Incest avoidance and bonding between siblings in gerbils

Summary Social and sexual preferences for siblings versus non-siblings have been investigated in Mongolian gerbils (Meriones unguiculatus) in a series of laboratory and outdoor enclosure (100 m²) studies. When first social contact took place at pairing in adulthood full siblings and nonsiblings did not differ with respect to onset of reproduction. Correspondingly, both siblings and non-siblings paired at weaning age had a delayed onset of reproduction. Thus, no effect could be established in either case, related to the individuals' relatedness, but the importance of social exposure was clear. Non-siblings paired when 2 months old had a delayed onset of reproduction, which did not differ statistically from the onset in siblings, raised together, and housed pairwise since the same age. When sexually mature animals were paired at 3 months of age, siblings were found to start reproducing later than non-siblings (Ågren 1981). Following an initial delay in both siblings and nonsiblings paired when 5 months old, all non-sibling pairs reproduced before any sibling pair. At pair formation, at least the females in both groups were known to be sexually immature. These results indicate that for sibling-bonding to occur social exposure may be delayed until the animals are old enough, or somatically developed, to mature sexually. Thus, social exposure before weaning age during the period for primary socialization seem not to be crucial, nor the actual maturational state, sexually, in older females. To study the stability of the social bonds between siblings and non-siblings, animals kept pairwise in the laboratory were released in large outdoor enclosures. Pairs brought together before the age of sexual maturity did not remain stable, whether or not the former cagemates were siblings. Non-sibling pairs formed after this age, which had also reproduced successfully in the laboratory, did remain stable. Social and sexual interactions were studied within and between two mixed-sex sibling groups of four. The sibling groups had the possibility to establish group territories before being exposed to each other. Although the sibling groups remained stable, the females still preferred non-sibling males as sexual partners. However, socially dominant brothers copulated more frequently than subordinant brothers. This rank difference was not evident in non-siblings.