations
□
Pacemaker-motorneuron circuit in type I
males firest at a frequency higher than type I
and females
!
--> specifically adapted to fire more
frequently and without attenuation for a
longer period to support the activity of
their enlarged sonic muscle during
prespawning periods of signing
□
Cell bodies, dendrities, and axons are 1-3x
larger in type I
!
Findings:
○
Brainwork:
•
Type I males, type II males and females grow along
alternative growth trajectoris (mutually exclusive)
○
Therefore, alternative mating tactics among sexually
mature males are paralled by alternative phenotypes for
the neurons in the relevant circuit
•
GnRH --> gonadotropins
○
In all morphs
!
Type II > female > type 3
!
Testosterone:
○
Only in females
!
Estradiol:
○
Only in type I males (5x more than
testosterone)
!
11-ketotestosteron:
○
Hormonal differences:
•
**number of type II males is a function of population
density
•
Type II males reach sexual maturity fast but remain
physically and behaviourally immature with regard
to ability to vocalize
○
--> increased body size
!
--> hypertrophy of vocal motor system
!
*have increased chance of not surviving to
sexual maturity (more investment; more time)
!
Type I males delay maturation but have a fully
developed sexual behaviour repertoire
○
Heterochrony -dissociation in time between sexual
and physical maturity
○
Type II male morph developed under conditions of
intense (intra) sexual selection
○
Implies that type I male morph represents ancestral
behavioural state
○
Trade-offs:
•
Shaping Brain Sexuality:
Sexually
Polymorp
hic Traits
Type I Male Type II Male Female
Nest
building
Yes No No
Egg-
guarding
Yes No No
Body size Large Small Intermedi
ate
Gonad:B
ody Size
Small Large Large
(gravid),
Small
(spent)
Ventral
colourati
on
Olive-gray Mottled yellow Bronze
(gravid),
mottled
(spent)
Circulatin
g
Steroids
Testosterone,
11-
ketotesosterone
Testosterone Testoster
one,
estradiol
Vocal
behaviour
Hums, grunt
trains
Isolated grunts Isolated
grunts
Vocal
muscle
Large Small Small
Vocal
neurons
Large Small Small
Vocal
discharge
frequency
High Low Low
Males clear and decorate courts and build bowers at
display sites where they mate
•
Type and colour of court decorations
○
Form of bower
○
Differences:
•
Some male bowerbirds possess bright crest and body
plumage, and others do not
•
Highly sculptures structure of bower and male's use of
brightly coloured decorations may influence female mate
choice, thereby directing the evolution of these display
traits
•
More vigorous males might have better
bowers
□
Male-display traits (including bowers) might
indicate a male's vigor and quality as a sire
!
Good genes model:
○
A bower could even directly benefit a female,
protecting her from threats like predators or males
that might try to force her to copulate
○
Building bowers could even arise from an arbitrary
or pre-existing female preference, such as an
attraction to nest-like structures
○
Several over mechanisms could have driven evolution:
•
Three species employ monogamy with both
parents caring for young
!
All other bower birds are polygynous
!
All species of bowerbirds evolved from a single
ancestral species
○
Second major divergence developed between
species that build avenue bowers and maypole
bowers
○
Proposed function of incipient bowers should be
consistent with the design of the supposed ancestral
bower
○
Proposed function of earliest bowers should be
consistent with the design of modern bower types
○
Should possess compensatory behaviours,
which work in the absence of a bower to
protect females from forced copulations by
the courting male
!
Species that do not build bowers should possess
alternative solutions to the problem solved by a
bower
○
Evaluating bower-building hypotheses:
•
Display court at north end with blue, yellow
and white objects
!
Male trims leaves from above court so sun
can illuminate decorated site
!
Males of several species destroy each other's
bowers and steal decorations
!
Ex. Satin bowerbird
○
On display court, male makes vocalizations
!
Male then stops at one side of the bower
entrance, puffs up his body feathers, hold his
wings at his side and then faces the female
with a small decoration in his mouth, and
performs a series of knee bends
!
Visiting female usually lands in cover south of the
bower and then moves rapidly into the avenue
between stick walls
○
Although a female may visit several bowers,
she usually only mates with one male
!
In courtships that lead to copulation, a female in the
bower avenue crouches deeply as courtship
progresses, and a slight lifting of her tail signals her
willingness for mating
○
Males with high quality bowers (symmetrical
walls formed from thin, densely packed
sticks) and many decorations mate most often
!
Females exert strong preferences in mating, and
only a small proportion of males achieve most of
the matings
○
The higher rate of courtship success by specific
males, the significant effort of small decorations
and the fine details of bowers on mating success,
and the changes in a female's behaviour to mate
after she arrives at the male's bower indicates that a
female makes her mating decision after she arrives
at the court
○
Avenue-Bower builders:
•
Build a central "pole" surrounded by a circular
display court
○
Decorates sapling with sticks and moss
!
Most similar to ancestral bowers
!
Selects thin sapling and surrounds it
with horizontal piles of sticks
□
Covers lowest part of maypole and
court floor with fine compressed moss
mat
□
He decorates the court with small
objects and hands regurgitated fruit
pulp near the ends of the maypole
sticks
□
On courts rim and nearby logs, adds a
woody black fungi
□
Mechanism:
!
Functional correspondence between trees
used by young males and the size of
maypoles built by adults
!
Male calls and makes a countermove to
keep maypole between them
□
The female then stops moving and
male expands his bright orange head
plume, and shakes his head from side
to side, giving the female a good view
□
While shaking his head, the male
moves towards the female to copulate
□
Female arriving for courtship usually lands
on maypole and hops down to court
!
Ex. Macgregor's bowerbird
○
Maypole-Bower builders:
•
Two species of bowerbirds, clear and decorate
courts but have lost bower-building behaviour
○
Leks = courts of different males are
aggregated
!
Dominant males interrupt calls of males on
adjacent courts
!
Use of exceptionally loud calls and large
decorations and evidence of a female
preference for central males on leks suggests
that females may assess males before arriving
on the court --> little need for a bower's
protection from forced copulation
!
Males at centre of aggregation have highest mating
success
○
Bowerbirds without bowers:
•
Female not prepared to mate can escape
!
Bowers provide barrier that protects a visiting
female from forced copulation from a courting mal
○
Bowers allow female to observe court decorations
from a close range with reduced threat of forced
copulation
○
Toothbill -females select desirable males
before arriving on court (do not need
protection of bower)
!
Archold's -male while courting allows
female to escape
!
Birds that do not build bowers:
○
A female that freely chooses her male should
also be less likely to mate with another male
!
Combination of behaviours provides bower-
building males with increased visitation by
females and a high chance of being a female's
only mate
!
