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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 y= one char, x=another, a=coeff. of allometry, and b=constant proportion relating y and x) if “a” = 1 then b = y/x which means that y changes in direct proportion to x if “a” = 1 then b = y/x which means that y changes in direct proportion to x a<1  y increases less rapidly than x a<1  y increases less rapidly than x a>1  y increases more rapidly than x a>1  y increases more rapidly than x 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 y= one char, x=another, a=coeff. of allometry, and b=constant proportion relating y and x) if “a” = 1 then b = y/x which means that y changes in direct proportion to x if “a” = 1 then b = y/x which means that y changes in direct proportion to x a<1  y increases less rapidly than x a<1  y increases less rapidly than x a>1  y increases more rapidly than x a>1  y increases more rapidly than x

2 Many times it is easiest to express this equation like this: Many times it is easiest to express this equation like this: log y = log b + a log x log y = log b + a log x This gives a straight line with slope = a and an intercept = log y This gives a straight line with slope = a and an intercept = log y Most morphological evolution can be described in terms of Allometric relationships. Most morphological evolution can be described in terms of Allometric relationships. Allometric relationships with body mass are often the consequence of adaptation Allometric relationships with body mass are often the consequence of adaptation Many times it is easiest to express this equation like this: Many times it is easiest to express this equation like this: log y = log b + a log x log y = log b + a log x This gives a straight line with slope = a and an intercept = log y This gives a straight line with slope = a and an intercept = log y Most morphological evolution can be described in terms of Allometric relationships. Most morphological evolution can be described in terms of Allometric relationships. Allometric relationships with body mass are often the consequence of adaptation Allometric relationships with body mass are often the consequence of adaptation Allometry and Isometry

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4 Structures that support an organism must change disproportionately in shape as weight increases. Structures that support an organism must change disproportionately in shape as weight increases. Tree trunk mass to cross sectional is 3/2 power of height Tree trunk mass to cross sectional is 3/2 power of height Structures that support an organism must change disproportionately in shape as weight increases. Structures that support an organism must change disproportionately in shape as weight increases. Tree trunk mass to cross sectional is 3/2 power of height Tree trunk mass to cross sectional is 3/2 power of height

5 Evolution of Tolerance In animals, a series of responses occur sequentially in response to stress In animals, a series of responses occur sequentially in response to stress Lets examine these steps... Lets examine these steps... In animals, a series of responses occur sequentially in response to stress In animals, a series of responses occur sequentially in response to stress Lets examine these steps... Lets examine these steps...

6 Example: Example: In cold environments, large size is advantageous in birds and mammals because they lose heat more slowly, Thus requiring less food to maintain constant body temp. In cold environments, large size is advantageous in birds and mammals because they lose heat more slowly, Thus requiring less food to maintain constant body temp. Bergmann’s Rule  “birds and mammals larger in colder climates than same/related species in warmer climates Bergmann’s Rule  “birds and mammals larger in colder climates than same/related species in warmer climates Example: Example: In cold environments, large size is advantageous in birds and mammals because they lose heat more slowly, Thus requiring less food to maintain constant body temp. In cold environments, large size is advantageous in birds and mammals because they lose heat more slowly, Thus requiring less food to maintain constant body temp. Bergmann’s Rule  “birds and mammals larger in colder climates than same/related species in warmer climates Bergmann’s Rule  “birds and mammals larger in colder climates than same/related species in warmer climates Allometry and Isometry

7 1. Changes in behavior 2. Hormone-modulated biochemical and physiological functions 3. Slower, longer lasting changes in physiology (“acclimation”) 4. In some instances, developmental changes in morphology 5. At population level, genetic changes due to differences among genotypes in survival and reproduction rates caused by the stress 1. Changes in behavior 2. Hormone-modulated biochemical and physiological functions 3. Slower, longer lasting changes in physiology (“acclimation”) 4. In some instances, developmental changes in morphology 5. At population level, genetic changes due to differences among genotypes in survival and reproduction rates caused by the stress Evolution of Tolerance

