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

ABSTRACT

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.

KEYWORDS:

• Body size
• clinal variation
• multi-scale approach
• pulmonate snails
• spatial autocorrelation

Acknowledgements

The authors thank all colleagues who sent them samples of G. truncatula for this study: Dr Dmitry M. Palatov (Moscow, Russia), Dr Katrin Schniebs (Dresden, Germany), Dr Nina Hural-Sverlova (Lviv, Ukraine) and Dr Eugeny S. Babushkin (Ugut settlement, Russia). We acknowledge Dr Don Colgan for polishing our English and for providing suggestions to improve the manuscript. We also thank the careful reading and valuable suggestions of an anonymous reviewer.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Partial financial support for this research was obtained from grants from the President of Russia Grant Council [no. MD-2394.2017.4], the Russian Ministry of Education and Science [no. 6.1352.2017/4.6] and the Russian Foundation for Basic Research [no. 14-04-01236].