Variation in Ligand-Accessible Genome Size and Its Ecomorphological Correlates in a Pond Snail

Abstract

Genome size was assessed by flow cytometry with DNA-specific fluorescent ligand olivomycin in six populations of a snail Viviparus contectus (Gastropoda, Viviparidae). Shell and aperture sizes were recorded for the same animals. It was found that across all the populations the relative aperture size (residuals of aperture/shell size regression) was negatively correlated with the ligand-accessible genome size (LA-GS). The effect was mainly due to interpopulation differences and seemed to be associated with the relative abundance of other gastropod molluscs. The populations inhabiting ponds where V. contectus occurred alone, showed higher LA-GS and lower relative aperture size. In a population from the pond where V. cuntectus was most rare as compared with other gastropods, the reverse pattern was observed. In one of the six populations only, the effect was significant at the within-population level. In addition, average genome sizes were determined for 15 gastropod species. Genome of V. cuntectus was found to be the largest among non-terrestrial gastropods, which had significantly smaller genomes than terrestrial mollpscs. The findings are discussed in relation to the possible role of redundant (non-coding) DNA, genome cytoecology, and evolution of genome size.