Effects of group size on nest attendance in the communally breeding colonial tuco-tuco

Abstract

Communal nesting is generally assumed to be adaptive, meaning that it confers a fitness advantage on the individuals that share a nest site. This advantage may accrue directly to adults, or it may affect adult fitness through gains in offspring survival. In particular, survival of juveniles reared in communal groups may be greater because adults are present in the nest more often to provide care to young. To test the hypothesis that communal nesting is associated with increased adult presence in the nest, we used radiotelemetry to examine patterns of adult nest attendance as a function of group size for free-living colonial tuco-tucos (Ctenomys sociabilis). Burrow systems of this social, subterranean rodent are inhabited by 1-6 adult females and, in some cases, a single adult male. Data obtained from residents of 26 burrow systems monitored during 1996-2000 indicated that the percentage of time that the nest was unattended (no adult present) did not vary predictably with date or time of day during the period between the birth and weaning of young. The percentage of time that the nest was unattended, however, decreased significantly as the number of adults per burrow system increased. This difference was most evident when the percentage of time that the nest was unattended was compared for lone females versus multi-adult groups. We suggest that increased nest attendance has important implications for the survival of juveniles reared in multi-adult burrow systems but that this effect may be confounded by the fitness consequences of other costs and benefits associated with communal nesting in this species.

The ecological value of long-term studies of birds and mammals in Central America, South America and Antarctica

“…Lifetime reproductive success and survival to a second breeding year did not differ between social strategies (disperser vs. philopatric) leading [30] to argue that ecological constraints on dispersal explains group living in colonial tuco-tucos. Although the amount of time that adults attend a communal nest increased with the number of adults in the group [50], per capita direct fitness decreased with increasing adult group size [30], suggesting that group size benefits or benefits of communal care are minimal and/or do not exceed potential costs of living in groups.…”

Towards an integrative model of sociality in caviomorph rodents

“…In social tuco-tucos the percentage of time that pups are left unattended decreases with increasing group size (Izquierdo and Lacey 2007). The consistent presence of adult females at the nest may reduce the risk of predation or infanticide (Manning et al 1995) and enhance the thermal environment in which pups are reared (Hayes and Solomon 2006).…”

“…Ecological factors, including the distribution of resources such as food (Lacey and Ebensperger 2007; Lacey and Wieczorek 2003; Macdonald et al 2007; Maher and Burger 2011 [this issue]), predation risk (Ebensperger and Blumstein 2006; Lacey and Ebensperger 2007; Lacey and Sherman 2007; Macdonald et al 2007), and soil conditions associated with digging burrows (Ebensperger and Blumstein 2006; Ebensperger and Cofré 2001; Lacey and Ebensperger 2007; Lacey and Sherman 2007) have been identified as potential causes for the formation of social groups. With regard to evolution and adaptive significance, behavioral ecologists have identified numerous costs and benefits of social living (Ebensperger and Bozinovic 2000; Ebensperger and Wallem 2002; Izquierdo and Lacey 2007; Quirici et al 2008; Vásquez 1997). To a much lesser extent we have quantified some of the consequences to reproductive fitness of social behavior (Ebensperger et al 2007; Hayes et al 2009; Lacey 2004; Sachser et al 1999; Trillmich et al 2008).…”