April 21, 2010

Spiders’ Sex Lives Often Involve Incest, Cannibalism

A new study by researchers in Germany, which appears in the Wednesday edition of the journal Biology Letters, provides new insight into the unusual sex life of spiders.

Scientists Klaas W. Welke and Jutta M. Schneider of the University of Hamburg's Zoological Institute and Museum raised a handful of common European spiders from eggs that they discovered in a nearby meadow. The spiders were fed fruit flies until they reached adulthood, and Welke and Schneider observed their mating patterns.

Among their findings, which were disclosed in a paper published on Wednesday as well as the topic of an April 21 AFP article, is that the male spider has a pair of mating organs--known as pedipalps--which are used up during intercourse. That means that they can copulate no more than twice in a lifetime.

Furthermore, if they remain sexually active for more than 10 seconds, they will be devoured by their female mate. That was more likely to occur if the males were mating with a non-sibling, according to the researchers. Conversely, if the male spider attempted to mate with a sister, the period of intercourse was typically much shorter, allowing the brother to escape cannibalism at the hands of his sister.

"Costs of inbreeding can lead to total reproductive failure and inbreeding avoidance is, therefore, common. In classical sex roles with no paternal care, the selective pressure to avoid inbreeding is mostly on the female, which carries the higher costs," the researchers say.

"In some orb-web spiders, this situation is very different because females are polyandrous and males are monogynous or at most bigynous," they added. "This increases the selective pressure on males to adjust their investment in a mating with regard to the compatibility to a female"¦ Our experiment"¦ suggests that males can adaptively adjust their investment relating to the compatibility of a female."


On the Net:

Biology Letters - http://rsbl.royalsocietypublishing.org/

University of Hamburg - http://www.uni-hamburg.de/index_e.html