Shell morphology, growth pattern and population dynamics of the land snail Xerolenta obvia (Menke, 1828) in two areas of different climatic conditions within a temperate climate region

Abstract

To determine the relative role of climatic variables (temperature and precipitation) on land snail Xerolenta obvia populations, field surveys were conducted in Poland at two sites (SW and NE) with striking differences in climatic regime during two growing seasons. In a temperate climate of Central Europe X. obvia is an annual species with the majority of snails hatching in autumn. They overwinter as juveniles, continue their growth in spring and summer, and reproduce in the following autumn. Due to the comparatively milder climate, the SW population is more plastic, some individuals can live and reproduce longer. The two variants of the growth model are presented. We found that the length of growing season and temperature were additional factors determining differences in snails' growth and population dynamics between the sites. The growth rate of X. obvia is negatively correlated with the initial size of their shells and varies among sites. These two geographically distant populations differ in terms of their shell size and morphology. The SW population is characterised by larger, dark banded shells compared to the NE one, which is dominated by snails with smaller, white shells. A pattern of decreasing body size in areas with shorter growing season may explain differences in the shell size of X. obvia. Larger shells in regions with warmer and drier environment perhaps constitute responses to selection by environmental factors.