Variation in Populations of Lymnaea palustris in Upstate New York

Studies were completed on aspects of physiological and morphological variation for 16 populations of Lymnaea palustris (Mill- ler) from a varie-ty of biotic and abiotic conditions in upstate New York. Life-cycle studies on three of the populations showed differences which were due largely to differences in trophic conditions. MAR (a feeder canal in Marcellus Falls, N.Y.) was a simple one-generation pattern; NED (a slow-flowing stream in Nedrow, N.Y.), a two-generation pat- tern, and FAY (a swamp in Fayetteville, N.Y.), a one-plus pattern having scattered reproduction in the autumn. Shell biometrics of 16 populations showed that ratios of SL/AL and SL/AW were allometric, while AL/AW ratios were isometric and highly consistent both within and between populations. Similarly, for 14 of the above population sites, shell calcium and dissolved calcium in environ- mental waters were not related over a wide range of concentrations. This pattern of calcium metabolism, while like that of Ferrissia rivularis, is different from that found in Lymnaea peregra. In ratios of certain measurements of radula teeth, the variation between rows of the same radula was less than the variation between radulas within the same popu- lation which, in turn, was less than the combined variation of the 16 populations. Approximately 40% of all paired comparisons between these ratios were significantly different at the 0.80 level or higher. The significance of this is not adaptational but is related to the genetics of partly isolated populations. The patterns of variation in Lymnaea palustris and their evolutionary significance are discussed and contrasted with those of Ferrissia rivularis a more specialized pulmonate. The lack of adaptation to specific micro- habitats, linked with a high degree of phenotypic plasticity, maximizes long-term fitness for Lymnaea palustris in its unpredictable environment.