Combined Effects of Beetle Density and Sex Ratio on Reproductive Trade-Offs and Dung Burial in Tunnelling Dung Beetles.

Dung beetle density and sex ratio play a significant role in intraspecific competition, and reproductive success depends on the beetle's maturity. We examined the impact of increasing density in small groups on dung burial and brood production using mature first-generation individuals of two dung beetle species (Onthophagus binodis and Digitonthophagus gazella) by manipulating the number of males and females in a dung pat. Beetles were reared under controlled laboratory conditions and provided with cattle dung, which was collected from pastureland. Weekly dung burial was calculated by measuring the residual dung organic matter content. The number of broods produced per dung pat, broods' dry weight, and their size were recorded. In both species, treatments with intermediate numbers of male and female beetles produced more broods than solitary beetles. On the other hand, treatments with moderate to high numbers of male and female beetles buried more dung than individual females. At higher-density treatments, brood size and brood dry weight declined, suggesting shifts in reproductive allocation under increasing intraspecific interactions. The two species showed very similar patterns, although O. binodis produced more broods while D. gazella buried more dung. We also observed a positive relationship between brood dry weight and brood size in both species. Overall, the results indicate that the combined effects of beetle density and sex ratio influenced reproductive investment and dung burial under controlled laboratory conditions. Further field studies are needed to determine whether similar patterns occur under higher density and natural ecological conditions.