Dr. Daisuke Shimada (1984–2024), a distinguished Japanese taxonomist with expertise in marine free-living nematodes, passed away unexpectedly on 19 November 2024 at the age of 40 due to an unidentified cause. His passing constitutes an irreplaceable loss to Japan’s zoological academia as well as the international nematological community.

Island species often have distinctive morphologies and higher densities than those on the mainland, and have attracted many researchers as a site for evolutionary ecological studies, to the extent that they are often referred to as nature’s laboratories. Often there are fewer species on islands than on the mainland, and interspecific relationships are less complex, making it easier to identify factors in studies of predator-prey relationships, seed dispersal, inter- and intraspecific competition, etc., and also making it possible to compare combinations if multiple islands are targeted. Focusing primarily on lizards, which have been the subject of the author’s research, this review presents species-area relationships, morphological and physiological evolution, increases in resources utilized through niche expansion, and behavioral changes that have been studied on islands around the world. Finally, I presented a case study of adaptive evolution in response to predator composition in the Izu Islands’ small terrestrial lizard (Plestiodon latiscutatus).

Island environments are an attractive field for the study of species diversity of terrestrial, terrestrial-water and coastal organisms. Amphibians, which are strongly dependent on freshwater environments for life, have difficulty in oversea dispersal and heavily influenced by the connections and fragmentation between land masses separated by the sea. Because of such physiological sensitivities to seawater, amphibians are often used as material for island biology, and in Japan, especially in the Ryukyus, they have been studied extensively. On the other hand, the geographical conditions of Kyushu Island, a relatively large land mass (mainland) with small islands distributed around it, require a different model for understanding the relationship between amphibian species diversity and land connectivity/separation than that of the Ryukyus, where small islands are arranged in an archipelago-like pattern. This paper introduces a case study of the effects of mainland-island connections and fragmentation on the species diversity of anuran amphibians.

The Japanese Archipelago consists of 6,852 islands, including four major and numerous small islands, that are distributed along the Pacific coast of East Asia and inhabited by a wide range of endemic organisms. In this study, we focused on the Japanese Genji firefly Nipponoluciola cruciata (formerly, Luciola cruciata), which belongs to the family Lampyridae (order Coleoptera) and is endemic to the Japanese Archipelago. Previous studies have shown that the eastern and western Japanese populations of N. cruciata exhibit distinct flashing patterns, while populations showing intermediate flashing patterns have also been reported (flashing intervals of Eastern type: 4 s, Western type: 2 s, Intermediate type: 3 s). Furthermore, N. cruciata individuals from the Goto Islands population have unique flashing patterns (flashing intervals: 1 s). We aimed to elucidate the gene flow of N. cruciata between the Goto Islands population and its neighbouring island populations, through molecular phylogenetic analyses based on the mitochondrial DNA regions of cytochrome oxidase subunit II and ND5, coupled also to genome-wide nuclear DNA single nucleotide polymorphisms analysis. Our results suggested that Goto Islands N. cruciata is genetically isolated from the other populations of this species.

This paper focuses on what is known about the life history, ecology, and behavior of the Japanese rhinoceros beetle Trypoxylus dichotomus. Five subspecies (T. d. septentrionalis, T. d. takarai, T. d. inchachina, T. d. tsuchiyai and T. d. shizuae) are currently distributed in Japan, and most previous studies have been conducted using the mainland subspecies, T. d. septentrionalis. Other subspecies have only been used for phylogenetic analysis, with few field-ecological studies concerning subspecies in each island.

A single specimen of Sargocentron iota Randall, 1998 (Beryciformes: Holocentridae), widely distributed around island groups in the eastern Indian to central Pacific Oceans, was collected from Chichi-jima Island, Ogasawara Islands, Japan, being the first record of the species in that region, although previously recorded from the Amami Islands, Ryukyu Islands. Although Japanese waters likely represent the northern limit of its distribution, the species may be more widely distributed around Japan than previously recognized. A detailed description of the specimen is provided.

The echinorhynchid acanthocephalan Pseudoacanthocephalus lucidus (Van Cleave, 1925) has been reported from a variety of vertebrates in Japan, but its larvae have never been detected. In this study, isopods of the genus Ligidium were sampled in Ibaraki Prefecture, Japan, and a cystacanth of unknown species was detected from them. The partial sequence of the mitochondrial COI gene determined from the cystacanth showed a p-distance of less than 6.2% to that of P. lucidus reported in the past study. The cystacanth was molecularly identified as P. lucidus on the basis of empirical intraspecific and interspecific variation in the genus, and thus the isopod Ligidium sp. is regarded as an intermediate host of P. lucidus.