Litter sex composition influences dominance status of Alpine marmots (Marmota marmota)

Abstract

In social species, the hierarchical status of an individual has important consequences for its fitness. While many studies have focused on individual condition to explain access to dominance, very few have investigated the influence of the social environment, especially during early life. Yet it is known that environmental conditions early in life may influence several traits at adulthood. Here, we examine the influence of early social environment on accession to dominance by investigating the influence of litter size and sex composition on survival and the probability of ascending to dominance later in life using a 20-year dataset from a wild population of Alpine marmots (Marmota marmota). Although litter size had no effect on the fate of individuals, litter sex composition affected male juvenile survival and both male and female probabilities of reaching dominant status when adult. Male juveniles incur lower survival when the number of male juveniles in the litter increases, and individuals of both sexes from male-biased litters are more likely to become dominant than individuals from female-biased litters. However, the absolute number of sisters in the litter, rather than the sex ratio, seems to be an important predictor of the probability of acquiring dominant status: pups having more sisters are less likely to become dominant. Several potential mechanisms to explain these results are discussed.

Early and Adult Social Environments Shape Sex-Specific Actuarial Senescence Patterns in a Cooperative Breeder

“…Although we do not yet have direct evidence of competition between male pups and helpers within a family group, previous results in our population provide evidence of competition between male littermates. Male juvenile survival decreases with an increasing number of brothers in the litter (Dupont et al 2015). Moreover, males form coalitions that often involve brothers of successive litters when dispersing in search for a breeding vacancy, a tactic commonly used by other social mammalian species, such as lions (Panthera leo; Packer et al 1991).…”

Revisiting the Trivers-Willard theory on birth sex ratio bias: Role of paternal condition in a Malagasy primate

“…Because paternal care does not occur in mouse lemurs, the reproductive value of the offspring is mostly influenced by mother quality and environment during early life. For example, litter sex composition in marmots affects life history traits and future dominance status [67, 68]. Preliminary results with captive mouse lemurs show that the reproductive value of male or female offspring varies according to the litter composition (unpublished data).…”

Uncovering ecological state dynamics with hidden Markov models

“…This difficulty has motivated models for individual histories that can not only account for multiple developmental states (Lebreton et al ., 2009), but also uncertainty arising from partially or completely unobservable states (Pradel, 2005). Such multi‐state models can be used for testing a broad range of formal biological hypotheses, including host–pathogen dynamics in disease ecology (Lachish et al ., 2011), reproductive costs in evolutionary ecology (Garnier et al ., 2016) and social dominance in behavioural ecology (Dupont et al ., 2015). For example, it is straightforward to extend the capture–recapture HMM to multiple ‘alive’ states parameterised in terms of state‐specific survival probabilities and transition probabilities between these ‘alive’ states .…”