chapter 9. 1. natural selection can change allele frequencies in the next generation, but it does...

Chapter 9Chapter 9

1.1. Natural selection can change allele Natural selection can change allele frequencies in the next generation, but it frequencies in the next generation, but it does not drive genotype frequencies away does not drive genotype frequencies away from predicted values under H-W.from predicted values under H-W.

2.2. Balancing selection, overdominance and Balancing selection, overdominance and heterozygote superiority are synonymous?heterozygote superiority are synonymous?

3.3. Heterozygote inferiority or disruptive Heterozygote inferiority or disruptive selection reduces genetic diversity within selection reduces genetic diversity within populations, but helps maintain genetic populations, but helps maintain genetic diversity among populations.diversity among populations.

4.4. Explain why random genetic drift is the Explain why random genetic drift is the antithesis of natural selection.antithesis of natural selection.

5.5. What is an extinction vortex? What is an extinction vortex?

1.1. Natural selection can change allele Natural selection can change allele frequencies in the next generation, but it frequencies in the next generation, but it does not drive genotype frequencies away does not drive genotype frequencies away from predicted values under H-W.from predicted values under H-W.

2.2. Balancing selection, overdominance and Balancing selection, overdominance and heterozygote superiority are synonymous?heterozygote superiority are synonymous?

3.3. Heterozygote inferiority or disruptive Heterozygote inferiority or disruptive selection reduces genetic diversity within selection reduces genetic diversity within populations, but helps maintain genetic populations, but helps maintain genetic diversity among populations.diversity among populations.

4.4. Explain why random genetic drift is the Explain why random genetic drift is the antithesis of natural selection.antithesis of natural selection.

5.5. What is an extinction vortex? What is an extinction vortex?

• While working on your tan at an island While working on your tan at an island in the Caribbean you determine that 22 in the Caribbean you determine that 22 iguanas migrated onto this island from iguanas migrated onto this island from a neighboring island. You ask the local a neighboring island. You ask the local witch doctor how many iguanas lived witch doctor how many iguanas lived on the island prior to the migration on the island prior to the migration event and he tells you 478. Please event and he tells you 478. Please calculate the migration coefficient (m).calculate the migration coefficient (m).

• While working on your tan at an island While working on your tan at an island in the Caribbean you determine that 22 in the Caribbean you determine that 22 iguanas migrated onto this island from iguanas migrated onto this island from a neighboring island. You ask the local a neighboring island. You ask the local witch doctor how many iguanas lived witch doctor how many iguanas lived on the island prior to the migration on the island prior to the migration event and he tells you 478. Please event and he tells you 478. Please calculate the migration coefficient (m).calculate the migration coefficient (m).

Function of Wing Markings and Wavings of ZonosemataFunction of Wing Markings

and Wavings of Zonosemata

• Tephritid fly that has Tephritid fly that has distinct dark bands on wingsdistinct dark bands on wings• 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 Perhaps flies mimic jumping spiders to

avoid predationavoid predation– Avoid predation by other predatorsAvoid predation by other predators– Or mimic jumping spiders to avoid predation Or mimic jumping spiders to avoid predation

by jumping spidersby jumping spiders

• Tephritid fly that has Tephritid fly that has distinct dark bands on wingsdistinct dark bands on wings• 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 Perhaps flies mimic jumping spiders to

avoid predationavoid predation– Avoid predation by other predatorsAvoid predation by other predators– Or mimic jumping spiders to avoid predation Or mimic jumping spiders to avoid predation

by jumping spidersby jumping spiders


and Wavings of Zonosemata• 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 mimic threat displays of jumping spiders and deter predation?jumping 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-Flies mimic jumping spiders to deter non-spider predatorsspider predators

– Flies mimic jumping spiders to deter Flies mimic jumping spiders to deter 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 mimic threat displays of jumping spiders and deter predation?jumping 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-Flies mimic jumping spiders to deter non-spider predatorsspider predators

– Flies mimic jumping spiders to deter Flies mimic jumping spiders to deter jumping spidersjumping spiders



