Causation of a riverine radiation: Assessment and evaluation of the morphological and genetical differentiation in a species flock of viviparous gastropods (Cerithioidea: Pachychilidae)

The proposed project focuses on an endemic, morphologically diverse species flock of viviparous freshwater gastropods of the genus Brotia inhabiting the Kaek River (Chao Praya drainage, Central Thailand). Similar invertebrate species flocks have frequently been examined in lakes in an attempt to elucidate the underlying evolutionary mechanisms of adaptive radiations. In contrast to that, riverine radiations are rare and hardly studied. However, due to specific characteristics a riverine setting provides a new perspective for studying potential factors of speciation and, thus, the genesis of biological diversity. Preliminary results indicate the Mekong drainage system as a putative area of origin, the monophyly of the species flock, and its rapid diversification. Sympatric occurrence of two to three species at sampling localities, their ecological separation by varying substrate preferences, and a correlated trophic specialization (radula morphology) renders this fluviatile radiation a new and potentially highly informative model system. This project combines sophisticated sampling of material and ecological data in the field with morphological and molecular genetic analyses. It will employ AFLP genotyping as powerful tool to produce well-resolved phylogenetic reconstructions and to assess levels of genetic variation and cohesion (estimation of gene flow within and between populations) to illuminate the role of intrinsic and extrinsic factors in the course of allopatric and/or ecological speciation. This will be supplemented by data on environment-phenotype correlation and life-history parameters (brood size and performance as estimator for fitness) that is necessary to test assumptions on the causations of the evolution of this species flock.