Phylogeny, species delimitation, and biogeography of the arboreal land snail genus Amphidromus on Java Island, Sundaland
The arboreal land snail genus Amphidromus, which is distributed from Southeast Asia to northern Australia, is unusual among snails because most species are dimorphic concerning the coiling direction. A phylogenetic analysis showed that the stem species of Amphidromus was already dimorphic and that monomorphic dextral and sinistral species evolved several times. Based on the phylogeny, we propose a new classification of the Amphidromus species into six subgenera. Java Island, the focus area of our study, was colonised several times from the Southeast Asian mainland, at least one time by species of the subgenus Amphidromus (Amphidromus) and two times by species of the subgenus Amphidromus (Syndromus). The colonisation of Java was facilitated when the sea level dropped during the glacials, and Java became connected with the mainland and the other Greater Sunda Islands. Using genomic ddRAD markers, we could delimit six species on Java. Two species from western Java, which are adapted to a more humid climate, show a deep population structure, which probably reflects the repeated subdivision of the populations of these species in refugia that provided suitable climatic conditions also during the arid glacials. In contrast, the other species show a shallow population structure. This indicates that there were severe bottlenecks, probably caused by a drastic reduction in the forested area. Species Distribution Models predict that the ongoing climate change will allow some species from eastern and central Java to expand their ranges, whereas the ranges of the humid-adapted species from western Java may shrink.