BIOB51H3 Lecture Notes - Lecture 21: Nuptial Gift, Sexy Son Hypothesis, Hangingfly
5 Jul 2018
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TYPES OF SEXUAL SELECTION
1) Intrasexual selection
a. The agent of selection = competition
2) Intersexual selection
a. Agent fo selection = choice
INTRA SEXUAL SELECTION
-Members of the sex w/ more variable reproductive success, compete for mating access to
the other sex
-Usually males competing for females
-For examples, deer fighting other deer
-Traits that are favored
o1) larger body size
o2) weapons (eg. Adaptations for combat)
o3) armor
od) can also have: alternative tactics
(individuals not likely to win in direct
competitions may try other tactics)
oeg. Coho Salmon: hooknoses (large
males, fight for access to females) and have jacks (small males, try to
sneak fertilizations during spawning)
oeg. Redback spiders (black widows) larger males usually win, but small
males can also mate
typically, the larger male will bite down the small male, killing it
oe) adaptations for sperm competition (competition between sperm from
different males for access to a female’s eggs)
this is common when: females mate > 1male in a fertile period
females store sperm
has tradeoffs: increased sperm production = possibly smaller
body
we can see this in primates (eg. In multi-male systems, they
produce more sperm)
also see this through sperm removal tactics eg. Damselfly
penis is specialized for sperm removal
oin balck widows females an store sperm for 2
years males have an adaptation called sperm
plugs: males leave part of their copulatory organ
in the female’s genital tract (it physically blocks
other sperm from entering) thus: first male to
mate, fathers the most offspring
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-Intrasexual selection can be before
mating (eg. Physically removing
sperm) or after mating (eg. Sperm
plugs)
INTERSEXUAL SELECTION
-Agent of selection = mate choice
oMembers of the sex w/ more
variable reproductive success
try to convince members of
the other sex, to mate with
them
oUsually: females are choosy, and males try to convince them to mate
-The traits that are favoured (in competing sex)
a.i.a) Ornaments (eg. Peacock’s tail adaptation for
attractiveness)
a.i.b) Displays (eg. Courtship song, plumage)
-Why are the females choosy? Does the choosiness increase their fitness?
oThe reason is that because females often don’t mate as often as males, they
can’t increase their fitness by mating many time thus: females typically don’t
compete for mates (eg. Rough-skinned newt example)
oThus: they can increase their fitness by acquiring things that increase the #
and quality of their offspring
-There are 2 ways that they can increase the number/quality
o1. DIRECT BENEFITS
o Acquire resources to invest in eggs
oAcquire help in caring for eggs/offspring
o2. INDIRECT BENEFITS (genetic)
oacquire heritable traits to increase offspring fitness
-HYPOTHESIS #1: DIRECT BENEFITS
Predictions
o1. Females receive some resources from males
o2. The resource increases their chance of survival and ability to produce/take
care of the young
o3. Females prefer males that provide more or better resources
resources = food/parental care/protection from predators/breeding territory etc.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Types of sexual selection: intrasexual selection, the agent of selection = competition, intersexual selection, agent fo selection = choice. Members of the sex w/ more variable reproductive success, compete for mating access to the other sex. Intrasexual selection can be before mating (eg. physically removing sperm) or after mating (eg. sperm plugs) The traits that are favoured (in competing sex) a. i. a) Ornaments (eg. peacock"s tail (cid:0) adaptation for attractiveness) a. i. b) There are 2 ways that they can increase the number/quality: 1. Direct benefits: acquire resources to invest in eggs, acquire help in caring for eggs/offspring, 2. Indirect benefits (genetic: acquire heritable traits to increase offspring fitness. Females receive some resources from males: 2. The resource increases their chance of survival and ability to produce/take care of the young: 3. Females prefer males that provide more or better resources. Resources = food/parental care/protection from predators/breeding territory etc. for example: female hangingflies: 1. 2 hypotheses: a) good genes, b) sexy sons hypothesis.
