For Spiders, "Remote Copulation" Results in "Eunuch Phenomenon"

Whatever issues human males have with sex, at least we do not get eaten, literally, by the female following copulation. In some spiders species, however, the males have learned to "cut and run," so to speak. They end up sterile, but they live to see another day.

This sort of humorous story comes from the Wired UK edition. Maybe I just have a twisted sense of humor.

Male spiders castrate themselves during sex to avoid being eaten

By Olivia Solon

02 February 12

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Biologists have identified a new sex technique used by certain spiders, called "remote copulation", where the males castrate themselves during sex to avoid being eaten, yet still successfully transfer sperm.

This method not only allows the males to transfer more sperm -- making paternity more likely -- but it also allows them to scuttle away from cannibalistic females. The broken male parts may effectively plug the female genitals, preventing them from mating with other males. The flipside is that they are left sterile. This has come to be known as the "eunuch phenomenon".

Evolutionary biologists Daiqin Li and Joelyn Oh from the National University of Singapore, along with Simona Kralj Fier and Matjaz Kuntner from the Slovenian Academy of Sciences, studied the sexually cannibalistic orb-web spider Nephilengys malabarensis. The findings are likely to apply to other spiders such as the Herennia and Tidarren. They published their findings in Biology Letters.

Li, Oh, Fier and Kuntner collected wild virgin spiders and monitored them until adulthood. When they were mature, the researchers introduced a virgin male to a virgin female web. According to the study "all trials ended with copulation and genital damage, either through entire palp (spider penis) severance or only partial palp damage". Both male and female spiders could cause the castration, but when the female was responsible the male was generally eaten.

Once the not-so-sexy time had taken place, researchers removed the palp from the female spider's reproductive organs and then dissected the female genitals so that they could check how much sperm could be found -- this was done by counting them under a compound microscope.

The results showed that remote copulation allows for continual sperm transfer from the severed spider peen to the female genitalia even after complete detachment from the male body. This prolongs the duration of potential sperm transfer and increases the amount of transferred sperm.

The authors suspect that remote copulation evolved as a male counter-adaptation to female aggression towards mates, the short average duration of spider sex, and the high prevalence of female sexual cannibalism, which can be as high as 75 percent.

You can read the full study, entitled Remote copulation: male adaptation to female cannibalism here.