Disclosing dung beetle diversity and evolution in the Eastern Arc Mountains sky islands, Tanzania: A tale of forest breakups and microendemism

The rainforest archipelago of the Eastern Arc Mountains (EAMs) of Tanzania and Kenya is one of the major biodiversity hotspots on the Earth, hosting an exceptional amount of endemic taxa. While vertebrates are relatively well studied, EAMs arthropod fauna is still very poorly known. Dung beetles (Coleoptera: Scarabaeinae) are a model group in ecology and evolutionary biology, providing insights into nutrient cycling and ecosystem functioning. However, their diversity in the EAMs remains largely unexplored.

We investigated the taxonomic diversity and evolution of five different lineages of EAMs dung beetles. We used an integrative taxonomic approach, combining morphology to molecular species delimitation and phylogenetics. Additionally, we used these taxa as a test bench to implement PhenoScript, an ontology-based language for writing computer parsable taxonomic descriptions.

Our results show that several undescribed species occur in the EAMs, with almost each lineage showing different speciation scenarios. Strikingly, the endemic genus Grebennikovius presents four distinct species that evolved microallopatrically on the Uluguru Mountains. The genera Janssensantus and two groups of Onthophagini seem to show a “one species per mountain block” pattern. Lastly, preliminary work on Tanzanolus reveals a complex morphological and molecular scenario, with one population having evolved brachyptery.

Overall, EAMs dung beetle diversity appears to have been shaped by unique interplays between past rainforest fragmentation, local scale topography and species characteristics such as flightlessness. Our work stresses the urgent need of further research to thoroughly understand the diversity and evolution of dung beetles in the EAMs, which is essential for their conservation.