Ontogeny and symmetry of social partner choice among free-living yellow-bellied marmots

The benefits of being dominant: health correlates of male social rank and age in a marmot

The benefits of dominance may not come without costs, particularly for males. For example, the “immunocompetence handicap hypothesis” states that males with enhanced mating success allocate resources to enhance reproductive output at a cost to their current health, whereas the “resource quality hypothesis” predicts that high-ranking males may benefit from increased reproduction and good health. Whereas the predictions from each have been well tested in captive animals and in a variety of highly social primates, fewer studies have been carried out in free-living, facultatively social animals. Using adult male yellow-bellied marmots (Marmota flaviventer), we evaluated predictions of these hypotheses by examining the relationship between social rank and 2 health indicators—fecal glucocorticoid metabolite (FCM) levels, and neutrophil/lymphocyte (N/L) ratios—after accounting for variation explained by age, body mass, and seasonality. We found that higher-ranking males tended to have a lower N/L ratio (reflecting good health) than lower-ranking individuals, whereas FCM levels were not significantly related to rank. In addition, heavier male marmots had lower N/L ratios, whereas body mass was not associated with FCM levels. We also found that older adult males had lower FCM levels (reflecting less physiological stress) but higher N/L ratios than younger adults. Finally, we found that FCM levels decreased as the active season progressed and FCM levels were associated with the time of the day. Overall, our results suggest that socially-dominant male marmots enjoyed better, not worse health in terms of lower N/L ratios.

Split between two worlds: automated sensing reveals links between above- and belowground social networks in a free-living mammal

Many animals socialize in two or more major ecological contexts. In nature, these contexts often involve one situation in which space is more constrained (e.g. shared refuges, sleeping cliffs, nests, dens or burrows) and another situation in which animal movements are relatively free (e.g. in open spaces lacking architectural constraints). Although it is widely recognized that an individual's characteristics may shape its social life, the extent to which architecture constrains social decisions within and between habitats remains poorly understood. Here we developed a novel, automated-monitoring system to study the effects of personality, life-history stage and sex on the social network structure of a facultatively social mammal, the California ground squirrel (Otospermophilus beecheyi) in two distinct contexts: aboveground where space is relatively open and belowground where it is relatively constrained by burrow architecture. Aboveground networks reflected affiliative social interactions whereas belowground networks reflected burrow associations. Network structure in one context (belowground), along with preferential juvenile-adult associations, predicted structure in a second context (aboveground). Network positions of individuals were generally consistent across years (within contexts) and between ecological contexts (within years), suggesting that individual personalities and behavioural syndromes, respectively, contribute to the social network structure of these free-living mammals. Direct ties (strength) tended to be stronger in belowground networks whereas more indirect paths (betweenness centrality) flowed through individuals in aboveground networks. Belowground, females fostered significantly more indirect paths than did males. Our findings have important potential implications for disease and information transmission, offering new insights into the multiple factors contributing to social structures across ecological contexts.This article is part of the theme issue 'Interdisciplinary approaches for uncovering the impacts of architecture on collective behaviour'.

Temporal modification of social interactions in response to changing group demographics and offspring maturation in African lions (Panthera leo)

In group living animals, affiliative social interactions maintain cohesion between individuals. Involvement in these interactions is likely to differ between individuals, depending on their sex, age and life history stages. Here we investigated different social network measures to describe greeting interactions within two prides of captive-origin African lions (Panthera leo). We aimed to determine if the introduction of cubs to these prides altered the strength of greeting networks among female lions. We also tested if the strength of greeting interactions changed between the age classes as younger lions matured. We found that interactions amongst female lions decreased from the period before cubs were born (least square means [95% CIs] 15.3 [7.67-22.93]) compared to after their integration into a pride (5.63 [-1.99-13.26] χ²₁ = 210.03, p < 0.001). In contrast, greeting network strength increased as offspring matured, with adults directing more interactions towards younger lions from 30 months of age (12.89 [1.96-23.82]) compared to when offspring were cubs (-0.69 [-11.63--10.24] χ²₁₀ = 156.03, p < 0.001). We suggest that social interactions between age classes may mediate recruitment and dispersal in lion prides.

Social play among juvenile wild Japanese macaques (Macaca fuscata) strengthens their social bonds

Social play and grooming are typical affiliative interactions for many primate species, and are thought to have similar biological functions. However, grooming increases with age, whereas social play decreases. We proposed the hypothesis that both social grooming and social play in juveniles strengthen their social bonds in daily activities. We carried out field research on the social relationships among juvenile wild Japanese macaques in a troop in Kinkazan, Miyagi Prefecture, Japan, from fall 2007 to spring 2008 to investigate this hypothesis. We evaluated three relationships among juveniles, play indices (PI), grooming indices (GI), and 3-m-proximity indices (3mI) of each dyad (i.e., interacting pair), and compared these social networks based on the matrices of the indices. The play and grooming networks were correlated with the association network throughout the two research periods. The multiple network level measurements of the play network, but not the grooming network, resembled those of the association network. Using a causal step approach, we showed that social play and grooming interactions in fall seem to predict associations in the following spring, controlling for the PI and GI matrix in spring, respectively. Social play and grooming for each juvenile were negatively correlated. The results partially support our predictions; therefore, the hypothesis that the biological function of social play among immature Japanese macaques is to strengthen their social bonds in the near future and develop their social life appears to be correct. For juvenile macaques, social play, rather than grooming, functions as an important social mechanism to strengthen affiliative relationships.

The importance of social play network for infant or juvenile wild chimpanzees at Mahale Mountains National Park, Tanzania

Along with social grooming and food sharing, social play is considered to be an affiliative interaction among wild chimpanzees. However, infant, juvenile, and adolescent animals engage in social play more frequently than adult animals, while other affiliative interactions occur more commonly between adults. We studied the social play of well-habituated and individually identified wild chimpanzees of the M group in Mahale Mountains National Park, Tanzania over two research periods in 2010 and 2011 (21 and 17 observation days, respectively). In both periods, most members of the M group, including adolescents and adults, took part in social play at least once. The degree centralities of the play network in infants, juveniles, and adolescents were significantly higher than those seen in adults. There was a significant and positive correlation between the total number of participations in social play and the degree centrality of play networks. Partial play networks and partial association networks consisting of individuals in same-age categories were significantly and positively correlated in infants and juveniles, although they were not correlated in adolescents or adults. These results suggest that infants, juveniles and adolescents who played frequently were more central in the group, whilst the adults who played infrequently were more peripheral. In addition, the overall structure of the social play network was stable over time. The frequency of participation in social play positively contributed to the development of affiliative social relationships within the chimpanzee group during the infant or juvenile period, but did not have the same effect during the adolescent and adult period. The social play network may allow individuals to develop the social techniques necessary to acquire a central position in a society and enable them to develop affiliative relationships during the infant or juvenile period.