Comparative genomics reveals how gene regulatory evolution shapes weapon diversity in horned beetles

Researchers at Indiana University, led by Phillip L. Davidson, Isabel G. Manley, and Armin P. Moczek, have published a study in PLOS Genetics examining the molecular basis of horn diversification in beetles of the genus Onthophagus. These beetles produce a remarkable diversity of horns — novel secondary sexual structures used in reproductive competition — whose development is condition-responsive, varying according to an individual's nutritional state and sex.

Using a combination of comparative genomics, chromatin profiling (to map regions of open chromatin associated with active gene regulation), and functional analyses, the team investigated whether horn diversification across species is driven primarily by changes in protein-coding sequences or by evolution of gene regulatory elements. Their findings point to regulatory evolution — changes in the genomic regions controlling where, when, and how much genes are expressed — as a central mechanism.

Focusing on bone morphogenetic protein (BMP) signalling, a conserved pathway involved in tissue growth and patterning across animals, the authors found that differences in regulatory architecture of BMP pathway genes correlate with differences in horn type and degree of condition-responsiveness across Onthophagus species.

The study contributes to a longstanding question in evolutionary developmental biology (evo-devo) about the relative roles of coding versus regulatory sequence change in driving morphological diversification. Onthophagus beetles are an established model system for studying the genetics of novel trait evolution.