Male-directed infanticide in spider monkeys (Ateles spp.)

Abstract

Infanticide is considered a conspicuous expression of sexual conflict amongst mammals, including at least 35 primate species. Here we describe two suspected and one attempted case of intragroup infanticide in spider monkeys that augment five prior cases of observed or suspected infanticide in this genus. Contrary to the typical pattern of infanticide seen in most primate societies, where infants are killed by conspecifics independent of their sex, all eight cases of observed or suspected infanticide in spider monkeys have been directed toward male infants within their first weeks of life. Moreover, although data are still scant, infanticides seem to be perpetrated exclusively by adult males against infants from their own social groups and are not associated with male takeovers or a sudden rise in male dominance rank. Although the slow reproductive cycles of spider monkeys might favor the presence of infanticide because of the potential to shorten females' interbirth intervals, infanticide is nonetheless uncommon among spider monkeys, and patterns of male-directed infanticide are not yet understood. We suggest that given the potentially close genetic relationships among adult males within spider monkey groups, and the need for males to cooperate with one another in territorial interactions with other groups of related males, infanticide may be expected to occur primarily where the level of intragroup competition among males outweighs that of competition between social groups. Finally, we suggest that infanticide in spider monkeys may be more prevalent than previously thought, given that it may be difficult for observers to witness cases of infanticide or suspected infanticide that occur soon after birth in taxa that are characterized by high levels of fission-fusion dynamics. Early, undetected, male-biased infanticide could influence the composition of spider monkey groups and contribute to the female-biased adult sex ratios often reported for this genus.

Are Male Orangutans a Threat to Infants? Evidence of Mother–Offspring Counterstrategies to Infanticide in Bornean Orangutans (Pongo pygmaeus wurmbii)

“…Infanticide is the killing of an infant by an individual of the same species (Hrdy and 57 Hausfater 1984). Infanticide committed by males is widespread across primate species, 58 documented in the wild in 36 primate species and inferred in the wild in an additional 17 species 59 (Alvarez et al 2015;Gursky-Doyen 2011;Kane and Gnépa 2016;Palombit 2012;van Schaik 60 2000a). The widespread prevalence of infanticide in primates has necessitated its inclusion in 61 socioecological models explaining patterns of primate sociality and group fission-fusion 62 dynamics (Aureli et al 2008;Janson 2000;Koenig et al 2013;Sterck et al 1997).…”

Demography and life history of a group of white‐bellied spider monkeys (Ateles belzebuth) in western Amazonia

“…Two female infants disappeared at <1 month and sometime between 12 and 22 months of age, simultaneously with their mothers. Three infant males disappeared within their first few days of life, and, for at least one of them, there was circumstantial evidence of intragroup infanticide (Alvarez et al, ). Finally, we could not determine the causes of disappearance for the three remaining offspring.…”

“…The average interbirth interval of female spider monkeys at TBS (44.2 ± SD 7.8 months) is similar to some previously published estimates for other spider monkey populations (Shimooka et al, ), but quite a bit higher than the estimate of 34.5 months for Ateles b. chamek in Manu National Park, Péru (Symington, ) and the estimate of 36.6 months for Ateles geoffroyi in Punta Laguna, Mexico (Vick, ). Potential explanations for these differences in IBI among different populations of spider monkeys are not clear, but may include factors associated with sample size, and further research is needed to determine if episodes of spontaneous abortion (Campbell, Shideler, Todd, & Lasley, ), male‐directed infanticide (Alvarez et al, ; Gibson et al, ), or degree of seasonality at different field sites (Shimooka et al, ) might help explain the variation. In fact, average interbirth intervals for female spider monkeys at TBS are among the longest reported for living atelines.…”

Measuring stress responses in female Geoffroy's spider monkeys: Validation and the influence of reproductive state

“…In comparison, the risk of infanticide in spider monkeys is comparatively low. In a single population of chacma baboons, 40% of infant mortality could be attributed to infanticide [Palmobit et al, ], whereas only eight infanticides have been reported across the Ateles genus [Alvarez et al, ; Gibson et al, ].…”

“…To add to the body of empirical work on this topic, we chose to study variation in GCs based on estradiol concentrations, reproductive state, and stage of lactation among both captive and wild Geoffroy's spider monkeys ( Ateles geoffroyi ). Although predation [Matsuda & Izawa, 2008] and infanticide [Alvarez et al, ; Gibson et al, ] are potential risks for species in the Ateles genus, the frequency of these incidents are low. However due to potential risks, we may expect mothers of young infants to maintain higher levels of vigilance.…”