2.1 To eat or to mate? sexual cannibalism in mantodea and arachnid  (Page 10/15)

Discussion question:

Sexual cannibalism and sexual selection

Though these economic models are enticingly straightforward, they still do not explain all incidences of sexual cannibalism. Sexual size dimorphic species (prominently spiders) pose a problem when males are not complicit. Because their males are too small to provide a nutritionally substantive meal for females, these species elude the foraging strategy hypothesis. Consuming diminutive males may even be costly to the female if she neglects hunting larger food items while busy consuming her tiny mate (Elgar 1991). Since many male spiders are not willing self-sacrificers like the redback, cannibalism appears to be unfavorable to male fitness as well (Wilder and Rypstra 2008). How can non-complicit sexual cannibalism in mate size dimorphic couples be considered adaptive?

One hypothesis for this quandary claims that the cannibalistic behavior is an extreme form of mate selection, in which females reject miniscule, undesirable males by consuming them. According to the sexual selection hypothesis, the female is not driven to cannibalism by a proximate, nutrition-related cause, but instead by the function of ultimately beneficial sexual selection. Females may prefer larger males because body size reflects foraging skill: males who are able to obtain higher mass may be more capable of constructing and placing their webs, as well as capturing trapped prey (Wilder and Rypstra 2008b). If foraging abilities are heritable, then females can use male size as an indicator of the fitness of her offspring. Though sexual size dimorphic females may not obtain survival benefit from cannibalism, they use is as a mechanism of choosing males to sire fitter sons. This strategy is only costly if females are too selective and cannibalize all potential mates.

Testing the sexual selection hypothesis