Abstract
Comparative studies aid in our understanding of specific conditions favouring the initial evolution of different types of social behaviours, yet there is much unexplained intraspecific variation in the expression of social behaviour that comparative studies have not yet addressed. The proximate causes of this individual variation in social behaviour within a species have been examined in some species but its fitness consequences have been less frequently investigated. In this study, we quantified the fitness consequences of variation in the sociality of prairie voles, Microtus ochrogaster. We characterized sociality of voles in seminatural enclosures using an automated behavioural tracking system paired with social network analyses to quantify the degree of spatial and temporal co-occurrence of different voles. We then assessed the relationship between sociality and both mating success (number of different conspecifics with which an individual produced offspring) and reproductive success (total number of offspring surviving to first capture). We measured the number of social connections each individual had with all voles and with only opposite-sex voles (unweighted degree) through social network analyses. Both female and male voles varied in the number of social connections they had with all conspecifics and with opposite-sex conspecifics. In both analyses, females and males with an intermediate number of social connections had higher mating success overall and, for the analysis with all connections, produced more offspring. Males with many or few social connections also had the lowest average body mass. Overall, our results suggest some limit on the fitness benefits of sociality. Although there was substantial individual variation in our measure of vole social behaviour, intermediate levels of social connections may be most favourable.
Highlights
Sociality comes in many forms across a diversity of taxa, ranging from loose, temporary associations during breeding to long-term group associations whose members exhibit complex social behaviors such as cooperative hunting or alloparental care
Other comparative studies have shown that cooperative breeding, where subordinate group members care for offspring produced by dominant breeders, is more likely to be found in mammalian species that live in arid areas (Faulkes et al, 1997; Lukas and Clutton-Brock, 2017) or in avian species that inhabit areas where rainfall is low and unpredictable (Jetz and Rubenstein, 2011)
0.84; opposite-sex social connections: b = -0.20, t = -0.31, P =0.76, Table 4). Both female and male prairie voles varied in the frequency of social interactions, as reflected in our social network analyses that quantified social network degree using the frequency of temporal and spatial co-occurrence generated by our radio-frequency identification (RFID) system
Summary
Sociality comes in many forms across a diversity of taxa, ranging from loose, temporary associations during breeding to long-term group associations whose members exhibit complex social behaviors such as cooperative hunting or alloparental care. Sociality may come with costs associated with group-living, including increased disease transmission (Ewald, 1994; Langwig et al, 2012; Kappeler et al, 2015), parasite load (Côté, and Poulinb, 1995; Whiteman and Parker, 2004), physiological stress (Creel et al, 2013), reproductive interference by other group members (Clutton-Brock et al, 1998; Lukas and Huchard, 2014), as well as the time and energy costs devoted to developing and maintaining social connections that could otherwise be devoted towards activities directly related to individual survival or reproduction such as foraging or parental care Given that these fitness benefits and costs of sociality may vary in direction or magnitude due to ecological circumstances such as food abundance, weather patterns, or temporal variability in these factors
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