Geographic isolation and human-assisted dispersal in land snails: a Mediterranean story ofHelix borealisand its relatives (Gastropoda: Stylommatophora: Helicidae)

Abstract

The Mediterranean basin is a major centre for land-snail diversity, with many localized endemics, but there are also species widely spread by humans. Both endemics and introductions can be found in the snail genus Helix, which comprises many large-bodied species used for human consumption in the past and present. The Mediterranean clade of Helix is currently distributed throughout this region, but the phylogenetic and biogeographic relationships among its forms from different parts of the basin remain enigmatic. The reasons include insufficient sampling, taxa with unclear taxonomy and a significant impact of human-assisted transport obscuring the natural distribution of phylogenetic lineages. We provide evidence that European and Anatolian populations of H. cincta and its relatives are not native to those regions, but originate from the northern Levant. These results have implications for taxonomy of the genus, but also for the understanding of its evolutionary history. We posit that the Mediterranean clade consists of four geographically separated groups, which diversified in Northern Africa, the Apennine Peninsula and Corsica, the Aegean and Greece, and the northern Levant. This geographic pattern has been subsequently blurred by multiple instances of human-assisted dispersal. However, revealing the founding populations with certainty requires thorough sampling in currently inaccessible countries.

Multiple Introductions of the Pestiferous Land Snail Theba pisana (Müller, 1774) (Gastropoda: Helicidae) in Southern California

“…These results contribute to a growing body of literature that documents repeated introduction of terrestrial gastropod taxa at sites around the world, e.g., Ambigolimax valentianus (Férussac, 1821) in Japan [68], Arion subfuscus (Draparnaud, 1805) in the U.S. [69,70], Cepaea nemoralis (Linnaeus) in North America [71,72], Cornu aspersum (Müller, 1774) in North and South America [73][74][75], Deroceras invadens Reise, Hutchinson, Schunack and Schlitt, 2011 in Europe and North America [76], Helix spp. in Europe [77], and Lissachatina fulica (Bowdich, 1822) in South America [78,79]. Such studies also highlight the phenomenon of biotic homogenization [80], identify anthropogenic pathways of introduction [81], may improve protocols for species interception and quarantine, and inform strategies for invasive species eradication or control [81].…”

Phylogeny of the land snail Levantina reveals long‐distance dispersal in the Middle East

“…This conclusion has been criticised on grounds of insufficient sampling in the Levant by Neubert et al (2015), and it remains possible that there are only two (sub)species (one umbilicated, the other with a closed umbilicus; Neubert et al, 2015) and that both were introduced to the Aegean by humans. That would not be surprising as there are edible helicids other than Levantina, where anthropogenic introductions from the Levant to southwestern Anatolia and the eastern Aegean were suspected (Korábek et al, 2015(Korábek et al, , 2021.…”