Testing the role of the Himalaya Mountains as a dispersal barrier in freshwater gastropods (Gyraulusspp.)

Abstract

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.

The Schistosoma indicum species group in Nepal: presence of a new lineage of schistosome and use of the Indoplanorbis exustus species complex of snail hosts

“…It will be of particular interest to learn whether members of the S. indicum group extend to areas north of the Himalayas as I. exustus occurs in Tibet and China. The Himalayas have been shown to have a strong effect in isolating Gyraulus snails north of the mountains from those to the south (Oheimb et al, 2013) and might also have similar effects on Indoplanorbis and associated parasites. Once the I. exustus species complex has been better fleshed out, it will be interesting to determine whether any of its lineages are susceptible to infection with any members of the S. haematobium group, or if S. indicum group parasites ever infect any (particularly Asian representatives of) bulinid snails.…”

A comparative study on floras in Nepal and Southern Tibet

“…The results also showed that the similarity indices of the floristic composition between the two regions decreased from 0.89 to 0.41 with the descending of taxonomical level. This may reflect the hypothesis that at lower taxonomical ranks, e.g., species level, floras may be comprised of more diverse taxa and more strongly influenced by allopatric speciations induced by the uplift of the range during the Tertiary (Cox, 2000;Sakka et al, 2000;Hoffmann, 2001;Gayden et al, 2007;Cun and Wang, 2010;Von Oheimb et al, 2013), and hence lead to lower similarity indices of the floristic composition. In other words, though one cannot deny the boundary effects of the Himalayan Range on floras, to a certain extent, its strength may depend on the taxonomical ranks investigated.…”

“…However, as one shifts from considering the family to genus level, the similarity decreased, mainly characterized by contrast proportions of the tropical and temperate elements between the two regions. This may hint that, although both regions have close biogeographical affinities, the boundary effects or the uplift of the range may, to certain extent, have caused strong allopatric speciations in the geographical elements of the Himalayan regions, and also may have prevented the migration of geographical elements at genus level between the two regions (Cox, 2000;Sakka et al, 2000;Hoffmann, 2001;Gayden et al, 2007;Cun and Wang, 2010;Von Oheimb et al, 2013). The results also showed that the similarity indices of the floristic composition between the two regions decreased from 0.89 to 0.41 with the descending of taxonomical level.…”

“…A flurry of studies has been conducted to test this hypothesis. For instance, several studies show that the Himalayan Range strictly impeded the dispersal of some gastropod and mammalian taxa, and prevented gene exchange across the range (Cox, 2000;Sakka et al, 2000;Gayden et al, 2007;Von Oheimb et al, 2013;Wang, 2013). However, studies of avian taxa show that some species (e.g., Anser indicus and Tadorna ferruginea) can migrate over the Himalayan Range (Hawkes et al, 2011;Newman et al, 2012), suggesting that their populations in Nepal and Southern Tibet may have some genetic interaction.…”

“…However, studies of avian taxa show that some species (e.g., Anser indicus and Tadorna ferruginea) can migrate over the Himalayan Range (Hawkes et al, 2011;Newman et al, 2012), suggesting that their populations in Nepal and Southern Tibet may have some genetic interaction. It was also observed that most scientists tested this hypothesis on specific species or genera (Sakka et al, 2000;Von Oheimb et al, 2013), while a few large scale studies have been conducted on either the region's flora or fauna. In conclusion, one is led to believe that further investigations related to this hypothesis, the hypothesis that the Himalayan Range led to distinct Nepal and Southern Tibet biota, are needed.…”