8 If the responses of individual organisms cannot fully compensate for the stress, fitness is reduced If the responses of individual organisms cannot fully compensate for the stress, fitness is reduced This may lead to genetic changes This may lead to genetic changes Some changes entail developmental responses and these are reversible Some changes entail developmental responses and these are reversible – e.g., Seasonal Responses If the responses of individual organisms cannot fully compensate for the stress, fitness is reduced If the responses of individual organisms cannot fully compensate for the stress, fitness is reduced This may lead to genetic changes This may lead to genetic changes Some changes entail developmental responses and these are reversible Some changes entail developmental responses and these are reversible – e.g., Seasonal Responses Evolution of Tolerance

9 What Limits Geographical Ranges of Species? Some ranges are set by biotic factors, interspecific competition & predation, or by abiotic factors such as temperature and water availability Some ranges are set by biotic factors, interspecific competition & predation, or by abiotic factors such as temperature and water availability This question is thus complex and difficult to answer This question is thus complex and difficult to answer The simplest hypothesis is the lack of genetic variation for tolerance of physiological stress The simplest hypothesis is the lack of genetic variation for tolerance of physiological stress – However, in general this is not likely... Some ranges are set by biotic factors, interspecific competition & predation, or by abiotic factors such as temperature and water availability Some ranges are set by biotic factors, interspecific competition & predation, or by abiotic factors such as temperature and water availability This question is thus complex and difficult to answer This question is thus complex and difficult to answer The simplest hypothesis is the lack of genetic variation for tolerance of physiological stress The simplest hypothesis is the lack of genetic variation for tolerance of physiological stress – However, in general this is not likely...

10 Successful colonization of sites may require numerous coincident adaptive changes Successful colonization of sites may require numerous coincident adaptive changes This suite of adaptations may be an improbable concatenation of genetic variants for many characteristics This suite of adaptations may be an improbable concatenation of genetic variants for many characteristics – e.g. Seasonal timing of reproduction & Growth... Successful colonization of sites may require numerous coincident adaptive changes Successful colonization of sites may require numerous coincident adaptive changes This suite of adaptations may be an improbable concatenation of genetic variants for many characteristics This suite of adaptations may be an improbable concatenation of genetic variants for many characteristics – e.g. Seasonal timing of reproduction & Growth... What Limits Geographical Ranges of Species?

11 Trade-offs exist between adaptation to conditions within and beyond the margin of the range Trade-offs exist between adaptation to conditions within and beyond the margin of the range Trade-offs limit adaptation to a new environment due to gene flow from Trade-offs limit adaptation to a new environment due to gene flow from old  new (center of range  periphery) Trade-offs exist between adaptation to conditions within and beyond the margin of the range Trade-offs exist between adaptation to conditions within and beyond the margin of the range Trade-offs limit adaptation to a new environment due to gene flow from Trade-offs limit adaptation to a new environment due to gene flow from old  new (center of range  periphery) What Limits Geographical Ranges of Species?

12 The explanation put fourth by Mayr The explanation put fourth by Mayr Gene flow from the main range of a species into the marginal populations prevents them from further adapting by breaking down adaptive combinations of interacting genes Gene flow from the main range of a species into the marginal populations prevents them from further adapting by breaking down adaptive combinations of interacting genes So, a marginal population may be better if able to adapt & expand range if it could not exchange genes with interior populations So, a marginal population may be better if able to adapt & expand range if it could not exchange genes with interior populations Perhaps species have evolved broader ranges then we give them credit  because the adapted extralimital population we call different species Perhaps species have evolved broader ranges then we give them credit  because the adapted extralimital population we call different species The explanation put fourth by Mayr The explanation put fourth by Mayr Gene flow from the main range of a species into the marginal populations prevents them from further adapting by breaking down adaptive combinations of interacting genes Gene flow from the main range of a species into the marginal populations prevents them from further adapting by breaking down adaptive combinations of interacting genes So, a marginal population may be better if able to adapt & expand range if it could not exchange genes with interior populations So, a marginal population may be better if able to adapt & expand range if it could not exchange genes with interior populations Perhaps species have evolved broader ranges then we give them credit  because the adapted extralimital population we call different species Perhaps species have evolved broader ranges then we give them credit  because the adapted extralimital population we call different species What Limits Geographical Ranges of Species?

