FEEDING AND ENERGY ALLOCATION IN NEPHELOPSIS-OBSCURA FOLLOWING EXPOSURE TO WINTER STRESSES

Comparisons of growth rates, feeding rates and life-history traits are made between initially similarly sized Nephelopsis obscura (Erpobdellidae) collected as overwintering individuals, and others from summer cocoons hatched in the laboratory at 20°C and with Tubifex tubifex available ad lib. Overwintering leeches initially had significantly lower body lipids concentrations. Mean feeding rates differed significantly, being twice as high in overwintering leeches, but though growth rates were similar, both groups produced similar dry weights and energy values of faeces plus mucus. Despite the resulting energy surplus in overwintering leeches they required a longer time to reach maturity, and did so at a larger size primarily because body lipids concentrations had to be restored. Results are discussed in terms of responses to winter stresses (low temperatures and oxygen concentrations and low feeding activity). Allocating energy to storage reserves (lipids) rather than maximizing growth rate of other somatic tissues, suggests lipid storage is related to fitness and that winter stresses tune energy allocation to enhance survivorship in an unpredictable environment. -Authors