A first date, even if it fizzles, can make a big difference to a wolf spider.
If an almost-grown-up female’s last impression of a suitor is his sexy leg-waving display, she won’t mate with him just then, but she’ll grow up with a preference for males like him, says Eileen Hebets, of the University of California, Berkeley. Also, that female spider as an adult will prove less likely to eat males with her original pursuer’s looks than with other male spiders, Hebets reports in an upcoming Proceedings of the National Academy of Sciences (PNAS).
What shapes mating preferences matters because these forces end up shaping a species’ traits and evolutionary changes. The previewing of courtship “is potentially a new way females develop preferences that we haven’t thought about before,” says Hebets.
Earlier investigations with other animals into how social experiences shape subsequent mating preferences have turned up various influences affecting the very young and adult, but not adolescent, animals. For example, lambs, if raised by adult goats, will grow up to prefer their fostering species for mating. On the other side of adolescence, adult females of a variety of vertebrate species tend to copy each other’s mating choice.
The new experiment took the unusual tack of testing for social influences on mate choice in invertebrates, says Bennett Galef of McMaster University in Hamilton, Ontario. “It’s a very straightforward experiment with a surprising result,” he says.
For her experiment, Hebets caught young Schizocosa uetzi spiders in Mississippi and brought them to her lab, then at Cornell University.
Males sport splashes of black and brown on a forward segment of their front legs. Hebets shopped around for nail polish that matched the shades (“Midnight Metal” and “Bronze Ice”) and painted the segments either all black or all brown.
When Hebets placed a painted male with a young female, the male readily performed his courtship display. “He lifts first one leg, then the other–really slowly,” Hebets says. At the same time, he sends vibrations through the enclosure floor.
The young females, who didn’t yet have sex organs, showed no interest in mating, but they evidently were impressed by the males who sought them. When the females reached adulthood, they were twice as likely to mate with males with the leg color of the original suitor than with males with legs of the alternate color. The suitor look-alikes were also half as likely to be eaten by their female partners.
The laboratory finding that female spiders are sexually impressionable when young, “opens up a lot of questions about social learning,” says Gail E. Stratton of the University of Mississippi in Oxford, who discovered the species.
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