March 20, 2006 — Diving beetles engage in such exhausting, uncomfortable sex that these insects have actually evolved two different types of females, as well as unusual variations among males, according to a new study.

The find adds to the growing body of evidence that sexual conflict between males and females influences evolution. In many cases, individuals over time develop characteristics that are appealing to the opposite sex.

For diving beetles, however, researchers believe females have tried to avoid the painful sex for so long that some have actually evolved a feature that enables them to spurn most suitors.

The result is that the insect family Dytiscidae includes species, such as the diving beetles Dytiscus lapponicus and Graphoderus zonatus verrucifer, which each have two distinct types of females.

D. lapponicus has females with smooth and furrowed backs, while G.z. verrucifer has females with smooth and granulated backs. The furrows and granulation allow these types to avoid frequent sex with males, which grab onto the females with suction-cupped feet.

Findings are published in the current issue of The American Naturalist.

Lead authors Roger Härdling and Johannes Bergsten told Animal Planet News, "Here is one vivid description of mating in diving beetles from Wichard et al (2002, Biological Atlas of Aquatic Insects) 'At the beginning of sexual union, during precopulation, the male constantly shakes the female back and forth with the middle legs while swimming. This mating game increases the need for oxygen.'

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