13 Adaptation Let’s examine some methods used by evolutionary biologists to test hypotheses about adaptations Let’s examine some methods used by evolutionary biologists to test hypotheses about adaptations – Experiments – Observational studies – Comparative Method Let’s examine some methods used by evolutionary biologists to test hypotheses about adaptations Let’s examine some methods used by evolutionary biologists to test hypotheses about adaptations – Experiments – Observational studies – Comparative Method

14 All Hypotheses Must be Tested: the Giraffe’s Neck Everyone knows that the giraffe evolved a long neck to be able to eat the tallest leaves, thereby escaping from competition with other herbivores Everyone knows that the giraffe evolved a long neck to be able to eat the tallest leaves, thereby escaping from competition with other herbivores Simmons and Scheepers challenged this notion and offered an alternative explanation for the giraffe’s long neck Simmons and Scheepers challenged this notion and offered an alternative explanation for the giraffe’s long neck Everyone knows that the giraffe evolved a long neck to be able to eat the tallest leaves, thereby escaping from competition with other herbivores Everyone knows that the giraffe evolved a long neck to be able to eat the tallest leaves, thereby escaping from competition with other herbivores Simmons and Scheepers challenged this notion and offered an alternative explanation for the giraffe’s long neck Simmons and Scheepers challenged this notion and offered an alternative explanation for the giraffe’s long neck

15 All Hypotheses Must be Tested: the Giraffe’s Neck They found that giraffe’s most often ate leaves at shoulder height, not from the tops of trees They found that giraffe’s most often ate leaves at shoulder height, not from the tops of trees

16 All Hypotheses Must be Tested: the Giraffe’s Neck They also found that males with the longest necks have the largest, hardest skulls They also found that males with the longest necks have the largest, hardest skulls Maybe long necks evolved for competition for females Maybe long necks evolved for competition for females – Female necks became longer because of selection for longer male necks Neck-as-a-weapon hypothesis Neck-as-a-weapon hypothesis They also found that males with the longest necks have the largest, hardest skulls They also found that males with the longest necks have the largest, hardest skulls Maybe long necks evolved for competition for females Maybe long necks evolved for competition for females – Female necks became longer because of selection for longer male necks Neck-as-a-weapon hypothesis Neck-as-a-weapon hypothesis

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18 All Hypotheses Must be Tested: the Giraffe’s Neck Pratt and Anderson classified social status of males Pratt and Anderson classified social status of males – Class C were young adults – Class A were large adults – Class B were small adults Class A males had wider, stronger heads Class A males had wider, stronger heads Studied displacement by classes and receptivity of females of classes Studied displacement by classes and receptivity of females of classes Pratt and Anderson classified social status of males Pratt and Anderson classified social status of males – Class C were young adults – Class A were large adults – Class B were small adults Class A males had wider, stronger heads Class A males had wider, stronger heads Studied displacement by classes and receptivity of females of classes Studied displacement by classes and receptivity of females of classes

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20 All Hypotheses Must be Tested: the Giraffe’s Neck There is evidence for selection on longer necks for reaching high and male-male competition There is evidence for selection on longer necks for reaching high and male-male competition When studying adaptation remember that: When studying adaptation remember that: – Differences among populations or species are not always adaptive – Not every trait is an adaptation – Not every adaptation is perfect There is evidence for selection on longer necks for reaching high and male-male competition There is evidence for selection on longer necks for reaching high and male-male competition When studying adaptation remember that: When studying adaptation remember that: – Differences among populations or species are not always adaptive – Not every trait is an adaptation – Not every adaptation is perfect

