A comparative study of shell variation in two morphotypes of Lymnaea stagnalis (Mollusca: Gastropoda: Pulmonata)

Abstract

Background: Lymnaea stagnalis (L., 1758), the great pond snail, is among the most common and ubiquitous species of aquatic pulmonate gastropods of Palearctic. It is notorious for its enormous conchological variation, and many students tried to separate varieties, subspecies and even distinct species within the L. stagnalis s. l. Recent molecular studies have revealed that there are at least two genetically indistinguishable morphotypes of L. stagnalis in Palearctic that earlier were accepted by some authors as biological species under the binomial names L. stagnalis s. str. and L. fragilis (L., 1758). In this article, the comparative analysis of their conchological variation in a large physical geographical region (Western Siberia, Asiatic Russia) is provided.Results: The two morphotypes proved to be rather similar in their ecological preferences, but the patterns of their ontogenic, ecological, and geographical variation look rather distinct as well as the areas of their distribution in Western Siberia. U-shaped body size clines are reported in both morphotypes with the largest individuals tending to occur in the middle (forest-steppe) belt of Western Siberia. The causal analysis of the patterns of geographical variation in conchological traits of the great pond snail has identified the annual precipitation and the length of the growth season as the two main factors to shape the spatial clines in shell size and proportions. Among hydrological parameters, the water flow characteristics (lotic vs. lentic habitats) may influence shell morphology in the great pond snails though ecologically induced variation proved to be rather weak. The differences between populations living under different hydrological regimes may be captured by statistical techniques but are not enough to warrant separation of 'ecological' subspecies or other subspecific categories of ecophenotypic origin. Conclusions: Though there is no doubtless evidence of their specific independence, the two morphotypes, in a sense, 'behave' as two distinct entities with no identical ranges worthwhile to be recognized taxonomically. Their proper position in practical taxonomy should be discussed elsewhere.

One Beringian genus less: A re‐assesment ofPacifimyxasKruglov & Starobogatov, 1985 (Mollusca: Gastropoda: Lymnaeidae) questions the current estimates of Beringian biodiversity

“…We examined both external and internal morphology of newly obtained specimens of P. magadanensis , which was compared to the morphology of mollusks constituting the type series of P. magadanensis and P. streletzkajae . The scheme of standard shell measurements applied in this study is that of Vinarski (2014). In total, 72 shells were measured.…”

Conceptual shifts in animal systematics as reflected in the taxonomic history of a common aquatic snail species (Lymnaea stagnalis)

“…Though numerous morphs and varieties of the great pond snail lack the genetic support, the reality of some morphologically distinct entities within it has been proved by statistical methods (Vinarski 2014a). Four or five conchologically defined "morphotypes" can be delineated within L. stagnalis in Palearctic, with two of them, L. stagnalis (f. typica) and L. fragilis sensu Kruglov and Starobogatov being the most widely distributed (Vinarski 2014a). From the phylogenetic point of view, however, these morphotypes do not constitute separate clades and may arise in both geogroups in parallel.…”

“…From the phylogenetic point of view, however, these morphotypes do not constitute separate clades and may arise in both geogroups in parallel. Their spatial distribution is apparently not governed by ecological or physical geographical factors (Vinarski et al 2012;Vinarski 2014a).…”

“…The morphotypes reflect another, functional aspect of biodiversity additional to the taxonomic one that may be measured at the infraspecific level (Albert et al 2012). It has been assumed that conchological differences between the morphotypes may be of some adaptive value (Vinarski 2014a).…”

“…1) using atmospheric air for breathing that allows it to migrate over long distances and to gain a foothold in waterbodies of different types. L. stagnalis is characterized also by extreme ecological plasticity and enormous variation in its shell size and proportions (Kobelt 1871;Hubendick 1951;Arthur 1982;Vinarski 2014a). Being, very likely, the largest species of freshwater snails in Europe, the great pond snail had attracted the attention of naturalists long before Linnaeus.…”