杏吧原创

Species: , an orb-weaver spider
Habitat: The forests of Costa Rica

It鈥檚 a hairy affair. Two spiders are locked in an embrace, their mouthparts pressed tightly against each other.

The embrace was instigated by the female: she had signalled she was interested in mating. Now, the male is putting in his best efforts to seal the deal, using his hairy mouthparts to keep the female鈥檚 interest high.

These are spiders of the Leucauge mariana species. Males have evolved hairy mouthparts and use them to stimulate the female during mating, apparently ensuring their new-found partner鈥檚 commitment and tickling their way to reproductive success.

To test the function of these male hairs, from the Clemente Estable Biological Research Institute in Montevideo, Uruguay, and her colleagues reduced stimulation between males and females in two ways.

Close shave

In one experiment, they removed hair-like setae from the male鈥檚 mouthparts. In another scenario, they removed the setae from female mouthparts that touch the male鈥檚 hairs during mating, plus the nerve-sensitive regions that are also touched by the male鈥檚 hairs.

In both cases, the reduced stimulation made the female less enthusiastic: the female was more likely to stop mating, and she was more likely to mate again with other males.For males, tickling his mate appears to be a way of winning her favour.

鈥淏y reducing the stimulation, we lowered the male鈥檚 ability to inhibit remating by the female,鈥� says of the Smithsonian Tropical Research Institute in Baton Rouge, Louisiana, who also worked on the study.

Pincer mouth

A female indicates her interest in mating by grasping a male鈥檚 chelicerae 鈥� pincer-like appendages on the front of the mouthparts 鈥� with her own.

鈥淚f the female is receptive, she orientates towards the male so they are facing each other. She then opens wide her chelicerae and the male approaches her,鈥� says Aisenberg. 鈥淭hen the female clasps male chelicerae with her chelicerae, as if hugging him, until the end of mating, when she releases him.鈥�

But sometimes the female gets distracted. Females were more likely to release their hold on the male鈥檚 chelicerae when stimulation by the male鈥檚 setae was experimentally reduced.

Dissatisfied females also reveal their displeasure by not helping to produce a genital plug.

Genital plugs are fairly common in spiders. They can be made from secretions, semen or even a broken-off part of the male鈥檚 genitalia, and they help to block up a female鈥檚 genital opening.

鈥淢ost plugs are thought to impede the entry of the genitalia of subsequent males into the female鈥檚 genital tract,鈥� says Eberhard.

Fangs that make you go hmmm

In a small number of species, including L. mariana, females help make this plug. But when a female is not stimulated by a male鈥檚 setae, she stops producing the substance she normally contributes to form the plug, making it easier for future males to mate with her.

So tickling seems to be an essential trick for males wanting to keep a female interested in siring his little ones.

Next, Eberhard wants to investigate whether male stimulation of the hairs on the female鈥檚 sternum using his fangs has a similar effect on her reproductive decisions.

Journal reference: Behavioural Ecology and Sociobiology, DOI: 10.1007/s00265-014-1844-2