Fitness and hormonal correlates of social and ecological stressors of female yellow-bellied marmots

Abstract

The effects of social and ecological stressors on female reproductive success vary among species and, in mammals, previous reviews have identified no clear patterns. However, few studies have focused on both of these relationships simultaneously-the one between social rank and stressors, and the relationships among rank, stressors and reproductive success. We used a longterm data set to study free-living facultatively social yellow-bellied marmots (Marmota flaviventris) to isolate the relationship between female social dominance rank and faecal glucocorticoid metabolites (FGM) levels (our measure of basal stress) in adult females. In addition, we asked whether rank and FGM levels were associated with reproductive success by quantifying the probability of an individual successfully weaning a litter and, for those who did, litter size. High-ranking females had lower FGM levels and larger litters. However, females with the highest FGM levels were significantly more likely to wean a litter. Importantly, body condition (as measured by previous year's August mass)was also positively associated with breeding and with weaning larger litters. Thus, although low-ranking females likely experienced more social stressors than did high-ranking females and adult females often delayed their first reproduction until they were of a sufficient mass, our data suggest that elevated baseline FGM levelsfailed to mediate reproductive suppression. Perhaps, in species like marmots that only have a single chance per year to reproduce, reproductive suppression should be rare. These results highlight the importance of social status, body condition and predator abundance on determining reproductive success in highly seasonal breeders.

How social behaviour and life-history traits change with age and in the year prior to death in female yellow-bellied marmots

“…We know that traits reflecting social networks in the marmots are heritable [44] and can negatively impact longevity [45]; and, while we know that older females are less social [42], we are aware of no previous studies that have specifically focused on latelife variation in social behaviour. As for life-history traits, we know that stress hormone levels (faecal glucocorticoid metabolites), which negatively affect marmot survival [46], are negatively associated with age [47], as is vigilance behaviour, but only when adults are in good body condition [48]. In addition, separate studies have found evidence in support of senescence in reproduction and body mass [18,49], and of a terminal decrease in body mass [18].…”

Age‐specific reproduction in relation to body size and condition in female Eurasian beavers

“…In this socially monogamous species, the subordinate social status of younger female colony members is one such particular factor, as suggested for other socially living mammals (e.g. Sparkman et al ., ; Blumstein et al ., ). Since barren females were leaner than pregnant individuals, another factor may be attaining a certain pre‐breeding body fat threshold.…”

“…However, a direct effect of fatness on ovulation in mammals has been difficult to demonstrate (Bronson, ) and support for the critical body fat hypothesis (Frisch, ) is weak at best. Alternatively, some barren adult female members of the colony may have been sub‐dominant and socially inhibited from breeding by the colony's dominant female (as demonstrated, for example, in yellow‐bellied marmots Marmota flaviventris , Blumstein, Keeley & Smith, ; or red wolves Canis rufus , Sparkman et al ., ), which in turn may have affected their fat deposition cycle. At present, the factors controlling autumn fat deposition in beavers are poorly understood.…”

The impact of the built environment on health behaviours and disease transmission in social systems

“…For example, yellow-bellied marmots rely on burrows for wintering and for escaping from predators, thus forming facultative social structures [114]. Interestingly, individuals in larger groups express higher levels of faecal glucocorticoid metabolites, an indicator of stress [115]. Thus, living in a built structure can, in some cases, lead to chronic stress, and dispersing to find a less crowded burrow system might be the best way to contain such chronic stress.…”