3-6-08 - Psyc-131 March 6 2008 What criteria do females use...

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Psyc-131 March 6, 2008 - What criteria do females use in choosing mates? o Good resources? o Good condition? Ex: displays that a male in poor condition cannot do o Good genes independent of resources - How important has female choice been in the evolution of male traits that are: o Not used in male-male competition? o Costly in terms of the male’s survival? - The degree of sexual dimorphism is a good indication of the intensity of sexual selection o Monomorphic – often monogamous Males invest in parental effort than females do; and than they do for mating effort Males and females tend to look more similarly o Dimorphic – often polygamous Males invest in mating effort than females do Sexual dimorphism by color and/or body size - Prairie voles monogamous o Males and females have same-sized territories o They perform equally well in mazes o The hippocampus (area where the spatial memory is stored) is the same size in both sexes - Meadow voles polygamous o One male’s territory encompasses several females’ o Males out-perform females in mazes o Males have bigger hippocampus - Cowbird: brood parasite o Males and females do mate monogamously, and then females lay their eggs in the nest of other species and then never contribute anything more in the form of parental care o Parasitism have to be careful of timing of where and when they lay their eggs if they lay their eggs before the host lays eggs, host will toss them out Need to keep accurate watch on the other nests of other species and time that they lay their eggs o Females fly over large range and remember the locations of other nests; they have larger hippocampus than the males do o Sexual selection shapes the function of the brain - Redwinged blackbird: mildly polygynous - Grackle: monogamous 1
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Psyc-131 March 6, 2008 - Sexually monomorphic species – look the same o Typically monogamous but there are exceptions cardinal Monogamous bird, but males more brightly colored than females Redness reflects carotinoids in their diet reflect condition of males Why would you find sexual dimorphism like this in a monogamous bird? Even in monogamous species, females should be choosy because they want to live in a territory of high quality and want male that will invest in offspring and bring food to offspring o Males that were redder in color, feed offspring at higher rate o Redness signals to female that he will be a better father o 40-50% are monogamous Males may pursue 2 alternatives of mating: 1) Feeds young of female at the nest 2) But may have extra fertilization of neighboring females -
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3-6-08 - Psyc-131 March 6 2008 What criteria do females use...

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