ZOO 4910 Lecture Notes - Lecture 14: Haikouichthys, Haikouella, Mollusca
2 May 2018
School
Department
Course
Professor
10/30/17
Mass-specific metabolic rate decreases with body mass
•
Whole-animal metabolic rate increases with body mass
•
The age of maturity increases with body mass
•
Physiology:
The abundance (or population density) decreases with body
mass
•
Ecology:
Haikouella: ~15mm long
•
Haikouichthys: ~10mm long
•
The earliest known chordates were very small:
Blue whale: 30m long (190 tonnes)
•
Paediphryne amauensis: 7.7mm long
•
Etruscan shrew: 5cm long (<2g)
•
Brookesia micra chameleon: 16mm long
•
Kitti's hog-nosed bat: 2.5cm long (~2g)
•
There has been a major increase overall with large disparity:
Metabolic
○
Thermoregulatory
○
Physiological:
•
Habitat
○
Taxon dependent
○
Resource availability:
•
Biomechanical
•
Factors that limit body size:
Lineages tend to increase in body size over the course of
their evolution
•
Is it a true artifact of sampling bias?
○
Descendant species tend to be larger in size than their
ancestors
•
Not apparent in mollusca
○
Generally applies to most invertebrates but not all
•
A detailed study of molluscs show that lineages were
equally likely to decrease in size as to increase
○
Cope's rule may simply reflect a bias in which only
increases are studies and rates of decreases are not
usually examined
○
Sampling artifact:
•
Therefore, the predominance of positive directional
selection on size within populations could translate into
macroevolutionary trend toward increased size and thereby
explain Cope's rule
•
Prey capture/predator escape
○
Resource competition/utilization
○
Resistance to extreme environmental conditions
○
Fecundity
○
Competition for mates
○
Larger body size tends to be favoured within populations:
•
Consistent organism-level selection favours larger
body size for mammals but not aves
○
Acquire mates
!
Defend territories
!
Escape predation
!
Acquire prey
!
Undergo longer migrations
!
Larger individuals are more fit because they have a
better chance to:
○
Most lineages start out small, so any change
that occurs tends to be toward increased size
!
Cope's rule would be a byproduct of a passive
trend (diffusion) away from the starting
condition
!
There have been slightly more increases
than decreases in size
□
In mammals, the largest body size began to
increase after the K-T extinction, but the
smallest size did not change
!
Data set spans over 500 million years and
includes >17000 marine animal species
□
Body volumes have increased 5 orders of
magnitude, statistical modelling suggests
that such a massive increase is not
neutral
□
Integration of physiology, phylogeny and
biostatistics
□
Tested Cope's rule: selection for increased body
size
!
Bounded increase in variance:
○
Hypotheses for Vertebrates:
•
Consistent organism-level selection favouring larger
body size
○
Bounded increase in variance and directional
speciation
○
Byproduct of some other trend (thermal niche
expansion?)
○
*these are not mutually exclusive and some may
apply in certain taxa but not in others
Hypotheses:
•
Cope's Rule:
Ex. Swedish moose -increase in body mass with
latitude
○
Ratio decreases with decreases size
!
Less of an area to lose heat from surrounding
environment
!
Limiting factors to ectotherms
□
Facilitates expansion to colder temperatures
!
Due to ratio of surface area/volume
○
Bergmann's rule: populations (and species) of a larger size
are found in colder environments
•
Animals get rounder in colder climates by decreases
appendage length
○
Decreases SA/volume ratio
○
Ex. Hares, foxes
○
Allen's rule: length of appendages negatively correlated
with latitude (and positively with temperature)
•
Geography and Body Size:
Rate of tail growth is highest in warm
environments
!
Rate of tail growth is decreased in colder
environments with similar rates of body growth
○
Ex. Mouse
•
% growth from baseline (metatarsal
growth)
□
--> more number of cells produced
by mitosis
!
%BrdU proliferation index (positive
cells)
□
Mitotic rate decreases in colder environmental
temperatures
!
Femur sizes in mouse -chondrogenesis decreases in
colder temperatures
○
Is appendage length a by product of thermally-reugulated
ontogenetic shifts in development?
•
Number of cells increases with temperature
○
Relatively constant in homeotherms
!
Gestation rate increases at a lesser rate with
temperature
○
--> total number of cells increases with temperature
○
Model: heterochrony in developmental timing (ectotherms)
•
Number of vertebrate increase with
latitude
□
Ex. Medaka population in Japan
!
