Habitat and seasonal occurrence differ among closely related species of the Drosophila auraria species complex (Diptera: Drosophilidae)

Closely related species often exhibit similar niches and reproductive interactions. As competition for shared resources, reproductive interference, and hybridization may exclude one or the other species, the coexistence of closely related species is one of the main research topics in ecology and evolution. Drosophila biauraria and D. triauraria are closely related species with a broad sympatric distribution in Japan. To understand the mechanism underlying their coexistence, we investigated their habitat-use pattern, seasonal occurrence, and the frequency at which they were collected together in Sugadaira Montane (Nagano Prefecture), where grasslands, young forests, and mature forests are present. Slight differences in habitat-use pattern and seasonal occurrence were found between D. biauraria and D. triauraria. However, both species were sometimes collected together. Especially, D. triauraria females were collected together with heterospecific males, suggesting that D. triauraria females may be at risk of reproductive interference and hybridization. Female mate preference for conspecific males was expected to play an important role in reducing their reproductive interaction; however, abnormal genital structures in a few males found in this study suggest the possibility of their hybridization.