INTERCOLONIAL ENCOUNTERS AND XENOPHOBIA IN THE COMMON MOLE-RAT, CRYPTOMYS HOTTENTOTUS HOTTENTOTUS (BATHYERGIDAE) - THE EFFECTS OF ARIDITY, SEX, AND REPRODUCTIVE STATUS

The ecological constraints prevalent in arid environments have promote d the evolution of social groups with a high reproductive skew in mole rat species occurring there. Outbred social bathyergids face conflict between maintaining colony integrity to enhance personal foraging suc cess and hence survival, and dispersal to maximize individual lifetime reproductive success (LRS). This conflict will be a crucial determina nt of the response of colony members to the presence of foreign conspe cifics. We investigated how ecological constraints, sex, and reproduct ive status influence the outcome of meetings between foreign common mo le rats (Cryptomys hottentotus hottentotus) in a series of dyadic enco unters. Individuals from two localities, at the extremes of an aridity gradient, were used to assess the effects of aridity. The effects of sex and reproductive status were investigated by trials between indivi duals of differing sex and status. The arid population revealed substa ntially higher levels of rejection than the mesic population. Sex and status played a significant role in moderating individual response. Fo r both populations, encounters between different-sexed individuals pro duced lower levels of rejection than those between same-sexed individu als. For the mesic site, rejection was greatest for encounters between reproductive animals. Conversely, for the arid site, the levels of re jection were comparatively high and comparable for all combinations of reproductive status. Ecological constraints, sex, and reproductive st atus are significant factors in interactions between foreign common mo le rats, ultimately influencing individual survival, colony integrity and the differential LRS of all colony members. Our results provide in sight into the evolution and maintenance of family groups within the b athyergids.