Taxonomic revision and phylogenetic analysis of the trees snail genus Amphidromus Albers and implication for biogeography of Thai species

Abstract

The genus Amphidromus is the colourful land snail occupying the arboreal habitat and extensive distribution over Southeast Asia. The snails exhibit various peculiar biological features which apparently represent adaptive specializations, and it is presently under severe extinction pressure due to forest destruction. Although Amphidromus have consistently attracted the attention of biologist, these studies have generally lacked an accurate taxonomy and evolutionary perspective. This thesis addresses this shortcoming by concerning systematic studies focusing on the two subgenera, Amphidromus and Syndromus. A combined approach of morphology and molecular phylogeny were used in effort to test previously proposed conventional shell taxonomy. Taxonomic studies using genitalia, radula and shell of 10 species from Thailand. The result revealed that the subgenus Amphidromus has a longer epiphallic caecum and larger shell size than the subgenus Syndromus. The terminal portion of male organ, the sculpture of both sex organs and radula morphology are also significant for classification of the two subgenera. The anatomy of genitalia and radula characteristic are congruent with the conventional shell taxonomy. It should be noted that, at least as far as the close relations within the complicated species of A. atricallosus, A. inversus and A. glaucolarynx are concerned. The phylogenies of 17 Amphidromus species were examined based on morphological characters and mtl6S rDNA sequences. Both results perform monophyly of the genus and subgenus Amphidromus, but the morphological cladogram could not reflect the relationship among species level. While, the mtDNA phylogeny exhibits a paraphyletic of the subgenus Syndromus. Amphidromus glaucolarynx was arranged into the most basal clade in the genus. The rest members of Syndromus S. str. were clustered monophyletic. Intraspecific polyphyly of mtDNA haplotypes was detected in several taxa of both subgenera. The results indicate that taxonomic relations in many cases have to reviewed, for example A. glaucolarynx should be classified separately from the two subgenera. The revision of the subgenus Syndromus based on reproductive isolation between populations seems to discover the existence of multiple cryptic species with similar shell-color patterns for example in A. (Syndromus) xiengensis. In addition, the present study is the first hand information providing the evidence of phylogenetic constraint of chiral dimorphism of the genus Amphidromus. The substitution rates available for pulmonate mitochondrial rDNA suggest that the ancestral dimorphism originated in the Oligocene (35 Mya) based on the most conservative estimate of the substitution rate, or in the Pliocene (3.5 Mya) at the youngest age of divergence.