Environmental heterogeneity and morphological variability in Pisidium subtruncatum (Sphaeriidae, Bivalvia)

On the example of P. subtruncatum, a widely distributed bivalve, we studied the relationship between environmental and morphological variability. The main questions addressed were: (1) are there differences in shell morphology between different populations, (2) are they dependent on sediment composition, hydrology or water chemistry, (3) are there differences in morphological variability between stable and unstable environments. Measurements of specimen from nine sampling sites showed high variability in shell shape and size. Length-height relation, symmetry width and dry weight of the shell all varied significantly. Shell shape was significantly correlated with sediment composition and dependent on hydrological connectivity, with higher, asymmetric shells occurring in sandy sediments and lower, rounded shells in muddy sediments. Analysis of intrapopulation morphometric variation showed that variability is higher in habitats with high temporal and spatial environmental variability and lower in habitats with low or reduced environmental heterogeneity.