Females of an Asian species of water strider keep their genitalia hidden to avoid any forceful copulation attempts, and expose them only after males produce a courtship “song” by tapping the water surface, according to a new study of Professor Piotr Jablonski and his graduate students CHANG Seok Han.

CHANG and Jablonski of Laboratory of Behavioral Ecology and Evolution at the School of Biological Sciences found that females evolve a morphological shield to protect their genitalia from an approaching male.

It is already known that the mechanisms for the way Darwinian natural selection, acts separately on males and females, result in different traits in males than in females.

However, at times, a behavioural trait, such as mating frequency, depends on both the male and the female characteristics.

In many animals, including humans, natural selection favours higher mating frequency in males than in females, which leads to an evolutionary “arms race” where males evolve adaptations that force females to mate, while females evolve defences against males’ attempts.

In the study, it was observed that females of an Asian species of water striders, Gerris gracilicornis, win the evolutionary race by evolving a morphological shield behind which their genitalia are hidden from males, protecting them against the males’ forceful attempts to mate.

Thus, in response to the female adaptation, after the violent mounting onto the female’s back (typical in water striders), males of this species produce courtship signals by tapping the water surface with their middle legs.

And only after receiving the male’s “song” that the females expose their genitalia for copulation.

The study has been published in the open-access, peer-reviewed journal PLoS ONE.(ANI)

June 15, 2009
SNU PR Officce