Sexual selection and Sexual selection and mate choicemate choice

鄭先祐鄭先祐靜宜大學 生態學系靜宜大學 生態學系

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性擇與交配選擇性擇與交配選擇►A central concern in sexual selection is unA central concern in sexual selection is un

derstanding how female mating preferencderstanding how female mating preferences evolve.es evolve.

►How can female mating preferences evolvHow can female mating preferences evolve if there is no effect of preference on feme if there is no effect of preference on female fitness?ale fitness?

►Two hypotheses, runaway sexual selectioTwo hypotheses, runaway sexual selection and good genes.n and good genes.

►參閱 參閱 Andersson (1994) Sexual selection Andersson (1994) Sexual selection

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Sexual selection and mate Sexual selection and mate choicechoice

► 8.1 introduction8.1 introduction► 8.2 Sexual selection by female mate choice8.2 Sexual selection by female mate choice► 8.3 The null model for the evolution of female 8.3 The null model for the evolution of female

mating preferencesmating preferences► 8.4 Direct selection on female mating 8.4 Direct selection on female mating

preferencespreferences► 8.5 Indirect selection on female mating 8.5 Indirect selection on female mating

preferences : Fisher’s runaway sexual selectionpreferences : Fisher’s runaway sexual selection► 8.6 Indirect selection on female mating 8.6 Indirect selection on female mating

preferences: good genes hypothesespreferences: good genes hypotheses

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Sexual selection and mate Sexual selection and mate choicechoice

►8.7 Interacting forces8.7 Interacting forces►8.8 Multiple traits and their 8.8 Multiple traits and their

preferencespreferences►8.9 Mate copying: a new horizon?8.9 Mate copying: a new horizon?►8.10 summary8.10 summary

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8.2 Sexual selection by female 8.2 Sexual selection by female mate choicemate choice

►The female mate choice is influenced by vThe female mate choice is influenced by variation in male traits. ariation in male traits. Elaborate trains of peacocks, the hyperdeveloElaborate trains of peacocks, the hyperdevelo

ped tail fins forming the sword of swordtails, tped tail fins forming the sword of swordtails, the complex acoustic repertoire of songbirds ahe complex acoustic repertoire of songbirds and frogs, pheromones of moths.nd frogs, pheromones of moths.

這些特徵，有些增加雄性的死亡率。這些特徵，有些增加雄性的死亡率。►有三個研究的途徑：有三個研究的途徑： functional, mechanistifunctional, mechanisti

c, historical approaches.c, historical approaches.

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Three kinds of approachesThree kinds of approaches

► Functional approaches are concerned with the Functional approaches are concerned with the behavioural interactions that bring about mate behavioural interactions that bring about mate choice and how this generates selection on choice and how this generates selection on male traits and female preferences.male traits and female preferences.

►Mechanistic studies attempt to identify the Mechanistic studies attempt to identify the physiological process underlying mating physiological process underlying mating preferences.preferences.

► Historical approaches acknowledge that extant Historical approaches acknowledge that extant traits and preferences have experienced a long traits and preferences have experienced a long history of selection and constraints that history of selection and constraints that influence their current expression.influence their current expression.

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三種途徑間的關係三種途徑間的關係

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8.3 The null model for the 8.3 The null model for the evolution of female mating evolution of female mating

preferencespreferences►Kirkpatrick and Ryan (1991), the evolution Kirkpatrick and Ryan (1991), the evolution

of female mating preferences (Fig. 8.3)of female mating preferences (Fig. 8.3)►The null model assumes the female preferThe null model assumes the female prefer

ence is a constant which predicts trait evoence is a constant which predicts trait evolution.lution. 但是 但是 female preference female preference 有可能會改變。有可能會改變。

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Fig. 8.3 (a) under Fig. 8.3 (a) under direct selection, direct selection,

mating preference mating preference genes also affect genes also affect female survival or female survival or

fecundity.fecundity.

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Fig. 8.3 (b) in Fig. 8.3 (b) in a runaway a runaway

process, the process, the equilibrium equilibrium

curve curve becomes becomes unstable.unstable.