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

• Other predators Other predators killed and ate test killed and ate test fliesflies

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

• Other predators Other predators killed and ate test killed and ate test fliesflies



• Results consistent with hypothesis 3 Results consistent with hypothesis 3 but not 1 or 2but not 1 or 2• Support for hypothesis that Support for hypothesis that

ZonosemataZonosemata deters its predators by deters its predators by acting like oneacting 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 Results consistent with hypothesis 3 but not 1 or 2but not 1 or 2• Support for hypothesis that Support for hypothesis that

ZonosemataZonosemata deters its predators by deters its predators by acting like oneacting 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 conditions (variance)individuals or conditions (variance)– 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 conditions (variance)individuals or conditions (variance)– 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

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



• 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 alot during day and cool Thin rocks heat alot during day and cool

alot during nightalot 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 alot during day and cool Thin rocks heat alot during day and cool

alot during nightalot 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 analysis (phylogenetic history from an analysis (phylogenetic independence)independence)

• 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 analysis (phylogenetic history from an analysis (phylogenetic independence)independence)

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

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

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

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

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

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

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

• Female bats may mate with more than one Female bats may mate with more than one male so the more sperm deposited by a male so the more sperm deposited by a male, the better chance he has of fertilizing male, the better chance he has of fertilizing the eggsthe 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 Joe Felsenstein developed a way to evaluate cross-species correlation evaluate cross-species correlation among traitsamong 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 Does the species that evolves larger group

sizes also evolve larger testes?sizes 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 Erase origin points and examine

independent contrastsindependent contrasts

• Joe Felsenstein developed a way to Joe Felsenstein developed a way to evaluate cross-species correlation evaluate cross-species correlation among traitsamong 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 Does the species that evolves larger group

sizes also evolve larger testes?sizes 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 Erase origin points and examine

independent contrastsindependent contrasts

•Significant positive correlationSignificant positive correlation•Sperm competition and testes Sperm competition and testes sizesize

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

Phenotypic PlasticityPhenotypic Plasticity

• We have assumed that phenotypes are We have assumed that phenotypes are fixedfixed• In reality, many phenotypes are plastic, In reality, many phenotypes are plastic,

i.e., individuals with identical i.e., individuals with identical genotypes may have different genotypes may have different phenotypes if they live in different phenotypes if they live in different environmentsenvironments• Phenotypic plasticity is a trait that can Phenotypic plasticity is a trait that can

evolveevolve• It may or may not be adaptiveIt may or may not be adaptive

• We have assumed that phenotypes are We have assumed that phenotypes are fixedfixed• In reality, many phenotypes are plastic, In reality, many phenotypes are plastic,

i.e., individuals with identical i.e., individuals with identical genotypes may have different genotypes may have different phenotypes if they live in different phenotypes if they live in different environmentsenvironments• Phenotypic plasticity is a trait that can Phenotypic plasticity is a trait that can

evolveevolve• It may or may not be adaptiveIt may or may not be adaptive


• Water flea, Water flea, Daphnia magnaDaphnia magna, lives in lakes, lives in lakes• Usually reproduces asexuallyUsually reproduces asexually

– Good for studies of phenotypic plasticity Good for studies of phenotypic plasticity because genotype is knownbecause genotype is known

• Luc de Meester studied plasticity in Luc de Meester studied plasticity in phototactic behaviorphototactic behavior

• Selected 10 genotypes and used clones of Selected 10 genotypes and used clones of each to testeach to test

• In graduated cylinder, illuminated from In graduated cylinder, illuminated from above and recorded which direction they above and recorded which direction they swamswam

• Water flea, Water flea, Daphnia magnaDaphnia magna, lives in lakes, lives in lakes• Usually reproduces asexuallyUsually reproduces asexually

– Good for studies of phenotypic plasticity Good for studies of phenotypic plasticity because genotype is knownbecause genotype is known

• Luc de Meester studied plasticity in Luc de Meester studied plasticity in phototactic behaviorphototactic behavior

