A male nursery web spider | (Pisaura mirabilis) approaches a female spider with a gift.
If he remembers to bring a gift, he is allowed to provide her with more sperm, and the duration of the copulation is longer. Furthermore, 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 until it is eaten up.
When a male has mated with a female spider, the sperm is stored in a special organ under the rear part of the female's body, from which it can be released when the female has eggs that need 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.
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, or nursery web spider. Responsible for the research are Maria J. Albo and Trine Bilde, Department of Bioscience at Aarhus University, and Prof. Gabriele Uhl, University of Greifswald. (© Aarhus University, AcademiaNet)