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8.4 Direct selection on female 8.4 Direct selection on female mating preferencesmating preferences

►8.4.1 Fecundity 8.4.1 Fecundity ►8.4.2 Pleiotropic (8.4.2 Pleiotropic ( 多型的多型的 ) effects) effects►8.4.3 Historical studies of sensory biases a8.4.3 Historical studies of sensory biases a

nd sensory exploitationnd sensory exploitation

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8.4.1 fecundity effects8.4.1 fecundity effects

► In many cases a female’s mate choice In many cases a female’s mate choice has an immediate effect on her has an immediate effect on her reproductive success; when males reproductive success; when males offer parental care, defend young or offer parental care, defend young or feed their mates.feed their mates.

► In resource-based mating systems, In resource-based mating systems, direct selection on preference is direct selection on preference is expected to be the rule.expected to be the rule.

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Fecundity effectsFecundity effects

►Robertson(1990) and Bourne (1993), two fRobertson(1990) and Bourne (1993), two frog species, females select mates of a size rog species, females select mates of a size that maximizes fertility rates.that maximizes fertility rates.

►Eisner & Meinwald (1995) Eisner & Meinwald (1995) 蛾蛾 , pyrrolizidin, pyrrolizidine alkaloids (Pas)e alkaloids (Pas) 保護免於保護免於 predation. predation. 這種這種 Pas Pas 是取食獲得的。是取食獲得的。 雄性的使用作雄性的使用作 pheromone, pheromone, 於交配的時候，可透於交配的時候，可透

過過 spermatophore spermatophore 傳送給雌性。傳送給雌性。

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8.4.2 Pleiotropic effects8.4.2 Pleiotropic effects►非直接的天擇，其他的管道非直接的天擇，其他的管道►譬如：譬如： water miteswater mites ，雄性的靠水面的震動，，雄性的靠水面的震動，

吸引雌性，誤以為是獵物吸引雌性，誤以為是獵物►Reproductive character displacement (GeReproductive character displacement (Ge

rhardt, 1994)rhardt, 1994)

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8.4.3 Historical studies of 8.4.3 Historical studies of sensory biases and sensory sensory biases and sensory

exploitationexploitation► The sensory exploitation hypothesis predicts The sensory exploitation hypothesis predicts

that the evolution of sexually selected traits is that the evolution of sexually selected traits is influenced by these pre-existing sensory influenced by these pre-existing sensory biases.biases.

► This generates a prediction about the This generates a prediction about the historical pattern of traits – that is distinct historical pattern of traits – that is distinct from the prediction of good genes and from the prediction of good genes and runaway sexual selection in which the runaway sexual selection in which the preference and trait evolve in concert.preference and trait evolve in concert.

► One can discriminate between these two sets One can discriminate between these two sets of hypotheses: Sensory exploitation vs. of hypotheses: Sensory exploitation vs. indirect selection (good genes and runaway)indirect selection (good genes and runaway)

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Sensory exploitation Sensory exploitation hypothesishypothesis

►The tungara frog produces a call consistinThe tungara frog produces a call consisting of a whine and a chuck.g of a whine and a chuck.

►The whine is always present and is necessThe whine is always present and is necessary and sufficient to elicit mate recognitioary and sufficient to elicit mate recognition from females. n from females.

►The chuck is not always produced, but whThe chuck is not always produced, but when added to the whine it increases the attren added to the whine it increases the attractiveness of the call to females as well as activeness of the call to females as well as to frog-eating bats (Ryan, 1985).to frog-eating bats (Ryan, 1985).

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Fig. 8.4 Phylogenetic relationships of frogs of the P. pFig. 8.4 Phylogenetic relationships of frogs of the P. pustulosus species complex showing the advertisemeustulosus species complex showing the advertiseme

nt calls of each species.nt calls of each species.

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►The most parsimonious explanation for thThe most parsimonious explanation for the occurrence of a chuck preference in bote occurrence of a chuck preference in both clades within the species group is that th clades within the species group is that the preference is shared from a common ahe preference is shared from a common ancestor.ncestor.

►A pre-existing preference.A pre-existing preference.

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8.5 Indirect selection on mating 8.5 Indirect selection on mating preferences: Fisher’s runaway sexual preferences: Fisher’s runaway sexual

selectionselection

►Fisher’s theory of runaway sexual Fisher’s theory of runaway sexual selection has been a difficult one to selection has been a difficult one to evaluate empirically.evaluate empirically.

►This might be because the runaway This might be because the runaway process is very rapid and thus unlikely process is very rapid and thus unlikely to be observed.to be observed.

