Intra‐ and interspecific variation in body size of Protohermes (Megaloptera: Corydalidae)

Abstract

AbstractThe life history of three populations of Protohermes grandis and two populations of Protohermes immaculatus (Megaloptera: Corydalidae) was compared. In general, the larvae lived in stream riffles for 2 years and the adults appeared in summer. Adult body size differed between these closely related species and also between the populations of P. grandis. Dwarfism occurred in P. immaculatus, a species that is endemic to the small, isolated island, Amami Island. The population of P. grandis on Yaku Island, located between Amami Island and the mainland Kyushu, had an intermediate body size between that of P. immaculatus and the mainland population of P. grandis. Despite being an insular population, P. grandis on Tsushima Island had a similar body size to mainland P. grandis. In these populations with large adults, some larvae lived in the streams for 3 years. The size distribution of benthic animals, which are the prey available to Protohermes larvae, differed between the streams studied. The density of large prey was lowest on Amami Island, intermediate on Yaku Island, and highest on the mainland and Tsushima Island. Different size distributions of available prey may be caused by the differences of benthic fauna; most of Ecdyonuridae and Ephemerellidae (large mayflies) and Perlidae (large stoneflies) were not found on Amami and Yaku Islands. Thus, there is a tendency to dwarfism in the populations of Protobermes inhabiting streams where the density of large prey is low.