Protection of bower probably attracts females and
increases their visitation, which more than
compensates a male for losing forced copulations
○
If bowers served originally as protection
against aggressive attacks from courting
males, the evolution of the avenuebowers
would require the loss of that function and
replacement by others
!
**unlikely
!
In some species, males attach visiting females -->
would be protected by bower (only in maypole
bowers)
○
Tendency for females to choose vigorous
males and the intense athletic displays of
males in species with widely separated
bowers
!
*seems unlikely early in evolution
(when only a few males have bowers)
□
Female might assess a male's genetic quality
from his ability to maintain his bower in the
face of destruction by rivals
!
Assessing male quality by his bower
probably arose as a secondary function after
bower building evolved
!
Good-genes hypothesis:
○
Suggest that female preferences and male
traits evolve together, driven by a mating
advantage gained by males that possess an
extreme version of the trait (bower building)
!
No evidence suggests that males with larger
bowers mate more
!
No evidence of high cost, despite strong
effects of bower quality on mating success
!
Runaway model:
○
Predation hypothesis seems unlikely as well
○
Why build bowers?
•
First bowers consisted of a sapling on a display
court
○
A court with a natural barrier could separate a
female from a courting male and allow her to
closely observe the male's display and decorations
without committing to mating
○
Utilize a much wider range of saplings by
enhancing the diameter with sticks
!
Soft edge created allows males and females
to observe and anticipate each other
!
Stick-built bowers would have been an
improvement --> enhance court's protective
qualities --> simple maypole bower
!
By placing sticks around a sapling, male would be
less constrained by sapling size and location
○
Bower form could diversify to serve other
functions
!
Free-standing stick barriers would allow
males even more freedom in selecting bower
sites and in concentrating decorations
!
Two trends could then emerge:
○
Required losing use of sapling as bower
support and addition of different barrier
!
Two walled barrier --> orients female
towards parts of the court with concentrated
decorations of well-lit stage for male's
advantage
!
Decorations are a complementary colour to
male's crest and probably increase contrast of
his display
!
Avenue bowers:
○
Degree of male head-crest elaboration
correlates inversely with number of
decorations in maypole bowers?
!
Development of complex bowers may have
strongly influenced the use of decorations and
evolution of male plumage
○
Behaviour contracts with most avenus
builders that either have reduced/no crest and
build more complex bowers
!
Macgregors & Archbold's decorations are spread
widely around bower (both have well developed
crests)
○
Simple/no bowers: position of males and females
varies during displays, and for females to see bright
colours, males must carry bright plumage
○
Costly bright plumage may be replaced by
strategically located arrays of decorations
!
More complex bowers: focus a female's attention
on concentrations of decorations
○
--> females seek protection from unwanted mating
○
Evolution:
•
Bowerbirds:
Readings for Final
Monday,*December* 4,*2017
12:12*PM
Killing a brother or a sister may be a common adaptive
strategy among nestling birds, benefiting both the
surviving offspring and the parents
•
Involves the death of younger offspring by their older
sibling
•
Simple push out of the net
○
Daily barrage of pecks to the head
○
Methods of execution:
•
Aka are there certain environmental conditions
under which killing a close relative is an adaptive
behaviour?
○
Are there other behaviours or biological features
that distingush them from non-siblicidal species?
○
Does siblicide promote the fitness of the individuals that
practice it, or is such behaviours pathological ?
•
Nestling birds are easy to observe
○
Because birds tend to monogamous, siblicide is
likely to involve full sublings
○
Young birds require a lot of food during first few
weeks of development --> high competition
between nestlings
○
Some avian parents may not be expending their
max possible effort toward brood's survival
○
Factors:
•
Usually lay 2 eggs
○
Eaglets hatch 3 days apart, so older one is
significantly larger
○
Elder eaglet launches relentless attack upon sibling
the moment it hatches
○
Black Eagle:
•
Brood = 3 chicks
○
Arboreal
○
Osprey:
•
Generally ground-nesting birds
○
*predict direction of aggressive between
siblings
!
Two-three chicks hatch ~4 days apart -->
considerable size disparity
○
Blue-footed booby:
•
Best in trees or reed beds
○
3-4 nestlings hatch at 1-2 day intervals
○
Fighting starts as soon as second sibling has
hatched
○
Egret:
•
Species typically lay 2 eggs, and older (more
powerful) chick kills its nestmate
!
Ex. Black easle
!
Obligate
○
Fighting does not always lead to death
!
Osprey: fighting is present in some but not
others
!
Blue-footed booby: chick may hit its sibling a
few times per day and then rapidly escalate to
a lethal rate of attach
!
Egrets: have frequency sibling fights, but
birds do not always kill each other
!
Facultative:
○
Obligate and Facultative Siblicide:
•
Most fundamental
!
*provision of additional food diminishes
nestling mortality
!
Resource competition
○
Size of food and sibling aggression link lies
in relation between intimidation and
monopolization
!
Position of bird to obtain small amount of
food from parents can be enhanced through
physical aggression or threat
!
*Ex. Great Blue Heron: birds only
express siblicidal aggression when food
is small enough to be taken directly
from parent
□
When food units are large, sublethla fishting
may be less effective
!
Provision of food to the nestlings in small units
○
Most siblicidal birds are predatory and have
hooked or pointed breaks
!
Weaponry
○
No escape
!
Spatial confinement
○
Asynchonous hatching is a behavioural
adaptations that allows for secondary
adjustment in brood size to match resource
levels
!
Competitive disparities between siblings
○
*first 4 are considered essential preconditions for
evolution of sibling aggression
Traits:
•
Natural selection should always reward the
most selfish act
!
**trouble with this is that it implies that all
organisms should be as selfish as possible
(not the case)
!
Elimination a competitor improves one's own
chance of survival, and thereby increases the
likelihood that genes promoting such behaviour will
be represented in the next generation
○
A gene's fitness also depends on the way it
influences the reproductive prospects of close
genetic relatives = inclusive fitness
!
In all siblicidal species, there is a tendency
for the victim to be the youngest in the brood
!
*usually when resources are high
in a "good" season
!
If marginal individual survives with
siblings, it represents an extra unit or
parental success (or extra reproductive
value)
□
Marginal offspring may serve as a
replacement for an elder sibling that
dies prematurely --> insurance
□
The youngest sibling is marginal in the sense
that its reproductive value can be assessed in
terms of what it adds to or subtracts from the
success of other family members
!
If the senior chick is alive but weakening and
incapable of killing the younger chick, the
younger one may be able to kill the senior
chick
!
Removing the "insurance" eggs results in a
reduction I the mean number of fledglings per
nest
!
Marginal offspring provides a greater
total reproductive value to the parents
when the brood size is smaller
□
Magnitude of the total reproductive values
depend on the size of the brood
!
