Genetics, Shell Morphology, and Life History of the Freshwater Pulmonate LimpetsFerrissia rivularisandFerrissia fragilis

Abstract

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 selffertilization. Thus in the absence of any reliable morphological distinction, we propose that F. fragilis be considered a junior synonym of F. rivularis.

The first finding of the North American freshwater limpets Ferrissia fragilis (Tryon, 1863) (Mollusca, Gastropoda) in the Middle Volga basin

“…Morpho logical variability of mollusk shells found in the same habitats was noted, in particular, for the Austrian pop ulation of F. fragilis (Reischutz, 1983). Researchers note prominent plasticity in the morphology of Ferris sia shells in the habitat of mollusks in North America; the habitat conditions of F. fragilis make an imprint on the shape and size of their shells, which determine ecophenotypic variations (Basch, 1963;Dillon and Herman, 2009).…”

“…fragilis is a eurybiontic species and its adaptabil ity to a wide range of different types of ponds, life cycle peculiarities, the capacity for self fertilization and for mation of protective septal stages, etc. (Dillon and Herman, 2009) are the basis of successful colonization of freshwater ecosystems of the Eurasian continent. Within its historic range in North America, F. fragilis is an intermediate host for many species of trema todes.…”

Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata

“…Reared in the presence of crushing predators, basommatophoran snails tend to develop shells with broad body whorls (Lakowitz et al 2008;Brönmark et al 2011), while in the presence of predators extracting snails from their apertures, body whorls tend to develop more narrowly (DeWitt 1998;Langerhans and DeWitt 2002;Hoverman et al 2005). The phenotypic effects of temperature, current, and environmental calcium on shell morphology have also been well documented in laboratory populations of basommatophoran snails (Britton and McMahon 2004;Rundle et al 2004;Dillon and Herman 2009).…”

The Heritability of Shell Morphometrics in the Freshwater Pulmonate Gastropod Physa

“…Evidence of ecophenotypic responses in shell morphology to predator pressure have also been documented in populations of the pulmonate planorbid Helisoma [ 20 , 21 ] and in the prosobranch pleurocerids [ 22 – 24 ]. Rearing morphologically diverse populations in a constant environment (“common garden experiments”) suggest a significant ecophenotypic component to shell height in the pulmonate limpet Ferrissia [ 25 ].…”