The influence of temperature on the life cycle and occurrence of three species of lake‐dwelling leeches (Annelida: Hirudinea)

Abstract

The influence of constant temperatures on the growth, maturation and reproduction of field‐collected and F, generation Helobdella stagnalis, Glossiphonia complanata and Erpobdella octoculata was investigated. Leech material from a lowland, productive lake and from an upland, unproductive lake was cultured at each of the temperatures: l·5,5·5,8, 10·5, 13,16, 19 and 23°C. Field‐collected and F1 generation H. stagnalis and E. octoculata matured and produced eggs and young over the range 10·5–23°C, whereas the range for egg production was 8–23°C for field‐collected G. complanata, F, generation leeches failing to mature at any temperature due to an additional limiting factor being involved.Optimal temperatures for cocoon/egg production were observed for E. octoculata, but egg production was similar at all temperatures for G. complanata and H. stagnalis. In contrast, the viability of eggs was greater at certain temperatures for the last two species but was similar at all temperatures for E. octoculata. Differences in egg production between field‐collected and F, generation leeches are discussed. Rising temperatures accelerated rates of egg hatching, and of growth and maturation of leeches. The observed differences in survival of leeches at the various temperatures are discussed. Ecotypic adaptation to temperature within the small geographical area of Britain may not occur. It is concluded that though temperature may be a contributory factor determining distribution and abundance in British lakes, other causative factors, such as the occurrence and abundance of food organisms, are more likely to be implicated.