Reproductive skew and communal breeding in the subsocial beetle Parastizopus armaticeps

The monogamous beetle Parastizopus armaticeps (Tenebrionidae) constructs breeding burrows in the Kalahari Desert after rainfall, and shows extensive biparental care. However, occasional communal breeding has been reported, where the male shares the burrow with more than one female (ca. 5% of breeding burrows). We induced communal breeding in the laboratory by confining one male with two females in a small breeding cage. In 33% of these trios females stopped being aggressive towards each other and reared offspring communally. Larger females dominate smaller females, so we expected the incidence of communal breeding to be higher, and the reproductive skew to be lower, for equally sized females than for unequally sized females competing for the male. These predictions were not borne out: the incidence of communal breeding was similar in both situations and reproductive skew was independent of the (difference in) body measurements of the two females. The calculated binomial reproductive skew was in close agreement with the distribution expected from random sharing of maternity among the two females. Time spent in parental care per individual and (group) reproductive success of trios were not different from those of monogamous breeding pairs.