Behaviors such as cannibalism are often dependent on the social and ecological contexts in which they occur. Cannibalism may function as an extreme form of interference competition and results in elimination of competitors while providing nutrition to the aggressor. Consumption of viable individuals of different life stages (i.e., oophagy, infanticide, and gerontophagy) occurs frequently and, in many situations, has influenced the evolution of parental care strategies, territoriality and mating systems. For instance, in many nest-guarding fishes, the male parent invests more heavily in parental care than does the female and filial cannibalism (the consumption of current offspring by a parent) may result in partial or complete brood loss. Males of many species adjust their activities among mating, nest guarding, and feeding depending upon the size and age of their brood. A male may shift from the mating to the parental phase once an appropriate number of eggs have been deposited in his nest. Broods that are smaller than average (i.e., of low value relative to the cost of parental care) are typically consumed by the parental male, although the probability of such cannibalism decreases with brood age and stage of the breeding season.
Perhaps one of the most seemingly enigmatic contexts in which cannibalism occurs is that of courtship and mating. Sexual cannibalism occurs when the female kills then eats its conspecific male mate at some stage during courtship and mating. This phenomenon has been observed in several invertebrate groups, most notably in some insects (e.g., the praying mantid, Mantis religiosa) and many species of spiders and other arachnids. Historically regarded as anomalous behavior, sexual cannibalism is currently of interest in understanding the evolution of reproductive behavior and mating systems. In particular, sexual cannibalism may have evolved as an integral component of monogyny (male monogamy), which includes dramatic examples of male self-sacrifice (e.g., as occurs in the Australian redback spider, Latrodectus hasselti). Such a mating system is predicted to occur when the benefits of paternal investment exceed those of searching for additional mates.
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