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Lecture 11

Lecture 11 (Chapter 6) - April 1- PSYCH 2TT3

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Brett Beston

Course Code Year Lecture 11 Chapter 6Sexual SelectionMales and females look different because of sexual selectiondifferences driven by selective force o Males often more colorful more ornamented eg antlers o Intrasexual selectionwhen one sex of the species compete for mates o Intersexual selectionindividual chooses a mate from the opposite sexNatural Selectiondifferential survival andor reproduction of individuals differing in one or more heritable traits o Changes of the frequency of a traito Changes in a characteristic of a population due to variation of fitness of traitsSexual selectiondifferential reproduction owing to variation in the ability to obtain mates by individuals differing in one or more heritable traitso Variants in reproductive success owing to one or more traitsNatural vs Sexual Selection Natural Selection Sexual Selection Utilitarian functional Showy elaborate Solves a problem Impresses an audience Sensible WhimsicalEconomical Wastefula lot of energy expenditure Fixed Changeable Constructive Destructive Dull ExcitingOptimal gamete sizeo Gameteegg or spermo Favours small and quick and large and slow gametes intermediate gametes are unsuccessful not fast or healthy enough o Frequencybimodal distribution with small and large gametes Divergent selection on gamete size o Each egg is more valuable in terms of relative size and relative rarity sperm is cheap o Female usually have large gametes more rare and valuable with males making smaller ones mass produced and cheap Investment per gamete o Large in femalessmall in males o Females are limited by resources to gametesthey can invest in relatively few gametesmust be choosey o Males can produce many gametesthey are limited by access to femalesAnisogamydifference between sizes of gametes in males and females o Evolution of AnisogamyFemales and males o Consequences of AnisogamyUnequal parental investmentUnequal variance in fitnessmales can produce millions of sperm have higher fitnessEg Intrasexual selectionelephant seals fight often to the death for female mateTwo outcomesmales compete with other males for access to females o Eg Elephant Sealsfemales tend to be about 5 times lighter than average male males can fight until injured or death males can fight for up to 10 hours in a single match o Eg Red Deer1Course Code YearOnly the strongest males hold harems23 of harem holders have woundsRoaring in red deer to ward off other males and attract females shows strength Only strongest are capable of holding6 of all harem holders are permanently injuredBehaviour to show strength without actually fightingfavored by natural selection to avoid dangerous fightingStrongest males have lowest roarsize proportional to length of vocal chords longerlouderGraph Prerutprebreeding little roaring per minuteHoldersroaring more than solitariesPost rutroaring down to base levelMales only seen roaring at particular time pointAssess by sizethen roaring contest o Close in sizehave roaring contest o Not close in sizeno contest o Most mature males have approximately equal fighting ability Parallel walk that can end in either one male walking away or a fight MaleMale Competition via Cuckoldry o No actual competition o Cuckoldrythe practice of making cuckolds sexual conquests of married women o In the animal worldExtra pair copulationsMonogamy used to be considered the normMale and female work together to produce offspringFemales seeking out more EPC during peak of copulation still spends more time with socially monogamous male but some time with EPCMonogamous male may not have the best genesEPCs can be beneficial Figureleft with mate right EPC extra pair copulations o Leftamount of copulation per hour with mate 2
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