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8.5.1 genetic correlation of trait 8.5.1 genetic correlation of trait and preferenceand preference

►Bakker (1993), sticklebacks , Bakker (1993), sticklebacks , 不同的特徵不同的特徵(( 基因型基因型 )) 各自喜歡相類似特徵的對象。各自喜歡相類似特徵的對象。

►Wilkinson and Reillo (1994) conducted bidWilkinson and Reillo (1994) conducted bidirectional selection experiment on eye spairectional selection experiment on eye span of stalk-eyed flies. n of stalk-eyed flies. 經過經過 1313 世代，長眼的世代，長眼的後代，仍是喜歡長眼的，短眼的則是喜歡短後代，仍是喜歡長眼的，短眼的則是喜歡短眼的。眼的。

►There was a positive genetic correlation bThere was a positive genetic correlation between trait and preference.etween trait and preference.

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8.6 good genes hypotheses8.6 good genes hypotheses

►The focus of good genes studies can be clThe focus of good genes studies can be classified into four categoriesassified into four categories (i) the general relationship between ornament (i) the general relationship between ornament

elaboration and offspring viabilityelaboration and offspring viability (ii) the hypothesis of female choice for parasit(ii) the hypothesis of female choice for parasit

e resistance genese resistance genes (iii) female choice of trait asymmetry as an ind(iii) female choice of trait asymmetry as an ind

icator of genetic qualityicator of genetic quality (iv) choice for genetic complementarity. (iv) choice for genetic complementarity.

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8.7 interacting forces8.7 interacting forces► Direct selection, runaway selection and selectioDirect selection, runaway selection and selectio

n for good genes are often portrayed as mutualln for good genes are often portrayed as mutually exclusive hypotheses for the evolution of femay exclusive hypotheses for the evolution of females preferences.les preferences.

► This need not be the case.This need not be the case.► 這些不同的因素是有可能相互同時存在。這些不同的因素是有可能相互同時存在。► Searcy (1992), song repertoires were initially favSearcy (1992), song repertoires were initially fav

oured by a pre-existing preference for complex aoured by a pre-existing preference for complex auditory stimulation, but larger repertoires and tuditory stimulation, but larger repertoires and the preference for them coevolved through a runhe preference for them coevolved through a runaway or a good genes processes. away or a good genes processes.

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8.8 multiple traits and their 8.8 multiple traits and their preferencespreferences

►Some studies have demonstrated empiricSome studies have demonstrated empirically that females do attend to more than oally that females do attend to more than on trait.n trait.

►Moller and Pomiankowski (1993) indicateMoller and Pomiankowski (1993) indicated that multiple sexual ornaments are mord that multiple sexual ornaments are more likely in lek breeding and other polygyne likely in lek breeding and other polygynous species of birds while single sexual orous species of birds while single sexual ornaments seem to be the rule in monogamnaments seem to be the rule in monogamous species.ous species.

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8.9 mate copying: a new 8.9 mate copying: a new horizon?horizon?

►Recent studies have shown that mating prRecent studies have shown that mating preferences can be influenced by social cues.eferences can be influenced by social cues. Females copy the mate choice of others (GibsFemales copy the mate choice of others (Gibs

on and Hoglund, 1992)on and Hoglund, 1992)►Mate copying also can occur between speMate copying also can occur between spe

cies. cies. Schlupp, et al. (1994) studies mating preferenSchlupp, et al. (1994) studies mating preferen

ces in a sexual-asexual species complex of moces in a sexual-asexual species complex of mollies, the sailfin molly and the Amazon molly.llies, the sailfin molly and the Amazon molly.

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8.10 summary8.10 summary

► Sexual selection studies have moved from Sexual selection studies have moved from the single debate over Fisher’s runaway the single debate over Fisher’s runaway sexual selection versus selection fro good sexual selection versus selection fro good genes.genes.

►Direct selection had always been considered Direct selection had always been considered an important influence on preferences in an important influence on preferences in resource-based mating systems.resource-based mating systems.

► There is some strong support for the genetic There is some strong support for the genetic correlations between trait and preference.correlations between trait and preference.

►Historical approaches have introduced a Historical approaches have introduced a new dimension in attempting to reconstruct new dimension in attempting to reconstruct the history of traits and preferences.the history of traits and preferences.

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