Scale-dependence in geographic variation in a freshwater gastropod across the Palearctic

• Published in: Molluscan research Vol. 39; no. 2; pp. 159 - 170
• Main Authors: Vinarski, Maxim V., Kramarenko, Sergei S.
• Format: Journal Article
• Language: English
• Published: Sydney Taylor & Francis 03.04.2019; Taylor & Francis Ltd
• Subjects: analytical methods; Animal behavior; Autocorrelation; Body size; clinal variation; Clines; Correlation analysis; Data processing; Dependence; Freshwater; Freshwater molluscs; Galba truncatula; Gastropoda; geographical variation; Growing season; Inland water environment; Latitude; Marine molluscs; Mollusks; multi-scale approach; Palearctic region; Ponds; Pulmonata; pulmonate snails; Regression analysis; Shells; Snails; Spatial analysis; spatial autocorrelation; Spatial variations; Statistical analysis; Temperature; Variation
• ISSN: 1323-5818; 1448-6067; 1448-6067
• DOI: 10.1080/13235818.2018.1497570

The reality of spatial clinal variation in morphological traits of freshwater pulmonate snails (Gastropoda: Pulmonata) has repeatedly been questioned or totally discounted. There is a lack of sound statistical evidence in the articles hitherto published on this subject supporting these claims. Here, by means of different analytical methods (analysis of spatial autocorrelation, linear regression analysis, canonical correlation analysis and others), we demonstrate that shell variation in the dwarf pond snail, Galba truncatula, is patterned in space throughout the northern and central Palearctic, with latitudinally-oriented clines in body size and in some shell proportions. Shell size in G. truncatula decreases with latitude and temperature, representing a special case of converse Bergmann cline. However, the temperature itself is hardly the main driver of shell size variation. It is argued that the shorter growing seasons at high latitudes may represent a better explanation for the observed trend. Shell proportions in the dwarf pond snails vary weakly at the macrogeographic scale, being spatially patterned at lower (mesogeographic) scales around 1200-1500 km. In general, spatial variation in G. truncatula shell size is decoupled from variation in shell shape, demonstrating clear scale-dependence similar to that found in different species of terrestrial (non-aquatic) pulmonate snails.