• Selected 10 genotypes and used clones of Selected 10 genotypes and used clones of each to testeach to test

• In graduated cylinder, illuminated from In graduated cylinder, illuminated from above and recorded which direction they above and recorded which direction they swamswam


• Each lake population has genetic Each lake population has genetic variationvariation• Tested Tested DaphniaDaphnia by using water from by using water from

lakes where fish occurred and where lakes where fish occurred and where they were absentthey were absent• Hypothesized that when fish are Hypothesized that when fish are

present negative phototaxis is more present negative phototaxis is more adaptiveadaptive• Phototactic behavior was Phototactic behavior was

phenotypically plasticphenotypically plastic

• Each lake population has genetic Each lake population has genetic variationvariation• Tested Tested DaphniaDaphnia by using water from by using water from

lakes where fish occurred and where lakes where fish occurred and where they were absentthey were absent• Hypothesized that when fish are Hypothesized that when fish are

present negative phototaxis is more present negative phototaxis is more adaptiveadaptive• Phototactic behavior was Phototactic behavior was

phenotypically plasticphenotypically plastic


• Genetic variation in plasticityGenetic variation in plasticity– Some populations were more plastic than Some populations were more plastic than

othersothers– Genotype-by-environment interactionGenotype-by-environment interaction

• Genetic variation in plasticityGenetic variation in plasticity– Some populations were more plastic than Some populations were more plastic than

othersothers– Genotype-by-environment interactionGenotype-by-environment interaction

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

Evolution of Adaptive TraitsEvolution of Adaptive Traits

• 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

Trade-Offs and ConstraintsTrade-Offs and Constraints

• Organisms cannot optimize all features Organisms cannot optimize all features at onceat once

• Many factors limit adaptive evolutionMany factors limit adaptive evolution– Trade-offsTrade-offs– Functional constraintsFunctional constraints– Lack of genetic variationLack of genetic variation

• Organisms cannot optimize all features Organisms cannot optimize all features at onceat once

• Many factors limit adaptive evolutionMany factors limit adaptive evolution– Trade-offsTrade-offs– Functional constraintsFunctional constraints– Lack of genetic variationLack of genetic variation


• Begonia involucrataBegonia involucrata is a monoecious is a monoecious plant pollinated by beesplant pollinated by bees

• Male flowers offer pollen to beesMale flowers offer pollen to bees

• Female flowers offer nothingFemale flowers offer nothing

• Female flowers resemble male flowers Female flowers resemble male flowers to trick bees into visiting themto trick bees into visiting them

• What mode of selection do bees What mode of selection do bees impose on flower size?impose on flower size?

• Begonia involucrataBegonia involucrata is a monoecious is a monoecious plant pollinated by beesplant pollinated by bees

• Male flowers offer pollen to beesMale flowers offer pollen to bees

• Female flowers offer nothingFemale flowers offer nothing

• Female flowers resemble male flowers Female flowers resemble male flowers to trick bees into visiting themto trick bees into visiting them

• What mode of selection do bees What mode of selection do bees impose on flower size?impose on flower size?


• Schemske and Agren’s two hypothesesSchemske and Agren’s two hypotheses– The more closely female flowers resemble The more closely female flowers resemble

males, the more often they are visited by males, the more often they are visited by beesbees• Stabilizing selection toward mean male Stabilizing selection toward mean male

phenotypephenotype

– The more closely female flowers resemble The more closely female flowers resemble the most rewarding males, the more often the most rewarding males, the more often they are visited by beesthey are visited by bees• If large male flowers offer bigger rewards, If large male flowers offer bigger rewards,

directional selection for larger flowersdirectional selection for larger flowers

• Schemske and Agren’s two hypothesesSchemske and Agren’s two hypotheses– The more closely female flowers resemble The more closely female flowers resemble

males, the more often they are visited by males, the more often they are visited by beesbees• Stabilizing selection toward mean male Stabilizing selection toward mean male

phenotypephenotype

– The more closely female flowers resemble The more closely female flowers resemble the most rewarding males, the more often the most rewarding males, the more often they are visited by beesthey are visited by bees• If large male flowers offer bigger rewards, If large male flowers offer bigger rewards,

directional selection for larger flowersdirectional selection for larger flowers


• Schemske and Agren made artificial Schemske and Agren made artificial flowers put equal numbers of three flowers put equal numbers of three sizes in a forestsizes in a forest

