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Common genetic toolkit shapes horns in scarab beetles

Rhinoceros beetles and dung beetles use the same genes to form their elaborate horns



IMAGE: Rhinoceros beetles and Dung beetles use the same genes to form their elaborate horns. view more 

Credit: Takahiro Ohde and colleagues

Horns have evolved independently multiple times in scarab beetles, but distantly related species have made use of the same genetic toolkit to grow these prominent structures, according to a study publishing October 4, 2018 in the open-access journal PLOS Genetics by Teruyuki Niimi at the National Institute for Basic Biology in Okazaki, Japan, and colleagues.

There are over 35,000 species of scarab beetle (Scarabaeidae), and many scarab beetles grow horns on the head and/or upper body. Horns are considered to be independent radiation in rhinoceros beetles and their distant relatives dung beetles. Rhinoceros beetles include some of the largest insect species on earth, such as the famous Atlas and Hercules beetles. To investigate the genetic mechanisms that control horn development in these distant groups, the team examined gene expression and function in early horn cells in developing larvae of the Japanese rhinoceros beetle (Trypoxylus dichotomus), and compared this with published data for dung beetles.

From the high-throughput sequence analysis, they identified 49 genes that indicated possible involvement in horn development of the rhinoceros beetle, and used RNA interference to deactivate each gene to measure the effect on adult horn size and shape. Eleven genes expressed during larval development showed measureable effects on horn formation in the rhinoceros beetle. They found that these eleven genes include head and appendage patterning genes, and the same category of genes have also been linked to horn development in dung beetles. The results suggest that (1) horns developmentally derive from the similar head regions, and that (2) the same set of ancestral genes were co-opted repeatedly in distinctly originated horns between rhinoceros and dung beetles. This study reveals deep parallels in development between independently evolved horns, but it is also possible that the ancestor of the Scarabaeidae family had horns that were subsequently lost in the evolution of the majority of modern scarab beetles. A wider taxon-sampling is required to clarify whether horns originate single or multiple times, and this study provides a promising way to discover horn formation genes in a species.


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Citation: Ohde T, Morita S, Shigenobu S, Morita J, Mizutani T, Gotoh H, et al. (2018) Rhinoceros beetle horn development reveals deep parallels with dung beetles. PLoS Genet 14(10): e1007651.

Image Credit: Takahiro Ohde and colleagues

Funding: TN was supported by MEXT KAKENHI (The Ministry of Education,Culture,Sports,Science and Technology; (23128505, 25128706, 16H01452 and 18H04766)and NIBB Cooperative Research Programs (18-433). DE was supported by NSF IOS (Integrative Organismal Systems, National Science Foundation; (0919781). RZ was supported by an NSF/JSPS EAPSI fellowship (East Asia and Pacific Summer Institutes for U.S. Graduate Students; (1311025) and an NIH PERT Post-doctoral fellowship (NIH-Training Program: Postdoctoral Excellence in Research and Teaching; (2K12GM000708-16). LL was funded by NSF IOS (Integrative Organismal Systems, National Science Foundation; (0919730) and the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch Project (1001738). The roles of these funders are the study design, data collection and analysis and preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

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