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Guppy (Poecilia reticulata)
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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
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The Panda’s Thumb
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Spotted Hyena
In spotted hyenas, females are dominant to males
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Hyena genitalia
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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
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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