Effects of habitat on development, fecundity, and susceptibility to parasites in Parameletus chelifer and Parameletus minor (Ephemeroptera)

Abstract

Life history parameters of two mayflies were studied for 4 years in two habitats in northern Sweden: a river margin and a seasonal stream. Water temperature before river peak flood was higher and the C/N ratio of the dominating food fraction was lower in the seasonal stream than at the river margin. Over the entire season, the growth rate of Parameletus chelifer nymphs was higher in the seasonal stream than at the river margin, whereas that of Parameletus minor nymphs was similar in both habitats in 2 out of 4 years. Because of desiccation, emergence success of P. chelifer in the seasonal stream was low in some years while almost no specimens emerged successfully from the river. Emergence success was always high in P. minor, and in some years emergence was further advanced in the seasonal stream than at the river margin. Subimagoes of both species were larger in the seasonal stream than at the river margin. Males of both species were larger than females in the seasonal stream, as were males of P. minor at the river margin. The fecundity of P. chelifer females was higher in the seasonal stream than at the river margin, while no difference could be found in P. minor between the two habitats. Only P. chelifer specimens were infested by mermithid nematodes; in some years as many as 21% of the female subimagoes were infested. Such females were unable to reproduce.