Burrow limitations and group living in the communally rearing rodent,Octodon degus

Abstract

Group living is thought to evolve whenever individuals attain a net fitness advantage due to reduced predation risk or enhanced foraging efficiency, but also when individuals are forced to remain in groups, which often occurs during high-density conditions due to limitations of critical resources for independent breeding. The influence of ecological limitations on sociality has been studied little in species in which reproduction is more evenly shared among group members. Previous studies in the caviomorph rodent Octodon degus (a New World hystricognath) revealed no evidence that group living confers an advantage and suggest that burrow limitations influence formation of social groups. Our objective was to examine the relevance of ecological limitations on sociality in these rodents. Our 4-year study revealed no association between degu density and use of burrow systems. The frequency with which burrow systems were used by degus was not related to the quality of these structures; only in 1 of the 4 years did the frequency of burrow use decrease with decreasing abundance of food. Neither the number of females per group nor total group size (related measures of degu sociality) changed with yearly density of degus. Although the number of males within social groups was lower in 2008, this variation was not related clearly to varying density. The percentage of females in social groups that bred was close to 99% and did not change across years of varying density. Our results suggest that sociality in degus is not the consequence of burrow limitations during breeding. Whether habitat limitations contribute to variation in vertebrate social systems is discussed.

Ecological drivers of group living in two populations of the communally rearing rodent, Octodon degus

“…First, while degu abundance was similarly high in 2008 compared with 2007 at Rinconada, the number of predators sighted increased 2.9 times in the area, implying that more frequent predator visits were not simply the direct consequence of more abundant degu prey. Secondly, there is no evidence so far that density influences the size and composition of degu social groups in Rinconada (Ebensperger et al 2011). Finally, degu groups form not only as a result of delayed dispersal of offspring and adult fidelity, but also as the consequence of offspring dispersal and immigration of adults (Ebensperger et al 2009) resulting in groups that lack kin structure (Quirici et al 2011).…”

Octodon degus (Molina 1782): A Model in Comparative Biology and Biomedicine

“…Degus are plurally breeding rodents with communal care, meaning that multiple lactating females share underground nests and rear their litters communally (Ebensperger et al 2002, 2007). Thus, suppression of reproduction does not seem to occur, given that all members of a female group exhibit signs of pregnancy and lactation (Ebensperger et al 2011). Laboratory studies indicate that females provide communal care to their offspring and transfer immunoglobulin to their young during pregnancy and lactation (Becker et al 2007).…”

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents

“…High-density populations of southern bamboo rats correlate with polygynous mating (Stallings et al 1994), whereas social monogamy is related to low population densities (Silva et al 2008). In degus population density appears to have no effect on social group size (Ebensperger et al 2011 [this issue]). However, areas of degu home ranges increase at higher population density, although it is unclear whether this change is related directly to population density or to food availability (Quirici et al 2010).…”