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Better sex in return for good gifts

A male spider that gives its selected female a nuptial gift is allowed to mate with her for a longer period of time and provide more sperm than a male that fails to come with a gift.

2013.10.24 | Anne-Mette Siem

This photo shows a female with a white gift, and a male about to transfer sperm to the sperm storage organs under the rear part of the female’s body. The male has silky threads going to the gift from the silk glands at the rear of its abdomen. This enables the male to remain attached to the gift. (Photo: Allan Lau)

If a male spider goes to the trouble of finding a good gift, wraps it up nicely in spider silk and offers it to a female he would like to mate, he has far better chances of fathering her offspring than if he skipped the present. This is shown in new research from Aarhus University’s Spiderlab, where researchers studied what it means for female spiders to receive gifts.

Culinary gifts

The male’s nuptial gift consists of something deliciously edible, such as a fly, which he wraps up nicely in white silk prior to offering it to the female. He can then transfer sperm while she is eating the gift. If he remembers to bring a gift, he is allowed to provide her with more sperm than if he forgot, and the duration of the copulation is longer.

Sperm ‘receptacle’

When a male has mated with a female spider, the sperm is stored in a special organ from which it can be released when the female has eggs to be fertilised. The researchers discovered that the female stores more sperm in this organ if the male has brought a gift, and he is therefore more likely to be the father of her offspring. It can thus be demonstrated that the female is capable of regulating how much sperm she stores, enabling her to favour males that provide her with culinary gifts.

Gifts reveal resourceful males

The female presumably prefers sperm from the gift bearer because it shows that he is resourceful and good at hunting and catching food. If these are good hereditary traits, the female can transfer the qualities to her offspring by favouring the male. The female spider thus selects sperm from the males she prefers, and has the benefit of passing on their good characteristics to her male offspring.

The study was made on the Pisaura mirabilis species (nursery web spider). Whether or not there is scientific justification of any advantages in providing human females with gifts was not mentioned in the study!

The video begins by showing a male wrapping up a fly. He then presents it to the female and transfers sperm. The male subsequently plays dead and is dragged away by the female. He then ends up as food for the female, which has killed him. This takes place in approximately 2% of matings. The video was produced by Cristina Tuni.

The study has just been published in Proceedings of the Royal Society B in an article entitled Sperm storage mediated by cryptic female choice for nuptial gifts.

Responsible for the research are Maria J. Albo and Trine Bilde, Department of Bioscience, Aarhus University, and Gabriele Uhl, University of Greifswald.

Trine Bilde talks about spiders and gifts in a lecture (in Danish only) during the Festival of Research 2011. The lecture was entitled ‘Affection, courting and cannibalism’. .

For more information, please contact

Professor Trine Bilde
Department of Bioscience
Aarhus University
+45 8715 6565/6020 2702
trine.bilde@biology.au.dk
www.spiderlab.dk

Department of Bioscience
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Revised 2014.10.31

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