COOPERATIVE BREEDING AND MONOGAMY IN PRAIRIE VOLES - INFLUENCE OF THESIRE AND GEOGRAPHICAL VARIATION

Mammalian monogamy is characterized by pair bonding and a relative abs ence of sexual dimorphism in body size. Alloparental behaviour is a ch aracteristic of mammalian cooperative breeding systems. Studies of pra irie voles, Microtus ochrogaster, from stock captured in a resource-ab undant habitat in Illinois have supported the assumption that this spe cies is a monogamous, cooperative breeder, while other studies of prai rie voles from a more arid habitat in Kansas have called this assumpti on into question. We hypothesized that reported differences between th ese populations represented true intraspecific variation. Patterns of sexual dimorphism in body size, partner preferences and parental conta ct behaviour were compared in prairie voles from stocks originating in Illinois or Kansas. Both Illinois and Kansas voles showed a strong pr eference for a familiar partner, which is suggestive of monogamy. Sexu al dimorphism in body size was observed in Kansas, but not Illinois vo les. Illinois voles displayed significantly higher levels of parental contact behaviour than did voles from Kansas. When animals from Illino is and Kansas were crossed, the expression of parental contact behavio ur of the 'hybrid' offspring followed the pattern seen in the populati on of origin of the sire. Removal of the sire prior to the birth of th e litter increased alloparenting in Kansas voles, but removal of the s ire was associated with lower levels of alloparenting in Illinois vole s. Thus, some traits associated with the social system may show intras pecific variation and can be influenced by the presence or absence of the sire during rearing. (C) 1998 The Association for the Study of Ani mal Behaviour.