Molecular phylogeny and body size-related convergent evolution of nesting behaviour in small dung beetles (Coleoptera: Scarabaeidae: Aphodiinae)

Aphodiini Leach comprises approximately 2,200 species. This great diversity is thought to derive from their specialization in feeding on a wide variety of detritus, particularly mammal dung. Despite their diversity and ecological role as decomposers, the evolutionary processes and ecological traits in this group are still largely unknown. Therefore, the present study aims to reconstruct the first molecular phylogeny of the Aphodiinae group and to explore the evolutionary history of nesting behaviours within the coprophagous tribe Aphodiini, utilizing a comprehensive multi-gene dataset (COI, 16S, 28S, and 18S) with ecological data. Our analyses recovered the monophyly of the Aphodiinae group, while revealing paraphyly in Psammodiini, and polyphyly in Aphodiini and Eupariini. The phylogenetic position of Aphodiini suggests that this largely coprophagous lineage derived from broad detritivore lineages. Ancestral state reconstruction of nesting behaviour revealed that the stem group of Aphodiini was predominantly non-nesting, with other nesting behaviours evolving independently at the generic or species’ levels. Notably, larger-bodied taxa have evolved a paracoprid strategy that appears to confer advantages in both inter- and intraspecific resource competition at dung pats. In contrast, small body size does not associate with kleptocoprid behaviour, but this behaviour might be more variable depending on environmental conditions. Our results offer new insights into the evolutionary history of small dung beetles, particularly highlighting the body size-related convergent evolution of nesting behaviour in coprophagous Aphodiini.