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.

密切相关的物种通常表现出相似的生态位和生殖相互作用。由于对共享资源的竞争、生殖干扰和杂交可能会排斥一个或另一个物种，因此密切相关的物种的共存是生态学和进化的主要研究课题之一。Drosophila biuraria和D. triauraria是密切相关的物种，在日本具有广泛的同域分布。为了了解它们共存的机制，我们调查了它们的栖息地利用模式、季节性发生以及它们在菅平山（长野县）聚集在一起的频率，那里有草地、幼林和成熟森林。生境利用模式和季节性发生率之间存在细微差异D. biararia和D. triauraria。然而，这两个物种有时被收集在一起。特别是，D. triauraria雌性与异种雄性一起收集，表明D. triauraria雌性可能存在生殖干扰和杂交的风险。预计女性对同种男性的择偶偏好在减少其生殖互动方面发挥重要作用；然而，在这项研究中发现的少数男性生殖器结构异常表明它们存在杂交的可能性。