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The often extraordinary shell forms and shapes of gastropods found in palaeolakes, such as the highly diverse Gyraulus fauna of the famous Steinheim Basin, have been puzzling evolutionary biologists for centuries, and there is an ongoing debate whether these aberrant shell forms are indicative of true species (or subspecies) or ecophenotypic morphs. Interestingly, one of the Steinheim Gyraulus morphs - a corkscrew-like open-coiled shell - has a recent analogue in the Lake Bangong drainage system on the western Tibetan Plateau. Therefore, a combination of morphological, molecular, palaeolimnological, and ecological analyses was used in this study to assess whether the extraordinary shell shape in Gyraulus sp. from this drainage system represents a (young) ecophenotypic phenomenon or if it has been genetically fixed over an extended period of time. Our morphological, ecological, and palaeolimnological data suggest that the corkscrew-like specimens remain restricted to a small pond near Lake Bangong with an elevated pH value and that the colonization may have occurred recently. The phylogenetic reconstruction based on two gene fragments shows that these nonplanispiral specimens cluster within the previous described Tibetan Plateau Gyraulus clade N2. A network analysis indicates that some haplotypes are even shared by planispiral and nonplanispiral specimens. Given the ephemerality of the phenomenon, the compact network patterns inferred, the likely young phylogenetic age of the aberrant Gyraulus shells studied, and the ecological peculiarities of the study site, we suggest that the evolution of the aberrant shell forms on the Tibetan Plateau could likely be considered as a rapid ecophenotypic response, possibly induced by ecological stress. This finding may thus have implications for the ongoing debate about the processes that have caused the extraordinary shell diversity in palaeolakes such as the Steinheim Basin. [ABSTRACT FROM AUTHOR]

The Himalayas are considered to constitute a biogeographical boundary between the Palaearctic and Oriental regions. However, this mountain range does not form a uniform barrier because several large river valleys deeply cut into the Himalayas, crossing drainage divides and potentially forming dispersal corridors, particularly for freshwater organisms. In the present study, the effectiveness of these corridors is tested for the first time based on molecular data, using the amphi-Himalayan freshwater gastropod genus Gyraulus as a model group. Based on a broad spatial sampling from the Himalayas and the Tibetan Plateau, phylogenetic analyses were performed using mitochondrial DNA sequence data. The resulting phylogeny shows that northern and southern Himalayan clades are geographically distinct (i.e. they exclusively consist of either northern or southern specimens). This pattern suggests a lack of gene flow across the Himalayas probably at least since the late Pliocene/early Pleistocene. Successful dispersal and/or establishment of gastropods might have been impeded by geographical and ecological features. Instead of direct dispersal across the range, multiple colonizations of regions north and south of the Himalayas from extralimital areas have to be assumed. The Himalayas thus represent a very strong dispersal barrier for freshwater snails, and probably for other taxa as well. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 526-534. [ABSTRACT FROM AUTHOR]

Background: The Tibetan Plateau is not only the highest and largest plateau on earth; it is also home to numerous freshwater lakes potentially harbouring endemic faunal elements. As it remains largely unknown whether these lakes have continuously existed during the Last Glacial Maximum (LGM), questions arise as to whether taxa have been able to exist on the plateau since before the latest Pleistocene, from where and how often the plateau was colonized, and by which mechanisms organisms conquered remote high altitude lentic freshwater systems. In this study, species of the plateau-wide distributed freshwater gastropod genus Radix are used to answer these biogeographical questions. Methodology/Principal Findings: Based on a broad spatial sampling of Radix spp. on the Tibetan Plateau, and phylogenetic analyses of mtDNA sequence data, three probably endemic and one widespread major Radix clade could be identified on the plateau. Two of the endemic clades show a remarkably high genetic diversity, indicating a relatively great phylogenetic age. Phylogeographical analyses of individuals belonging to the most widely distributed clade indicate that intra-plateau distribution cannot be explained by drainage-related dispersal alone. Conclusions/Significance: Our study reveals that Radix spp. persisted throughout the LGM on the Tibetan Plateau. Therefore, we assume the continuous existence of suitable water bodies during that time. The extant Radix diversity on the plateau might have been caused by multiple colonization events combined with a relatively long intra-plateau evolution. At least one colonization event has a Palaearctic origin. In contrast to freshwater fishes, passive dispersal, probably by water birds, might be an important mechanism for conquering remote areas on the plateau. Patterns found in Radix spp. are shared with some terrestrial plateau taxa, indicating that Radix may be a suitable model taxon for inferring general patterns of biotic origin, dispersal and survival on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: Carbon and oxygen isotope ratios have been measured for nine aragonite shells of the gastropod genus Radix from the lake Bangda Co (30°29′N, 97°04′E, 4450 m a.s.l.) at the south-eastern edge and from two characteristic sites at the lake Kyaring Co (31°09′N, 88°17′E, 4650 m a.s.l.) on the central Tibetan Plateau. Radix shells were sampled for isotope ratio analysis with high spatial resolution along the ontogenetic spiral of growth providing the basis of isotope records with a sub-seasonal time-resolution. δ18O values of shells from Bangda Co are on average ∼−15.0‰ relative to PDB and the pattern exhibits a clear onset and progression of the summer monsoon precipitation indicated by a strong “amount effect”. This pattern mirrors the precipitation pattern in the respective year and region as expected for a small (surface area ca 0.3 km2) and shallow (<5 m) lake or habitat with short water residence times and little evaporative 18O enrichment of the lake water. In contrast, δ18O values of Radix shells from Kyaring Co habitat A which is connected to the deep (several tens of metres) and big (surface area ca 660 km2) lake, average at ∼−13.0‰ consistent with a higher evaporation rate and longer water residence time. The latter is supported by more 18O enriched water in this habitat. The δ18O values of Radix shells from Kyaring Co habitat B are nearly as low as shells from Bangda Co due to the similar habitat characteristic but isotopic patterns of these shells exhibit a weaker “amount effect”. In both lake systems δ13C values of the shells are coupled with oxygen isotopes because a large amount of isotopically light carbon is washed from mountain slopes into the lake during the rainy season. Although other processes influence the isotopic patterns, e.g. biological productivity (δ13C) or temperature (δ18O), these influences are minor compared with the monsoon signal or the effect of evaporation in the Radix shell records. The overall weaker amount effect in Radix shells from Kyaring Co habitat B compared with shells from Bangda Co are consistent with a current decreasing monsoon influence from the south-eastern edge towards the central Tibetan Plateau. Thus, fossil shells of the gastropod genus Radix are a valuable archive for reconstructing climatic and environmental changes on the Tibetan Plateau and provide information about former habitat sizes and depths. [Copyright &y& Elsevier]