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Berkeley BIOLOGY 1B - Whiptail Lizard

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Whiptail LizardSexual SelectionCharles Darwin and Alfred Russell WallaceNoticed that males of many species have highly elaborated traits that seem maladaptive (secondary sexual characters)AntlersIrish Elk (extinct)Hercules BeetleMaleFemaleHornsBighorn SheepElephant TusksAfrican Lion: Mane is used for protection during male clashes (male-male competition)Pheasant: Elaboratebright red wattle oncheekPheasant: Elaboratespur used in male-malefighting and by femalesto choose.(Notice the fake spur on the right. Some males try to trick females, but do not fight.)Two Types of Sexual SelectionMale-male competition (intra-sexual selection)Mate (female) choice (inter-sexual selection)Male-male competitionWithin group dominanceFemale-defense polygynyTerritorial polygynyLekking (competition for a position in the lek)Within group dominanceGrey WolvesFemale defense polygynyNorthern Elephant SealsTerritorial defense polygynyImpalaWaterbucks head buttingSperm competitionMate ChoiceResource basedNon-resource basedTwo broad categories:In most cases, females are the choosy sex, but not always.Why?Grouse, a lekking speciesWhy are females choosy?Investment costeggs are expensive relative to sperminternal fertilization and carrying young to term is costlyWhen are males choosy?When their contributions exceed the cost of making eggsThe chances of mating with multiple females is small (biased sex ratio—many females and very few males)(sex-role reversal)Example: Sea Horse (males care for the young)Mate choicemate with correct speciesbetter fertilization ability or higher fecundityprovides more foodbetter parental abilitybetter breeding territory or defended resourcelower risks or hazards (e.g., predation)partner offers higher heritable viability or other heritable qualities that are important(Why choose in the first place?)Mate choiceDirect benefits (proximate benefits)Example: Bush crickets (nuptial gifts)1. Males provide spermatophoreswhich females feed on. Often consistof up to 30-40% of male body weight(i.e., very costly)2. More spermatophores allow femaleto lay more eggs.Mate ChoiceIndirect benefits (ultimate benefits)Good genesOthers (e.g., Fisherian runaway sexual selection, which will not be discussed)Good GenesFemales (or males) choose a mate which offers high quality genes influencing survivalMate quality is indicated by a secondary traitSecondary trait must be heritableMust be heritable variation in mate qualityNo, low, or high cost to males bearing the trait (e.g., bearing the cost is an indicator of good genes...”handicap model”)Good Genes ExampleGray Tree Frog (Hyla versicolor)Short vs. Long CallsFitness MeasureHigh FoodLow FoodLarval growthLCLCTime to meta.LCMass at meta.Larval survivalPostmeta. growthLCFinal TopicsLekking and the evolution of leksSensory bias/exploitationWhat are leks?No male parental care (only contribution is sperm)An area that males aggregate and mate with females that is not associated with feeding, etc.Display sites of males contain no significant resources to females (e.g., nesting site)Females have the opportunity to choose, or shop, among available malesAn aggregation of males which femalesvisit only for the purpose of mating.Evolution of lekslower predation risk for males and femalespassive attraction; more males is betterhotspot model (males congregate in areas that increase the probability of encountering females)black hole model (females are not choosy, but wish to avoid dangers associated with mating)hotshot model (females choose the “best” male; poor males congregate near good males in the hopes of increasing their chances)BowerbirdsAn example of sexual selection in a lekking species:Males build and decorate courtship arenas, calledbowers, on leks for the purpose of courting females.Females prefer males with lots of blue and yellow objects atthe bower. They also prefer neat bowers.While the female (grey) sights and watches, the male produces an elaborate courship display, including dances, jigs, wingflips, and vocalization. Males, hoping to woo females, will even clasp a yellow flower or feather in the beak.Males with the best of all these traits get the most matings.Many species of bowerbirds build elaborate bowers, decorate them with colorful objects, and have elaborate courship displaysFembotsSensory Bias/ExploitationLatent preferences in females are used by males to gain greater reproductive success.Physaleumus FrogsP. coloradum P. postulosumP. coloradum: Males attract mates by calling using WHINESP. postulosum: Males attract mates by calling using WHINES and some use CHUCKSCHUCKS evolvein malesCHUCK preferenceevolves in femalesExperimentTake tape playback unit with recording of P. coloradum WHINES with P. postulosumCHUCKS to pond. Play and observed, relative to just WHINES, how many females are attracted.Female Pref.WHINENOWHINE+CHUCKYESSwordtailsSwordtailsPlatyfish SwordtailsSwords evolvein malesSword preferenceevolves in femalesPlatyfish: No swords. When males are modified to have swords, the female Platyfish prefer themSwordtails: The males of some species have swords. Females prefer males with long swords.Helpful behaviorsAlarm calls (e.g., Belding ground squirrel)Sentinel behavior (e.g., meerkats)Nest helpingEusocial behaviorActor performs some action that benefitsanother (the recipient).How do you explain the evolution ofhelpful behavior?Mutualism (actor benefits)Reciprocal altruism (actor eventually benefits)Kin selection (indirect selection)InteractionSocial DonorSocial RecipientMutualism++Reciprocity+ (delayed)+Altruism-+Selfishness+-Spitefulness--MutualismGroups of lions can bring down largerprey and better defend the preyfrom other lions and hyenas.Bluegill Male: Males form nest sites of 50to 100 males. Mutualistic because predationis lower if your nest is surrounded by others.Male lions will often cooperate in oustingresident males from a pride, or in defendinga pride from other (outside) groups of males.Often, the males in a pride are closely related.Reciprocal AltruismRepeated interactions between individualsMany opportunities for altruismGood memoriesPotential altruists interact in symmetrical situationsDispense an altruistic (beneficial) act, whichis later returned as an equally beneficial act.Most likely when:Prisoner’s dilemma:C(cooperate)D(defect)C(cooperate)R(both receive light sentence)S(suckers payoff)D(defect)T(reduced sentence for defector)P(both receive intermediate sentences)Player BPlayer APrisoners dilemma:T > R >


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Berkeley BIOLOGY 1B - Whiptail Lizard

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Notes 1

Notes 1

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EVOLUTION

EVOLUTION

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Evolution

Evolution

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