Hamilton: fitness of a gene is more than its
contribution to the reproduction of the individual
○
Siblicide as an adpatation:
•
Senior sibling's own viability seems secure
!
Resources are inadequate for the survival of
both siblings
!
Two conditions must be met:
○
Average food supply is in adequate for
supporting two chicks at reasonable levels of
parental effort
!
As a result, the second chick is dispatched as
soon as possible
!
In obligate siblicide species:
○
Mean longevity of the victim is usually
greater
!
In facultative siblicide species:
○
Timing of Siblicide:
•
Evolutionary difference between obligate and
facultative forms may be function of the risk that a
junior chick poses to the welfare of its senior
sibling
○
Risk = resource consumption and potential for
bodily harm
○
If there is enough food for both chicks and if
the younger sibling can be subjugated so it
does not pose a threat, the survival of the
younger one is beneficial by increases their
inclusive fitness
!
If resources are adequate only for survival of one
chick, or if a young chick poses a significant
physical threat, the senior sibling may be expected
to destroy the younger one
○
Not a direct relationship between immediate
availability of food and level of sibling
aggression
!
Favoured in order to obviate any future
competition
!
*usually less food is delivered to nest vs.
facultative
!
Obligate siblicide --> when resources are routinely
limited and siblings tend to pose a threat to each
other
○
Increase in amount of aggressive
pecking in boobys was delayed by a
day --> aggression is controlled by a
factor that changes over time
(hunger/growth status_)
□
Once tape was removed, aggressive
pecking rate returned to normal -->
reversible response in facultative
species is sensitive to the weight level
of the senior chick
□
Tested for food supply and aggression (senior
chick's neck was taped to prevent it from
swallowing food --> pecks nest mates more
frequently)
!
Therefore, aggression is based on food
delivery rate as well
□
Junior siblings are lost from the nest at higher
rates following prolonged periods of bad
weather, when parental foraging is reduced
!
Facultative siblicide --> in circumstances in which
resources are not always limited
○
Causes of Siblicide:
•
Avian Siblicide:
Sexual-strategies theory holds that patterns in mating
behaviour exist because they are evolutionary
advantageous
•
Greater strength, size, agility,
confidence/cunning
□
Intrasexual -competition between members
of the same sex to gain preferential access to
mating partners
!
Intersexual -preferential mate choice of
opposite sexes
!
Sexual selection -evolution of characteristics that
confer a reproductive advantage to an organism
○
Darwin: showed that mate preference could affect human
evolution
•
The sex that invests more in offspring is selected to
be more discriminating in choosing a mate
○
Sex that invests less in offspring is more
competitive with members of the same sex for
sexual access to the high-investing sex
○
Trivers: parental investment of the sexes influences the
two processes of sexual selection
•
After internal fertilization, the gestation period lasts
~9 months and is usually followed by lactation
○
Consider necessary minimum parental investment by a
female:
•
Contribution of sperm
○
Consider necessary minimum parental investment by
male:
•
Disparity in parental investment means that the
replacement of a child typically cost more to females than
males
•
Where men can provide resources, women should
desire those who are able and willing to commit
those resources to her and her children
○
Parental-investment theory predicts that women will be
more choosy and selective about their mating partners
•
Hypothesis 1: short-term mating is more important
for men than women
○
Hypothesis 2: men seeking a short-term mate will
solve the problem of identifying women who are
sexually accessible
○
Hypothesis 3: men seeking a short-term mate will
minimize commitment and investment
○
Hypotheses 4-5: men seeking a short-term mate
will solve the problem of identifying fertile women,
whereas men seeking a long-term mate will solve
the problem of identifying reproductively valuable
women
○
Hypothesis 6: men seeking a long-term mate will
solve problem of paternity confidence
○
Hypothesis 7: women seeking a short-term mate
will prefer men willing to impart immediate
resources
○
Hypothesis 8: women will be more selective than
men in choosing a short-term mate
○
Hypothesis 9: women seeking a long-term mate
will prefer men who can provide resources for their
offspring
○
Sexual Strategies:
•
A women's physical appearance is the most
powerful predictor of the occupational status of the
man she marries
○
Similarities among cultures and between sexes
implies a degree of psychological unity or species
typicality that transcends geographic, racial,
political, ethnic, and sexual diversity
○
Identifying mates who show a proclivity to
cooperate and mates who show evidence of
having good parenting skills
!
Adaptive problems men and women face equally:
○
Conclusion:
•
Strategies of Human Mating:
Type of
Mating
Men's Reproductive
Challenges
Women's Reproductive
Challenges
Short-
term
Partner number
•
Identifying
women that are
sexually
accessible
•
Minimizing
cost/risk/commit
ment
•
Identifying
women who are
fertile
•
Immediate resource
extraction
•
Evaluation short-
term mates as
possible long-term
mates
•
Attaining men with
high-quality genes
•
Cultivating potential
back up mates
•
Long-
term
Paternity
confidence
•
Assessing a
woman's
reproductive value
•
Commitment
•
Identifying
women with good
parenting skills
•
Attaining women
with high-quality
genes
•
Identifying men who
are able and willing
to invest
•
Physical protection
from aggressive men
•
Identifying men who
will commit
•
Identifying men with
good parenting skills
•
Attaining men with
high-quality genes
•
The developmental trade-offs involved shape two
brain phenotypes
○
Male plainfin midshipman fish exercise alternative
reproductive tactics
•
To acquire these abilities, type I males take
longer to reach sexual maturity
!
Type I males build the nests in which females
deposit their eggs and attract the females with their
almost indefatigable humming
○
Reproductive strategy is to sneak into the
type I's nest or lie perched outside the nest's
entrance and deposit their sperm there -->
"sneaker" or "satellite" males
!
Type II males may become sexually mature earlier,
but they are smaller and do not build nests/attract
females
○
For midshipman, type I males are the largest and the only
morph capable to attracting females
•
Behavioural differences translate into differences in
the structure and function of the nervous system
○
Having two distinct male forms (each exhibiting distinct
behaviours)presents an opportunity to study a brain-
behaviour relationship
•
Behavioural trade-off exhibited reflect sexual phenotype
of the nervous system, which in tem directs the
expression of an adult individual's sexual behaviour
•
Type I males "hum" and wait the arrival of females
in nests they have built under rocks in intertidal and
tidal zones
○
Females deposit their eggs and leave the male to
guard the nest soon after spawning
○
*type II male also releases sperm while
fanning water towards the nest's opening
!
Type II males lie perched outside of or sneak into
type I male's nest and shed sperm in competition
with the type I male for the eggs
○
Type II males have the advantage in gonad
size (9x greater gonad:body weight vs. type I)
!
Type II males may therefore invest up to 15%
of their weights in testes (vs. 1% in type I)
!