Jordan's rule: meristic character counts (fin rays,
vertebrae, lateral line scales) are inversely
proportional to developmental temperatures
○
Heterochrony -developmental programs can be altered by
temperature
•
Number of vertebrae increase with latitude
(decrease within areas with increasing
temperature)
!
Ex. Medaka
○
Response trend = plasticity
○
Population-specific = not expected
○
Developmental programs that are constrained
by the genetic architecture of the parents
!
E.g. relative rankings of phenotypic
differences will remain….
□
Generally reflects past adaptive events in
evolutionary history of the population
!
Canalized development:
○
Population effects can be 'canalized' --> genetic daptations
•
TSR -ecotherms that develop in warmer
environments have smaller adult body size (hotter is
smaller)
○
Faster growth rates as juveniles in warmer
water coupled to earlier maturation rates (fish
in warmer water mature earlier at a smaller
size)
1.
Faster growth rates coupled to larger body sizes
as adults (fish in colder environments may have
intrinsically higher growth rates)
2.
*studies mostly support faster growth rates in
northern populations
Causes:
○
Age at maturity and longevity increases in
northern populations
!
Growth curve (K) and body length increases in
northern populations
!
Ex. European minnows
○
North American Fish: evidence for size varying with
latitude was not evident
○
Final length is correlated with larval and YOY
growth rates
!
See final adult size vs. early juvenile growth
○
Fish Growth: Temperature-size rule (TSR)
•
Tadpoles of nothern population grew faster and
attained slightly greater size
!
Growth rate was increased in low density
populations
!
Ex. Swedish Rana tempoaria
○
Accepts hypothesis that faster growth rates coupled to
larger body sizes as adults --> colder environments
have intrinsically higher growth rates
○
Frog Growth: Temperature-size rule (TSR)
•
Temperature and Body Size:
Development rates -more susceptible to temperature
influences
•
Developmental rates -faster in warmer temperatures
•
Metabolic rates -higher in warmer tempreatures
•
Ectotherms: factors influencing early body size and growth
6m long, 2300kg
○
Great white is largest predatory fish
•
Known only from fossil teeth
○
Related to great white
○
Probably largest carnivorous fish every and largest
shark
○
Estimate 15-20m long, 50 tonnes
○
Probably fed on large prey, including early whales
○
Went extinct 1.5mya
○
Carcharodon megalodon
•
Sharks:
Andrias davidianus -<1.8m long, 25-30kg
○
Conraua goliath -3kg
○
Temnospondyl of the late Permian
!
Reached 9m in length
!
How did it become so large?
!
Prionosuchus
○
Large size disparity:
•
Amphibians:
Titanoboa snakes was probably the largest non-marine
creature on earth (43ft)
•
Mean temperature required to sustain body size is
higher than current temperatures
○
Historical temperatures were warmer near equator -->
larger ectotherms
○
Thermophysiology drives body size evolution
○
Giant boid snake from the Palaeocene neotropics reveals
hotter past equatorial temperatures --> Bergmann's rule?
•
Reptiles:
From late Cretaceous (China)
○
Gigantoraptor
•
Flightless predatory birds
○
Top carnivore in its time
○
Up to 2m
○
Gastornis
•
Birds:
Other selection forces (e.g. development time may limit
increase in size)
•
Species with large body sizes tend to have lower population
sizes, lower geographic distribution, and longer generation
times -all of which make them more prone to extinction
(especially in mass extinctions)
•
Multiple intermediate-sized species required as prey
○
The 'goldilocks effect' -->species that are not too big
and not too small are favoured
○
Competition for resources could not maintain a 'top-down'
species rich food-web pyramid
•
Why aren't all taxa at maximum size?
Larger-sized species of aves, mammalian and
chondrichthyes are most threatened
•
Habitat loss threatens smaller non-vagile species
•
Species of intermediate size are least threatened with extinction:
11/01/17
Comparisons between species populations living on islands
and nearby mainland areas = presumed source of colonizing
founders for island populations
•
On islands there is graded trend for gigantism in small
species and dwarfism in large species
•
Si= massi/massmainland
○
If S>0, then the relative size of the island population
is greater
○
If S<0, then relative size of the island population is
less
○
S decreases with increasing body size in
mainland population
!
