Male Dwarf Spiders Fight for Paternity Rights

It seems that male dwarf spiders were one of the first to event chastity belts, according to a study published in the journal Behavioral Ecology and Sociobiology.

To ensure paternity, male dwarf spiders will use mating plugs to block off the genital tract of females they have just mated with. The larger and older the plug, the more secure the chance that other males can not make sperm deposits in the female's sperm storage organ, says Katrin Kunz and co-authors of the Zoological Institute and Museum in Griefswald, Germany.

This study builds on previous research led by co-author Gabriele Uhl that showed that dwarf spider males (Oedothorax retusus) insert mating plugs into the two copulatory ducts of the females they have mated with.

To study this information further, researchers examined how dwarf spiders use the mating plugs. They found that the material that the plugs are made of is transferred in a liquid state from the male to the female, during which time it needs to harden before it can withstand penetration or removal by a rival male. Researchers then stated remating trials with females who received different size plugs during a first round of copulation, in which the effectiveness was tested over a period of time. Female spiders were then studied under an electron scanning microscope.

The study showed smaller plugs to be less effective than larger ones, suggesting that translucent plug material can be more easily removed by a male looking to mate. The smaller plugs were also less likely to harden following insertion, providing easier access to new mating partners.

However, part of the sperm from subsequent males will still remains outside of the females genital tract, confirming the partial effectiveness of the mating plug.

"The mating plug in the dwarf spider clearly functions as a mechanical obstacle to rival males," says Kunz, in a news release. "Mating plugs are a powerful mechanical safeguard whose efficacy varies with plug size and age."