Spiders go for violent, but effective sex

May 1st, 2009 - 3:25 pm ICT by ANI  

London, May 1 (ANI): Spiders in Israel have been seen indulging in a violent but evolutionarily effective mating strategy, which guarantees direct fertilisation of eggs in the ovaries.

In the so-called traumatic insemination, males of the Harpactea sadistica species pierce the abdomen of females, and thus fertilise their eggs directly in the ovaries.

Such a practice provides the first male to inseminate a reproductive advantage by bypassing structures in the females’ genitalia, reports The BBC.

Although, other insects, including mites and bedbugs, have been known to use a similar strategy, but this is the first time that it has been seen in spiders.

Usually, spider males deliver their genetic package via sperm that is deposited into a small web and manually inserted via a pair of appendages on their undersides known as pedipalps.

Then, the sperm are held in a receptacle between the ovipore and ovary, known as a spermatheca, till the release of an egg.

But, the spermatheca is a “last in, first out” structure, thus if any further males inseminate a female, the last mate’s sperm is the first in line to fertilise an egg.

Milan Rezic, an entomologist at the Crop Research Institute in Prague, spotted a spider evade this problem by delivering sperm directly to the ovaries via holes that the males bore directly in the females’ abdomens.

Rezac named the species H. sadistica and pointed out that the species has specialised sex organs at the ends of its pedipalps, with one part specialised for gripping and another, hypodermic needle-like structure for injecting sperm.

And just like many spider mating rituals, H. sadistica ’s approach follows an elaborate pattern-male taps the female, subdues her, and then wraps himself around her to properly position the sex organs.

Alter, he alternates between the two, piercing and injecting the sperm on one side, then the other, forming two neat rows of holes in her abdomen.

The researchers analysed the females of the species and found that their spermathecae are atrophied, or shrunken, in comparison to other spiders.

In an apparent case of co-evolution, they are apparently slowly shrinking into non-existence, as their purpose is being sidestepped by the males’ more direct approach.

The findings are reported in Proceedings of the Royal Society B. (ANI)

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