Measurements for carnivora species were based upon
relative skull sizes between mainland and island
population sizes
○
*see comparisons to other classes
○
Study by Lomolino devised Siindex
•
As island distance increases, body size
difference increases
!
Body size differences of island/mainland populations
proportional to the distance of the island from the
mainland
○
As island area increases, body size difference
decreases
!
Body size differences between island/mainland
populations are reduced in larger island
○
Possible confounding factors:
•
Body evolution in insular vertebrates:
Species either get larger or smaller depending on ecological
factors when colonizing islands
•
Resource storage
○
Travel capacity
○
Competitive ability/founder effect
○
Sexual selection
○
Predation release --> gigantism
•
Gestation time
○
Generation time
○
Thermoregulation
○
Resource limitation --> dwarfing
•
4 extinct species of Moa
○
Haast's eagle and moa
○
Extreme island Gigantism --> birds of New Zealand
(exceptions to rule)
•
Gigantism vs. Dwarfing: Island Rule
Positive response = larger body size
○
General trend = reduction in body size among species
○
Negative response = smaller body size in relation to global
warming (38)
•
>40 years of body size data exists for more
than 100 populations
!
Used sex, and latitude/longitude of collections
as covariates in analysis
!
Final analysis: 20496 records across 44 species
!
Correlation coefficient is higher in
aquatic birds and mammals
□
Correlation:
!
Aquatic environment is less susceptible
to temperature fluctuations
□
Global warming favours higher
productivity in aquatic environments in
higher latitudes
□
Bias in sampling? -aquatic animal
records obtained from higher latitude
species
□
Therefore, body sizes appear to be decreasing
among terrestrial species, but increasing among
aquatic species (in both birds and mammals)
!
Utilized mammalian and bird database records where:
○
Are body changes uniform across terrestrial and aquatic
bird/mammal species?
•
*see slide
○
Metabolic rates: decreases in small species at lower
temperatures
○
Water loss: increase in small species at higher
temperatures
○
Increases in the level, frequency and duration
of daily temperature might select for larger
body size
!
Increases in mean temperature might select for
smaller body size
○
Advantage for large species if temperature
increases are irregular
!
Advantage for small species if temperature increase is
constant
○
Responses to global warming:
•
Small body size is favoured
○
Scenario 1: gradual increase in warming --> targeted
adaptation to increasing TNZ size
•
Large body size is favoured
○
Scenario 2: fluctuating increase in warming --> adaptive
responses more difficult (generalist strategy is most
optimal)
•
Body Size & Global Warming
Intense competition = management decisions
○
In the Italian Alps, Alpine Chamois weight 25% less but
food quality, phenology remain the same
•
Body size decreasing in Appalachian salamanders
○
Ectotherms:
•
Increase in the winter survival of small females
○
Endotherms:
•
Climate Change
Evolution of Body Size
Monday,*October*30,*2017
12:26*PM
10/30/17
Mass-specific metabolic rate decreases with body mass
•
Whole-animal metabolic rate increases with body mass
•
The age of maturity increases with body mass
•
Physiology:
The abundance (or population density) decreases with body
mass
•
Ecology:
Haikouella: ~15mm long
•
Haikouichthys: ~10mm long
•
The earliest known chordates were very small:
Blue whale: 30m long (190 tonnes)
•
Paediphryne amauensis: 7.7mm long
•
Etruscan shrew: 5cm long (<2g)
•
Brookesia micra chameleon: 16mm long
•
Kitti's hog-nosed bat: 2.5cm long (~2g)
•
There has been a major increase overall with large disparity:
Metabolic
○
Thermoregulatory
○
Physiological:
•
Habitat
○
Taxon dependent
○
Resource availability:
•
Biomechanical
•
Factors that limit body size:
Lineages tend to increase in body size over the course of
their evolution
•
Is it a true artifact of sampling bias?
○
Descendant species tend to be larger in size than their
ancestors
•
Not apparent in mollusca
○
Generally applies to most invertebrates but not all
•
A detailed study of molluscs show that lineages were
equally likely to decrease in size as to increase
○
Cope's rule may simply reflect a bias in which only
increases are studies and rates of decreases are not
usually examined
○
Sampling artifact:
•
Therefore, the predominance of positive directional
selection on size within populations could translate into
macroevolutionary trend toward increased size and thereby
explain Cope's rule
•
Prey capture/predator escape
○
Resource competition/utilization
○
Resistance to extreme environmental conditions
○
Fecundity
○
Competition for mates
○
Larger body size tends to be favoured within populations:
•
Consistent organism-level selection favours larger
body size for mammals but not aves
○
Acquire mates
!