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22 Function of Wing Markings and Wavings of Zonosemata Tephritid fly that has distinct dark bands on wings Tephritid fly that has distinct dark bands on wings Holds wings up and waves them Holds wings up and waves them Display seems to mimic threat display of jumping spiders Display seems to mimic threat display of jumping spiders Perhaps flies mimic jumping spiders to avoid predation Perhaps flies mimic jumping spiders to avoid predation – Avoid predation by other predators – Or mimic jumping spiders to avoid predation by jumping spiders Tephritid fly that has distinct dark bands on wings Tephritid fly that has distinct dark bands on wings Holds wings up and waves them Holds wings up and waves them Display seems to mimic threat display of jumping spiders Display seems to mimic threat display of jumping spiders Perhaps flies mimic jumping spiders to avoid predation Perhaps flies mimic jumping spiders to avoid predation – Avoid predation by other predators – Or mimic jumping spiders to avoid predation by jumping spiders

23 Function of Wing Markings and Wavings of Zonosemata Phrase a precise question Phrase a precise question – Do wing markings and waving behavior of Zonosemata mimic threat displays of jumping spiders and deter predation? List three alternative hypotheses List three alternative hypotheses – Flies do not mimic jumping spiders Display may be used in courtship Display may be used in courtship – Flies mimic jumping spiders to deter non-spider predators – Flies mimic jumping spiders to deter jumping spiders Phrase a precise question Phrase a precise question – Do wing markings and waving behavior of Zonosemata mimic threat displays of jumping spiders and deter predation? List three alternative hypotheses List three alternative hypotheses – Flies do not mimic jumping spiders Display may be used in courtship Display may be used in courtship – Flies mimic jumping spiders to deter non-spider predators – Flies mimic jumping spiders to deter jumping spiders

24 Function of Wing Markings and Wavings of Zonosemata Experimental procedure Experimental procedure – Clipped wings of Zonosemata and house flies, exchanged wings, and glued them on opposite fly Clipping and gluing did not affect flying or displaying Clipping and gluing did not affect flying or displaying – Created five experimental groups to test hypotheses Experimental procedure Experimental procedure – Clipped wings of Zonosemata and house flies, exchanged wings, and glued them on opposite fly Clipping and gluing did not affect flying or displaying Clipping and gluing did not affect flying or displaying – Created five experimental groups to test hypotheses

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26 Function of Wing Markings and Wavings of Zonosemata Jumping spiders retreated from flies displaying with marked wings Jumping spiders retreated from flies displaying with marked wings Other predators killed and ate test flies Other predators killed and ate test flies Jumping spiders retreated from flies displaying with marked wings Jumping spiders retreated from flies displaying with marked wings Other predators killed and ate test flies Other predators killed and ate test flies

27 Function of Wing Markings and Wavings of Zonosemata Results consistent with hypothesis 3 but not 1 or 2 Results consistent with hypothesis 3 but not 1 or 2 Support for hypothesis that Zonosemata deters its predators by acting like one Support for hypothesis that Zonosemata deters its predators by acting like one Important experimental design Important experimental design – Testing control groups – All treatments handled identically – Randomization of order of treatments – Replication of treatments Results consistent with hypothesis 3 but not 1 or 2 Results consistent with hypothesis 3 but not 1 or 2 Support for hypothesis that Zonosemata deters its predators by acting like one Support for hypothesis that Zonosemata deters its predators by acting like one Important experimental design Important experimental design – Testing control groups – All treatments handled identically – Randomization of order of treatments – Replication of treatments

28 Function of Wing Markings and Wavings of Zonosemata Why was replication important? Why was replication important? – Reduced distortion of results by unusual individuals or conditions – Can estimate precision of results Study successful because many variables were tested, but each was tested independently Study successful because many variables were tested, but each was tested independently Why was replication important? Why was replication important? – Reduced distortion of results by unusual individuals or conditions – Can estimate precision of results Study successful because many variables were tested, but each was tested independently Study successful because many variables were tested, but each was tested independently

