Male redback spiders place their bodies near the mouth of their female mating partner, in an act of apparent tacit compliance regarding the female’s post-copulation cannibalistic practices. In her paper, Andrade argues that such actions are evidence of an adaptation amongst male spiders that excites a willingness to undergo such predation as it increases their chances of successfully mating. This observed behavior is especially interesting as it most likely has little impact upon the gestation of the female; the male spider’s small size limits the amount of nutrients his body could provide, thus severely limiting any paternal effort effects upon the female. The paper suggests that the longer copulation time available to a male that commits suicide results in a higher paternity rate.
I believe that such behavioral characteristics could potentially be an adaptation that has been naturally selected for throughout generations. Male spiders that committed suicide had higher paternity rates, and thus a greater relative fitness compared to those that did not. I believe it would be interesting to discover if there is a genetic basis to this behavior.
Another particularly striking example of sexual selection is the reproductive practices of ducks. Male ducks have large phalluses, typically ranging around 40 centimeters in length, which are supported by lymph. Additionally, unlike most birds, whose oviducts a tubular in structure, the female duck has a complex winding vaginal track, comprised of spirals, branches, and crevices.
The present theory behind these strange morphological characteristics is the forced copulation practices among waterfowl. In a study conducted by Dr. Patricia Brennan in affiliation with the Department of Evolutionary Biology at Yale University, male ducks that had been selectively bred to have larger phalluses, were able to penetrate an artificial vaginal tract, while wild type ducks were unable to copulate. The study provided supportive evidence that the male duck phallus size is directly related to individual fitness.
For more information regarding redback spider sexual cannibalism, please refer to: Andrade, M., 1996. Sexual Selection for Male Sacrifice in the Australian Redback Spider. Science. 272(5245):70-72.
For more information regarding duck reproductive habits, please refer to: Laskin, M. 2010. Unraveling the Mysteries of Duck Mating. Yale Scientific Magazine. http://www.yalescientific.org/2010/09/unraveling-the-mysteries-of-duck-mating/