Defend territories
!
Escape predation
!
Acquire prey
!
Undergo longer migrations
!
Larger individuals are more fit because they have a
better chance to:
○
Most lineages start out small, so any change
that occurs tends to be toward increased size
!
Cope's rule would be a byproduct of a passive
trend (diffusion) away from the starting
condition
!
There have been slightly more increases
than decreases in size
□
In mammals, the largest body size began to
increase after the K-T extinction, but the
smallest size did not change
!
Data set spans over 500 million years and
includes >17000 marine animal species
□
Body volumes have increased 5 orders of
magnitude, statistical modelling suggests
that such a massive increase is not
neutral
□
Integration of physiology, phylogeny and
biostatistics
□
Tested Cope's rule: selection for increased body
size
!
Bounded increase in variance:
○
Hypotheses for Vertebrates:
•
Consistent organism-level selection favouring larger
body size
○
Bounded increase in variance and directional
speciation
○
Byproduct of some other trend (thermal niche
expansion?)
○
*these are not mutually exclusive and some may
apply in certain taxa but not in others
Hypotheses:
•
Cope's Rule:
Ex. Swedish moose -increase in body mass with
latitude
○
Ratio decreases with decreases size
!
Less of an area to lose heat from surrounding
environment
!
Limiting factors to ectotherms
□
Facilitates expansion to colder temperatures
!
Due to ratio of surface area/volume
○
Bergmann's rule: populations (and species) of a larger size
are found in colder environments
•
Animals get rounder in colder climates by decreases
appendage length
○
Decreases SA/volume ratio
○
Ex. Hares, foxes
○
Allen's rule: length of appendages negatively correlated
with latitude (and positively with temperature)
•
Geography and Body Size:
Rate of tail growth is highest in warm
environments
!
Rate of tail growth is decreased in colder
environments with similar rates of body growth
○
Ex. Mouse
•
% growth from baseline (metatarsal
growth)
□
--> more number of cells produced
by mitosis
!
%BrdU proliferation index (positive
cells)
□
Mitotic rate decreases in colder environmental
temperatures
!
Femur sizes in mouse -chondrogenesis decreases in
colder temperatures
○
Is appendage length a by product of thermally-reugulated
ontogenetic shifts in development?
•
Number of cells increases with temperature
○
Relatively constant in homeotherms
!
Gestation rate increases at a lesser rate with
temperature
○
--> total number of cells increases with temperature
○
Model: heterochrony in developmental timing (ectotherms)
•
Number of vertebrate increase with
latitude
□
Ex. Medaka population in Japan
!
Jordan's rule: meristic character counts (fin rays,
vertebrae, lateral line scales) are inversely
proportional to developmental temperatures
○
Heterochrony -developmental programs can be altered by
temperature
•
Number of vertebrae increase with latitude
(decrease within areas with increasing
temperature)
!
Ex. Medaka
○
Response trend = plasticity
○
Population-specific = not expected
○
Developmental programs that are constrained
by the genetic architecture of the parents
!
E.g. relative rankings of phenotypic
differences will remain….
□
Generally reflects past adaptive events in
evolutionary history of the population
!
Canalized development:
○
Population effects can be 'canalized' --> genetic daptations
•
TSR -ecotherms that develop in warmer
environments have smaller adult body size (hotter is
smaller)
○
Faster growth rates as juveniles in warmer
water coupled to earlier maturation rates (fish
in warmer water mature earlier at a smaller
size)
1.
Faster growth rates coupled to larger body sizes
as adults (fish in colder environments may have
intrinsically higher growth rates)
2.
*studies mostly support faster growth rates in
northern populations
Causes:
○
Age at maturity and longevity increases in
northern populations
!
Growth curve (K) and body length increases in
northern populations
!
Ex. European minnows
○
North American Fish: evidence for size varying with
latitude was not evident
○
Final length is correlated with larval and YOY
growth rates
!
See final adult size vs. early juvenile growth
○
Fish Growth: Temperature-size rule (TSR)
•
Tadpoles of nothern population grew faster and
attained slightly greater size
!
Growth rate was increased in low density
populations
!