On average, type I males are ~2x longer than 8x
heavier than type II males at the time of sexual
maturity
○
Similar colouration and size to type II males
!
Females only select one type I male to mate
with each season
!
Number of eggs per female increases with
body size
!
Males will mate with numerous
females
□
Each female leaves her entire clutch in the
nest of the chosen male
!
Gravid females resemble type II males in having a
large gonad:body
○
Short grunts -threat to any potential intruder
males
!
Helps females select the best male
□
Mating hums -last from minutes-hours
!
Contracting muscle causes
swimbladder to act like a drum
□
Higher vocal muscle:body weight
□
More muscle fibers with larger
diameter
□
Wider Z lines (actin overlap)
□
SR (with Ca2+) is more highly
branched
□
Muscles contain more mitochondria
□
--> better equipped to sustain
continuous singing
□
*have specializations in sonic musculature
!
Nesting type I male vocalization:
○
Nests and Songfests:
•
Apply biocytin crystals to the cut ends of the
motorneurons (that innervate and stimulate the
sonic muscles) and the biocytin would be carried
backwards from the nerve ending along an axon to
its parent cell body
○
Each pacemaker neuron connects to
motorneurons on both sides of the brain and
fire in a constant rhythm
!
Sonic motorneurons in midshipman receive direct
input from a set of pacemaker cells
○
Ventral medullary neurons form the major route
connecting the two sides of the pacemaker-
motorneuron circuit and likely make a major
contribution to coordinating the activities of both
sides of the brain --> simultaneous contraction of
both sonic muscles
○
Same ratio of nerve cells:body weight
□
Male morphs and females possess identical
circuitry
!
--> frequency of vocalizations
□
Pacemaker-motorneuron circuit in type I
males firest at a frequency higher than type I
and females
!
--> specifically adapted to fire more
frequently and without attenuation for a
longer period to support the activity of
their enlarged sonic muscle during
prespawning periods of signing
□
Cell bodies, dendrities, and axons are 1-3x
larger in type I
!
Findings:
○
Brainwork:
•
Type I males, type II males and females grow along
alternative growth trajectoris (mutually exclusive)
○
Therefore, alternative mating tactics among sexually
mature males are paralled by alternative phenotypes for
the neurons in the relevant circuit
•
GnRH --> gonadotropins
○
In all morphs
!
Type II > female > type 3
!
Testosterone:
○
Only in females
!
Estradiol:
○
Only in type I males (5x more than
testosterone)
!
11-ketotestosteron:
○
Hormonal differences:
•
**number of type II males is a function of population
density
•
Type II males reach sexual maturity fast but remain
physically and behaviourally immature with regard
to ability to vocalize
○
--> increased body size
!
--> hypertrophy of vocal motor system
!
*have increased chance of not surviving to
sexual maturity (more investment; more time)
!
Type I males delay maturation but have a fully
developed sexual behaviour repertoire
○
Heterochrony -dissociation in time between sexual
and physical maturity
○
Type II male morph developed under conditions of
intense (intra) sexual selection
○
Implies that type I male morph represents ancestral
behavioural state
○
Trade-offs:
•
Shaping Brain Sexuality:
Sexually
Polymorp
hic Traits
Type I Male Type II Male Female
Nest
building
Yes No No
Egg-
guarding
Yes No No
Body size Large Small Intermedi
ate
Gonad:B
ody Size
Small Large Large
(gravid),
Small
(spent)
Ventral
colourati
on
Olive-gray Mottled yellow Bronze
(gravid),
mottled
(spent)
Circulatin
g
Steroids
Testosterone,
11-
ketotesosterone
Testosterone Testoster
one,
estradiol
Vocal
behaviour
Hums, grunt
trains
Isolated grunts Isolated
grunts
Vocal
muscle
Large Small Small
Vocal
neurons
Large Small Small
Vocal
discharge
frequency
High Low Low
Males clear and decorate courts and build bowers at
display sites where they mate
•
Type and colour of court decorations
○
Form of bower
○
Differences:
•
Some male bowerbirds possess bright crest and body
plumage, and others do not
•
Highly sculptures structure of bower and male's use of
brightly coloured decorations may influence female mate
choice, thereby directing the evolution of these display
traits
•
More vigorous males might have better
bowers
□
Male-display traits (including bowers) might
indicate a male's vigor and quality as a sire
!
Good genes model:
○
A bower could even directly benefit a female,
protecting her from threats like predators or males
that might try to force her to copulate
○
Building bowers could even arise from an arbitrary
or pre-existing female preference, such as an
attraction to nest-like structures
○
Several over mechanisms could have driven evolution:
•
Three species employ monogamy with both
parents caring for young
!
All other bower birds are polygynous
!
All species of bowerbirds evolved from a single
ancestral species
○
Second major divergence developed between
species that build avenue bowers and maypole
bowers
○
Proposed function of incipient bowers should be
consistent with the design of the supposed ancestral
bower
○
Proposed function of earliest bowers should be
consistent with the design of modern bower types
○
Should possess compensatory behaviours,
which work in the absence of a bower to
protect females from forced copulations by
the courting male
!
Species that do not build bowers should possess
alternative solutions to the problem solved by a
bower
○
Evaluating bower-building hypotheses:
•
Display court at north end with blue, yellow
and white objects
!
Male trims leaves from above court so sun
can illuminate decorated site
!
Males of several species destroy each other's
bowers and steal decorations
!
Ex. Satin bowerbird
○
On display court, male makes vocalizations
!
Male then stops at one side of the bower
entrance, puffs up his body feathers, hold his
wings at his side and then faces the female
with a small decoration in his mouth, and
performs a series of knee bends
!
Visiting female usually lands in cover south of the
bower and then moves rapidly into the avenue
between stick walls
○
Although a female may visit several bowers,
she usually only mates with one male
!
In courtships that lead to copulation, a female in the
bower avenue crouches deeply as courtship
progresses, and a slight lifting of her tail signals her
willingness for mating
○
Males with high quality bowers (symmetrical
walls formed from thin, densely packed
sticks) and many decorations mate most often
!
Females exert strong preferences in mating, and
only a small proportion of males achieve most of
the matings
○
The higher rate of courtship success by specific
males, the significant effort of small decorations
and the fine details of bowers on mating success,
and the changes in a female's behaviour to mate
after she arrives at the male's bower indicates that a
female makes her mating decision after she arrives
at the court
○
Avenue-Bower builders:
•
Build a central "pole" surrounded by a circular
display court
○
Decorates sapling with sticks and moss
!
Most similar to ancestral bowers
!
Selects thin sapling and surrounds it
with horizontal piles of sticks
□
Covers lowest part of maypole and
court floor with fine compressed moss
mat
□
He decorates the court with small
objects and hands regurgitated fruit
pulp near the ends of the maypole
sticks
□
On courts rim and nearby logs, adds a
woody black fungi
□
Mechanism:
!
