Cost of dispersal in a social mammal: body mass loss and increased stress

Abstract

Dispersal is a key process influencing the dynamics of socially and spatially structured populations. Dispersal success is determined by the state of individuals at emigration and the costs incurred after emigration. However, quantification of such costs is often difficult, due to logistical constraints of following wide-ranging individuals. We investigated the effects of dispersal on individual body mass and stress hormone levels in a cooperative breeder, the meerkat ( Suricata suricatta ). We measured body mass and faecal glucocorticoid metabolite (fGCM) concentrations from 95 dispersing females in 65 coalitions through the entire dispersal process. Females that successfully settled lost body mass, while females that did not settle but returned to their natal group after a short period of time did not. Furthermore, dispersing females had higher fGCM levels than resident females, and this was especially pronounced during the later stages of dispersal. By adding information on the transient stage of dispersal and by comparing dispersers that successfully settled to dispersers that returned to their natal group, we expand on previous studies focusing on the earlier stages of dispersal. We propose that body mass and stress hormone levels are good indicators to investigate dispersal costs, as these traits often play an important role in mediating the effects of the environment on other life-history events and individual fitness.

When to stay and when to leave? Proximate causes of dispersal in an endangered social carnivore

“…Males, on the one hand, may thus compensate for diminished group hunting benefits (Creel & Creel, 1995; Hubel et al., 2016) resulting from leaving their pack, by dispersing when prey that is relatively easy for wild dogs to catch (Pole et al., 2004) is abundant. Females, on the other hand, whose dispersal peaks in March, appear to delay dispersal from the natal pack to a few months prior to the mating season (McNutt et al., 2019) to minimize the costs of dispersal (Bonte et al., 2012; Maag et al., 2019) and maximize mating opportunities.…”

“…Consistent with studies on other social carnivores (Fuller, 1989; Rood, 1987), rates of secondary dispersal were lower compared to natal dispersal and were mainly influenced by social status. If an individual (either a natal disperser or an immigrant) failed to acquire breeding status in the new pack, its dispersal rate increased, underlying the ultimate dispersal motivation of gaining direct fitness (Bowler & Benton, 2005) despite the costs associated with dispersal (Bonte et al., 2012; Maag et al., 2019). Failure to attain dominance in the new pack results in lower probabilities of breeding for females compared to males, for in wild dogs, cases of shared paternity are more common than shared maternity (Creel et al., 1997; Spiering et al., 2010) and may thus explain sex differences in the rate of secondary dispersal reported here.…”

“…Several individual, social and environmental factors have been shown to influence the decision to emigrate. At the individual level, emigration can be influenced by physiological traits, body condition and age (Clobert, Baguette, Benton, & Bullock, 2012; Maag et al., 2019). Despite dispersal being typical of younger individuals, it may occur at any age, for example following breeding failure (Rioux, Amirault‐Langlais, & Shaffer, 2011).…”

Accounting for demography in the assessment of wild animal welfare

“…If welfare is invariant with age, welfare expectancy will scale linearly with life expectancy. However, it seems highly likely that welfare would shift in some direction concurrent with major life history transitions, like the maturation of a tadpole or caterpillar, or sexual maturation in most species, especially when this is accompanied by changes in environment, such as with the ejection of young male hyenas or female meerkats from their natal groups (Maag et al, 2019).…”

The role of dispersal and school attendance on reproductive dynamics in small, dispersed populations: Choyeros of Baja California Sur, Mexico

“…However, while dispersal can assist in expanding an individual’s mating market, it can also be costly. This has been well-documented across a wide range of animal species and includes, for example, loss of body mass, elevated stress levels, compromised immune functioning, and delayed reproduction [ 32 – 34 ]. Dispersal costs are multivariate, but for group-living species they are typically tied to reliance on social relationships for reproductive opportunities, protection, and resource provisioning [ 34 ].…”