29 Observational Studies Experimental studies are preferred but it is often not feasible to experiment Experimental studies are preferred but it is often not feasible to experiment – e.g., cannot exchange giraffe’s necks with other animal Behavior is hard to experiment with because the experiment often alters the natural behavior Behavior is hard to experiment with because the experiment often alters the natural behavior Must use observational studies sometimes Must use observational studies sometimes – Often they are nearly as powerful as experimental studies Experimental studies are preferred but it is often not feasible to experiment Experimental studies are preferred but it is often not feasible to experiment – e.g., cannot exchange giraffe’s necks with other animal Behavior is hard to experiment with because the experiment often alters the natural behavior Behavior is hard to experiment with because the experiment often alters the natural behavior Must use observational studies sometimes Must use observational studies sometimes – Often they are nearly as powerful as experimental studies

30 Behavioral Thermoregulation Desert iguanas (Dipsosaurus dorsalis) are ectothermic Desert iguanas (Dipsosaurus dorsalis) are ectothermic – Must regulate body temperature behaviorally Can only function between 15° and 45°C Can only function between 15° and 45°C Examine thermal performance curve to see adaptation to particular temperature Examine thermal performance curve to see adaptation to particular temperature Body temperature affects physiological performance Body temperature affects physiological performance Keep body temperature close to 38°C Keep body temperature close to 38°C Desert iguanas (Dipsosaurus dorsalis) are ectothermic Desert iguanas (Dipsosaurus dorsalis) are ectothermic – Must regulate body temperature behaviorally Can only function between 15° and 45°C Can only function between 15° and 45°C Examine thermal performance curve to see adaptation to particular temperature Examine thermal performance curve to see adaptation to particular temperature Body temperature affects physiological performance Body temperature affects physiological performance Keep body temperature close to 38°C Keep body temperature close to 38°C

31 Desert iguanas (Dipsosaurus dorsalis)

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33 Night Retreats of Garter Snakes Do snakes make adaptive choices of where to sleep at night? Do snakes make adaptive choices of where to sleep at night? Ray Huey implanted garter snakes with radio transmitters with thermometers Ray Huey implanted garter snakes with radio transmitters with thermometers Preferred body temperature is 28– 32°C Preferred body temperature is 28– 32°C Keep body temperature near preferred during day Keep body temperature near preferred during day – Exposed or under rocks Do snakes make adaptive choices of where to sleep at night? Do snakes make adaptive choices of where to sleep at night? Ray Huey implanted garter snakes with radio transmitters with thermometers Ray Huey implanted garter snakes with radio transmitters with thermometers Preferred body temperature is 28– 32°C Preferred body temperature is 28– 32°C Keep body temperature near preferred during day Keep body temperature near preferred during day – Exposed or under rocks

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35 Night Retreats of Garter Snakes How do they choose good retreats at night? How do they choose good retreats at night? Thickness of rock determines microhabitat temperature Thickness of rock determines microhabitat temperature – Thin rocks heat a lot during day and cool a lot during night – Thick rocks heat and cool slowly – Medium rocks heat and cool just enough Garter snakes should choose medium rocks Garter snakes should choose medium rocks How do they choose good retreats at night? How do they choose good retreats at night? Thickness of rock determines microhabitat temperature Thickness of rock determines microhabitat temperature – Thin rocks heat a lot during day and cool a lot during night – Thick rocks heat and cool slowly – Medium rocks heat and cool just enough Garter snakes should choose medium rocks Garter snakes should choose medium rocks

