Zoo 425 1st Edition Exam 3 Study Guide Lectures 14 19 Lec 14 3 12 anisogamy asymmetry in gamete size sperm small energetically cheap to produce produced throughout male lifetime 300 million sperm ml of ejaculate 3 5mL eggs larger contain mitochondria and extra nutrient stores energetically costly in many species females have additional costs such as gestation lactation and offspring care offspring care isn t always strictly maternal higher energetic cost in lactating than in offspring care males may maximize fitness in terms of offspring produced by fertilizing multiple females females may maximize fitness by finding the best mates for their limited eggs in general eggs costly sperm cheap males experience greater variance in reproductive success on average every female finds a male to fertilize her eggs males should compete to fertilize limited female eggs females should be the choosier sex have the limited resource eggs sexual selection Arises from the advantages that certain individuals have over others of the same species in exclusive relation to reproduction Darwin sexual selection and natural selection color patterns songs mating behaviors often are used by predators and parasites to find prey hosts as well often used to explain the evolution of ornaments elaborate ex peacock s tail any characteristic of phenotype that affects reproductive success behaviors courtship displays infanticide morphology body size characteristics of reproductive tract physiology composition of seminal fluids mating pheromones intrasexual selection within sex male males female female intersexual selection between sexes male female sexually selected if only one sex has inherited the trait any instance of sexual dimorphism benefits of being choosy direct benefits females select particular males because they gain something directly from a good choice nuptial gifts from males ex nursery web spiders and hanging flies good genes traits used by females to select a male us presumably an honest indicator of the male s genetic quality coloration less susceptible to disease parasites male fighting ability symmetry asymmetry indicates lower genetic quality poor nutrition etc developmental stability how easily phenotype is perturbed by environment MHC dependent mate preferences in humans evolution of exaggerated traits Fischer s runaway selection once preference is linked to trait because females are selecting males their offspring will be born with males with this trait and females with preference for this choice indicator used for choice and choice itself covary halts when runs into another selective pressure when it has consequences related to survival not necessarily an indicator of good genes indicator of female preference preference exists good genes and sensory bias primate preference for red attracted to food that s red leads to sensory bias sensory exploitation exploiting previous bias in population for a sexual reproduction cue handicap hypothesis elaborate traits signal male quality bc only high quality males won t die with the elaborate trait persist along with burden cost of elaborate trait more feasible if male chooses to utilize trait Lec 15 3 17 mating system species specific pattern of mate finding reproduction and parenting of offspring Drickamer alt def social system that describes how males and females come together to breed components considerations number of sexual partners timing and duration of association between males and females male vs female perspectives on the benefits costs types monogamous each breeding adult mates with only one individual of the opposite sex during breeding season not necessarily life long polygamy general term for when one individual of either sex has more than one mate pair bond is often absent polygyny one male mates with greater than one female during breeding season polyandry one female mates with greater than one male during breeding season promiscuity any individual may mate with greater than 1 individual no real pair bond formation forces to influence mating systems parental care constrains options available to any species phylogenetic constraints sometime depends upon resource distribution components degree to which parental care influences offspring survival number of times adults can expect to have reproductive opportunities during their lifetime tradeoff between current care and future reproduction ecological constraints limiting resources resource distribution predation parasitism disease game theory model of parental care John Maynard Smith parameters P0 P1 P2 probability of egg survival with increasing parental care P0 no parental care P1 one parent cares P2 two parents care Ed number of eggs laid by a female who deserts doesn t contribute to offspring care Ec number of eggs laid by a female who cares for offspring m probability that a deserting male will mate again Male cares Male deserts Female cares Female deserts Female gets EcP2 EdP1 Male gets EcP2 Female gets EcP1 EdP1 EdP0 Male gets EcP1 EcP1m EcP1 1 m EdP0 EdP0m EdP0 1 m 4 ESS outcomes both parents desert req EdP0 EcP1 or female will care req P0 1 m P1 or male will care EdP0 1 m EdP1 female deserts male cares req EdP1 EcP2 or female will care red P1 P0 1 m or male will desert female cares male deserts req EcP1 EdP0 or female will desert req P1 1 m P2 or male will care female and male care req EcP2 EdP1 or female will desert req P2 P1 1 m or male will desert dependent upon costs benefits assumes male cant reproduce while caring for offspring ex fish parental care bony fishes internal vs external fertilization male or females parental care or none at all 79 have no parental care at all inc when external fertilization and and parent care male doesn t desert bc as likely to procure mating opportunities usually 1 P0 1 m P1 mammals parental care mostly female only 95 species in 5 of species there is biparental care no examples of male only care gestation and lactation are large constraints on female reproductive output males can do little to directly feed offspring usually 3 EcP1 PdP0 bc female obligated to care expect males to contribute when P2 P1 and or when m is small when both parents caring greatly inc survival birds male and female care in 90 of species although females often invest more remaining 10 are female only care 3 and 4 possible ESSs may be flexible within a species Emlen and Oring s perspective on mating systems prerequisite for monogamy economic defendability of a single mate