Brood Care And Subsocial Behavior

Investment in nesting behavior that enhances the survival of offspring is evident in brood care by adult female beetles. The female remains underground with the brood ball, providing care of her offspring during its development. In Copris, a male and a female make a chamber in the soil and carry dung down to construct a large dung cake of about 100 g. The male then leaves and the burrow is sealed. The female cuts up the cake into about four brood balls and lays one egg in each. The mother then remains with the brood balls during the development of her larvae, caring for them, repairing damage to the balls by the larvae, and removing fungal growth from the outside. Such behavior doubles the survival rate of the offspring. The mother emerges from the soil after her offspring have emerged from their brood balls.

FIGURE 5 Female K. nigroaeneus in a brood chamber with a single brood ball. Male has left and packed the chamber entrance closed. (A) Loose soil, (B) hard packed soil, and (C) chamber. (Reproduced, with permission, from Edwards and Aschenborn, 1988.)

An extreme case of low fecundity occurs with Kheper nigroaeneus, a large ball-rolling species, which produces only a single offspring on each nesting occasion. A pair of beetles forms a single large dung ball over 4 cm in diameter. The male rolls the ball away from the dung pat while the female clings to the top of it (Fig. 4). The ball is buried via a diagonal tunnel to a chamber about 14 cm deep. The male then leaves the nest while the female beetle stays in the chamber and lays a single egg. She remains underground with the ball for the 12 weeks taken for egg and larval development (Fig. 5). As with Copris spp., the presence of the female greatly enhances offspring survival. After the new adults have emerged, the mother leaves the nest.

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