Paraphyly and budding speciation in the hairy snail (<scp>P</scp>ulmonata, <scp>H</scp>ygromiidae)

Abstract

Delimitation of species is often complicated by discordance of morphological and genetic data. This may be caused by the existence of cryptic or polymorphic species. The latter case is particularly true for certain snail species showing an exceptionally high intraspecific genetic diversity. The present investigation deals with the <i>Trochulus hispidus</i> complex, which has a complicated taxonomy. Our analyses of the <i>COI</i> sequence revealed that individuals showing a <i>T. hispidus</i> phenotype are distributed in nine highly differentiated mitochondrial clades (showing p-distances up to 19%). The results of a parallel morphometric investigation did not reveal any differentiation between these clades, although the overall variability is quite high. The phylogenetic analyses based on <i>12S, 16S</i> and <i>COI</i> sequences show that the <i>T. hispidu</i>s complex is paraphyletic with respect to several other morphologically well-defined <i>Trochulus</i> species (<i>T. clandestinus, T. villosus, T. villosulus</i> and <i>T. striolatus</i>) which form well-supported monophyletic groups. The nc marker sequence (<i>5.8S</i>-<i>ITS2</i>-<i>28S</i>) shows only a clear separation of <i>T. o. oreinos</i> and <i>T. o. scheerpeltzi</i>, and a weakly supported separation of <i>T. clandestinus</i>, whereas all other species and the clades of the <i>T. hispidus</i> complex appear within one homogeneous group. The paraphyly of the <i>T. hispidus</i> complex reflects its complicated history, which was probably driven by geographic isolation in different glacial refugia and budding speciation. At our present state of knowledge, it cannot be excluded that several cryptic species are embedded within the <i>T. hispidus</i> complex. However, the lack of morphological differentiation of the <i>T. hispidus</i> mitochondrial clades does not provide any hints in this direction. Thus, we currently do not recommend any taxonomic changes. The results of the current investigation exemplify the limitations of barcoding attempts in highly diverse species such as <i>T. hispidus</i>.