VARIATION IN LIGAND-ACCESSIBLE GENOME SIZE AND ITS ECOMORPHOLOGICAL CORRELATES IN A POND SNAIL

Genome size was assessed by flow cytometry with DNA-specific fluoresce nt 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 re lative 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 t o be associated with the relative abundance of other gastropod mollusc s. 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. contectus was most rare as compared with other gastropods, the reverse pattern was observed. In one of the six popul ations only, the effect was significant at the within-population level . In addition, average genome sizes were determined for 15 gastropod s pecies. Genome of V. contectus was found to be the largest among non-t errestrial gastropods, which had significantly smaller genomes than te rrestrial molluscs. The findings are discussed in relation to the poss ible role of redundant (noncoding) DNA, genome cytoecology, and evolut ion of genome size.