The effect of the environment and copulatory movements on the taxonomic characters of three species of Ecdyonurus (Ephemeroptera)

Abstract

The majority of characters used to separate the nymphs of Ecdyonurus dispar, venosus and torrentis are related to the relative proportions of parts of the body. Extensive measurements suggest that at least certain of these characters are the consequence of heterogonic growth and are not of taxonomic significance. The characters of importance in the taxonomy of the imagines appear to be related either to the effect of the environment during nymphal development on the subsequent pigmentation, limb and body size of the adult, or to the changing spatial relationships between the sclerites of the genitalia during copulatory movements, relationships which are retained when the imago is killed.