Infanticide in Cercopithecus mitis stuhlmanni in the Kakamega Forest, Kenya: Variation in the Occurrence of an Adaptive Behavior

Abstract

Infanticide by males is widespread across mammals and especially prevalent among primates. Considerable research has examined how fitness benefits can explain the occurrence of this behavior; less is known, however, about intrapopulation variation in its occurrence. We evaluated 10 infanticides by males in wild blue monkeys according to the sexual selection hypothesis. To explore intrapopulation variation in occurrence of infanticide, we compared these cases to 38 cases that were contextually similar but in which infanticide did not occur. We examined male reproductive benefit, infant age, maternal parity, postconception estrus, group defense, available mating partners, and context of takeover. We based comparisons on daily or near daily records of male presence in the study groups, infant birth dates, and male-female sexual interactions. Infanticides followed predictions of the sexual selection hypothesis: males were unlikely to kill their own offspring, the period for the mother's return to conception was reduced by half, and males increased their chance of siring her next offspring. Difference in male reproductive benefit, costs, and motivation did not fully explain the observed variation in infanticide occurrence. Infants were more likely to be spared if they were older when a male first arrived, or if their mother had mated with the male in the second month after conception. The most important determinant of infant fate, however, was male identity, a finding consistent with 2 scenarios: 1) an infanticidal tendency may be influenced by a genetic polymorphism that is not fixed in this population or 2) infanticidal behavior may be a conditional male strategy. Further research on intrapopulation variation in infanticidal behavior should focus especially on characteristics of males.

Infanticide as Sexual Conflict: Coevolution of Male Strategies and Female Counterstrategies

“…This has led some researchers to propose that infanticide is a facultative strategy (a behavioral polymorphism?) (e.g., McLean 1983;Palombit et al 2000;Cords and Fuller 2010), as also suggested by theoretical models (e.g., Chapman and Hausfater 1979;Glass et al 1985;Yamamura et al 1990;Broom et al 2004). Consequently, rates of occurrence in an "infanticidal" population may vary considerably over time.…”

Infanticide by a male spectral tarsier (Tarsius spectrum)

“…The sexual selection hypothesis that the neighboring male committed infanticide to increase his reproductive opportunities by killing an unrelated and unweaned offspring, thus hastening the mother's next ovulation (Hrdy 1974(Hrdy , 1979Borries et al 1999;Soltis et al 2000;Cords and Fuller 2010), also does not fit this observation. Spectral tarsier females enter into estrus upon giving birth (Gursky 2007).…”

“…Numerous potential adaptive explanations for infanticidal behavior have been proposed, including: (1) organisms commit infanticide in order to obtain nutritive benefits from cannibalism (Elgar and Crespi 1992;Murray et al 2007;Dellatore et al 2009); (2) organisms commit infanticide as a means of eliminating competitors for limited resources (Takahata 1985;Pusey et al 1997;Watts and Mitani 2000); (3) males commit infanticide to increase their reproductive opportunities by killing unrelated, unweaned offspring, thus hastening the mother's next ovulation, at which time the infanticidal male can mate with her (also known as [aka] the sexual selection hypothesis) (Hrdy 1974(Hrdy , 1979Borries et al 1999;Soltis et al 2000;Cords and Fuller 2010); (4) infanticide in primates results in abnormal maladaptive behavior (aka the social pathology hypothesis) (Dolhinow 1977;Boggess 1984;Bartlett et al 1993); and (5) infanticide is an epiphenomenon of overall male aggression (Sussman et al 1995).…”

Conditional fetal and infant killing by male baboons

“…In several populations, infanticide has been described as a behavioural strategy that only some males employ [22][23][24], and our model provides some insight into the factors that create this contingency. Only Category 1 immigrations were associated with presumed feticide or infanticide, a finding that was consistent with expectations that high-quality males that became resident would be responsible for any male-induced increases in fetal and infant death in the population.…”

“…ursine colobus monkeys: [21]; chacma baboons: [22]). The frequency of infanticide varies within and across populations of a given species, but sources of variance in the frequency of infanticide are poorly understood [22][23][24].…”