• The larger the flower, the more often The larger the flower, the more often bees visited itbees visited it

• Why aren’t female flowers always Why aren’t female flowers always large?large?– MaladaptiveMaladaptive– Maybe not enough genetic variationMaybe not enough genetic variation

• Schemske and Agren made artificial Schemske and Agren made artificial flowers put equal numbers of three flowers put equal numbers of three sizes in a forestsizes in a forest

• The larger the flower, the more often The larger the flower, the more often bees visited itbees visited it

• Why aren’t female flowers always Why aren’t female flowers always large?large?– MaladaptiveMaladaptive– Maybe not enough genetic variationMaybe not enough genetic variation


• Expanded study to inflorescencesExpanded study to inflorescences

• Trade-off: the larger female flowers are, Trade-off: the larger female flowers are, the fewer they can have per the fewer they can have per inflorescenceinflorescence

• Begonia involucrataBegonia involucrata female flower size female flower size determined by directional selection for determined by directional selection for larger flowers and trade-off between larger flowers and trade-off between flower size and numberflower size and number

• Expanded study to inflorescencesExpanded study to inflorescences

• Trade-off: the larger female flowers are, Trade-off: the larger female flowers are, the fewer they can have per the fewer they can have per inflorescenceinflorescence

• Begonia involucrataBegonia involucrata female flower size female flower size determined by directional selection for determined by directional selection for larger flowers and trade-off between larger flowers and trade-off between flower size and numberflower size and number


• Flower color change in Flower color change in Fuchsia excoricataFuchsia excoricata

• Bird-pollinated tree in New ZealandBird-pollinated tree in New Zealand

• Bell-shaped hypanthium (floral tube) and Bell-shaped hypanthium (floral tube) and sepalssepals

• Hypanthium is green 5.5 days after openingHypanthium is green 5.5 days after opening

• Then it turns redThen it turns red– Transition is 1.5 daysTransition is 1.5 days

– Red flowers remain for 5 daysRed flowers remain for 5 days

– Then red flowers drop off of treeThen red flowers drop off of tree

• Flower color change in Flower color change in Fuchsia excoricataFuchsia excoricata

• Bird-pollinated tree in New ZealandBird-pollinated tree in New Zealand

• Bell-shaped hypanthium (floral tube) and Bell-shaped hypanthium (floral tube) and sepalssepals

• Hypanthium is green 5.5 days after openingHypanthium is green 5.5 days after opening

• Then it turns redThen it turns red– Transition is 1.5 daysTransition is 1.5 days

– Red flowers remain for 5 daysRed flowers remain for 5 days

– Then red flowers drop off of treeThen red flowers drop off of tree


• Pollination occurs during green and Pollination occurs during green and intermediate phasesintermediate phases

• Nectar is produced days 1–7Nectar is produced days 1–7

• Birds prefer green flowers and ignore Birds prefer green flowers and ignore red onesred ones

• Color change is cue to pollinatorColor change is cue to pollinator

• Why doesn’t Why doesn’t FuchsiaFuchsia drop its flowers drop its flowers after 7 days instead of changing color?after 7 days instead of changing color?

• Pollination occurs during green and Pollination occurs during green and intermediate phasesintermediate phases

• Nectar is produced days 1–7Nectar is produced days 1–7

• Birds prefer green flowers and ignore Birds prefer green flowers and ignore red onesred ones

• Color change is cue to pollinatorColor change is cue to pollinator

• Why doesn’t Why doesn’t FuchsiaFuchsia drop its flowers drop its flowers after 7 days instead of changing color?after 7 days instead of changing color?


