Presence or absence of carinae in closely related populations of Leptoxis ampla (Anthony, 1855) (Gastropoda: Cerithioidea: Pleuroceridae) is not the result of ecophenotypic plasticity

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Ecophenotypic plasticity, or nonheritable variation of the phenotype with local conditions, has been invoked in order to partly explain conchological differences within freshwater snail species as responses to fluvial conditions and stream size (Adams, 1915; Lam & Calow, 1988; Minton, Norwood & Hayes, 2008; Minton et al., 2011), river substrate (Urabe, 1998, 2000) and presence or absence of predators (Holomuzki & Biggs, 2006; Hoverman & Relyea, 2007; Lakowitz, Brönmark & Nyström, 2008). In the freshwater gastropod family Pleuroceridae, Dillon (2011) and Dillon & Robinson (2011) used similarities in allozyme loci to conclude that conchological differences (e.g. presence or absence of carinae, slenderness or robustness of shells) in multiple species of Pleurocera and Elimia were attributable to intraspecific ecophenotypic plasticity. However, no analysis of shell morphology was performed by Dillon (2011) or Dillon & Robinson (2011) to test for either an ecophenotypic or genetic component of the observed variation.

In order to understand the effects of ecophenotypic plasticity on the presence or absence of carinae on the shell of one species of Pleuroceridae, we cultured two populations of Leptoxis ampla (Anthony, 1855), one with a carinate shell morphology and one with a smooth shell morphology (Fig. 1). In culture, these snails were exposed to uniform environmental conditions. Therefore, observed morphological differences among juveniles raised from egg to adult were not affected by the environment. Culturing methods are ideal for analysing variation in shell morphology in the Pleuroceridae because not only can environmental conditions be controlled, but complications arising from translocation experiments (such as transfer of disease vectors and the potential for mating with native populations) are avoided. Although culturing methods have not previously been used for studying ecophenotypic plasticity in Pleuroceridae, they have been successfully applied to other freshwater gastropod families such as Planorbidae (Hoverman & Relyea, 2007) and Lymnaeidae (Lam & Calow, 1988; Lakowitz et al., 2008).