36 Night Retreats of Garter Snakes Huey placed snake models under different rocks, in burrows, and on surface Huey placed snake models under different rocks, in burrows, and on surface – Tested temperature fluctuations Found that snakes choose medium rocks to heat and cool near preferred temperature range Found that snakes choose medium rocks to heat and cool near preferred temperature range Huey placed snake models under different rocks, in burrows, and on surface Huey placed snake models under different rocks, in burrows, and on surface – Tested temperature fluctuations Found that snakes choose medium rocks to heat and cool near preferred temperature range Found that snakes choose medium rocks to heat and cool near preferred temperature range

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39 The Comparative Method Purpose of the comparative method is to remove the effects of evolutionary history from an analysis Purpose of the comparative method is to remove the effects of evolutionary history from an analysis The reasons why you need to remove effects of phylogeny from ecological or behavioral analyses are best demonstrated through examples The reasons why you need to remove effects of phylogeny from ecological or behavioral analyses are best demonstrated through examples Purpose of the comparative method is to remove the effects of evolutionary history from an analysis Purpose of the comparative method is to remove the effects of evolutionary history from an analysis The reasons why you need to remove effects of phylogeny from ecological or behavioral analyses are best demonstrated through examples The reasons why you need to remove effects of phylogeny from ecological or behavioral analyses are best demonstrated through examples

40 The Comparative Method 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 than others Some bats have larger testes for their body size than others Hosken hypothesized that bigger testes evolved for sperm competition Hosken hypothesized that bigger testes evolved for sperm competition Female bats may mate with more than one male so the more sperm deposited by a male, the better chance he has of fertilizing the eggs Female bats may mate with more than one male so the more sperm deposited by a male, the better chance he has of fertilizing the eggs – Bigger 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 than others Some bats have larger testes for their body size than others Hosken hypothesized that bigger testes evolved for sperm competition Hosken hypothesized that bigger testes evolved for sperm competition Female bats may mate with more than one male so the more sperm deposited by a male, the better chance he has of fertilizing the eggs Female bats may mate with more than one male so the more sperm deposited by a male, the better chance he has of fertilizing the eggs – Bigger testes mean more sperm

41 The Comparative Method Hosken reasoned that bat species that live in larger groups would have greater sperm competition Hosken reasoned that bat species that live in larger groups would have greater sperm competition Therefore, they should evolve larger testes Therefore, they should evolve larger testes Hosken collected data on roost group size and testes size and found a significant correlation Hosken collected data on roost group size and testes size and found a significant correlation Hosken reasoned that bat species that live in larger groups would have greater sperm competition Hosken reasoned that bat species that live in larger groups would have greater sperm competition Therefore, they should evolve larger testes Therefore, they should evolve larger testes Hosken collected data on roost group size and testes size and found a significant correlation Hosken collected data on roost group size and testes size and found a significant correlation

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43 The Comparative Method Hosken realized that this correlation may be misleading Hosken realized that this correlation may be misleading

44 The Comparative Method Joe Felsenstein developed a way to evaluate cross-species correlation among traits Joe Felsenstein developed a way to evaluate cross-species correlation among traits – Start with a phylogeny – Look at where sister species diverge – Does the species that evolves larger group sizes also evolve larger testes? – Plot pairs of sister species connected – Drag closest point to origin – Erase origin points and examine independent contrasts Joe Felsenstein developed a way to evaluate cross-species correlation among traits Joe Felsenstein developed a way to evaluate cross-species correlation among traits – Start with a phylogeny – Look at where sister species diverge – Does the species that evolves larger group sizes also evolve larger testes? – Plot pairs of sister species connected – Drag closest point to origin – Erase origin points and examine independent contrasts

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46 The Comparative Method Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Contrasts method Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Contrasts method Significant positive correlation Significant positive correlation Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Contrasts method Hosken repeated bat analysis with Felsenstein’s Phylogenetically Independent Contrasts method Significant positive correlation Significant positive correlation

47 Complex Adaptations in Current Research Will now examine how researchers use the methods mentioned above to investigate hypotheses about complex topics Will now examine how researchers use the methods mentioned above to investigate hypotheses about complex topics – Experiments – Observational studies – Comparative Method Will now examine how researchers use the methods mentioned above to investigate hypotheses about complex topics Will now examine how researchers use the methods mentioned above to investigate hypotheses about complex topics – Experiments – Observational studies – Comparative Method

