Growth, Fecundity, and Bioenergetics in Three Populations of Lymnaea palustris in Upstate New York

Abstract

Studies on linear and biomass growth and bioenergetics are reported on three populations of Lymnaea palustris in upstate New York. Growth rates are highest at NED (a slow flowing stream at Nedrow, N.Y.) and lowest at MAR (an abandoned feeder canal at Marcellus Falls, N.Y.). The relationship of carbon and nitrogen to shell length, can be simplified to two linear relationships each. Although these relationships do not show seasonal changes, they demonstrate differences between populations. Density determinations at MAR and FAY (Fayetteville Swamp) showed that the number of animals per square meter is lowest in late winter and highest (along with biomass) during the reproductive period in the late spring, whereas biomass is lowest in late summer. Animals in cages at FAY (whether they were native or transferred from MAR) show far higher fecundities (one to two orders of magnitude higher) than animals at MAR (whether they were native or transferred from FAY). Feeding and assimilation studies on MAR and FAY animals show that FAY animals had higher total ingestion (TI), egestion (NA), and assimilation (TA) rates than MAR animals event hough MAR animals had a higher assimilation efficiency (TI—NA/TI). Less extensive experiments show the rate of movement of the radula to be related to the density of the food material and not to any differences endogenous to MAR or FAY animals. Because respiration varies little between populations, a low TI results in markedly low nonrespired assimilation (N—RA or growth + fecundity). Thus net productivity at MAR was 3.67 mg C/m2 ° day whereas at FAY it was 22.84 mg C/m2 ° day. Biomass at MAR turned over 5.82 times per generation for a turnover time of 74 days whereas FAY turned over 5.63 times per generation for a turnover time of 75 days. The physiological plasticity and its evolutionary significance in a euryoecic species such as Lymnaea palustris is contrasted with the more specialized, stenoecic Ferrissia rivularis. Lymnaea palustris, having great bioenergetic plasticity, is strategically fitted to the margins of the whole freshwater environment unlike Ferrissia rivularis, which has a series of populations each tactically suited to specific freshwater habitats.