taxonomic rank. Morphological differences between H. retardatus individuals may be attributable to inducible defenses of their prey and the prevalence of cannibalism between larvae of the species. Home Range and Territoriality H. retardatus is an abundant endemic species on the island of Hokkaido, with a wide range across the island. They are the northernmost species of the Hynobius genus in Japan. Within Japan, populations have been found in the Iburi subprefecture, Kayabe district, the cities of Obihiro, Chitose, Hakodate, and Kitami, as well as the towns of Erimo, Teshio, and the Nopporo Shinrin Kōen Prefectural Natural Park. Ezo salamanders can only live within lentic freshwater habitats, so their mobility is restricted, and separate populations show very low levels of gene flow. However, relatively high levels of gene flow have been recorded between the Nopporo and Kitami populations despite the mountain range separating them. Diet Adults of the species feed on invertebrates like snails and worms. H. retardatus larvae are known to consume the tadpoles of multiple frog species such as the Japanese brown frog (Rana pirica) and the Hokkaido frog, as well as sewage worms (Tubifex), gammaridean amphipods, caddisfly larvae, and possibly larvae of Siberian salamanders. Cannibalism by the larvae is not uncommon when prey items are scarce. H. retardatus, like other salamander species, is a gape-limited predator that swallows its prey whole. Cannibalism Aquatic larvae of H. retardatus are known to utilize cannibalism under specific circumstances influenced by availability and inducible defenses of prey as well as asymmetry of size between conspecific larvae. Some Japanese brown frog tadpoles (R. pirica) have adapted thicker bodies to reduce predation by H. retardatus larvae (as they are gape-limited). In response, Ezo salamander larvae are capable of developing into a larger morphs with longer bodies, wider heads, and a relatively greater gape, allowing them to consume larger prey. However, as the difference between smaller and larger H. retardatus larvae increases, the propensity towards cannibalism increases as well. Ezo salamanders seem to be capable of distinguishing between conspecific and heterospecific prey, with a preference for heterospecific prey, but higher frequencies of the thicker R. pirica tadpoles and larger asymmetries between H. retardatus larvae forces the larger morph larvae into cannibalism. H. retardatus larvae artificially fed exclusively conspecific prey were found to more likely develop into the cannibalistic morph when subjected to high-density conditions. These larvae developed larger bodies and larger relative head widths. For