Ex. Swedish Rana tempoaria
○
Accepts hypothesis that faster growth rates coupled to
larger body sizes as adults --> colder environments
have intrinsically higher growth rates
○
Frog Growth: Temperature-size rule (TSR)
•
Temperature and Body Size:
Development rates -more susceptible to temperature
influences
•
Developmental rates -faster in warmer temperatures
•
Metabolic rates -higher in warmer tempreatures
•
Ectotherms: factors influencing early body size and growth
6m long, 2300kg
○
Great white is largest predatory fish
•
Known only from fossil teeth
○
Related to great white
○
Probably largest carnivorous fish every and largest
shark
○
Estimate 15-20m long, 50 tonnes
○
Probably fed on large prey, including early whales
○
Went extinct 1.5mya
○
Carcharodon megalodon
•
Sharks:
Andrias davidianus -<1.8m long, 25-30kg
○
Conraua goliath -3kg
○
Temnospondyl of the late Permian
!
Reached 9m in length
!
How did it become so large?
!
Prionosuchus
○
Large size disparity:
•
Amphibians:
Titanoboa snakes was probably the largest non-marine
creature on earth (43ft)
•
Mean temperature required to sustain body size is
higher than current temperatures
○
Historical temperatures were warmer near equator -->
larger ectotherms
○
Thermophysiology drives body size evolution
○
Giant boid snake from the Palaeocene neotropics reveals
hotter past equatorial temperatures --> Bergmann's rule?
•
Reptiles:
From late Cretaceous (China)
○
Gigantoraptor
•
Flightless predatory birds
○
Top carnivore in its time
○
Up to 2m
○
Gastornis
•
Birds:
Other selection forces (e.g. development time may limit
increase in size)
•
Species with large body sizes tend to have lower population
sizes, lower geographic distribution, and longer generation
times -all of which make them more prone to extinction
(especially in mass extinctions)
•
Multiple intermediate-sized species required as prey
○
The 'goldilocks effect' -->species that are not too big
and not too small are favoured
○
Competition for resources could not maintain a 'top-down'
species rich food-web pyramid
•
Why aren't all taxa at maximum size?
Larger-sized species of aves, mammalian and
chondrichthyes are most threatened
•
Habitat loss threatens smaller non-vagile species
•
Species of intermediate size are least threatened with extinction:
11/01/17
Comparisons between species populations living on islands
and nearby mainland areas = presumed source of colonizing
founders for island populations
•
On islands there is graded trend for gigantism in small
species and dwarfism in large species
•
Si= massi/massmainland
○
If S>0, then the relative size of the island population
is greater
○
If S<0, then relative size of the island population is
less
○
S decreases with increasing body size in
mainland population
!
Measurements for carnivora species were based upon
relative skull sizes between mainland and island
population sizes
○
*see comparisons to other classes
○
Study by Lomolino devised Siindex
•
As island distance increases, body size
difference increases
!
Body size differences of island/mainland populations
proportional to the distance of the island from the
mainland
○
As island area increases, body size difference
decreases
!
Body size differences between island/mainland
populations are reduced in larger island
○
Possible confounding factors:
•
Body evolution in insular vertebrates:
Species either get larger or smaller depending on ecological
factors when colonizing islands
•
Resource storage
○
Travel capacity
○
Competitive ability/founder effect
○
Sexual selection
○
Predation release --> gigantism
•
Gestation time
○
Generation time
○
Thermoregulation
○
Resource limitation --> dwarfing
•
4 extinct species of Moa
○
Haast's eagle and moa
○
Extreme island Gigantism --> birds of New Zealand
(exceptions to rule)
•
Gigantism vs. Dwarfing: Island Rule
Positive response = larger body size
○
General trend = reduction in body size among species
○
Negative response = smaller body size in relation to global
warming (38)
•
>40 years of body size data exists for more
than 100 populations
!
Used sex, and latitude/longitude of collections
as covariates in analysis
!
Final analysis: 20496 records across 44 species
!
Correlation coefficient is higher in
aquatic birds and mammals
□
Correlation:
!
Aquatic environment is less susceptible
to temperature fluctuations
□
Global warming favours higher
productivity in aquatic environments in
higher latitudes
□
Bias in sampling? -aquatic animal
records obtained from higher latitude
species
□
Therefore, body sizes appear to be decreasing
among terrestrial species, but increasing among
aquatic species (in both birds and mammals)
!
Utilized mammalian and bird database records where:
○
Are body changes uniform across terrestrial and aquatic
bird/mammal species?
