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 promoted 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 success and hence survival, and dispersal to maximum individual lifetime reproductive success (LRS). This conflict will be a crucial determinant of the response of colony members to the presence of foreign conspecifics. We investigated how ecological constraints, sex, and reproductive status influence the outcome of meetings between foreign common mole rats (Cryptomys hottentotus hottentotus) in a series of dyadic encounters. 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 individuals of differing sex and status. The arid population revealed substantially higher levels of rejection than the mesic population. Sex and status played a significant role in moderating individual response. For both populations, encounters between different-sexed individuals produced lower levels of rejection than those between same-sexed individuals. For the mesic site, rejection was greatest for encounters between reproductive animals. Conversely, for the arid site, the levels of rejection were comparatively high and comparable for all combinations of reproductive status. Ecological constraints, sex, and reproductive status are significant factors in interactions between foreign common mole rats, ultimately influencing individual survival, colony integrity and the differential LRS of all colony members. Our results provide insight into the evolution and maintenance of family groups within the bathyergids.