Variation in Adult Male-Juvenile Affiliative Behavior in Japanese Macaques (Macaca fuscata)

Abstract

Adult males of some primate species are known to positively interact with juveniles. In cases where paternal certainty is high, these behaviors have been largely attributed to the paternal investment hypothesis. Males have also been observed to interact with nonkin juveniles, which has often been explained in terms of mating effort. Here, we examined variation in adult male-juvenile affiliation in semi-free ranging Japanese macaques (<i>Macaca fuscata</i>) at the Oregon National Primate Research Center against possible influencing factors such as age, dominance rank, and female affiliation, and we also tested for fitness benefits. We conducted 154 h of focal observations of 14 adult males from June to September 2018. Males differed significantly in their rate of juvenile-directed affiliation, but not in their fitness in terms of number of offspring. There was a significant positive correlation between rank and age in the group, indicating that, in this group, rank does not conform to the classic inverted-U pattern observed elsewhere in this species. Although there was a significant positive correlation between rank and juvenile-directed affiliation, the highest-ranking male had few offspring and exhibited little juvenile-directed affiliation. These results suggest little to no preliminary support for either the paternal investment or mating effort hypotheses as explanations for juvenile-directed affiliation. This study suggests that there are multiple behavioral strategies for older males that may influence reproductive success.

Sex influences the effects of social status on socioemotional behavior and serotonin neurochemistry in rhesus monkeys

“…Less steep and more tolerant social hierarchies are also associated with less steep rank gradients in affiliation, perhaps driving the lack of any status or sex differences in rates of affiliative behaviors in the current study. While previous literature indicates that other aspects of social context, such as group size and mixed-sex groups, are also important factors that influence rates of agonistic and affiliative behaviors in monkeys [ 13 , 63 – 65 ], fluctuations in reproductive hormones (e.g., estradiol, testosterone, and oxytocin) may also be influencing these behaviors in the current study [ 57 , 66 ].…”

Dominance rank, female choice, and reproductive success in semi‐free ranging adult male Japanese macaques (Macaca fuscata)

“…Personal communications from ONPRC staff report a pattern in which many offspring are routinely sired by the younger (8-and 9-year old) adult males rather than the older and more hierarchically-established males, potentially supporting a pattern in which females prefer the more middle-ranking males. However, as with many primate species, age and rank are intertwined both in this population and in other populations of Japanese macaques (Gartland, 2021;Gartland et al, 2020;Hiroyuki Takahashi, 2002). As demonstrated by our results, a simple examination of reproductive success against rank and age does not fully address the variation observed in this population.…”

“…Dominance rank based upon a priority‐of‐access model for individuals within this population had been previously established and kept updated (Gartland, 2021; Gartland et al, 2020). Males were ranked as either high (1), middle (2), or low (3) (Table 1).…”

“…While there is some evidence for the importance of dominance on the paternity of infants (Soltis et al, 2001), this positive correlation between reproductive success and rank has not been consistently observed in Japanese macaques. Reproductive success of dominants may be significantly influenced by competition with non‐troop males, female estrous synchrony, operational sex ratio, and female choice (Gartland et al, 2020; Hayakawa, 2008; Hayawaka & Soltis, 2011; Inoue & Takenaka, 2008; Inoue et al, 1993; Kutsukake & Nunn, 2006; Soltis et al, 1997; Takahashi, 2001; Kutsukake & Hasegawa, 2005).…”

Infant adoptions in wild bonnet macaques (Macaca radiata)

“…Instances of males caring for infants have been observed in catarrhines where male care is otherwise rare, such as in Japanese macaques ( Macaca fuscata ) (Nakamichi et al 2021 ). By caring for infants, males may increase their interactions with mothers and their chances of future matings with the mothers, an alternative to direct male–male competition as a mating strategy ( M. fuscata : Gartland et al 2020 ; Nakamichi et al 2021 ; M. sylvanus : Ménard et al 2001 ; Gorilla beringei : Rosenbaum et al 2018 ).…”