Monday 10 September 2012

And now, ladies and gentlemen, spider sex!

ResearchBlogging.orgI have seen spider courting behaviour on a few occasions, but the courtship was either too slow for me to watch the end of it, or the affair ended when the female captured the male and had him for lunch. Yesterday I was luckier, as I watched the common spider, Linyphia triangularis sequence of courtship and copulation. Let me warn you: spider sex is weird. Male spiders produce their sperm in testes inside their abdomen and insemination is internal, but instead of penises, they use their pedipalps - or palps - as an intromitent organ. This requires that before copulation takes place, the male transfers semen dropplets to reservoirs in his palps. This is a delicate operations: the male spins a tiny web and deposits a drop of semen onto it, then picking it up with the palps. Spider palps are a pair of modified appendages at the side of his mouth. In females and immature males, palps look like small legs. Once the male spider moults into adulthood, the palps appear fully developed, with a bulbous end and often a darker shade of colour than in the female. Palps have complex and diverse shapes, depending of the species, and are often used to identify male spiders. Palps have an additional function in some spiders, produce visual signal, as in jumping spiders and wolf spiders.
 Liniphya triangularis lives hanging belly up from its hammock-like web and courtship occurs at the end of summer, right after the female undergoes her final moult. The pair of Liniphia were actually mating when I saw them in a web in a Sedum plant, but a Siver Y moth disturbed them and they separated. The male then walked its way slowly across the web in search of the female. When he touched her, she moved a little further away, he then followed, touching her lightly every now and then. Once he faced her, she stayed still and accepted him by lowering her body at an angle, so that he could reach the underside of her abdomen, near the cephalothorax, where her genital opening is. He proceeded to insert one palp into her genital opening at a time, then the palp swelled as it locked with the females genital opening (above shot), and he removed it, appeared to lick it and then inserted the other palp. This was repeated on for quite a while as the male may need more than 100 intromissions to inseminate the female with two dropplets of sperm! The female was quite cooperative troughout and there were no signs of agression. She seems to touch the male's head with her chelicerae. Today they were still sharing the same web. Female normally only accepts a single male for copulation if he has completed sperm transfer, but this species has an alternative mating tactic in which smaller males interfere with mating and try and mate with the female (more here).
 I took two videos of the behaviour. The first one is a short sequence of the copulation itself, it the second, the pair, which has been disturbed, are separated and the male finds the female again and proceeds to carry on mating.

More information
Weldingh, Ditte Louise, Søren Toft, &; Ole Næsbye Larsen (2011). Mating duration and sperm precedence in the spider Linyphia triangularis Journal of Ethology, 61, 143-152 DOI: 10.1007/s10164-010-0237-x

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