Functional correspondence between trees
used by young males and the size of
maypoles built by adults
!
Male calls and makes a countermove to
keep maypole between them
□
The female then stops moving and
male expands his bright orange head
plume, and shakes his head from side
to side, giving the female a good view
□
While shaking his head, the male
moves towards the female to copulate
□
Female arriving for courtship usually lands
on maypole and hops down to court
!
Ex. Macgregor's bowerbird
○
Maypole-Bower builders:
•
Two species of bowerbirds, clear and decorate
courts but have lost bower-building behaviour
○
Leks = courts of different males are
aggregated
!
Dominant males interrupt calls of males on
adjacent courts
!
Use of exceptionally loud calls and large
decorations and evidence of a female
preference for central males on leks suggests
that females may assess males before arriving
on the court --> little need for a bower's
protection from forced copulation
!
Males at centre of aggregation have highest mating
success
○
Bowerbirds without bowers:
•
Female not prepared to mate can escape
!
Bowers provide barrier that protects a visiting
female from forced copulation from a courting mal
○
Bowers allow female to observe court decorations
from a close range with reduced threat of forced
copulation
○
Toothbill -females select desirable males
before arriving on court (do not need
protection of bower)
!
Archold's -male while courting allows
female to escape
!
Birds that do not build bowers:
○
A female that freely chooses her male should
also be less likely to mate with another male
!
Combination of behaviours provides bower-
building males with increased visitation by
females and a high chance of being a female's
only mate
!
Protection of bower probably attracts females and
increases their visitation, which more than
compensates a male for losing forced copulations
○
If bowers served originally as protection
against aggressive attacks from courting
males, the evolution of the avenuebowers
would require the loss of that function and
replacement by others
!
**unlikely
!
In some species, males attach visiting females -->
would be protected by bower (only in maypole
bowers)
○
Tendency for females to choose vigorous
males and the intense athletic displays of
males in species with widely separated
bowers
!
*seems unlikely early in evolution
(when only a few males have bowers)
□
Female might assess a male's genetic quality
from his ability to maintain his bower in the
face of destruction by rivals
!
Assessing male quality by his bower
probably arose as a secondary function after
bower building evolved
!
Good-genes hypothesis:
○
Suggest that female preferences and male
traits evolve together, driven by a mating
advantage gained by males that possess an
extreme version of the trait (bower building)
!
No evidence suggests that males with larger
bowers mate more
!
No evidence of high cost, despite strong
effects of bower quality on mating success
!
Runaway model:
○
Predation hypothesis seems unlikely as well
○
Why build bowers?
•
First bowers consisted of a sapling on a display
court
○
A court with a natural barrier could separate a
female from a courting male and allow her to
closely observe the male's display and decorations
without committing to mating
○
Utilize a much wider range of saplings by
enhancing the diameter with sticks
!
Soft edge created allows males and females
to observe and anticipate each other
!
Stick-built bowers would have been an
improvement --> enhance court's protective
qualities --> simple maypole bower
!
By placing sticks around a sapling, male would be
less constrained by sapling size and location
○
Bower form could diversify to serve other
functions
!
Free-standing stick barriers would allow
males even more freedom in selecting bower
sites and in concentrating decorations
!
Two trends could then emerge:
○
Required losing use of sapling as bower
support and addition of different barrier
!
Two walled barrier --> orients female
towards parts of the court with concentrated
decorations of well-lit stage for male's
advantage
!
Decorations are a complementary colour to
male's crest and probably increase contrast of
his display
!
Avenue bowers:
○
Degree of male head-crest elaboration
correlates inversely with number of
decorations in maypole bowers?
!
Development of complex bowers may have
strongly influenced the use of decorations and
evolution of male plumage
○
Behaviour contracts with most avenus
builders that either have reduced/no crest and
build more complex bowers
!
Macgregors & Archbold's decorations are spread
widely around bower (both have well developed
crests)
○
Simple/no bowers: position of males and females
varies during displays, and for females to see bright
colours, males must carry bright plumage
○
Costly bright plumage may be replaced by
strategically located arrays of decorations
!
More complex bowers: focus a female's attention
on concentrations of decorations
○
--> females seek protection from unwanted mating
○
Evolution:
•
Bowerbirds:
Readings for Final
Monday,*December* 4,*2017 12:12*PM
Killing a brother or a sister may be a common adaptive
strategy among nestling birds, benefiting both the
surviving offspring and the parents
•
Involves the death of younger offspring by their older
sibling
•
Simple push out of the net
○
Daily barrage of pecks to the head
○
Methods of execution:
•
Aka are there certain environmental conditions
under which killing a close relative is an adaptive
behaviour?
○
Are there other behaviours or biological features
that distingush them from non-siblicidal species?
○
Does siblicide promote the fitness of the individuals that
practice it, or is such behaviours pathological ?
•
Nestling birds are easy to observe
○
Because birds tend to monogamous, siblicide is
likely to involve full sublings
○
Young birds require a lot of food during first few
weeks of development --> high competition
between nestlings
○
Some avian parents may not be expending their
max possible effort toward brood's survival
○
Factors:
•
Usually lay 2 eggs
○
Eaglets hatch 3 days apart, so older one is
significantly larger
○
Elder eaglet launches relentless attack upon sibling
the moment it hatches
○
Black Eagle:
•
Brood = 3 chicks
○
Arboreal
○
Osprey:
•
Generally ground-nesting birds
○
*predict direction of aggressive between
siblings
!
Two-three chicks hatch ~4 days apart -->
considerable size disparity
○
Blue-footed booby:
•
Best in trees or reed beds
○
3-4 nestlings hatch at 1-2 day intervals
○
Fighting starts as soon as second sibling has
hatched
○
Egret:
•
Species typically lay 2 eggs, and older (more
powerful) chick kills its nestmate
!
Ex. Black easle
!
Obligate
○
Fighting does not always lead to death
!
Osprey: fighting is present in some but not
others
!
Blue-footed booby: chick may hit its sibling a
few times per day and then rapidly escalate to
a lethal rate of attach
!
Egrets: have frequency sibling fights, but
birds do not always kill each other
!
Facultative:
○
Obligate and Facultative Siblicide:
•
Most fundamental
!
*provision of additional food diminishes
nestling mortality
!
Resource competition
○
Size of food and sibling aggression link lies
in relation between intimidation and
monopolization
!
Position of bird to obtain small amount of
food from parents can be enhanced through
physical aggression or threat
!
*Ex. Great Blue Heron: birds only
express siblicidal aggression when food
is small enough to be taken directly
from parent
□
When food units are large, sublethla fishting
may be less effective
!