•
*see slide
○
Metabolic rates: decreases in small species at lower
temperatures
○
Water loss: increase in small species at higher
temperatures
○
Increases in the level, frequency and duration
of daily temperature might select for larger
body size
!
Increases in mean temperature might select for
smaller body size
○
Advantage for large species if temperature
increases are irregular
!
Advantage for small species if temperature increase is
constant
○
Responses to global warming:
•
Small body size is favoured
○
Scenario 1: gradual increase in warming --> targeted
adaptation to increasing TNZ size
•
Large body size is favoured
○
Scenario 2: fluctuating increase in warming --> adaptive
responses more difficult (generalist strategy is most
optimal)
•
Body Size & Global Warming
Intense competition = management decisions
○
In the Italian Alps, Alpine Chamois weight 25% less but
food quality, phenology remain the same
•
Body size decreasing in Appalachian salamanders
○
Ectotherms:
•
Increase in the winter survival of small females
○
Endotherms:
•
Climate Change
Evolution of Body Size
Monday,*October*30,*2017 12:26*PM
10/30/17
Mass-specific metabolic rate decreases with body mass
•
Whole-animal metabolic rate increases with body mass
•
The age of maturity increases with body mass
•
Physiology:
The abundance (or population density) decreases with body
mass
•
Ecology:
Haikouella: ~15mm long
•
Haikouichthys: ~10mm long
•
The earliest known chordates were very small:
Blue whale: 30m long (190 tonnes)
•
Paediphryne amauensis: 7.7mm long
•
Etruscan shrew: 5cm long (<2g)
•
Brookesia micra chameleon: 16mm long
•
Kitti's hog-nosed bat: 2.5cm long (~2g)
•
There has been a major increase overall with large disparity:
Metabolic
○
Thermoregulatory
○
Physiological:
•
Habitat
○
Taxon dependent
○
Resource availability:
•
Biomechanical
•
Factors that limit body size:
Lineages tend to increase in body size over the course of
their evolution
•
Is it a true artifact of sampling bias?
○
Descendant species tend to be larger in size than their
ancestors
•
Not apparent in mollusca
○
Generally applies to most invertebrates but not all
•
A detailed study of molluscs show that lineages were
equally likely to decrease in size as to increase
○
Cope's rule may simply reflect a bias in which only
increases are studies and rates of decreases are not
usually examined
○
Sampling artifact:
•
Therefore, the predominance of positive directional
selection on size within populations could translate into
macroevolutionary trend toward increased size and thereby
explain Cope's rule
•
Prey capture/predator escape
○
Resource competition/utilization
○
Resistance to extreme environmental conditions
○
Fecundity
○
Competition for mates
○
Larger body size tends to be favoured within populations:
•
Consistent organism-level selection favours larger
body size for mammals but not aves
○
Acquire mates
!
Defend territories
!
Escape predation
!
Acquire prey
!
Undergo longer migrations
!
Larger individuals are more fit because they have a
better chance to:
○
Most lineages start out small, so any change
that occurs tends to be toward increased size
!
Cope's rule would be a byproduct of a passive
trend (diffusion) away from the starting
condition
!
There have been slightly more increases
than decreases in size
□
In mammals, the largest body size began to
increase after the K-T extinction, but the
smallest size did not change
!
Data set spans over 500 million years and
includes >17000 marine animal species
□
Body volumes have increased 5 orders of
magnitude, statistical modelling suggests
that such a massive increase is not
neutral
□
Integration of physiology, phylogeny and
biostatistics
□
Tested Cope's rule: selection for increased body
size
!
Bounded increase in variance:
○
Hypotheses for Vertebrates:
•
Consistent organism-level selection favouring larger
body size
○
Bounded increase in variance and directional
speciation
○
Byproduct of some other trend (thermal niche
expansion?)
○
*these are not mutually exclusive and some may
apply in certain taxa but not in others
Hypotheses:
•
Cope's Rule:
Ex. Swedish moose -increase in body mass with
latitude
○
Ratio decreases with decreases size
!
Less of an area to lose heat from surrounding
environment
!
Limiting factors to ectotherms
□
Facilitates expansion to colder temperatures
!
Due to ratio of surface area/volume
○
Bergmann's rule: populations (and species) of a larger size
are found in colder environments
•
Animals get rounder in colder climates by decreases
appendage length
○
Decreases SA/volume ratio
○
Ex. Hares, foxes
○
Allen's rule: length of appendages negatively correlated
with latitude (and positively with temperature)
•
Geography and Body Size:
Rate of tail growth is highest in warm
environments
!
