Monday, 08 Dec, 2008 Environment

Size Doesn't Really Matter in Spiders' World


One of the latest studies of redback spiders showed that, though in head-to-head mating competitions, big males were better than smaller ones, the latter proved to be better lovers, due to the fact that they run faster and are quicker to mature than larger males. The study was published in the latest issue of "Journal of Evolutionary Biology."

In their study scientists outlined the significance of maturation when explaining mating and paternity success. The research involved the simulation of two competitive contexts supporting the development of redback male spiders of different sizes (Latrodectus hasselti). Bigger males had more success in mating with females than smaller ones. In addition, they were more successful in impregnating the females during a direct competition with smaller spiders. Nevertheless, maturing smaller spiders had a 10 times higher rate of paternity than bigger males, being provided a one-day head start.

When spider males are involved in competition, the courtship between a male and a female redback spiders lasts for about 50 minutes. For non-competing males it takes 4.5 hours. The duration of the copulation may range from 6 to 31 minutes. Most often, during the process male spiders are injured or killed.

"The results reveal that big males don't get it all their own way," says Dr Michael Kasumovic, lead author, UNSW postdoctoral fellow. He was the one to co-author the paper together with Maydianne Andrade of the University of Toronto.

In their paper, scientists wrote that, depending on circumstances, nature might favor bigger or smaller male spiders. Larger redback spiders pass through a more durable maturation process, which is why they cannot search for a female and mate to produce an offspring as fast as smaller spiders.

The paper says: "Large size and weaponry are strong predictors of a male's competitive strengths because those traits help them dominate smaller males when they compete for food and mating rights." It also mentions that evidence, found after the examination of midges, dung flies and seed beetles, showed that smaller male spiders register a faster development than the larger ones and, in most cases, they mate before the arrival of larger spiders.

"Size isn't the only ruler by which we can measure a male's quality. Many other factors, including maturation time, are critical in that definition," researchers wrote.

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