January 09, 2012
“Wolf spiders are displaying more sophisticated behavior than we thought they were. Their brains are literally the size of a pinhead, but they’re eavesdropping, signal matching and processing information to attract female spiders.” — Dave Clark
Research led by Alma College professor David Clark has shed new light on the courtship behavior of male wolf spiders.
Supported by a National Science Foundation grant, the study, for which Clark was the lead author and co-investigator, found that the spiders eavesdrop on their male counterparts and copy courtship signals as a likely means of stealing their mate. This is a behavior mainly seen in vertebrate animals.
“Wolf spiders are displaying more sophisticated behavior than we thought they were,” says Clark. “Their brains are literally the size of a pinhead, but they’re eavesdropping, signal matching and processing information to attract female spiders.”
The biology professor and his co-authors, J. Andrew Roberts, associate professor of evolution, ecology and organismal biology a The Ohio State University at Newark, and George W. Uetz, professor of biological sciences at the University of Cincinnati, used innovative digital technology in the study. After collecting spiders from the field, they were observed in a lab with a video of a “virtual” male spider sending out courtship signals in a digital version of a natural habitat.
Because a previous study on lab-reared spiders was inconclusive, Clark says the reactions of the field-collected spiders were surprising.
“Spiders are supposed to be pre-programmed, so you would think that where they were raised wouldn’t matter,” he says. “We found that the field-collected spiders behaved as if their ‘rival’ was courting a female nearby, though.”
Uetz says the results of the study also confirmed a “hunch” they had since observing apparent eavesdropping when Clark and Alma students visited him at the Cincinnati Nature Center.
“The students repeated the study, this time with spiders collected from the field,” he says. “It was then that we realized the previous study was done with lab-reared, naïve spiders, and that field-collected spiders must have had some experience associating male courtship with female spiders.”
Because female wolf spiders typically mate only once, the mating selection process is especially intense. Male wolf spiders communicate with females using visual and sound cues. The brush on their legs also helps females determine which male is a worthy mate, Clark says.
“Male wolf spiders don’t provide anything to their young other than genes, so females are very careful about picking the male with the best gene quality,” he says. “They’re able to figure out that information by assessing the male spider’s cues.”
The complexity of spiders is one of the many things that Clark, who has spent more than 20 years researching spiders, finds so fascinating.
“The males absolutely have to do the right thing in the presence of the female,” he says. “Otherwise, they will get selected out quickly, as females are both predator and potential mate at the same time.”
The study was published in Biology Letters, a journal of the Royal Society of London.