Rate of tail growth is decreased in colder
environments with similar rates of body growth
○
Ex. Mouse
•
% growth from baseline (metatarsal
growth)
□
--> more number of cells produced
by mitosis
!
%BrdU proliferation index (positive
cells)
□
Mitotic rate decreases in colder environmental
temperatures
!
Femur sizes in mouse -chondrogenesis decreases in
colder temperatures
○
Is appendage length a by product of thermally-reugulated
ontogenetic shifts in development?
•
Number of cells increases with temperature
○
Relatively constant in homeotherms
!
Gestation rate increases at a lesser rate with
temperature
○
--> total number of cells increases with temperature
○
Model: heterochrony in developmental timing (ectotherms)
•
Number of vertebrate increase with
latitude
□
Ex. Medaka population in Japan
!
Jordan's rule: meristic character counts (fin rays,
vertebrae, lateral line scales) are inversely
proportional to developmental temperatures
○
Heterochrony -developmental programs can be altered by
temperature
•
Number of vertebrae increase with latitude
(decrease within areas with increasing
temperature)
!
Ex. Medaka
○
Response trend = plasticity
○
Population-specific = not expected
○
Developmental programs that are constrained
by the genetic architecture of the parents
!
E.g. relative rankings of phenotypic
differences will remain….
□
Generally reflects past adaptive events in
evolutionary history of the population
!
Canalized development:
○
Population effects can be 'canalized' --> genetic daptations
•
TSR -ecotherms that develop in warmer
environments have smaller adult body size (hotter is
smaller)
○
Faster growth rates as juveniles in warmer
water coupled to earlier maturation rates (fish
in warmer water mature earlier at a smaller
size)
1.
Faster growth rates coupled to larger body sizes
as adults (fish in colder environments may have
intrinsically higher growth rates)
2.
*studies mostly support faster growth rates in
northern populations
Causes:
○
Age at maturity and longevity increases in
northern populations
!
Growth curve (K) and body length increases in
northern populations
!
Ex. European minnows
○
North American Fish: evidence for size varying with
latitude was not evident
○
Final length is correlated with larval and YOY
growth rates
!
See final adult size vs. early juvenile growth
○
Fish Growth: Temperature-size rule (TSR)
•
Tadpoles of nothern population grew faster and
attained slightly greater size
!
Growth rate was increased in low density
populations
!
Ex. Swedish Rana tempoaria
○
Accepts hypothesis that faster growth rates coupled to
larger body sizes as adults --> colder environments
have intrinsically higher growth rates
○
Frog Growth: Temperature-size rule (TSR)
•
Temperature and Body Size:
Development rates -more susceptible to temperature
influences
•
Developmental rates -faster in warmer temperatures
•
Metabolic rates -higher in warmer tempreatures
•
Ectotherms: factors influencing early body size and growth
6m long, 2300kg
○
Great white is largest predatory fish
•
Known only from fossil teeth
○
Related to great white
○
Probably largest carnivorous fish every and largest
shark
○
Estimate 15-20m long, 50 tonnes
○
Probably fed on large prey, including early whales
○
Went extinct 1.5mya
○
Carcharodon megalodon
•
Sharks:
Andrias davidianus -<1.8m long, 25-30kg
○
Conraua goliath -3kg
○
Temnospondyl of the late Permian
!
Reached 9m in length
!
How did it become so large?
!
Prionosuchus
○
Large size disparity:
•
Amphibians:
Titanoboa snakes was probably the largest non-marine
creature on earth (43ft)
•
Mean temperature required to sustain body size is
higher than current temperatures
○
Historical temperatures were warmer near equator -->
larger ectotherms
○
Thermophysiology drives body size evolution
○
Giant boid snake from the Palaeocene neotropics reveals
hotter past equatorial temperatures --> Bergmann's rule?
•
Reptiles:
From late Cretaceous (China)
○
Gigantoraptor
•
Flightless predatory birds
○
Top carnivore in its time
○
Up to 2m
○
Gastornis
•
Birds:
Other selection forces (e.g. development time may limit
increase in size)
•
Species with large body sizes tend to have lower population
sizes, lower geographic distribution, and longer generation
times -all of which make them more prone to extinction
(especially in mass extinctions)
•
Multiple intermediate-sized species required as prey
○
The 'goldilocks effect' -->species that are not too big
and not too small are favoured
○
Competition for resources could not maintain a 'top-down'
species rich food-web pyramid
•
Why aren't all taxa at maximum size?
