An experimental examination of the consequences of communal versus solitary breeding on maternal condition and the early postnatal growth and survival of degu, Octodon degus, pups

Individuals of numerous rodent species engage in group living, in which they share an area of activity, a nest (or den), and interact more frequently with group members than with individuals from other such groups. Members of social groups may engage in communal breeding when they rear their young together in a common nest. We conducted an experimental study under laboratory conditions to explore the costs and benefits linked to early postnatal investment in offspring by female degus. In particular, we examined the quality and quantity of offspring produced by females rearing their litters in the presence of a second lactating (related or unrelated) female (‘communally breeding’) with offspring produced by lactating females in the presence of a nonbreeding (related or unrelated) female (‘singularly breeding’), and the offspring of solitary females. The physical condition of mothers (mass lost through lactation) was also examined. We studied 70 female degus and their litters, and 13 additional nonbreeding females, under constant conditions of adult density, nest availability, restricted food availability and breeding experience of subjects. The number of pups, the mass of pups, and the physical condition of mothers breeding communally did not differ from those of singularly and solitarily breeding females. Similar results were obtained when kinship of breeding females was considered. When reproductive performance of individuals within communally breeding groups was examined, we found that costs and benefits were not shared equally. Weanlings of litters born in the presence of a previous litter were smaller and less numerous than weanlings of litters born when no other young were present. Taken together, our results show that female degus derive no apparent reproductive benefits from early postnatal rearing of their offspring. Moreover, a proportion of females seem to pay a net cost.