January 25, 2007—For some animals, such as this female
ornate jumping spider, having a "healthy glow" means everything.
A new study of the species has shown that both ultraviolet reflectance and fluorescence are key to the animals' successful courtship and mating. (Related photo: "Glowing Butterflies Outshine LEDs" [November 17, 2005].)
Even more interesting is that these signals are gender specific, write researchers in tomorrow's edition of the journal Science.
Male jumping spiders reflect UV light using patches of scales on their faces and bodies that are displayed during mating stances. But females, when in the presence of UV light, give off green fluorescent light from their palps, small appendages close to their faces.
Scientists were led to study the animals because they have eyes particularly sensitive to ultraviolet and green light. The researchers quickly found that spiders showed no interest in members of the opposite sex that were not glowing.
"We conclude that sexual coloration is a crucial prerequisite for courtship," the team writes in Science.
Only one other animal has been known to use fluorescence as a possible courtship signal—the budgerigar, a type of parrot—said Daiqin Li, lead investigator of the study, via email. "But the effect merely boosted to a limited degree the brightness of the [bird's] yellow body color, and its behavioral relevance has been questioned."
So "it's quite important how [the spiders] use private channels for communication, only restricted to one sex," Li added in an interview with National Geographic News podcast host Peter Standring (listen to the full interview). "It's very interesting and unique in the animal kingdom."
Li speculates that the behavior may have evolved as a way for the spiders to signal their suitability as mates while minimizing unwanted attraction from predators. But it's still dangerous, since many spider predators, such as some birds, can see UV light.
"Both UV and UV-induced fluorescence may be costly," he said via email, "and thereby [may be] honest indicators of individual sex quality."
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