A relic of glacial isolation: deep phylogeographic splits in dwarf pond snail Galba truncatula (Gastropoda, Lymnaeidae)

The dwarf pond snail Galba truncatula (O.F. Müller, 1774) is a widespread freshwater species and a key intermediate host of Fasciola spp. Despite its ecological and medical significance, the evolutionary structure of its populations remains incompletely resolved. Using 78 mitochondrial COI sequences, including newly obtained material from Eastern Europe, Central Asia, and Caucasus, we reconstructed the phylogeographic pattern of Galba truncatula across Western Palearctic. Our analyses reveal the presence of three distinct phylogenetic lineages. A deeply divergent group, represented by a small number of sequences, occurs sympatrically with the main clade in Western Europe. The main clade, comprising the majority of sequences, is split into two geographically structured subclades: a western lineage (Western Europe and North Africa) and an eastern lineage (Eastern Europe, Caucasus, and Central Asia). Both major lineages are represented in South America, suggesting at least two independent colonization events. We propose that the initial divergence between the eastern and western lineages likely began in the early Pleistocene, whereas their present-day distribution may have been shaped by isolation during the Last Glacial Maximum. Highlights We reconstructed the phylogeographic structure of Galba truncatula using COI sequences from Eurasia and South America. Three distinct lineages were identified, including a deeply divergent group occurring sympatrically in Western Europe. The main lineage is split into eastern and western clades, likely diverging in the early Pleistocene. Both clades are represented in South America, indicating at least two independent colonization events. Our findings challenge the hypothesis of a South American origin and highlight the role of glacial history in shaping current diversity.