Genetics, shell morphology, and life history of the freshwater pulmonate limpets Ferrissia rivularis and Ferrissia fragilis

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The weak and variable nature of the shell morphometric criteria by which the North American ancylid limpets Ferrissia rivularis and Ferrissia fragilis are distinguished has led to speculation that they may be ecophenotypic variants. The shells of F. rivularis that we collected from a rocky river in the upper piedmont of South Carolina were significantly higher and wider per length than those of an F. fragilis population collected from a weedy ditch in the coastal plain. Both populations laid singleton eggs approximately 0.6-mm diameter in culture, hatching in one week and maturing in four–five weeks at 2.0–3.0-mm shell length. Adult F. rivularis reared in our laboratory environment were morphologically indistinguishable from F. fragilis, suggesting that the differences in shell shape displayed by their wild-collected parents may have little additive genetic component. Both populations were fixed for identical allozyme alleles at nine loci, with two alleles segregating at a tenth, IsdhF. The absence of ZsdhF heterozygotes in wild-collected samples of 104 F. rivularis individuals (p = 0.52, q = 0.48) and 102 F. fragilis individuals (p = 0.14, q = 0.86), together with no evidence of outcrossing in laboratory breeding experiments, suggests obligate self-fertilization. Thus in the absence of any reliable morphological distinction, we propose that F. fragilis be considered a junior synonym of F. rivularis.

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ELECTRONIC FILE - Zoology: Invertebrates

CSE-style citation: Dillon RT Jr, Herman JJ. 2009. Genetics, shell morphology, and life history of the freshwater pulmonate limpets Ferrissia rivularis and Ferrissia fragilis. Journal of Freshwater Ecology. 24(2): 261-271. Available at: http://www.tandfonline.com/doi/abs/10.1080/02705060.2009.9664291.