Provision of food to the nestlings in small units
○
Most siblicidal birds are predatory and have
hooked or pointed breaks
!
Weaponry
○
No escape
!
Spatial confinement
○
Asynchonous hatching is a behavioural
adaptations that allows for secondary
adjustment in brood size to match resource
levels
!
Competitive disparities between siblings
○
*first 4 are considered essential preconditions for
evolution of sibling aggression
Traits:
•
Natural selection should always reward the
most selfish act
!
**trouble with this is that it implies that all
organisms should be as selfish as possible
(not the case)
!
Elimination a competitor improves one's own
chance of survival, and thereby increases the
likelihood that genes promoting such behaviour will
be represented in the next generation
○
A gene's fitness also depends on the way it
influences the reproductive prospects of close
genetic relatives = inclusive fitness
!
In all siblicidal species, there is a tendency
for the victim to be the youngest in the brood
!
*usually when resources are high
in a "good" season
!
If marginal individual survives with
siblings, it represents an extra unit or
parental success (or extra reproductive
value)
□
Marginal offspring may serve as a
replacement for an elder sibling that
dies prematurely --> insurance
□
The youngest sibling is marginal in the sense
that its reproductive value can be assessed in
terms of what it adds to or subtracts from the
success of other family members
!
If the senior chick is alive but weakening and
incapable of killing the younger chick, the
younger one may be able to kill the senior
chick
!
Removing the "insurance" eggs results in a
reduction I the mean number of fledglings per
nest
!
Marginal offspring provides a greater
total reproductive value to the parents
when the brood size is smaller
□
Magnitude of the total reproductive values
depend on the size of the brood
!
Hamilton: fitness of a gene is more than its
contribution to the reproduction of the individual
○
Siblicide as an adpatation:
•
Senior sibling's own viability seems secure
!
Resources are inadequate for the survival of
both siblings
!
Two conditions must be met:
○
Average food supply is in adequate for
supporting two chicks at reasonable levels of
parental effort
!
As a result, the second chick is dispatched as
soon as possible
!
In obligate siblicide species:
○
Mean longevity of the victim is usually
greater
!
In facultative siblicide species:
○
Timing of Siblicide:
•
Evolutionary difference between obligate and
facultative forms may be function of the risk that a
junior chick poses to the welfare of its senior
sibling
○
Risk = resource consumption and potential for
bodily harm
○
If there is enough food for both chicks and if
the younger sibling can be subjugated so it
does not pose a threat, the survival of the
younger one is beneficial by increases their
inclusive fitness
!
If resources are adequate only for survival of one
chick, or if a young chick poses a significant
physical threat, the senior sibling may be expected
to destroy the younger one
○
Not a direct relationship between immediate
availability of food and level of sibling
aggression
!
Favoured in order to obviate any future
competition
!
*usually less food is delivered to nest vs.
facultative
!
Obligate siblicide --> when resources are routinely
limited and siblings tend to pose a threat to each
other
○
Increase in amount of aggressive
pecking in boobys was delayed by a
day --> aggression is controlled by a
factor that changes over time
(hunger/growth status_)
□
Once tape was removed, aggressive
pecking rate returned to normal -->
reversible response in facultative
species is sensitive to the weight level
of the senior chick
□
Tested for food supply and aggression (senior
chick's neck was taped to prevent it from
swallowing food --> pecks nest mates more
frequently)
!
Therefore, aggression is based on food
delivery rate as well
□
Junior siblings are lost from the nest at higher
rates following prolonged periods of bad
weather, when parental foraging is reduced
!
Facultative siblicide --> in circumstances in which
resources are not always limited
○
Causes of Siblicide:
•
Avian Siblicide:
Sexual-strategies theory holds that patterns in mating
behaviour exist because they are evolutionary
advantageous
•
Greater strength, size, agility,
confidence/cunning
□
Intrasexual -competition between members
of the same sex to gain preferential access to
mating partners
!
Intersexual -preferential mate choice of
opposite sexes
!
Sexual selection -evolution of characteristics that
confer a reproductive advantage to an organism
○
Darwin: showed that mate preference could affect human
evolution
•
The sex that invests more in offspring is selected to
be more discriminating in choosing a mate
○
Sex that invests less in offspring is more
competitive with members of the same sex for
sexual access to the high-investing sex
○
Trivers: parental investment of the sexes influences the
two processes of sexual selection
•
After internal fertilization, the gestation period lasts
~9 months and is usually followed by lactation
○
Consider necessary minimum parental investment by a
female:
•
Contribution of sperm
○
Consider necessary minimum parental investment by
male:
•
Disparity in parental investment means that the
replacement of a child typically cost more to females than
males
•
Where men can provide resources, women should
desire those who are able and willing to commit
those resources to her and her children
○
Parental-investment theory predicts that women will be
more choosy and selective about their mating partners
•
Hypothesis 1: short-term mating is more important
for men than women
○
Hypothesis 2: men seeking a short-term mate will
solve the problem of identifying women who are
sexually accessible
○
Hypothesis 3: men seeking a short-term mate will
minimize commitment and investment
○
Hypotheses 4-5: men seeking a short-term mate
will solve the problem of identifying fertile women,
whereas men seeking a long-term mate will solve
the problem of identifying reproductively valuable
women
○
Hypothesis 6: men seeking a long-term mate will
solve problem of paternity confidence
○
Hypothesis 7: women seeking a short-term mate
will prefer men willing to impart immediate
resources
○
Hypothesis 8: women will be more selective than
men in choosing a short-term mate
○
Hypothesis 9: women seeking a long-term mate
will prefer men who can provide resources for their
offspring
○
Sexual Strategies:
•
A women's physical appearance is the most
powerful predictor of the occupational status of the
man she marries
○
Similarities among cultures and between sexes
implies a degree of psychological unity or species
typicality that transcends geographic, racial,
political, ethnic, and sexual diversity
○
Identifying mates who show a proclivity to
cooperate and mates who show evidence of
having good parenting skills
!
Adaptive problems men and women face equally:
○
Conclusion:
•
Strategies of Human Mating:
Type of
Mating
Men's Reproductive
Challenges
Women's Reproductive
Challenges
Short-
term
Partner number
•
Identifying
women that are
sexually
accessible
•
Minimizing
cost/risk/commit
ment
•
Identifying
women who are
fertile
•
Immediate resource
extraction
•
Evaluation short-
term mates as
possible long-term
mates
•
Attaining men with
high-quality genes
•
Cultivating potential
back up mates
•
Long-
term
Paternity
confidence
•
Assessing a
woman's
reproductive value
•
Commitment
•
Identifying
women with good
parenting skills
•
Attaining women
with high-quality
genes
•
Identifying men who
are able and willing
to invest
•
Physical protection
from aggressive men
•
Identifying men who
will commit
•
Identifying men with
good parenting skills
•
Attaining men with
high-quality genes
•
The developmental trade-offs involved shape two
brain phenotypes
○
Male plainfin midshipman fish exercise alternative
reproductive tactics
•
To acquire these abilities, type I males take
longer to reach sexual maturity
!
