Behavioral Ecology and Secondary Seed Dispersal by Two Roller Dung Beetles, Sisyphus rubrus (Paschalidis, 1974) and Sisyphus spinipes (Thunberg, 1818) (Coleoptera: Scarabaeidae: Scarabaeinae)

Abstract

We assessed the behavior and seed dispersal ability of two introduced dung rollers in Australia, <I>Sisyphus rubrus</I> (Paschaladis) and <I>Sisyphus spinipes</I> (Thunberg). For each species, we measured the linear distance (cm) from the source when rolling brood balls, the ability to disperse seeds, and the gender roles during reproduction in an indoor arena that contained bead-laden dung pads, including beads of four different sizes. At the end of the trials, we recorded the number of brood balls, distance rolled, and the number of beads that were incorporated into the brood balls. We compared the sex roles in brood construction between the two species using three treatments: Male-only, female-only, and a male and female pair. The number of broods constructed by each treatment, as well as the number of eggs laid, were recorded. No difference was found in the distance rolled by each species, with both averaging distances between 100 cm and 200 cm. Both species only incorporated 0.5-mm beads into their brood balls. <I>Sisyphus spinipes</I> dispersed more beads per brood ball than <I>S. rubrus</I> (mean number of beads per <I>S. spinipes</I> and <I>S. rubrus</I> broods were 6.0 and 2.9, respectively). In brood construction, only the treatments containing females of both species produced broods and eggs, with no difference in brood number or eggs laid recorded between females alone and male plus female treatments. We conclude that <I>S. rubrus</I> and <I>S. spinipes</I> are capable of secondary dispersal of small seed such as those of many grasses in Australia. Their ability to disperse seeds over several meters, along with shallow or surface nesting behavior, is conducive to seedling germination. In these two scarab species, females are responsible for brood construction with continual male presence not required for brood construction and oviposition.