BIOL 105 Lecture Notes - Lecture 11: Bighorn Sheep, Sexual Dimorphism, Secondary Sex Characteristic
Document Summary
Outline: darwin and definitions, selection for body size, sexual selection: examples, sexual selection in humans, runaway selection, test your knowledge! Competition or combat for mates (intrasexual selection) Mate choice (intersexual selection) not necessarily conscious. Sexual dimorphism: species of the same sex develop different characteristics, beyond the differences of their sexual organs. Sexual selection for body size: males > females, clutch size is parallel to body size. Thus, should favor females: example: galapagos marine iguanas. Larger bodied species larger testes: species in which females are likely to copulate with less than 1 partner per estrus > Species in which females mate with only 1 male per estrus (sexual receptivity): males and females often show strange morphology, example: beetle and their horns. Trade-offs present in the sex-expressing enlarged horns; not size: example: running of the bulls, example: peacocks. Develop these elaborate feathers for a better chance of mating. Hard to reconcile with natural selection: example: fish - guppies.