Type I males build the nests in which females
deposit their eggs and attract the females with their
almost indefatigable humming
○
Reproductive strategy is to sneak into the
type I's nest or lie perched outside the nest's
entrance and deposit their sperm there -->
"sneaker" or "satellite" males
!
Type II males may become sexually mature earlier,
but they are smaller and do not build nests/attract
females
○
For midshipman, type I males are the largest and the only
morph capable to attracting females
•
Behavioural differences translate into differences in
the structure and function of the nervous system
○
Having two distinct male forms (each exhibiting distinct
behaviours)presents an opportunity to study a brain-
behaviour relationship
•
Behavioural trade-off exhibited reflect sexual phenotype
of the nervous system, which in tem directs the
expression of an adult individual's sexual behaviour
•
Type I males "hum" and wait the arrival of females
in nests they have built under rocks in intertidal and
tidal zones
○
Females deposit their eggs and leave the male to
guard the nest soon after spawning
○
*type II male also releases sperm while
fanning water towards the nest's opening
!
Type II males lie perched outside of or sneak into
type I male's nest and shed sperm in competition
with the type I male for the eggs
○
Type II males have the advantage in gonad
size (9x greater gonad:body weight vs. type I)
!
Type II males may therefore invest up to 15%
of their weights in testes (vs. 1% in type I)
!
On average, type I males are ~2x longer than 8x
heavier than type II males at the time of sexual
maturity
○
Similar colouration and size to type II males
!
Females only select one type I male to mate
with each season
!
Number of eggs per female increases with
body size
!
Males will mate with numerous
females
□
Each female leaves her entire clutch in the
nest of the chosen male
!
Gravid females resemble type II males in having a
large gonad:body
○
Short grunts -threat to any potential intruder
males
!
Helps females select the best male
□
Mating hums -last from minutes-hours
!
Contracting muscle causes
swimbladder to act like a drum
□
Higher vocal muscle:body weight
□
More muscle fibers with larger
diameter
□
Wider Z lines (actin overlap)
□
SR (with Ca2+) is more highly
branched
□
Muscles contain more mitochondria
□
--> better equipped to sustain
continuous singing
□
*have specializations in sonic musculature
!
Nesting type I male vocalization:
○
Nests and Songfests:
•
Apply biocytin crystals to the cut ends of the
motorneurons (that innervate and stimulate the
sonic muscles) and the biocytin would be carried
backwards from the nerve ending along an axon to
its parent cell body
○
Each pacemaker neuron connects to
motorneurons on both sides of the brain and
fire in a constant rhythm
!
Sonic motorneurons in midshipman receive direct
input from a set of pacemaker cells
○
Ventral medullary neurons form the major route
connecting the two sides of the pacemaker-
motorneuron circuit and likely make a major
contribution to coordinating the activities of both
sides of the brain --> simultaneous contraction of
both sonic muscles
○
Same ratio of nerve cells:body weight
□
Male morphs and females possess identical
circuitry
!
--> frequency of vocalizations
□
Pacemaker-motorneuron circuit in type I
males firest at a frequency higher than type I
and females
!
--> specifically adapted to fire more
frequently and without attenuation for a
longer period to support the activity of
their enlarged sonic muscle during
prespawning periods of signing
□
Cell bodies, dendrities, and axons are 1-3x
larger in type I
!
Findings:
○
Brainwork:
•
Type I males, type II males and females grow along
alternative growth trajectoris (mutually exclusive)
○
Therefore, alternative mating tactics among sexually
mature males are paralled by alternative phenotypes for
the neurons in the relevant circuit
•
GnRH --> gonadotropins
○
In all morphs
!
Type II > female > type 3
!
Testosterone:
○
Only in females
!
Estradiol:
○
Only in type I males (5x more than
testosterone)
!
11-ketotestosteron:
○
Hormonal differences:
•
**number of type II males is a function of population
density
•
Type II males reach sexual maturity fast but remain
physically and behaviourally immature with regard
to ability to vocalize
○
--> increased body size
!
--> hypertrophy of vocal motor system
!
*have increased chance of not surviving to
sexual maturity (more investment; more time)
!
Type I males delay maturation but have a fully
developed sexual behaviour repertoire
○
Heterochrony -dissociation in time between sexual
and physical maturity
○
Type II male morph developed under conditions of
intense (intra) sexual selection
○
Implies that type I male morph represents ancestral
behavioural state
○
Trade-offs:
•
Shaping Brain Sexuality:
Sexually
Polymorp
hic Traits
Type I Male Type II Male Female
Nest
building
Yes No No
Egg-
guarding
Yes No No
Body size Large Small Intermedi
ate
Gonad:B
ody Size
Small Large Large
(gravid),
Small
(spent)
Ventral
colourati
on
Olive-gray Mottled yellow Bronze
(gravid),
mottled
(spent)
Circulatin
g
Steroids
Testosterone,
11-
ketotesosterone
Testosterone Testoster
one,
estradiol
Vocal
behaviour
Hums, grunt
trains
Isolated grunts Isolated
grunts
Vocal
muscle
Large Small Small
Vocal
neurons
Large Small Small
Vocal
discharge
frequency
High Low Low
Males clear and decorate courts and build bowers at
display sites where they mate
•
Type and colour of court decorations
○
Form of bower
○
Differences:
•
Some male bowerbirds possess bright crest and body
plumage, and others do not
•
Highly sculptures structure of bower and male's use of
brightly coloured decorations may influence female mate
choice, thereby directing the evolution of these display
traits
•
More vigorous males might have better
bowers
□
Male-display traits (including bowers) might
indicate a male's vigor and quality as a sire
!
Good genes model:
○
A bower could even directly benefit a female,
protecting her from threats like predators or males
that might try to force her to copulate
○
Building bowers could even arise from an arbitrary
or pre-existing female preference, such as an
attraction to nest-like structures
○
Several over mechanisms could have driven evolution:
•
Three species employ monogamy with both
parents caring for young
!
All other bower birds are polygynous
!
All species of bowerbirds evolved from a single
ancestral species
○
Second major divergence developed between
species that build avenue bowers and maypole
bowers
○
Proposed function of incipient bowers should be
consistent with the design of the supposed ancestral
bower
○
Proposed function of earliest bowers should be
consistent with the design of modern bower types
○
Should possess compensatory behaviours,
which work in the absence of a bower to
protect females from forced copulations by
the courting male
!