Larger-sized species of aves, mammalian and
chondrichthyes are most threatened
•
Habitat loss threatens smaller non-vagile species
•
Species of intermediate size are least threatened with extinction:
11/01/17
Comparisons between species populations living on islands
and nearby mainland areas = presumed source of colonizing
founders for island populations
•
On islands there is graded trend for gigantism in small
species and dwarfism in large species
•
Si= massi/massmainland
○
If S>0, then the relative size of the island population
is greater
○
If S<0, then relative size of the island population is
less
○
S decreases with increasing body size in
mainland population
!
Measurements for carnivora species were based upon
relative skull sizes between mainland and island
population sizes
○
*see comparisons to other classes
○
Study by Lomolino devised Siindex
•
As island distance increases, body size
difference increases
!
Body size differences of island/mainland populations
proportional to the distance of the island from the
mainland
○
As island area increases, body size difference
decreases
!
Body size differences between island/mainland
populations are reduced in larger island
○
Possible confounding factors:
•
Body evolution in insular vertebrates:
Species either get larger or smaller depending on ecological
factors when colonizing islands
•
Resource storage
○
Travel capacity
○
Competitive ability/founder effect
○
Sexual selection
○
Predation release --> gigantism
•
Gestation time
○
Generation time
○
Thermoregulation
○
Resource limitation --> dwarfing
•
4 extinct species of Moa
○
Haast's eagle and moa
○
Extreme island Gigantism --> birds of New Zealand
(exceptions to rule)
•
Gigantism vs. Dwarfing: Island Rule
Positive response = larger body size
○
General trend = reduction in body size among species
○
Negative response = smaller body size in relation to global
warming (38)
•
>40 years of body size data exists for more
than 100 populations
!
Used sex, and latitude/longitude of collections
as covariates in analysis
!
Final analysis: 20496 records across 44 species
!
Correlation coefficient is higher in
aquatic birds and mammals
□
Correlation:
!
Aquatic environment is less susceptible
to temperature fluctuations
□
Global warming favours higher
productivity in aquatic environments in
higher latitudes
□
Bias in sampling? -aquatic animal
records obtained from higher latitude
species
□
Therefore, body sizes appear to be decreasing
among terrestrial species, but increasing among
aquatic species (in both birds and mammals)
!
Utilized mammalian and bird database records where:
○
Are body changes uniform across terrestrial and aquatic
bird/mammal species?
•
*see slide
○
Metabolic rates: decreases in small species at lower
temperatures
○
Water loss: increase in small species at higher
temperatures
○
Increases in the level, frequency and duration
of daily temperature might select for larger
body size
!
Increases in mean temperature might select for
smaller body size
○
Advantage for large species if temperature
increases are irregular
!
Advantage for small species if temperature increase is
constant
○
Responses to global warming:
•
Small body size is favoured
○
Scenario 1: gradual increase in warming --> targeted
adaptation to increasing TNZ size
•
Large body size is favoured
○
Scenario 2: fluctuating increase in warming --> adaptive
responses more difficult (generalist strategy is most
optimal)
•
Body Size & Global Warming
Intense competition = management decisions
○
In the Italian Alps, Alpine Chamois weight 25% less but
food quality, phenology remain the same
•
Body size decreasing in Appalachian salamanders
○
Ectotherms:
•
Increase in the winter survival of small females
○
Endotherms:
•
Climate Change
Evolution of Body Size
Monday,*October*30,*2017 12:26*PM
Document Summary
The age of maturity increases with body mass. The abundance (or population density) decreases with body mass. There has been a major increase overall with large disparity: Lineages tend to increase in body size over the course of their evolution. Descendant species tend to be larger in size than their ancestors. Generally applies to most invertebrates but not all. A detailed study of molluscs show that lineages were equally likely to decrease in size as to increase. Cope"s rule may simply reflect a bias in which only increases are studies and rates of decreases are not usually examined. Therefore, the predominance of positive directional selection on size within populations could translate into macroevolutionary trend toward increased size and thereby explain cope"s rule. Larger body size tends to be favoured within populations: Consistent organism-level selection favours larger body size for mammals but not aves. Larger individuals are more fit because they have a better chance to:
