Allometry and Isometry y changes as a function of x y changes as a function of x Allometric equation y = bx a Allometric equation y = bx a – (where

Allometry and IsometryAllometry and Isometry

• y changes as a function of xy changes as a function of x

• Allometric equation Allometric equation y = bxy = bxa a

– (where y= one char, x=another, a=coeff. of (where y= one char, x=another, a=coeff. of allometry, and b=constant proportion relating y allometry, and b=constant proportion relating y and x)and x)

• if “a” = 1 then b = y/x which means if “a” = 1 then b = y/x which means that y changes in direct proportion to xthat y changes in direct proportion to x

• a<1 a<1 y increases less rapidly than x y increases less rapidly than x

• a>1 a>1 y increases more rapidly than x y increases more rapidly than x

• y changes as a function of xy changes as a function of x

• Allometric equation Allometric equation y = bxy = bxa a

– (where y= one char, x=another, a=coeff. of (where y= one char, x=another, a=coeff. of allometry, and b=constant proportion relating y allometry, and b=constant proportion relating y and x)and x)

• if “a” = 1 then b = y/x which means if “a” = 1 then b = y/x which means that y changes in direct proportion to xthat y changes in direct proportion to x

• a<1 a<1 y increases less rapidly than x y increases less rapidly than x

• a>1 a>1 y increases more rapidly than x y increases more rapidly than x

• Many times it is easiest to express this Many times it is easiest to express this equation like this:equation like this:

• log y = log b + a log xlog y = log b + a log x

• This gives a straight line with slope = This gives a straight line with slope = aa and and an intercept = an intercept = log ylog y

• Most morphological evolution can be Most morphological evolution can be described in terms of Allometric described in terms of Allometric relationships.relationships.

• Allometric relationships with body mass are Allometric relationships with body mass are often the consequence of adaptationoften the consequence of adaptation

• Many times it is easiest to express this Many times it is easiest to express this equation like this:equation like this:

• log y = log b + a log xlog y = log b + a log x

• This gives a straight line with slope = This gives a straight line with slope = aa and and an intercept = an intercept = log ylog y

• Most morphological evolution can be Most morphological evolution can be described in terms of Allometric described in terms of Allometric relationships.relationships.

• Allometric relationships with body mass are Allometric relationships with body mass are often the consequence of adaptationoften the consequence of adaptation


• Structures that support an organism Structures that support an organism must change disproportionately in must change disproportionately in shape as weight increases.shape as weight increases.

• Tree trunk mass to cross sectional is Tree trunk mass to cross sectional is 3/2 power of height3/2 power of height

• Structures that support an organism Structures that support an organism must change disproportionately in must change disproportionately in shape as weight increases.shape as weight increases.

• Tree trunk mass to cross sectional is Tree trunk mass to cross sectional is 3/2 power of height3/2 power of height

Evolution of ToleranceEvolution of Tolerance

• In animals, a series of responses occur In animals, a series of responses occur sequentially in response to stresssequentially in response to stress

• Lets examine these steps... Lets examine these steps...

• In animals, a series of responses occur In animals, a series of responses occur sequentially in response to stresssequentially in response to stress

• Lets examine these steps... Lets examine these steps...

• Example:Example:• In cold environments, large size is In cold environments, large size is

advantageous in birds and mammals advantageous in birds and mammals because they lose heat more slowly, because they lose heat more slowly, Thus requiring less food to maintain Thus requiring less food to maintain constant body temp. constant body temp. • Bergmann’s RuleBergmann’s Rule “birds and “birds and

mammals larger in colder climates than mammals larger in colder climates than same/related species in warmer same/related species in warmer climatesclimates

• Example:Example:• In cold environments, large size is In cold environments, large size is

advantageous in birds and mammals advantageous in birds and mammals because they lose heat more slowly, because they lose heat more slowly, Thus requiring less food to maintain Thus requiring less food to maintain constant body temp. constant body temp. • Bergmann’s RuleBergmann’s Rule “birds and “birds and

mammals larger in colder climates than mammals larger in colder climates than same/related species in warmer same/related species in warmer climatesclimates


1.1. Changes in behaviorChanges in behavior2.2. Hormone-modulated biochemical and Hormone-modulated biochemical and

physiological functionsphysiological functions3.3. Slower, longer lasting changes in Slower, longer lasting changes in

physiology (“acclimation”)physiology (“acclimation”)4.4. In some instances, developmental changes In some instances, developmental changes

in morphologyin morphology5.5. At population level, genetic changes due to At population level, genetic changes due to

differences among genotypes in survival differences among genotypes in survival and reproduction rates caused by the and reproduction rates caused by the stressstress

1.1. Changes in behaviorChanges in behavior2.2. Hormone-modulated biochemical and Hormone-modulated biochemical and

physiological functionsphysiological functions3.3. Slower, longer lasting changes in Slower, longer lasting changes in

physiology (“acclimation”)physiology (“acclimation”)4.4. In some instances, developmental changes In some instances, developmental changes

in morphologyin morphology5.5. At population level, genetic changes due to At population level, genetic changes due to

differences among genotypes in survival differences among genotypes in survival and reproduction rates caused by the and reproduction rates caused by the stressstress


• If the responses of individual If the responses of individual organisms cannot fully compensate for organisms cannot fully compensate for the stress, fitness is reducedthe stress, fitness is reduced

• This may lead to genetic changesThis may lead to genetic changes

• Some changes entail developmental Some changes entail developmental responses and these are reversibleresponses and these are reversible– e.g., Seasonal Responsese.g., Seasonal Responses

• If the responses of individual If the responses of individual organisms cannot fully compensate for organisms cannot fully compensate for the stress, fitness is reducedthe stress, fitness is reduced

• This may lead to genetic changesThis may lead to genetic changes

• Some changes entail developmental Some changes entail developmental responses and these are reversibleresponses and these are reversible– e.g., Seasonal Responsese.g., Seasonal Responses


What Limits Geographical Ranges of Species?


• Some ranges are set by biotic factors, Some ranges are set by biotic factors, interspecific competition & predation, or by interspecific competition & predation, or by abiotic factors such as temperature and abiotic factors such as temperature and water availabilitywater availability

• This question is thus complex and difficult to This question is thus complex and difficult to answeranswer

• The simplest hypothesis is the lack of The simplest hypothesis is the lack of genetic variation for tolerance of genetic variation for tolerance of physiological stressphysiological stress– However, in general this is not likely...However, in general this is not likely...

• Some ranges are set by biotic factors, Some ranges are set by biotic factors, interspecific competition & predation, or by interspecific competition & predation, or by abiotic factors such as temperature and abiotic factors such as temperature and water availabilitywater availability

• This question is thus complex and difficult to This question is thus complex and difficult to answeranswer

• The simplest hypothesis is the lack of The simplest hypothesis is the lack of genetic variation for tolerance of genetic variation for tolerance of physiological stressphysiological stress– However, in general this is not likely...However, in general this is not likely...

• Successful colonization of sites may Successful colonization of sites may require numerous coincident adaptive require numerous coincident adaptive changeschanges

• This suite of adaptations may be an This suite of adaptations may be an improbable concatenation of genetic improbable concatenation of genetic variants for many characteristicsvariants for many characteristics– e.g. Seasonal timing of reproduction & e.g. Seasonal timing of reproduction &

Growth... Growth...

• Successful colonization of sites may Successful colonization of sites may require numerous coincident adaptive require numerous coincident adaptive changeschanges

• This suite of adaptations may be an This suite of adaptations may be an improbable concatenation of genetic improbable concatenation of genetic variants for many characteristicsvariants for many characteristics– e.g. Seasonal timing of reproduction & e.g. Seasonal timing of reproduction &

Growth... Growth...



• Trade-offs exist between adaptation to Trade-offs exist between adaptation to conditions within and beyond the conditions within and beyond the margin of the rangemargin of the range

• Trade-offs limit adaptation to a new Trade-offs limit adaptation to a new environment due to gene flow from environment due to gene flow from

old old new new

(center of range (center of range periphery) periphery)

• Trade-offs exist between adaptation to Trade-offs exist between adaptation to conditions within and beyond the conditions within and beyond the margin of the rangemargin of the range

• Trade-offs limit adaptation to a new Trade-offs limit adaptation to a new environment due to gene flow from environment due to gene flow from

old old new new

(center of range (center of range periphery) periphery)



• The explanation put fourth by MayrThe explanation put fourth by Mayr

• Gene flow from the main range of a species into the Gene flow from the main range of a species into the marginal populations prevents them from further marginal populations prevents them from further adapting by breaking down adaptive combinations adapting by breaking down adaptive combinations of interacting genesof interacting genes

• So, a marginal population may be better if able to So, a marginal population may be better if able to adapt & expand range if it could not exchange genes adapt & expand range if it could not exchange genes with interior populationswith interior populations

• Perhaps species have evolved broader ranges then Perhaps species have evolved broader ranges then we give them credit we give them credit because the adapted because the adapted extralimital population we call extralimital population we call different speciesdifferent species

• The explanation put fourth by MayrThe explanation put fourth by Mayr

• Gene flow from the main range of a species into the Gene flow from the main range of a species into the marginal populations prevents them from further marginal populations prevents them from further adapting by breaking down adaptive combinations adapting by breaking down adaptive combinations of interacting genesof interacting genes

• So, a marginal population may be better if able to So, a marginal population may be better if able to adapt & expand range if it could not exchange genes adapt & expand range if it could not exchange genes with interior populationswith interior populations

• Perhaps species have evolved broader ranges then Perhaps species have evolved broader ranges then we give them credit we give them credit because the adapted because the adapted extralimital population we call extralimital population we call different speciesdifferent species



AdaptationAdaptation

• Let’s examine some methods used by Let’s examine some methods used by evolutionary biologists to test evolutionary biologists to test hypotheses about adaptationshypotheses about adaptations– ExperimentsExperiments– Observational studiesObservational studies– Comparative MethodComparative Method

• Let’s examine some methods used by Let’s examine some methods used by evolutionary biologists to test evolutionary biologists to test hypotheses about adaptationshypotheses about adaptations– ExperimentsExperiments– Observational studiesObservational studies– Comparative MethodComparative Method

All Hypotheses Must be Tested: the Giraffe’s NeckAll Hypotheses Must be

Tested: the Giraffe’s Neck

• Everyone knows that the giraffe Everyone knows that the giraffe evolved a long neck to be able to eat evolved a long neck to be able to eat the tallest leaves, thereby escaping the tallest leaves, thereby escaping from competition with other herbivoresfrom competition with other herbivores

• Simmons and Scheepers challenged Simmons and Scheepers challenged this notion and offered an alternative this notion and offered an alternative explanation for the giraffe’s long neckexplanation for the giraffe’s long neck

• Everyone knows that the giraffe Everyone knows that the giraffe evolved a long neck to be able to eat evolved a long neck to be able to eat the tallest leaves, thereby escaping the tallest leaves, thereby escaping from competition with other herbivoresfrom competition with other herbivores

• Simmons and Scheepers challenged Simmons and Scheepers challenged this notion and offered an alternative this notion and offered an alternative explanation for the giraffe’s long neckexplanation for the giraffe’s long neck



• They found that giraffe’s most often ate They found that giraffe’s most often ate leaves at shoulder height, not from the tops leaves at shoulder height, not from the tops of treesof trees

• They found that giraffe’s most often ate They found that giraffe’s most often ate leaves at shoulder height, not from the tops leaves at shoulder height, not from the tops of treesof trees



• They also found that males with the They also found that males with the longest necks have the largest, hardest longest necks have the largest, hardest skullsskulls

• Maybe long necks evolved for Maybe long necks evolved for competition for femalescompetition for females– Female necks became longer because of Female necks became longer because of

selection for longer male necksselection for longer male necks

• Neck-as-a-weapon hypothesisNeck-as-a-weapon hypothesis

• They also found that males with the They also found that males with the longest necks have the largest, hardest longest necks have the largest, hardest skullsskulls

• Maybe long necks evolved for Maybe long necks evolved for competition for femalescompetition for females– Female necks became longer because of Female necks became longer because of

selection for longer male necksselection for longer male necks

• Neck-as-a-weapon hypothesisNeck-as-a-weapon hypothesis



• Pratt and Anderson classified social Pratt and Anderson classified social status of malesstatus of males– Class C were young adultsClass C were young adults– Class A were large adultsClass A were large adults– Class B were small adultsClass B were small adults

• Class A males had wider, stronger Class A males had wider, stronger headsheads• Studied displacement by classes and Studied displacement by classes and

receptivity of females of classesreceptivity of females of classes

• Pratt and Anderson classified social Pratt and Anderson classified social status of malesstatus of males– Class C were young adultsClass C were young adults– Class A were large adultsClass A were large adults– Class B were small adultsClass B were small adults

• Class A males had wider, stronger Class A males had wider, stronger headsheads• Studied displacement by classes and Studied displacement by classes and

receptivity of females of classesreceptivity of females of classes



• There is evidence for selection on There is evidence for selection on longer necks for reaching high and longer necks for reaching high and male-male competitionmale-male competition

• When studying adaptation remember When studying adaptation remember that:that:– Differences among populations or species Differences among populations or species

are not always adaptiveare not always adaptive– Not every trait is an adaptationNot every trait is an adaptation– Not every adaptation is perfectNot every adaptation is perfect

• There is evidence for selection on There is evidence for selection on longer necks for reaching high and longer necks for reaching high and male-male competitionmale-male competition

• When studying adaptation remember When studying adaptation remember that:that:– Differences among populations or species Differences among populations or species

are not always adaptiveare not always adaptive– Not every trait is an adaptationNot every trait is an adaptation– Not every adaptation is perfectNot every adaptation is perfect

Function of Wing Markings and Wavings of ZonosemataFunction of Wing Markings

and Wavings of Zonosemata

• Tephritid fly that has distinct dark bands on Tephritid fly that has distinct dark bands on wingswings

• Holds wings up and waves themHolds wings up and waves them

• Display seems to mimic threat display of Display seems to mimic threat display of jumping spidersjumping spiders

• Perhaps flies mimic jumping spiders to avoid Perhaps flies mimic jumping spiders to avoid predationpredation– Avoid predation by other predatorsAvoid predation by other predators– Or mimic jumping spiders to avoid predation by Or mimic jumping spiders to avoid predation by

jumping spidersjumping spiders

• Tephritid fly that has distinct dark bands on Tephritid fly that has distinct dark bands on wingswings

• Holds wings up and waves themHolds wings up and waves them

• Display seems to mimic threat display of Display seems to mimic threat display of jumping spidersjumping spiders

• Perhaps flies mimic jumping spiders to avoid Perhaps flies mimic jumping spiders to avoid predationpredation– Avoid predation by other predatorsAvoid predation by other predators– Or mimic jumping spiders to avoid predation by Or mimic jumping spiders to avoid predation by

jumping spidersjumping spiders



• Phrase a precise questionPhrase a precise question– Do wing markings and waving behavior of Do wing markings and waving behavior of

ZonosemataZonosemata mimic threat displays of jumping mimic threat displays of jumping spiders and deter predation?spiders and deter predation?

• List three alternative hypothesesList three alternative hypotheses– Flies do not mimic jumping spidersFlies do not mimic jumping spiders• Display may be used in courtshipDisplay may be used in courtship

– Flies mimic jumping spiders to deter non-spider Flies mimic jumping spiders to deter non-spider predatorspredators

– Flies mimic jumping spiders to deter jumping Flies mimic jumping spiders to deter jumping spidersspiders

• Phrase a precise questionPhrase a precise question– Do wing markings and waving behavior of Do wing markings and waving behavior of

ZonosemataZonosemata mimic threat displays of jumping mimic threat displays of jumping spiders and deter predation?spiders and deter predation?

• List three alternative hypothesesList three alternative hypotheses– Flies do not mimic jumping spidersFlies do not mimic jumping spiders• Display may be used in courtshipDisplay may be used in courtship

– Flies mimic jumping spiders to deter non-spider Flies mimic jumping spiders to deter non-spider predatorspredators

– Flies mimic jumping spiders to deter jumping Flies mimic jumping spiders to deter jumping spidersspiders



• Experimental procedureExperimental procedure– Clipped wings of Clipped wings of Zonosemata Zonosemata and house and house

flies, exchanged wings, and glued them on flies, exchanged wings, and glued them on opposite flyopposite fly• Clipping and gluing did not affect flying or Clipping and gluing did not affect flying or

displayingdisplaying

– Created five experimental groups to test Created five experimental groups to test hypotheseshypotheses

• Experimental procedureExperimental procedure– Clipped wings of Clipped wings of Zonosemata Zonosemata and house and house

flies, exchanged wings, and glued them on flies, exchanged wings, and glued them on opposite flyopposite fly• Clipping and gluing did not affect flying or Clipping and gluing did not affect flying or

displayingdisplaying

– Created five experimental groups to test Created five experimental groups to test hypotheseshypotheses



• Jumping spiders retreated from flies Jumping spiders retreated from flies displaying with marked wingsdisplaying with marked wings

• Other predators killed and ate test fliesOther predators killed and ate test flies

• Jumping spiders retreated from flies Jumping spiders retreated from flies displaying with marked wingsdisplaying with marked wings

• Other predators killed and ate test fliesOther predators killed and ate test flies



• Results consistent with hypothesis 3 but not Results consistent with hypothesis 3 but not 1 or 21 or 2

• Support for hypothesis that Support for hypothesis that ZonosemataZonosemata deters its predators by acting like onedeters its predators by acting like one

• Important experimental designImportant experimental design– Testing control groupsTesting control groups– All treatments handled identicallyAll treatments handled identically– Randomization of order of treatmentsRandomization of order of treatments– Replication of treatmentsReplication of treatments

• Results consistent with hypothesis 3 but not Results consistent with hypothesis 3 but not 1 or 21 or 2

• Support for hypothesis that Support for hypothesis that ZonosemataZonosemata deters its predators by acting like onedeters its predators by acting like one

• Important experimental designImportant experimental design– Testing control groupsTesting control groups– All treatments handled identicallyAll treatments handled identically– Randomization of order of treatmentsRandomization of order of treatments– Replication of treatmentsReplication of treatments



• Why was replication important?Why was replication important?– Reduced distortion of results by unusual Reduced distortion of results by unusual

individuals or conditionsindividuals or conditions– Can estimate precision of resultsCan estimate precision of results

• Study successful because many Study successful because many variables were tested, but each was variables were tested, but each was tested independentlytested independently

• Why was replication important?Why was replication important?– Reduced distortion of results by unusual Reduced distortion of results by unusual

individuals or conditionsindividuals or conditions– Can estimate precision of resultsCan estimate precision of results

• Study successful because many Study successful because many variables were tested, but each was variables were tested, but each was tested independentlytested independently

Observational StudiesObservational Studies

• Experimental studies are preferred but it is Experimental studies are preferred but it is often not feasible to experiment often not feasible to experiment – e.g., cannot exchange giraffe’s necks with e.g., cannot exchange giraffe’s necks with

other animalother animal

• Behavior is hard to experiment with because Behavior is hard to experiment with because the experiment often alters the natural the experiment often alters the natural behaviorbehavior

• Must use observational studies sometimesMust use observational studies sometimes– Often they are nearly as powerful as Often they are nearly as powerful as

experimental studiesexperimental studies

• Experimental studies are preferred but it is Experimental studies are preferred but it is often not feasible to experiment often not feasible to experiment – e.g., cannot exchange giraffe’s necks with e.g., cannot exchange giraffe’s necks with

other animalother animal

• Behavior is hard to experiment with because Behavior is hard to experiment with because the experiment often alters the natural the experiment often alters the natural behaviorbehavior

• Must use observational studies sometimesMust use observational studies sometimes– Often they are nearly as powerful as Often they are nearly as powerful as

experimental studiesexperimental studies

Behavioral ThermoregulationBehavioral Thermoregulation

• Desert iguanas (Desert iguanas (Dipsosaurus dorsalisDipsosaurus dorsalis) are ) are ectothermicectothermic– Must regulate body temperature behaviorallyMust regulate body temperature behaviorally

• Can only function between 15° and 45°CCan only function between 15° and 45°C

• Examine thermal performance curve to see Examine thermal performance curve to see adaptation to particular temperatureadaptation to particular temperature

• Body temperature affects physiological Body temperature affects physiological performanceperformance

• Keep body temperature close to 38°CKeep body temperature close to 38°C

• Desert iguanas (Desert iguanas (Dipsosaurus dorsalisDipsosaurus dorsalis) are ) are ectothermicectothermic– Must regulate body temperature behaviorallyMust regulate body temperature behaviorally

• Can only function between 15° and 45°CCan only function between 15° and 45°C

• Examine thermal performance curve to see Examine thermal performance curve to see adaptation to particular temperatureadaptation to particular temperature

• Body temperature affects physiological Body temperature affects physiological performanceperformance

• Keep body temperature close to 38°CKeep body temperature close to 38°C

Desert iguanas (Dipsosaurus dorsalis)

Desert iguanas (Dipsosaurus dorsalis)

Night Retreats of Garter Snakes


• Do snakes make adaptive choices of Do snakes make adaptive choices of where to sleep at night?where to sleep at night?

• Ray Huey implanted garter snakes with Ray Huey implanted garter snakes with radio transmitters with thermometersradio transmitters with thermometers

• Preferred body temperature is 28– 32°CPreferred body temperature is 28– 32°C

• Keep body temperature near preferred Keep body temperature near preferred during dayduring day– Exposed or under rocksExposed or under rocks

• Do snakes make adaptive choices of Do snakes make adaptive choices of where to sleep at night?where to sleep at night?

• Ray Huey implanted garter snakes with Ray Huey implanted garter snakes with radio transmitters with thermometersradio transmitters with thermometers

• Preferred body temperature is 28– 32°CPreferred body temperature is 28– 32°C

• Keep body temperature near preferred Keep body temperature near preferred during dayduring day– Exposed or under rocksExposed or under rocks

http://www.wildherps.com/images/herps/big/garter_1_Tillamook_Head.jpg



• How do they choose good retreats at How do they choose good retreats at night?night?• Thickness of rock determines Thickness of rock determines

microhabitat temperaturemicrohabitat temperature– Thin rocks heat a lot during day and cool a Thin rocks heat a lot during day and cool a

lot during nightlot during night– Thick rocks heat and cool slowlyThick rocks heat and cool slowly– Medium rocks heat and cool just enoughMedium rocks heat and cool just enough• Garter snakes should choose medium Garter snakes should choose medium

rocksrocks

• How do they choose good retreats at How do they choose good retreats at night?night?• Thickness of rock determines Thickness of rock determines

microhabitat temperaturemicrohabitat temperature– Thin rocks heat a lot during day and cool a Thin rocks heat a lot during day and cool a

lot during nightlot during night– Thick rocks heat and cool slowlyThick rocks heat and cool slowly– Medium rocks heat and cool just enoughMedium rocks heat and cool just enough• Garter snakes should choose medium Garter snakes should choose medium

rocksrocks



• Huey placed snake models under Huey placed snake models under different rocks, in burrows, and on different rocks, in burrows, and on surfacesurface– Tested temperature fluctuationsTested temperature fluctuations

• Found that snakes choose medium Found that snakes choose medium rocks to heat and cool near preferred rocks to heat and cool near preferred temperature range temperature range

• Huey placed snake models under Huey placed snake models under different rocks, in burrows, and on different rocks, in burrows, and on surfacesurface– Tested temperature fluctuationsTested temperature fluctuations

• Found that snakes choose medium Found that snakes choose medium rocks to heat and cool near preferred rocks to heat and cool near preferred temperature range temperature range

The Comparative MethodThe Comparative Method

• Purpose of the comparative method is Purpose of the comparative method is to remove the effects of evolutionary to remove the effects of evolutionary history from an analysishistory from an analysis

• The reasons why you need to remove The reasons why you need to remove effects of phylogeny from ecological or effects of phylogeny from ecological or behavioral analyses are best behavioral analyses are best demonstrated through examplesdemonstrated through examples

• Purpose of the comparative method is Purpose of the comparative method is to remove the effects of evolutionary to remove the effects of evolutionary history from an analysishistory from an analysis

• The reasons why you need to remove The reasons why you need to remove effects of phylogeny from ecological or effects of phylogeny from ecological or behavioral analyses are best behavioral analyses are best demonstrated through examplesdemonstrated through examples


• Why do some bat species have bigger testes?Why do some bat species have bigger testes?

• Some bats have larger testes for their body size Some bats have larger testes for their body size than othersthan others

• Hosken hypothesized that bigger testes evolved Hosken hypothesized that bigger testes evolved for sperm competitionfor sperm competition

• Female bats may mate with more than one male Female bats may mate with more than one male so the more sperm deposited by a male, the so the more sperm deposited by a male, the better chance he has of fertilizing the eggsbetter chance he has of fertilizing the eggs– Bigger testes mean more spermBigger testes mean more sperm

• Why do some bat species have bigger testes?Why do some bat species have bigger testes?

• Some bats have larger testes for their body size Some bats have larger testes for their body size than othersthan others

• Hosken hypothesized that bigger testes evolved Hosken hypothesized that bigger testes evolved for sperm competitionfor sperm competition

• Female bats may mate with more than one male Female bats may mate with more than one male so the more sperm deposited by a male, the so the more sperm deposited by a male, the better chance he has of fertilizing the eggsbetter chance he has of fertilizing the eggs– Bigger testes mean more spermBigger testes mean more sperm


• Hosken reasoned that bat species that Hosken reasoned that bat species that live in larger groups would have greater live in larger groups would have greater sperm competitionsperm competition• Therefore, they should evolve larger Therefore, they should evolve larger

testestestes• Hosken collected data on roost group Hosken collected data on roost group

size and testes size and found a size and testes size and found a significant correlationsignificant correlation

• Hosken reasoned that bat species that Hosken reasoned that bat species that live in larger groups would have greater live in larger groups would have greater sperm competitionsperm competition• Therefore, they should evolve larger Therefore, they should evolve larger

testestestes• Hosken collected data on roost group Hosken collected data on roost group

size and testes size and found a size and testes size and found a significant correlationsignificant correlation


• Hosken realized Hosken realized that this that this correlation may correlation may be misleadingbe misleading

• Hosken realized Hosken realized that this that this correlation may correlation may be misleadingbe misleading


• Joe Felsenstein developed a way to evaluate Joe Felsenstein developed a way to evaluate cross-species correlation among traitscross-species correlation among traits– Start with a phylogenyStart with a phylogeny– Look at where sister species divergeLook at where sister species diverge– Does the species that evolves larger group sizes Does the species that evolves larger group sizes

also evolve larger testes?also evolve larger testes?– Plot pairs of sister species connectedPlot pairs of sister species connected– Drag closest point to originDrag closest point to origin– Erase origin points and examine independent Erase origin points and examine independent

contrastscontrasts

• Joe Felsenstein developed a way to evaluate Joe Felsenstein developed a way to evaluate cross-species correlation among traitscross-species correlation among traits– Start with a phylogenyStart with a phylogeny– Look at where sister species divergeLook at where sister species diverge– Does the species that evolves larger group sizes Does the species that evolves larger group sizes

also evolve larger testes?also evolve larger testes?– Plot pairs of sister species connectedPlot pairs of sister species connected– Drag closest point to originDrag closest point to origin– Erase origin points and examine independent Erase origin points and examine independent

contrastscontrasts


• Hosken repeated bat analysis with Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Felsenstein’s Phylogenetically Independent Contrasts methodContrasts method

• Significant positive correlationSignificant positive correlation

• Hosken repeated bat analysis with Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Felsenstein’s Phylogenetically Independent Contrasts methodContrasts method

• Significant positive correlationSignificant positive correlation

Complex Adaptations in Current Research

Complex Adaptations in Current Research

• Will now examine how researchers use Will now examine how researchers use the methods mentioned above to the methods mentioned above to investigate hypotheses about complex investigate hypotheses about complex topicstopics– ExperimentsExperiments– Observational studiesObservational studies– Comparative MethodComparative Method

• Will now examine how researchers use Will now examine how researchers use the methods mentioned above to the methods mentioned above to investigate hypotheses about complex investigate hypotheses about complex topicstopics– ExperimentsExperiments– Observational studiesObservational studies– Comparative MethodComparative Method

Evolution of Adaptive TraitsEvolution of Adaptive Traits

• Every adaptive trait evolves from Every adaptive trait evolves from something elsesomething else

• How did the mammalian ear evolve?How did the mammalian ear evolve?

• Mammalian ear has three bones (ossicles)Mammalian ear has three bones (ossicles)– Malleus, incus, and stapesMalleus, incus, and stapes

• Other vertebrates do not have all threeOther vertebrates do not have all three

• Ear bones transmit energy from tympanic Ear bones transmit energy from tympanic membrane to oval window in inner earmembrane to oval window in inner ear

• Every adaptive trait evolves from Every adaptive trait evolves from something elsesomething else

• How did the mammalian ear evolve?How did the mammalian ear evolve?

• Mammalian ear has three bones (ossicles)Mammalian ear has three bones (ossicles)– Malleus, incus, and stapesMalleus, incus, and stapes

• Other vertebrates do not have all threeOther vertebrates do not have all three

• Ear bones transmit energy from tympanic Ear bones transmit energy from tympanic membrane to oval window in inner earmembrane to oval window in inner ear


• Why do we have three bones instead of Why do we have three bones instead of one?one?• Increases sensitivity of hearingIncreases sensitivity of hearing• To figure out where the bones came To figure out where the bones came

from we must:from we must:– Establish the ancestral conditionEstablish the ancestral condition– Understand the transformational sequenceUnderstand the transformational sequence• How and why they changed over timeHow and why they changed over time

• Why do we have three bones instead of Why do we have three bones instead of one?one?• Increases sensitivity of hearingIncreases sensitivity of hearing• To figure out where the bones came To figure out where the bones came

from we must:from we must:– Establish the ancestral conditionEstablish the ancestral condition– Understand the transformational sequenceUnderstand the transformational sequence• How and why they changed over timeHow and why they changed over time


• Acanthostega gunnariAcanthostega gunnari, one of the , one of the oldest tetrapods (360 My old)oldest tetrapods (360 My old)• One of the first animals to walk on land One of the first animals to walk on land

and have to listen to airborne soundsand have to listen to airborne sounds• Descended from rhipidistian Descended from rhipidistian

crossopterygian fishcrossopterygian fish• Fish have no ossicles but Fish have no ossicles but

AcanthostegaAcanthostega had a stapes had a stapes• Did the stapes help it hear?Did the stapes help it hear?

• Acanthostega gunnariAcanthostega gunnari, one of the , one of the oldest tetrapods (360 My old)oldest tetrapods (360 My old)• One of the first animals to walk on land One of the first animals to walk on land

and have to listen to airborne soundsand have to listen to airborne sounds• Descended from rhipidistian Descended from rhipidistian

crossopterygian fishcrossopterygian fish• Fish have no ossicles but Fish have no ossicles but

AcanthostegaAcanthostega had a stapes had a stapes• Did the stapes help it hear?Did the stapes help it hear?


• AcanthostegaAcanthostega’s stapes fit into a hole in ’s stapes fit into a hole in the side of the braincase that connects the side of the braincase that connects the inner ear and a notch near the the inner ear and a notch near the spiraclespiracle• In later tetrapods, notch holds In later tetrapods, notch holds

tympanumtympanum• Stapes of Stapes of AcanthostegaAcanthostega is homologous is homologous

with later groupswith later groups– Its function is probably homologous as Its function is probably homologous as

wellwell

• AcanthostegaAcanthostega’s stapes fit into a hole in ’s stapes fit into a hole in the side of the braincase that connects the side of the braincase that connects the inner ear and a notch near the the inner ear and a notch near the spiraclespiracle• In later tetrapods, notch holds In later tetrapods, notch holds

tympanumtympanum• Stapes of Stapes of AcanthostegaAcanthostega is homologous is homologous

with later groupswith later groups– Its function is probably homologous as Its function is probably homologous as

wellwell


• AcanthostegaAcanthostega’s stapes could not have appeared out ’s stapes could not have appeared out of nowhereof nowhere– Remember that the panda’s thumb was an exapted carpal Remember that the panda’s thumb was an exapted carpal

bonebone

• Stapes of Stapes of AcanthostegaAcanthostega is homologous to is homologous to crossopterygian hyomandibula bonecrossopterygian hyomandibula bone

• Hyomandibula acts as a brace between the jaw and Hyomandibula acts as a brace between the jaw and braincasebraincase

• Muscles attached to hyomandibula pump the jaws to Muscles attached to hyomandibula pump the jaws to open and close the spiracleopen and close the spiracle– Muscles attached to stapes in Muscles attached to stapes in AcanthostegaAcanthostega probably had probably had

same functionsame function

• AcanthostegaAcanthostega’s stapes could not have appeared out ’s stapes could not have appeared out of nowhereof nowhere– Remember that the panda’s thumb was an exapted carpal Remember that the panda’s thumb was an exapted carpal

bonebone

• Stapes of Stapes of AcanthostegaAcanthostega is homologous to is homologous to crossopterygian hyomandibula bonecrossopterygian hyomandibula bone

• Hyomandibula acts as a brace between the jaw and Hyomandibula acts as a brace between the jaw and braincasebraincase

• Muscles attached to hyomandibula pump the jaws to Muscles attached to hyomandibula pump the jaws to open and close the spiracleopen and close the spiracle– Muscles attached to stapes in Muscles attached to stapes in AcanthostegaAcanthostega probably had probably had

same functionsame function


• AcanthostegaAcanthostega was a transitional form was a transitional form• Hyomandibula was an exaptation for Hyomandibula was an exaptation for

hearinghearing• Hyomandibula and stapes are also Hyomandibula and stapes are also

developmentally homologousdevelopmentally homologous– Both form from second gill archBoth form from second gill arch

• What about malleus and incus?What about malleus and incus?– Only mammals have themOnly mammals have them– First appeared in fossil mammalsFirst appeared in fossil mammals

• AcanthostegaAcanthostega was a transitional form was a transitional form• Hyomandibula was an exaptation for Hyomandibula was an exaptation for

hearinghearing• Hyomandibula and stapes are also Hyomandibula and stapes are also

developmentally homologousdevelopmentally homologous– Both form from second gill archBoth form from second gill arch

• What about malleus and incus?What about malleus and incus?– Only mammals have themOnly mammals have them– First appeared in fossil mammalsFirst appeared in fossil mammals


• In position, malleus and incus are In position, malleus and incus are homologous with two jaw bones in homologous with two jaw bones in reptiles, amphibians, and early reptiles, amphibians, and early mammalsmammals– Articular and quadrateArticular and quadrate

• Malleus, incus, articular, and quadrate Malleus, incus, articular, and quadrate develop from first gill archdevelop from first gill arch– Are developmentally homologousAre developmentally homologous

• In position, malleus and incus are In position, malleus and incus are homologous with two jaw bones in homologous with two jaw bones in reptiles, amphibians, and early reptiles, amphibians, and early mammalsmammals– Articular and quadrateArticular and quadrate

• Malleus, incus, articular, and quadrate Malleus, incus, articular, and quadrate develop from first gill archdevelop from first gill arch– Are developmentally homologousAre developmentally homologous


• Ancestor of mammals, the cynodonts, jaw Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articularjoint is formed of quadrate and articular

• Stapes is only bone of hearingStapes is only bone of hearing• Examine fossils to see transition sequenceExamine fossils to see transition sequence• Later mammals, upper and lower jaws Later mammals, upper and lower jaws

articulate without quadrate and articulararticulate without quadrate and articular• These bones free to evolve new functionThese bones free to evolve new function• More recent mammals, quadrate and articular More recent mammals, quadrate and articular

articulate with stapesarticulate with stapes– Function only in conduction of soundFunction only in conduction of sound

• Ancestor of mammals, the cynodonts, jaw Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articularjoint is formed of quadrate and articular

• Stapes is only bone of hearingStapes is only bone of hearing• Examine fossils to see transition sequenceExamine fossils to see transition sequence• Later mammals, upper and lower jaws Later mammals, upper and lower jaws

articulate without quadrate and articulararticulate without quadrate and articular• These bones free to evolve new functionThese bones free to evolve new function• More recent mammals, quadrate and articular More recent mammals, quadrate and articular

articulate with stapesarticulate with stapes– Function only in conduction of soundFunction only in conduction of sound


• Natural selection caused adaptation for Natural selection caused adaptation for better airborne hearingbetter airborne hearing

• If ossicles are detached from jaw If ossicles are detached from jaw hearing is betterhearing is better

• In mammal evolution the three bones In mammal evolution the three bones reduced in size, moved away from jaw, reduced in size, moved away from jaw, and changed functionand changed function

• Natural selection caused adaptation for Natural selection caused adaptation for better airborne hearingbetter airborne hearing

• If ossicles are detached from jaw If ossicles are detached from jaw hearing is betterhearing is better

• In mammal evolution the three bones In mammal evolution the three bones reduced in size, moved away from jaw, reduced in size, moved away from jaw, and changed functionand changed function

Documents

Allometry and Isometry y changes as a function of x y changes as a function of x Allometric equation y = bx a Allometric equation y = bx a – (where