Guppy (Poecilia reticulata)

Rapid evolution in guppies n When guppies coexist with large predatory fish, the guppies mature earlier at a smaller size, have more numerous, smaller offspring, have discrete courtship behavior and are secretive n When guppies coexist with smaller predatory fish (that can only eat juvenile guppies), the guppies matured later and had larger offspring n Transplanting guppies from the former population to a habitat without large fish resulted in acquisition of reproductive and behavioral traits of second population within 18 generations

The Panda’s Thumb

Spotted Hyena n In spotted hyenas, females are dominant to males

Hyena genitalia

Hyena meeting ceremony n Hyenas form social groups but spend time foraging alone n To identify each other as members of their group, two hyenas perform the meeting ceremony n In the ceremony, the two hyenas stand next to each other, facing opposite directions n Each raises the inner hind leg and presents an erect penis or clitoris for the other to take into its teeth n The two hyenas sniff for seconds to conclude the ceremony n It is argued that the male-like female genitalia evolved for use in the meeting ceremony

An alternative explanation n In spotted hyenas, testosterone and other androgens are found at high levels n The penis and clitoris are sexual homologues n The scrotum and labia majora are sexual homologues n Because of high androgen levels, female spotted hyenas have male-like genitalia n The male-like genitalia are thereforce exaptations for the meeting ceremony