48 Evolution of Adaptive Traits Every adaptive trait evolves from something else Every adaptive trait evolves from something 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 stapes Other vertebrates do not have all three Other vertebrates do not have all three Ear bones transmit energy from tympanic membrane to oval window in inner ear Ear bones transmit energy from tympanic membrane to oval window in inner ear Every adaptive trait evolves from something else Every adaptive trait evolves from something 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 stapes Other vertebrates do not have all three Other vertebrates do not have all three Ear bones transmit energy from tympanic membrane to oval window in inner ear Ear bones transmit energy from tympanic membrane to oval window in inner ear

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50 Evolution of Adaptive Traits Why do we have three bones instead of one? Why do we have three bones instead of one? Increases sensitivity of hearing Increases sensitivity of hearing To figure out where the bones came from we must: To figure out where the bones came from we must: – Establish the ancestral condition – Understand the transformational sequence How and why they changed over time How and why they changed over time Why do we have three bones instead of one? Why do we have three bones instead of one? Increases sensitivity of hearing Increases sensitivity of hearing To figure out where the bones came from we must: To figure out where the bones came from we must: – Establish the ancestral condition – Understand the transformational sequence How and why they changed over time How and why they changed over time

51 Evolution of Adaptive Traits Acanthostega gunnari, one of the oldest tetrapods (360 My old) Acanthostega gunnari, one of the oldest tetrapods (360 My old) One of the first animals to walk on land and have to listen to airborne sounds One of the first animals to walk on land and have to listen to airborne sounds Descended from rhipidistian crossopterygian fish Descended from rhipidistian crossopterygian fish Fish have no ossicles but Acanthostega had a stapes Fish have no ossicles but Acanthostega had a stapes Did the stapes help it hear? Did the stapes help it hear? Acanthostega gunnari, one of the oldest tetrapods (360 My old) Acanthostega gunnari, one of the oldest tetrapods (360 My old) One of the first animals to walk on land and have to listen to airborne sounds One of the first animals to walk on land and have to listen to airborne sounds Descended from rhipidistian crossopterygian fish Descended from rhipidistian crossopterygian fish Fish have no ossicles but Acanthostega had a stapes Fish have no ossicles but Acanthostega had a stapes Did the stapes help it hear? Did the stapes help it hear?

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53 Evolution of Adaptive Traits Acanthostega’s stapes fit into a hole in the side of the braincase that connects the inner ear and a notch near the spiracle Acanthostega’s stapes fit into a hole in the side of the braincase that connects the inner ear and a notch near the spiracle In later tetrapods, notch holds tympanum In later tetrapods, notch holds tympanum Stapes of Acanthostega is homologous with later groups Stapes of Acanthostega is homologous with later groups – Its function is probably homologous as well Acanthostega’s stapes fit into a hole in the side of the braincase that connects the inner ear and a notch near the spiracle Acanthostega’s stapes fit into a hole in the side of the braincase that connects the inner ear and a notch near the spiracle In later tetrapods, notch holds tympanum In later tetrapods, notch holds tympanum Stapes of Acanthostega is homologous with later groups Stapes of Acanthostega is homologous with later groups – Its function is probably homologous as well

