Habitat composition and anthropogenic matrix shape male morph frequencies in the European rhinoceros beetle (Oryctes nasicornis)

Sexual selection promotes exaggerated weapons and alternative reproductive tactics, but the ecological factors maintaining male dimorphism remain poorly resolved. In the European rhinoceros beetle, Oryctes nasicornis Linnaeus, 1758, males occur as alpha morphs with combat horns or beta morphs with reduced horns that adopt sneaker tactics. We combined opportunistic records collected from 2005 to 2021 with standardized transect surveys conducted from 2022 to 2025 across seven landscapes in central Italy to test how anthropogenic matrix affects sex ratios, morph frequencies, and activity. Habitat composition and heterogeneity were quantified using land use data and diversity indices. Sex ratios differed among landscapes. Morph frequencies also varied with habitat structure and anthropogenic matrix intensity. Across landscapes, beta male frequency increased with anthropogenic matrix and decreased with habitat evenness, whereas alpha males were associated with semi natural, tree rich environments. Generalized linear models showed dataset dependent responses along the anthropogenic gradient and indicated that alpha male abundance reflected population size and morph specific processes. Generalized linear mixed models using one kilometer buffers confirmed increasing beta male frequency and declining alpha male abundance in landscapes. Seasonal activity followed sinusoidal patterns without interannual trends, supporting the allocation hypothesis.