Sexual behavior of group-housed stumptail macaques (Macaca arctoides): temporal, demographic and sociosexual relationships

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

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.

Dominance status and copulatory vocalizations among male stump-tailed macaques in Thailand

Male copulation calls sometimes play important roles in sexual strategies, attracting conspecific females or advertising their social status to conspecific males. These calls generally occur in sexually competitive societies such as harem groups and multi-male and multi-female societies. However, the call functions remain unclear because of limited availability of data sets that include a large number of male and female animals in naturalistic environments, particularly in primates. Here, we examined the possible function of male-specific copulation calls in wild stump-tailed macaques (Macaca arctoides) by analyzing the contexts and acoustic features of vocalizations. We observed 395 wild stump-tailed macaques inhabiting the Khao Krapuk Khao Taomor Non-Hunting Area in Thailand and recorded all occurrences of observed copulations. We counted 446 male-specific calls in 383 copulations recorded, and measured their acoustic characteristics. Data were categorized into three groups depending on their social status: dominant (alpha and coalition) males and non-dominant males. When comparing male status, alpha males most frequently produced copulation calls at ejaculation, coalition males produced less frequent calls than alpha males, and other non-dominant males rarely vocalized, maintaining silence even when mounting females. Acoustic analysis indicated no significant influence of status (alpha or coalition) on call number, bout duration, or further formant dispersion parameters. Our results suggest that male copulation calls of this species are social status-dependent signals. Furthermore, dominant males might actively transmit their social status and copulations to other male rivals to impede their challenging attacks, while other non-dominant males maintain silence to prevent the interference of dominants.

Sexual communication between breeding male and female cotton-top tamarins (Saguinus oedipus), and its relationship to infant care

Male cotton-top tamarins have been shown to be responsive to female scent cues of ovulation, and are known to actively participate in infant care during the time when their mates are fertile. We measured urinary androgen levels and glucocorticoids in seven father tamarins for the first month following the birth of infants to determine 1) whether male tamarins showed an androgen response to their mate's postpartum ovulation, 2) when androgens rise relative to ovulation, 3) whether there is a glucocorticoid response, and 4) whether males alter their parenting behavior during their mate's receptive period. All of the males showed a significant increase in urinary androgens prior to the female's postpartum LH peak, which indicated ovulation. The hormonal increase, which included estradiol, occurred 3-7 days prior to the female's LH peak at a time that coincided with the female's follicular period. Corticosterone levels also peaked during that time, but did not correlate with androgen changes. Fathers did not alter their daily infant-carrying patterns relative to the androgen increase or at the time of the mate's LH peak. We conclude that male cotton-top tamarins experience an increase in androgens that coincides with their mate's postpartum ovulation, which ensures optimal fertility. However, this sexual communication does not alter father-infant interactions, which already occur at a high rate in this species.