Species that do not build bowers should possess
alternative solutions to the problem solved by a
bower
○
Evaluating bower-building hypotheses:
•
Display court at north end with blue, yellow
and white objects
!
Male trims leaves from above court so sun
can illuminate decorated site
!
Males of several species destroy each other's
bowers and steal decorations
!
Ex. Satin bowerbird
○
On display court, male makes vocalizations
!
Male then stops at one side of the bower
entrance, puffs up his body feathers, hold his
wings at his side and then faces the female
with a small decoration in his mouth, and
performs a series of knee bends
!
Visiting female usually lands in cover south of the
bower and then moves rapidly into the avenue
between stick walls
○
Although a female may visit several bowers,
she usually only mates with one male
!
In courtships that lead to copulation, a female in the
bower avenue crouches deeply as courtship
progresses, and a slight lifting of her tail signals her
willingness for mating
○
Males with high quality bowers (symmetrical
walls formed from thin, densely packed
sticks) and many decorations mate most often
!
Females exert strong preferences in mating, and
only a small proportion of males achieve most of
the matings
○
The higher rate of courtship success by specific
males, the significant effort of small decorations
and the fine details of bowers on mating success,
and the changes in a female's behaviour to mate
after she arrives at the male's bower indicates that a
female makes her mating decision after she arrives
at the court
○
Avenue-Bower builders:
•
Build a central "pole" surrounded by a circular
display court
○
Decorates sapling with sticks and moss
!
Most similar to ancestral bowers
!
Selects thin sapling and surrounds it
with horizontal piles of sticks
□
Covers lowest part of maypole and
court floor with fine compressed moss
mat
□
He decorates the court with small
objects and hands regurgitated fruit
pulp near the ends of the maypole
sticks
□
On courts rim and nearby logs, adds a
woody black fungi
□
Mechanism:
!
Functional correspondence between trees
used by young males and the size of
maypoles built by adults
!
Male calls and makes a countermove to
keep maypole between them
□
The female then stops moving and
male expands his bright orange head
plume, and shakes his head from side
to side, giving the female a good view
□
While shaking his head, the male
moves towards the female to copulate
□
Female arriving for courtship usually lands
on maypole and hops down to court
!
Ex. Macgregor's bowerbird
○
Maypole-Bower builders:
•
Two species of bowerbirds, clear and decorate
courts but have lost bower-building behaviour
○
Leks = courts of different males are
aggregated
!
Dominant males interrupt calls of males on
adjacent courts
!
Use of exceptionally loud calls and large
decorations and evidence of a female
preference for central males on leks suggests
that females may assess males before arriving
on the court --> little need for a bower's
protection from forced copulation
!
Males at centre of aggregation have highest mating
success
○
Bowerbirds without bowers:
•
Female not prepared to mate can escape
!
Bowers provide barrier that protects a visiting
female from forced copulation from a courting mal
○
Bowers allow female to observe court decorations
from a close range with reduced threat of forced
copulation
○
Toothbill -females select desirable males
before arriving on court (do not need
protection of bower)
!
Archold's -male while courting allows
female to escape
!
Birds that do not build bowers:
○
A female that freely chooses her male should
also be less likely to mate with another male
!
Combination of behaviours provides bower-
building males with increased visitation by
females and a high chance of being a female's
only mate
!
Protection of bower probably attracts females and
increases their visitation, which more than
compensates a male for losing forced copulations
○
If bowers served originally as protection
against aggressive attacks from courting
males, the evolution of the avenuebowers
would require the loss of that function and
replacement by others
!
**unlikely
!
In some species, males attach visiting females -->
would be protected by bower (only in maypole
bowers)
○
Tendency for females to choose vigorous
males and the intense athletic displays of
males in species with widely separated
bowers
!
*seems unlikely early in evolution
(when only a few males have bowers)
□
Female might assess a male's genetic quality
from his ability to maintain his bower in the
face of destruction by rivals
!
Assessing male quality by his bower
probably arose as a secondary function after
bower building evolved
!
Good-genes hypothesis:
○
Suggest that female preferences and male
traits evolve together, driven by a mating
advantage gained by males that possess an
extreme version of the trait (bower building)
!
No evidence suggests that males with larger
bowers mate more
!
No evidence of high cost, despite strong
effects of bower quality on mating success
!
Runaway model:
○
Predation hypothesis seems unlikely as well
○
Why build bowers?
•
First bowers consisted of a sapling on a display
court
○
A court with a natural barrier could separate a
female from a courting male and allow her to
closely observe the male's display and decorations
without committing to mating
○
Utilize a much wider range of saplings by
enhancing the diameter with sticks
!
Soft edge created allows males and females
to observe and anticipate each other
!
Stick-built bowers would have been an
improvement --> enhance court's protective
qualities --> simple maypole bower
!
By placing sticks around a sapling, male would be
less constrained by sapling size and location
○
Bower form could diversify to serve other
functions
!
Free-standing stick barriers would allow
males even more freedom in selecting bower
sites and in concentrating decorations
!
Two trends could then emerge:
○
Required losing use of sapling as bower
support and addition of different barrier
!
Two walled barrier --> orients female
towards parts of the court with concentrated
decorations of well-lit stage for male's
advantage
!
Decorations are a complementary colour to
male's crest and probably increase contrast of
his display
!
Avenue bowers:
○
Degree of male head-crest elaboration
correlates inversely with number of
decorations in maypole bowers?
!
Development of complex bowers may have
strongly influenced the use of decorations and
evolution of male plumage
○
Behaviour contracts with most avenus
builders that either have reduced/no crest and
build more complex bowers
!
Macgregors & Archbold's decorations are spread
widely around bower (both have well developed
crests)
○
Simple/no bowers: position of males and females
varies during displays, and for females to see bright
colours, males must carry bright plumage
○
Costly bright plumage may be replaced by
strategically located arrays of decorations
!
More complex bowers: focus a female's attention
on concentrations of decorations
○
--> females seek protection from unwanted mating
○
Evolution:
•
Bowerbirds:
Readings for Final
Monday,*December* 4,*2017 12:12*PM
Document Summary
Killing a brother or a sister may be a common adaptive strategy among nestling birds, benefiting both the surviving offspring and the parents. Involves the death of younger offspring by their older sibling. Because birds tend to monogamous, siblicide is likely to involve full sublings. Young birds require a lot of food during first few weeks of development --> high competition between nestlings. Some avian parents may not be expending their max possible effort toward brood"s survival. Eaglets hatch 3 days apart, so older one is significantly larger. Elder eaglet launches relentless attack upon sibling the moment it hatches. Two-three chicks hatch ~4 days apart --> considerable size disparity. Fighting starts as soon as second sibling has hatched. Species typically lay 2 eggs, and older (more powerful) chick kills its nestmate. Osprey: fighting is present in some but not others.
