Guppy (Poecilia reticulata)

Rapid evolution in guppies

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

When guppies coexist with smaller predatory fish (that can only eat juvenile guppies), the guppies matured later and had larger offspring

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

In spotted hyenas, females are dominant to males

Hyena genitalia

Hyena meeting ceremony Hyenas form social groups but spend time foraging alone

To identify each other as members of their group, two hyenas perform the meeting ceremony

In the ceremony, the two hyenas stand next to each other, facing opposite directions

Each raises the inner hind leg and presents an erect penis or clitoris for the other to take into its teeth

The two hyenas sniff for 10-15 seconds to conclude the ceremony

It is argued that the male-like female genitalia evolved for use in the meeting ceremony

An alternative explanation In spotted hyenas, testosterone and other androgens are

found at high levels

The penis and clitoris are sexual homologues

The scrotum and labia majora are sexual homologues

Because of high androgen levels, female spotted hyenas have male-like genitalia

The male-like genitalia are thereforce exaptations for the meeting ceremony