The Natural Selection of Sexual Cannibalism

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Abstract
Sexual cannibalism, in which a male is eaten by his mate following copulation, is expected to convey a selective advantage to the male under certain conditions. As shown quantitatively in a model the phenomenon is expected when a male can mate only a few times in his lifetime and the cannibalism significantly increases the number and/or viability of eggs fertilized by his own sperm. The expected number of male matings appears to be the more important of these 2 conditions. The few available observations of sexual cannibalism in several species of arthropods agree qualitatively with the predictions of this model. The same parameters of the model also explain why sexual cannibalism is generally rare among vertebrates. Phenomena selecting for sexual cannibalism appear more closely related to paternal investment strategies than to ecological factors associated with other forms of cannibalism. Because few field studies of invertebrates have followed the mating history of marked males, the model can not be tested quantitatively with existing data. Specific field observations are suggested which would provide quantitative estimates of the expected number of male matings. Possible laboratory experiments which would give more precise measurements of the increase in fecundity of the cannibalized male are described.