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Bio220 Lectures 1-6 notes.docx

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University of Toronto St. George

Mating systems in sexual animals When choosing mates, animals evolve species typical strategies for maximizing their reproductive success Asexually animals pass on all of their chromosomes, all their copies to their offspring. In contrast, due to meiosis, diploid sexually reproducing animals have two copies of each chromosome but only pass one copy of each chromosome on to an egg or sperm cell meaning that sexual reproduction is much more common than asexual reproduction because it gives an advantage also, they only pass on half of their genes  major advantage comes from genetic recombination which gives diversity Aphids when the environment is cold, they reproduce asexually because sexual reproduction produces eggs that are freeze tolerant and can diapause during winter Genetic diversity may lead to evolved defenses against parasites and disease sexual reproduction is necessary for this species to defend parasites, as asexual individuals may not easily survive in areas where parasites are high Females typically produce significantly fewer gametes than males and invest heavily in each one and males produce many gametes and invest little in each onebecause of this, females may take more time choosing a male carefully Bateman’s principle helps to make predictions about mating success and number of mates it says that variance among females in mating success is low, whereas variance among males in mating success is high females almost always invest more energy into producing offspring females are limiting resource Male success depends on the number of mates they have mated with Relatively few males mate successfully but nearly all females in a population mate have offspring Those males that do mate tend to mate with many females thus a few males have very high reproductive output but many males have little or no reproductive output and this leads to the prediction that sexual selection should act more strongly in males, leading to greater elaboration of behavior and structures used in attracting mates in males than in females Although mating is important, it can be costly event females are predicted to be choosier about selecting their mates than males because of risks during mating  such as disease transmission or the negative effects of female’s reproductive output If males are choosy about their mate, then over time females may evolve ornamentation or coloration that is subject to sexual selection Monogamy is the behavioural pairing of a single male with a single female common in birds and rare in other animals Monogamy reduces the potential for genetic variation among a female’s offspring by mating with more than male over the course of her life time  females will be able to gain genetic variation among her offspring The benefits of monogamy sharing of duties resources Polygyny strategy used by males to increase their reproductive fitness Resource defense polygyny groups of females are attracted to a resource males then compete for territorial possession of the resource Harem a defended groups of females associated wit one male dominance hierarchy Lek aggregation of males that are each seeking to attract a mate males perform displays not associated with resources it is thought to be this way since leks attract more females than isolated males Polyandry group of males and one female strategy that helps a female ensure reproductive success by providing her with multiple mating options Resource defense polyandry females control resources  controls male mating ass
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