Breeding suppression between two unrelated and initially unfamiliar females occurs with or without social tolerance in common voles (<Emphasis Type="Italic">Microtus arvalis</Emphasis>)

Female common voles can breed in small groups or in isolation. Given the option, will isolated females opt for communal breeding with unrelated females and a probable low reproductive bias, or will they remain isolated, forgoing the advantages of group living? This laboratory work examined the response of two unrelated females to a foreign male in order to determine their social and breeding strategies. Before encountering a male, 70% of the females lived communally and 30% were solitary with a dominance hierarchy. In the presence of the male, only 33% of the females were still associated and lived with the male in a communal nest. In the other triads, only the oldest female lived with the male and she dominated the younger female. Although all animals were then experimentally separated to avoid late abortion due to social stress or infanticide, in 89% of the dyads only one female littered. This breeding suppression happened in hierarchic dyads but also in tolerant ones. This laboratory study on the social influence on reproduction showed that breeding suppression can occur in unrelated female common voles even when they are not closely grouped. It suggests that cooperative breeding between unrelated females should remain rare.