Differentiation in the Trochulus hispidus complex and related taxa (Pulmonata: Hygromiidae): morphology, ecology and their relation to phylogeography

Abstract

In this study we investigated the morphology and ecology of representatives of the taxonomically ambiguous genus Trochulus. The main focus was on the T. hispidus complex, which comprises several genetically highly divergent mitochondrial clades, as determined in a parallel molecular genetic study. We analysed shell morphology and anatomical traits and asked whether the clades are differentiated in these characters. In addition, the related species T. oreinos and T. striolatus were investigated and compared with the T. hispidus complex. Finally, we compared the ecological requirements of the taxa. Among the genetic clades of the T. hispidus complex there was no clear morphological differentiation and geographic populations could not be distinguished based on their morphology. The investigated characters of the genital anatomy did not allow discrimination of any of the T. hispidus clades and were not even diagnostic for the group as a whole. The morphotype of T. sericeus is present in all clades and thus cannot be assigned to a genetic group or any specific population. Thus, our morphological data do not provide evidence that any of the mitochondrial T. hispidus clades represent separate species. Concerning interspecific delimitation, the T. hispidus complex was clearly differentiated from T. striolatus and T. oreinos by shell morphological and anatomical characters, e.g. sculpture of shell surface and details of the penis. Finally, the habitat of T. oreinos is different from those of the other two species. In contrast to the lack of correspondence between genetic and morphological differentiation within the T. hispidus complex, related species display intraspecific morphological differentiation corresponding with mitochondrial clades: within T. striolatus there was a slight morphological differentiation between the subspecies T. s. striolatus, T. s. juvavensis and T. s. danubialis. The two subspecies of T. oreinos could be discriminated by a small but consistent difference in the cross-section of the penis. The unequal levels of intraspecific differentiation are caused by different evolutionary histories as a consequence of disparities in ecological demands, dispersal ability and use of glacial refugia: both the T. hispidus complex and T. striolatus are fast-spreading, euryoecious organisms which are able to (re-)colonize habitats and survive under different climate conditions. While the T. hispidus complex probably survived the Pleistocene in several glacial refugia, for T. striolatus one glacial refugium is suggested. Trochulus oreinos differs from the other taxa, as it is a slow disperser with a narrow ecological niche. We suggest that its subspecies spent at least the last glaciation in or close to the presently inhabited areas.

Ongoing Speciation and Gene Flow between Taxonomically Challenging Trochulus Species Complex (Gastropoda: Hygromiidae)

“…Each snail was classified into two clusters, 1 and 2, six were assigned simultaneously to clusters 1 and 2, and one individual showed mixed affiliation to clusters 1 and 3, whereas the other was grouped to clusters 1, 2 and 3. Both here and in the results obtained by other authors [27], the taxonomic status of T . coelomphala remains unclear.…”

“…hispidus complex were morphologically attributed to T . sericeus by Duda et al [27] and Kruckenhauser et al [16]. …”

“…caelatus [38] and T . oreinos [26,72], regional speciation with local persistence seems to be common within the genus Trochulus [13,16,27,71]. In general, the poor dispersal power of snails give rise to rather clear patterns of genetic differentiation related to distance; gene flow is limited [73].…”

“…sericeus should be considered as T . hispidus complex [27] because none of them meets the criterion of monophyly [16]. In these two parallel studies, nine highly differentiated mitochondrial clades were identified, also revealing no morphometric differentiation between the clades.…”

Groping through the black box of variability: An integrative taxonomic and nomenclatural re-evaluation of Zospeum isselianum Pollonera, 1887 and allied species using new imaging technology (Nano-CT, SEM), conchological, histological and molecular data (Ellobioidea, Carychiidae)

“…These authors not only found many morphologically unrecognized evolutionary lineages within this taxon, but also revealed that several alleged Zospeum species are ambiguously classified products of past taxonomic lumping traditions. However, in light of this past work, consideration of historical designations and recent investigations cannot ignore the fact that conventional molecular genetic methods, on the one hand, have not only solved many taxonomic conundrums in biological systematics, but have, on the other, also confounded the situation by uncovering more complicated patterns of unrecognized genetic variability, which otherwise, may never have been detected (Sauer and Hausdorf 2012, Jörger and Schrödl 2013, Duda et al 2014, for detailed discussion of cryptic speciation see Jörger and Schrödl 2013). Still, and in all due respect of this work, we strive for clarity and understanding of these microgastropods: for accuracy in biodiversity studies, for basic biogeographical investigations and for forming conservation strategies.…”