Female Australian redback spider eating male spider. Image: Ken Jones, UTSC
(taken from http://www.physorg.com/news63467462.html)
What do the biologists have to say about this baffling phenomenon? I have referred to some research and tried to make sense out of it. Maydianne C. B. Andrade, a zoologist from Canada, has done some research in this area. You can read the original paper here [http://www.sciencemag.org/cgi/content/abstract/271/5245/70]. I will try to cut the very long story short.
Redback spiders (Latrodectus hasselti: Theridiidae) were observed for the experiment. An interesting thing about their anatomy is that the mass of the male is only 1 to 2 % of that of the female. In order to facilitate death, during copulation male positions itself above the female’s jaws. It was found that not all males die after mating, but some do survive. It is claimed that the males actually ‘benefit’ from being eaten. Firstly, cannibalized males copulate longer and fertilize more eggs than those that survived copulation. Secondly, females were more likely to reject subsequent suitors after consuming their first mate. These results represent empirical evidence for male copulatory suicide as an adaptive behavior.
Many male arthropods present food gifts to their mates and thereby ensure complete sperm transfer. Such mating gifts apparently differ from the somatic gift of the male redback only in the degree of their effect on male survivorship. Because females may mate multiply, male redbacks are selected to invest heavily in mechanisms that protect their paternity in the single mating they may achieve. Therefore, the two paternity advantages of sexual cannibalism outweigh the low cost of suicide for males. Male facilitation of cannibalism probably evolved through sexual selection as the most extreme mating gift.
Whatever. It is still contradictory with my common sense. But, as it happens, nature has its own queer ways. Perhaps our common sense itself is flawed. Read More ..















