Ancient Female Mites Called the Sexual Shots
Two mites, frozen in amber in the act of mating. The female is on the left and the male is on the right.
Credit: Ekaterina Sidorchuk

Talk about coitus interruptus: A pair of mites preserved in amber during the act of mating reveals that the female took the reins during sex.

The mites, an extinct species called Glaesacarus rhombeus, were getting busy 40 million years ago when they became trapped in sticky tree sap. The sap eventually hardened into amber, preserving the mite tableau inside. Compared with modern mites, a new study finds, G. rhombeus was sexually progressive.

"In this species, it is the female who has partial or complete control of mating," study researcher Pavel Klimov, of the University of Michigan Museum of Zoology, said in a statement. "This is in contrast to the present-day reproductive behavior of many mite species where almost all aspects of copulation are controlled by males."

All species undergo an evolutionary battle of the sexes, vying for the ability to choose their mates and thus maximize the potential for their genes to survive over time. In the case of the itsy-bitsy arthropods called mites, males take charge of mating, coercing females and guarding them from mating with others. Modern male mites have specialized organs made to cling to reluctant females.

That's not a great arrangement for female mites, who don't get to pick superior males to mate with (weaker males may still be able to coerce the females to mate). The females also have to put up with harassment by and frequent matings with pushy male mites, which can cause injury.

The ancient mites didn't have this problem, Klimov and his colleague Ekaterina Sidorchuk of the Russian Academy of Sciences found. The extinct male preserved in amber lacked specialized grasping organs. Instead, the female had a projection on her rear end that allowed her to control the male's clinging.

The researchers reported their results March 1 in the Biological Journal of the Linnean Society.

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