Female mate choice in a subsocial beetle: male phenotype correlates with helping potential and offspring survival

In Parastizopus armaticeps (Tenebrionidae), a nocturnal desert beetle, the males excavate breeding burrows and maintain their moisture level while the females provision the larvae with detritus collected on the surface. The beetles court in small groups on the surface at night after rain. Male size distribution in these groups corresponded to that in the population but more large and fewer small females were present than expected and more large beetles of both sexes bred. Offspring number correlated positively with burrow depth and body length for males but not for females. Since large males dig deeper burrows, which results in higher larval survival rate, females should prefer them. In choice experiments, females selected larger males. Behavioural analyses showed that choice was not dependent on differences in male courtship activity or intermale dominance. When the mass of the smaller male was increased experimentally by a dorsally attached weight, the smaller male was preferred, females estimating male size difference by mass. Partner choice is therefore epigamic for a male phenotypic character which correlates with both parenting ability and greater reproductive success for females. Copyright 1998 The Association for the Study of Animal Behaviour.