Beetles Are Thirsty for Sex

Matt Kaplan
for National Geographic News
February 11, 2009

It may seem odd that female seed beetles seem to really like sex, since they're often beaten up by their paramours in the process.

But a new study reports that the insects may be seeking out intimate moments not to increase their chances of becoming fertilized, but for hydration.

"We were curious about the behavior of these females—males are known to inflict damage during mating, and yet the females keep going back for more," said study lead author Claudia Ursprung of the University of Toronto Mississauga.

"We wanted to find out whether females were getting food or drinks from the ejaculated fluid," said Ursprung, whose research appears in a recent issue of the journal Behavioral Ecology and Sociobiology.

Ursprung and her colleagues kept 79 female seed beetles in enclosures for eight days. Some were given food and water, some just food, and some just water.

In the absence of water but not food, females were much more likely to try breeding. Being given water, however, left the females with little appetite for sex.

The beetles probably evolved this bizarre tactic because the species lives in a dry environment, the researchers suspect.

"It is kind of like a bribe for mating, a way of ensuring that the female will produce offspring," said co-author Darryl Gwynne, also at the University of Toronto.

Karim Vahed, an entomologist at the University of Derby who was not involved in the study, said that "a possible alternative explanation could be that water-deprived females are less able to meet the costs of sperm storage and therefore store less sperm."

"They may be remating for [more] sperm rather than water," he said.

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