Fecal DNA Metabarcoding Analyses Imply Seasonally Opportunistic Feeding by the Japanese Marten, Martes melampus (Mammalia: Carnivora), in Southwestern Honshu Island, Japan

An understanding of the food web in forest ecosystems is essential to ensuring that society lives in harmony with nature; however, this can be challenging in areas mainly composed of forest environments, such as in the Japanese Archipelago. Examining fecal samples collected from the forest edge can aid in determining the ecological roles of host species. In this study, a DNA barcoding method using original primers was applied to identify the carnivoran host species from fecal samples. DNA metabarcoding using ITS2 and COI markers was then conducted to elucidate the plant and invertebrate diets of the Japanese marten, Martes melampus (Carnivora, Mustelidae). The dietary analyses revealed that M. melampus consumed a diverse array of plants and animals. Most of the consumed plant species were fresh fruits, reflecting the fruiting season of the detected plants. This implies a role for M. melampus in seed dispersal and thus in forest maintenance. Considering the activity seasons, we also found that various adult-stage insects (beetles, cicadas, sphinx moths, and grasshoppers) contributed to the marten's diet, together with invertebrates (earthworms, etc.), which are easily digested and therefore difficult to detect through traditional methods. Although the COI marker used was designed for invertebrate species, one bird species, the brown-eared bulbul, Microscelis amaurotis, was found to make up a small part of the winter to early spring diet. These results show that, while M. melampus mainly consumes seasonal fruits, it can adapt its diet in response to environmental changes, such as by including invertebrates and small vertebrates.