• Two hypotheses of Delph and LivelyTwo hypotheses of Delph and Lively– Red attracts pollinator to tree because of Red attracts pollinator to tree because of

bright colorbright color• Green flowers surrounded by red flowers Green flowers surrounded by red flowers

should be pollinated mostshould be pollinated most

– Removed red flowers from some trees and Removed red flowers from some trees and found no evidence for pollinator-attraction found no evidence for pollinator-attraction hypothesishypothesis

• Two hypotheses of Delph and LivelyTwo hypotheses of Delph and Lively– Red attracts pollinator to tree because of Red attracts pollinator to tree because of

bright colorbright color• Green flowers surrounded by red flowers Green flowers surrounded by red flowers

should be pollinated mostshould be pollinated most

– Removed red flowers from some trees and Removed red flowers from some trees and found no evidence for pollinator-attraction found no evidence for pollinator-attraction hypothesishypothesis


• Two hypotheses of Delph and LivelyTwo hypotheses of Delph and Lively– Physiological constraint keeps Physiological constraint keeps FuchsiaFuchsia

from dropping flowers soonerfrom dropping flowers sooner– Growth of pollen tube takes timeGrowth of pollen tube takes time– Flower should not drop before pollen Flower should not drop before pollen

fertilizes eggfertilizes egg– Hand pollinated flowers and examined how Hand pollinated flowers and examined how

long pollen took to reach ovarylong pollen took to reach ovary– Takes three days to reach ovaryTakes three days to reach ovary

• Two hypotheses of Delph and LivelyTwo hypotheses of Delph and Lively– Physiological constraint keeps Physiological constraint keeps FuchsiaFuchsia

from dropping flowers soonerfrom dropping flowers sooner– Growth of pollen tube takes timeGrowth of pollen tube takes time– Flower should not drop before pollen Flower should not drop before pollen

fertilizes eggfertilizes egg– Hand pollinated flowers and examined how Hand pollinated flowers and examined how

long pollen took to reach ovarylong pollen took to reach ovary– Takes three days to reach ovaryTakes three days to reach ovary


• FuchsiaFuchsia cannot drop flowers until after cannot drop flowers until after pollen reaches ovary (3 days) and pollen reaches ovary (3 days) and abcission zone forms to drop flower (1.5 abcission zone forms to drop flower (1.5 days)days)

• Flower must wait 4.5 daysFlower must wait 4.5 days

• FuchsiaFuchsia cannot drop flowers until after cannot drop flowers until after pollen reaches ovary (3 days) and pollen reaches ovary (3 days) and abcission zone forms to drop flower (1.5 abcission zone forms to drop flower (1.5 days)days)

• Flower must wait 4.5 daysFlower must wait 4.5 days

Strategies for Asking Interesting QuestionsStrategies for Asking Interesting Questions

• Study natural historyStudy natural history– Wing markings of Wing markings of ZonosemataZonosemata

• Question conventional wisdomQuestion conventional wisdom– Neck of giraffeNeck of giraffe

• Question assumptions of research techniqueQuestion assumptions of research technique– Felsenstein’s independent contrastsFelsenstein’s independent contrasts

• Draw analogies among fieldsDraw analogies among fields– Testes size in other mammalsTestes size in other mammals

• Ask why notAsk why not– Why aren’t female begonia flowers larger?Why aren’t female begonia flowers larger?

• Study natural historyStudy natural history– Wing markings of Wing markings of ZonosemataZonosemata

• Question conventional wisdomQuestion conventional wisdom– Neck of giraffeNeck of giraffe

• Question assumptions of research techniqueQuestion assumptions of research technique– Felsenstein’s independent contrastsFelsenstein’s independent contrasts

• Draw analogies among fieldsDraw analogies among fields– Testes size in other mammalsTestes size in other mammals

• Ask why notAsk why not– Why aren’t female begonia flowers larger?Why aren’t female begonia flowers larger?

chapter 9. 1. natural selection can change allele frequencies in the next generation, but it does...

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spiders tephritid fly

courtship display

genetic diversity

neighboring island

courtship flies

precise question

alternative hypotheses

function of wing markings