54 Evolution of Adaptive Traits Acanthostega’s stapes could not have appeared out of nowhere Acanthostega’s stapes could not have appeared out of nowhere – Remember that the panda’s thumb was an exapted carpal bone Stapes of Acanthostega is homologous to crossopterygian hyomandibula bone Stapes of Acanthostega is homologous to crossopterygian hyomandibula bone Hyomandibula acts as a brace between the jaw and braincase Hyomandibula acts as a brace between the jaw and braincase Muscles attached to hyomandibula pump the jaws to open and close the spiracle Muscles attached to hyomandibula pump the jaws to open and close the spiracle – Muscles attached to stapes in Acanthostega probably had same function Acanthostega’s stapes could not have appeared out of nowhere Acanthostega’s stapes could not have appeared out of nowhere – Remember that the panda’s thumb was an exapted carpal bone Stapes of Acanthostega is homologous to crossopterygian hyomandibula bone Stapes of Acanthostega is homologous to crossopterygian hyomandibula bone Hyomandibula acts as a brace between the jaw and braincase Hyomandibula acts as a brace between the jaw and braincase Muscles attached to hyomandibula pump the jaws to open and close the spiracle Muscles attached to hyomandibula pump the jaws to open and close the spiracle – Muscles attached to stapes in Acanthostega probably had same function

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56 Evolution of Adaptive Traits Acanthostega was a transitional form Acanthostega was a transitional form Hyomandibula was an exaptation for hearing Hyomandibula was an exaptation for hearing Hyomandibula and stapes are also developmentally homologous Hyomandibula and stapes are also developmentally homologous – Both form from second gill arch What about malleus and incus? What about malleus and incus? – Only mammals have them – First appeared in fossil mammals Acanthostega was a transitional form Acanthostega was a transitional form Hyomandibula was an exaptation for hearing Hyomandibula was an exaptation for hearing Hyomandibula and stapes are also developmentally homologous Hyomandibula and stapes are also developmentally homologous – Both form from second gill arch What about malleus and incus? What about malleus and incus? – Only mammals have them – First appeared in fossil mammals

57 Evolution of Adaptive Traits In position, malleus and incus are homologous with two jaw bones in reptiles, amphibians, and early mammals In position, malleus and incus are homologous with two jaw bones in reptiles, amphibians, and early mammals – Articular and quadrate Malleus, incus, articular, and quadrate develop from first gill arch Malleus, incus, articular, and quadrate develop from first gill arch – Are developmentally homologous In position, malleus and incus are homologous with two jaw bones in reptiles, amphibians, and early mammals In position, malleus and incus are homologous with two jaw bones in reptiles, amphibians, and early mammals – Articular and quadrate Malleus, incus, articular, and quadrate develop from first gill arch Malleus, incus, articular, and quadrate develop from first gill arch – Are developmentally homologous

58 Evolution of Adaptive Traits Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articular Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articular Stapes is only bone of hearing Stapes is only bone of hearing Examine fossils to see transition sequence Examine fossils to see transition sequence Later mammals, upper and lower jaws articulate without quadrate and articular Later mammals, upper and lower jaws articulate without quadrate and articular These bones free to evolve new function These bones free to evolve new function More recent mammals, quadrate and articular articulate with stapes More recent mammals, quadrate and articular articulate with stapes – Function only in conduction of sound Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articular Ancestor of mammals, the cynodonts, jaw joint is formed of quadrate and articular Stapes is only bone of hearing Stapes is only bone of hearing Examine fossils to see transition sequence Examine fossils to see transition sequence Later mammals, upper and lower jaws articulate without quadrate and articular Later mammals, upper and lower jaws articulate without quadrate and articular These bones free to evolve new function These bones free to evolve new function More recent mammals, quadrate and articular articulate with stapes More recent mammals, quadrate and articular articulate with stapes – Function only in conduction of sound

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60 Evolution of Adaptive Traits Natural selection caused adaptation for better airborne hearing Natural selection caused adaptation for better airborne hearing If ossicles are detached from jaw hearing is better If ossicles are detached from jaw hearing is better In mammal evolution the three bones reduced in size, moved away from jaw, and changed function In mammal evolution the three bones reduced in size, moved away from jaw, and changed function Natural selection caused adaptation for better airborne hearing Natural selection caused adaptation for better airborne hearing If ossicles are detached from jaw hearing is better If ossicles are detached from jaw hearing is better In mammal evolution the three bones reduced in size, moved away from jaw, and changed function In mammal evolution the three bones reduced in size, moved away from jaw, and changed function


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