Mating and Reproductive Success in Free-Ranging Stump-Tailed Macaques: Effectiveness of Male–Male Coalition Formation as a Reproductive Strategy

Abstract

Male coalition-like formation, recently found in stump-tailed macaques (Macaca arctoides), occurs when several top-ranking males collaboratively guard females to prevent mating with other rival males and actively share secured mating opportunities with their allies. We lack a comprehensive understanding of the proximate mechanisms underlying such male coalitions, e.g., the effect of genetic relatedness. Such cooperative partner choice among males is particularly interesting in animals, such as M. arctoides, that live in matrilineal (female philopatry/male dispersal) society. Theoretically, in such a social system, females, and not males, are often related to each other by kinship. Thus, the occurrence of cooperative behavior between related females are generally common, but it would be rare between unrelated/non-kin males in such matrilineal society. Herein, for the first time, we report detailed copulatory behaviors, including mating and reproductive success, in relation to male coalition-like formation in free-ranging M. arctoides following direct behavioral observation and genetic analysis. We found that coalition-forming male–male alliances often occur among both individuals that are highly related and those that are less related. We identified two groups with different mating strategies, i.e., single-male monopoly and coalition-male monopoly groups. In both groups, nearly 80% of copulations were monopolized by a single male or by coalition males. However, the single-male monopoly strategy allows opportunistic/sneaky copulations by other males with a relatively high probability. Thus, the degree of reproductive success did not reflect mating success. In contrast, the males employing a coalition strategy successfully shared their mating and reproductive success, particularly in the largest group. Compared with single-male monopolized groups, the coalition-male monopoly groups copulated with a considerably more number of females, suggesting that coalition males can effectively guard against opportunistic/sneaky copulation by rival males. We also found that coalition-forming male–male alliances often occur regardless of the degree of kinship/relatedness, indicating the complexity and flexibility inherent in the male social bond of M. arctoides.

Comparisons of paternity success for resident and non-resident males and their influences on paternal sibling cohorts in Japanese macaques on Shodoshima Island

“…This is in accordance with previous studies on macaque species (e.g. Hayakawa 2008;Toyoda et al 2022). Furthermore, the alpha male, which is the most dominant male, was identified each year as one among the dominant males.…”

Sex differences in cooperative coalitions: a mammalian perspective

“…However, in male olive and yellow baboons and Barbary macaques [15,133,134], low- and mid-ranking males may join forces against higher-ranking males to take over a consortship, and male chimpanzees sometimes form coalitions to guard mates [135]. Male Camargue horses [103], Indo-Pacific bottlenose dolphins [97], and stump-tailed macaques [72] also form intragroup coalitions, often with non-kin, to gain access to sexually receptive females. However, in some cases, such as male fallow deer, coalition frequency fails to predict mating success [89].…”

“…In some species, males do not limit coalitionary support to kin (e.g. chimpanzees [70], dolphins [71], stump-tailed macaques ( Macaca artoides ) [72]).…”

Necrophilic behaviour in wild stump-tailed macaques (Macaca arctoides)

“…The study site is home to six multi-male/multi-female social groups of stump-tailed macaques (group sizes range from 41 to 120 individuals) totaling more than 460 individuals. The study population has been named as Ting-Group, Nadam-Group, Third-Group, Fourth-Group, Wngklm-Group, and Ruay-Group, and > 80% of individuals have been identified 23 .…”