The Kaek River in central Thailand is unique in harbouring a diverse species assemblage of viviparous gastropods of the genus Brotia. A stretch of this river less than 100 km long is inhabited by seven, mostly endemic species that are essentially differentiated by their shell morphology. Earlier, it has been suggested that this species flock fulfils some basic requirements of a radiation (monophyly and phenotype-habitat correlation). However, the present study has shown that there is no strict correlation between radula and shell morphology and the utilisation of substrates, such as rock or sand, thereby refuting the hypothesis that ecological speciation may have played a significant role. Phylogenetic analyses based on mtDNA show that haplotypes cluster together in drainage-specific clades rather than according to the taxonomy. There are also strong indications that introgressive hybridisation has occurred, which may have resulted from secondary contact of previously isolated species due to dispersal or river captures during the Cenozoic. It is assumed that the high species diversity in the Kaek River results from two phenomena that interdigitate. Firstly, the Kaek River fauna may have originated from multiple species invasions from different source areas, while traces of these events may have been obscured by introgression of Kaek River-specific haplotypes. Secondly, waterfalls in the Kaek River seem to affect the directionality and amount of gene flow between local populations within the river and several smaller tributaries. Together with temporally changing water regimes, this highly structured environment may have conserved local genetic differentiation and triggered diversification and speciation in peripheral isolates within relatively short periods of time.
CITATION STYLE
Köhler, F., Panha, S., & Glaubrecht, M. (2010). Speciation and radiation in a river: Assessing the morphological and genetic differentiation in a species flock of viviparous gastropods (Cerithioidea: Pachychilidae). In Evolution in Action: Case studies in Adaptive Radiation, Speciation and the Origin of Biodiversity (pp. 513–550). Springer-Verlag Berlin Heidelberg. https://doi.org/10.1007/978-3-642-12425-9_24
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