Fatal attraction takes on an entirely new meaning in the behavior of sexual cannibalism. In many spider and mantis species, mating can turn fatal when the female consumes the male before, during, or immediately after copulation. This curious behavior has widely contested adaptive value. Males incur obvious fitness costs from being consumed because it prevents them from mating in the future. Females may also compromise their own mating opportunity because spider and mantis females often cannibalize males before copulation. A variety of hypotheses have arisen to explain the evolution of sexual cannibalism, including an economic model that depicts the cost-benefit conditions needed for the behavior to have fitness value. Alternate sexual selection and predator-prey hypotheses emphasize the interaction between sexual dimorphism and cannibalism during mating. Hypotheses differ in that some consider the behavior to be adaptive for individuals, while others view it as a non-adaptive by-product of separate traits’ evolution. Hypotheses also differ in the extent to which they view the behavior as a conflict of interest between the sexes (more beneficial for one sex than the other). Ultimately, no hypothesis appear to fit all cases; instead different explanations may apply to different species depending on environmental conditions and species characteristics. Overall, in both mantises and spiders, sexual cannibalism highlights
proximate and
ultimate causes underlying the sexes’ asymmetric reproductive tactics, and may illustrate a compelling intersection between
natural and
sexual selection pressures
Author: Rachel Carlson
Introduction
Mating interactions are frequently marked by conflict. Males and females have asymmetric goals in optimizing reproductive fitness, but they must rely on each other to produce offspring in sexual species (
[link] ). A dramatic example of intersexual conflict is sexual cannibalism, in which the female consumes the courting male before, during, or immediately after copulation (Buskirk et al. 1984). The male appears to be victimized, a hapless casualty of the female’s selfish drive to increase her nutrient store. However, examination of sexual cannibalism in the context of spider and mantis species reveals that these sexual selection pressures are accompanied by a host of costs and benefits to females as well as males
Box
Intersexual conflict with respect to paternal investment
Intersexual conflict occurs when individuals in a mating interaction jockey for the greatest reproductive benefit at the lowest cost. Though individuals must cooperate at least during the mating act to produce viable offspring, their investment in the common young is often highly asymmetrical (Schneider and Lubin 1998). This fact is founded on the anisogamy of the sexes. Female eggs are significantly more nutrient-rich and exacting to produce than male sperm. The female also has fewer eggs than males do sperm. Since the donation of an egg is costlier than that of a sperm, females are immediately more committed to the offspring produced than males. Embryonic food demand places restrictions on the amount of offspring a female can produce in her lifetime, while male reproductive potential has a very high internal upper limit (Schneider and Lubin 1998). There are some rare species (sea horses, jacanas, for example) where males care more for progeny than females, reversing these strategies.
OpenStax, Mockingbird tales: readings in animal behavior. OpenStax CNX. Jan 12, 2011 Download for free at http://cnx.org/content/col11211/1.5
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