Sex Ratio Modulates Reproductive Output and Dung Burying Behavior in Dung Beetle Gymnopleurus sturmi (Macleay, 1821) (Coleoptera: Scarabaeidae)

Authors: ZAMPROGNA, ALBERTO - Csiro European Laboratory; SERIN, JOSÉ - Csiro European Laboratory; RENE, MARI-ANGE - Csiro European Laboratory; HAJJI, HASNAE - Sidi Mohamed Ben Abdellah University; GLEESON, PATRICK - Csiro, Black Mountain Laboratories; PEREZ VILA, SALETA - Csiro, Black Mountain Laboratories; LUMARET, JEAN-PIERRE - Csiro European Laboratory; DESURMONT, GAYLORD - European Biological Control Laboratory (EBCL); CARON, VALERIE - Csiro, Black Mountain Laboratories

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2025
Publication Date: 10/16/2025
Citation: Zamprogna, A., Serin, J., Rene, M., Hajji, H., Gleeson, P., Perez Vila, S., Lumaret, J., Desurmont, G., Caron, V. 2025. Sex Ratio Modulates Reproductive Output and Dung Burying Behavior in Dung Beetle Gymnopleurus sturmi (Macleay, 1821) (Coleoptera: Scarabaeidae). Ecology and Evolution. 15:e72289. https://doi.org/10.1002/ece3.72289.
DOI: https://doi.org/10.1002/ece3.72289

Interpretive Summary: Dung beetles help keep ecosystems healthy by cleaning up animal waste. Some species of dung beetles collect dung and roll it into balls, which they use to lay their eggs. This ball-rolling behavior varies between species and can involve both males and females. Sometimes males do all the work to attract a mate, while in other cases, males and females team up. This study focused on one species called Gymnopleurus sturmi, which tends to live in groups, and investigated how males and females divide the work of making dung balls, and how different male:female ratios affect how many balls are made, how many are used for raising young, and how many offspring are produced. Results showed that both males and females can make dung balls, but groups with more females made more buried balls, which are better for raising young. When only females were present, they made the most balls—but hardly any young survived, probably because they didn’t have enough sperm stored to fertilize their eggs. More males, on the other hand, led to higher survival of the offspring. Interestingly, the total number of offspring per female didn’t vary significantly as long as both sexes were present. This suggests that in G. sturmi, males may compete more with each other, and females may not need to store sperm for long periods.

Technical Abstract: Dung beetles are important ecosystem engineers as they play an important role in recycling dejections from animals. Dung beetles have evolved different behaviours, including dung ball rolling for their egg and developing offspring. Ball rolling is a complex behaviour that varies between species. In some species, males roll the dung ball and females choose partners based on this, while in other species, males and females work together to form the ball. Competition can be fierce, and fighting and ball stealing are common. Gymnopleurus sturmi is a ball rolling species that exhibit gregarious behaviours. This study assess sex-related roles in ball rolling as well as the impact of varying sex ratios on the number of balls produced, either left at the surface or buried and fertilized (pear-shaped), and emergence rates of the offspring. Results show that both males and females are capable of producing dung balls, and higher numbers were obtained when males and females were separated. Female-biased sex-ratio produced mostly buried and fertilized balls, while male-biased sex-ratio produced more unburied balls left on surface. When females were alone, they produced the maximum number of total dung balls compared to the rest of the treatment. On the other hand, emergence rate was found to be higher when more males were present. When females were alone, emergence rate was extremely low, suggesting a lack or a scarce sperm storage. In a gregarious species like G. sturmi, finding a partner would be easier than for other dung beetle species, which could explain an increasing competition between males and reducing the need to store sperm on the longer term. An additional calculation was made in order to obtain a measure of fitness, meaning theoretical number of offspring per female. No difference of fitness was observed when males and females are both present in the rearing set-up, disregarding of the sex-ratio. This study highlights the diversity of behaviours present in this important type of animal.