Image of the Day: Sex More Important Than Food For Male Redbacks

Male Australian redback spiders develop and mature faster depending on how many females around and how stiff the competition is, a new study finds.

"It's the first time that it's been shown that males are actually changing their development in response to both sexual and natural selection," said study team member Michael Kasumovic from the University of Toronto.

Redback spiders are related to black widow spiders, and like their deadlier cousin, the female redbacks dwarf the males and live longer. Female redbacks can live for up to two years, while males live for only one or two months.

After hatching and reaching maturity, males stop eating and focus solely on finding a mate. The male spiders face a kind of Catch-22: they have to store up enough provisions to find a female and successfully mate, but they also have to develop and mature quickly to beat out other males.

To see how the spiders deal with this dilemma, the researchers reared male spiders either with or without females. But when they were raised in the absence of females, the males were still allowed to smell the female's scent.

The researchers found that when the males could smell females, they developed rapidly, and were willing to trade smaller body sizes and less fat reserves to get to virgin females sooner. When there was a lot of male competition present, however, the male spiders were still smaller but they had more fat on their bodies. The extra fat probably came in handy for the extended courtship rituals: males are supposed to pluck and vibrate the female's web strings for up to eight hours. Males that don't make can get the cut get flicked off the web.

The finding is detailed in the April 4 issue of the journal Current Biology.