Social factors affecting litters in families of Mongolian gerbils, Meriones unguiculatus

Mongolian gerbils (Meriones unguiculatus) live territorially in families consisting of a reproducing founder pair and their non-reproducing young. Intra-family aggression occurs and is reported to be mainly caused by reproductive competition between females and the loss of reproducing founder animals. The current study investigated the impact of family traits (size, density and sex ratio) and aggressive inter-individual interactions on litters. Characteristics like pup mortality, litter size, sex ratio, and weekly body mass gain were tested. Across litters, significant correlations were found between litter size and family size (r = - 0.507, df = 25, p = 0.008) and between litter size and family density (r = - 0.404, df = 25, p = 0.01). Pup mortality was influenced by family size (r = 0.556, df = 25, p = 0.003) and by family density (r = 0.328, df = 25, p = 0.04). Unexpectedly, the influencing factor "occurrence of aggression" between adult family members or "expulsion of the mother" during lactation of the young had no influence on litters' features. Family size and family density could be shown to be the most dominant parameters affecting the fate of the offspring and regulating the reproduction of the family.