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Sexual Selection Sheet.docx

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Biology 3466B
Yolanda Morbey

Sexual Selection Ch. 11 401-441 Sexual selection – differential reproductive success due to Sexual Selection Males vs. Females variation among individuals in mating success The strength of sexual selection differs in males than in females. Objectives When mother makes a larger investment:  Predict whether traits will be subject to sexual selection  Females potential success is small  Realized success is limited by number of eggs  Explain why the strengths of sexual selection differ between the sexes (pregnancies)  Males potential success is large  Contrast intrasexual and intersexual selection and their effects on mating behaviors (competition and  Realized success is limited by # of female mates mate choice) Limits of reproductive success:  In the sex with greater parental investment limit is Sexual Dimorphism and Sex time and resources Sexual dimorphism – a difference between males and females  In sex with lower parental investment limit is mating success of a species  Darwin realized that individuals vary not only in theLimits of Reproductive Success in Newts success at surviving and reproducing but also in theiMating system success at persuading members of the opposite sex to mate  Males arrive at breeding ponds early and stay long  Failing to mate is the same as dying young (no genetic  Females visit ponds to mate with males contribution)  Females lay 300 eggs over several weeks or months  No parental care Theory of Evolution by Sexual Selection Results: If there is heritable variation in a trait that affects the ability to  Sexual selection was more powerful force in the obtain mates, then variants conductive to success will become evolution of males more common over time  Heritable traits in males that are associated with failure to mate will disappear Asymmetries in Sexual Reproduction  Heritable traits in males linked to mating success will become common  For sexual selection to explain differences between  For males more than females in many species fitness is sexes it must act on the sexes differently determined by access to mates  In many animals, eggs (pregnancies) are more expensive than ejaculates Limits of Reproductive Success in Pipefish (Sexual Parental investment - Energy and time expended in Roles Reversed) constructing and caring for an offspring (measure of fitness) Mating system  Mothers typically make larger parental investment to each offspring than fathers  Female lays eggs in brood pouch of makes  Males provide all parental care until eggs hatch o Eggs more expensive than sperm  Increases the reproductive success of the offspring receiving it Results:  Decreases the reproductive success that investing  Females invested less energy which resulted in more parent may achieve in the future (additional offspring) females with eggs to lay than males with space to  In most animal species neither parents care for young accept them  More females than males fail to mate Sexual Selection Ch. 11 401-441  Reproductive success of females is more strongly  Males get larger than females even when it is costly dependent on mating success  Stronger sexual selection in males  Sexual selection is more important in evolution of  Medium sized iguanas survive at higher rate that small females or large (optimal size)  Heritable traits associated with limiting mating Male iguanas fight over territories where females success tends to disappear  Heritable traits associated with mating success congregate. Large iguanas win more fights, claim better become common territories and thus get to copulate with more females. This has lead to the large body size in males despite the high cost and suboptimal size for survival. Consequences of Limiting Fitness When sexual selection is strong for one sex and weak for Alt. Reproductive Tactics in Males another:  Pre-ejaculation – small territorial males solve  Members of the sex subjected to strong sexual problem of disrupted copulation (by larger males) by selection will be competitive ejaculating ahead of time  Members of the sex subjected to weak sexual  Guard behavior – either of the female or territory selection will be choosy  Sneak fertilization –(Salmon) hide near a female, then dart out and spawn over eggs. This can play out in 2 ways:  I.e. Sneak into another guarded territory to get past males guarding it Intrasexual selection – involves the competition (combat) among members of one sex for:  Direct control of mates Male-Male Comp: Sperm Competition  Direct control of resources  Producing as many sperm as possible is a form of  Top rank in dominance hierarchy competition  If a female mates with 2+ males the male who wins the Intersexual selection – involves display among members of race to the eggs has higher reproduct
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