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Lecture 17

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Biology 1001A
Tom Haffie

Biology November 11 2013 Lecture 17: Before: Mates as a resource:  Mating systems have evolved to maximize reproductive success o Due to extra level of parental care for offspring o Also due to other aspects of a species ecology Monogamy:  Male and female form a pair bond  For a mating season or for reproductive lives  Usually occurs when young require a great deal of care that both parents can provide o White-crowned sparrows are altricial (naked and helpess) when hatched o The young must beg for food that both parents can provide  Rates of reproduction higher  Mammals is slightly different because mother provides food (milk) o Monogamy occurs because males indirectly feed the children by feeding the mother Polygamy  Polygyny o One male is with many females o Males often contribute nothing to reproduction but sperm o If males have high-quality territories then females can raise young on there own o The males role is a sperm donor who protects the territory as opposed to actually playing a role in the raising of the offspring  Red-winged blackbirds, males often hold large resource filled territories that support several females  females are still attracted to males even if other females are already present in the territory o polygyny is prevalent among mammals because females have a much larger investment in the care of young then males  Polyandry o One female is with many males o Females contribute nothing but eggs to reproduction Promiscuity  Males and females have no pair bonds beyond the time it takes to mate  Females only stay long enough to receive sperm  These males make no contribution to raising young o Sage Gouse and hammer-headed bats form leks  Leks are congregations of displaying males where females go to mate Biology November 11 2013 Viviparous animals (the animals that get pregnant)  May bear the costs of housing and feeding developing young Sexual Selection: Competition for access to mates coupled with mate choice sets the stage for sexual selection Sexual dimorphism  One gender is larger and more colorful than the other  Can be an outcome of sexual selection Males compete for Females  Males are often larger  May have ornaments and weapons used to attract females and to butt, stab or
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