Ancient lakes as hotspots of diversity: a morphological review of an endemic species flock of Tylomelania (Gastropoda: Cerithioidea: Pachychilidae) in the Malili lake system on Sulawesi, Indonesia

Hydrobiologia (Impact Factor: 2.21). 11/2007; 592(1):11-94. DOI: 10.1007/s10750-007-0765-8

ABSTRACT The viviparous freshwater gastropod Tylomelania (Caenogastropoda: Cerithioidea: Pachychilidae) endemic to the Indonesian island Sulawesi has radiated extensively in two
ancient lake systems. We here present the first systematic species-level review of taxa in the five lakes of the Malili lake
system, which contains the most diverse and best studied freshwater fauna on Sulawesi. Our results indicate a significantly
higher diversity of Tylomelania in these lakes than previously perceived based on morphological evidence for delimiting the taxa. We describe nine new species,
thus increasing the number of taxa known from the Malili lakes to 25. Tylomelania species are inhabiting all available substrates in the lakes, and the diversity of habitats is reflected in an unparalleled
range of radula types in this closely related group. Several species show a high intraspecific variability in some characters,
and their closer investigation will probably lead to the discovery of more cryptic species. As it is, this species flock on
Sulawesi is among the largest freshwater mollusc radiations known. Since the Malili lake system also contains other large
endemic species flocks of e.g. crustaceans and fishes, it is a major hotspot of freshwater biodiversity in Asia to become
a conservation priority.

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    ABSTRACT: The complex geological history of the Indonesian island Sulawesi has shaped the origin and subsequent diversification of its taxa. For the endemic freshwater snail Tylomelania a vicariant origin from the Australian margin has been hypothesized. Divergence time estimates from a mtDNA phylogeny based on a comprehensive island-wide sampling of Tylomelania fit regional tectonic constraints and support the 'out-of-Australia' vicariance hypothesis. The Banggai-Sula region of the Sula Spur, the Australian promontory colliding with West Sulawesi during the Miocene, is identified as a possible source area for the colonization of Sulawesi by the ancestor of Tylomelania. The molecular phylogeny also shows a rapid diversification of Tylomelania into eight major lineages with very little overlap in their distribution on the island. Haplotype networks provide further evidence for a strong spatial structure of genetic diversity in Tylomelania. Distribution boundaries of the major lineages do at best partially coincide with previously identified contact zones for other endemic species groups on Sulawesi. This pattern has likely been influenced by the poor dispersal capabilities and altitudinal distribution limits of this strict freshwater inhabitant. We suggest that late Miocene and Pliocene orogeny in large parts of Sulawesi has been the vicariant event driving primary diversification in Tylomelania.
    PLoS ONE 06/2014; 9(6):e98917. DOI:10.1371/journal.pone.0098917 · 3.53 Impact Factor
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    ABSTRACT: 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 sub-strates, 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 interdigi-tate. 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. F. Köhler (*) Museum f€ ur Naturkunde, Invalidenstr.
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