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: 1.99). 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.
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    ABSTRACT: The Cerithioidea is an ecologically important superfamily of basal Caenogastropoda with speciose marine, brackish water, and freshwater lineages primarily in tropical, subtropical, and warm temperate regions of the world. They often represent significant components of the communities where they occur and have given rise to several spectacular endemic radiations in rivers and ancient lakes. Earlier attempts to resolve the phylogenetic history of the group have been based on smaller taxon and character subsets with incongruent results. Here the monophyly and phylogeny of the group is evaluated with expanded morphological and molecular (16S, 28S rRNA) data sets. For morphological analyses, 151 characters (shell, operculum, radula, alimentary tract, kidney, nervous system, reproductive anatomy, and sperm ultrastructure) were scored for 47 cerithioideans (representing 17 families) and nine outgroup taxa. To test monophyly of the Cerithioidea, extended molecular data sets of 16S and 28S sequences for 57 and 44 taxa, respectively, were compiled using new and previously published sources. For combined analyses, a pruned molecular data set was combined with the morphological partition. The morphological data were analysed alone using only parsimony; molecular and simultaneous analyses were performed using both parsimony and Bayesian inference. The effect of excluding unconserved regions of the alignments was also explored. All analyses, with the exception of the individual 16S and 28S data sets, support monophyly of the Cerithioidea as currently formulated. Of the 12 families represented by more than one terminal, only two (Planaxidae, Potamididae) are always supported as monophyletic; Batillariidae, Cerithiidae, Pachychilidae, Pleuroceridae, Semisulcospiridae, Thiaridae, and Turritellidae are monophyletic in most but not all topologies. The combination of diverse data sources (morphology, 16S and 28S sequences) and inclusion of unconserved regions of the alignments improved the recovery of monophyletic families. At deeper levels, a consensus is beginning to emerge in the recognition of three main assemblages, but whether these represent clades or grades is still unclear; the resolution of these assemblages and the branching order within them are sensitive to exclusion of unconserved regions and choice of optimality criterion. No clear conclusion is reached with respect to the number of freshwater invasions, with two invasions supported on some topologies and three supported on others. Progress toward a robust and stable resolution of cerithioidean relationships will require (1) strategically coordinated sampling for additional morphological and molecular data; (2) comprehensive anatomical treatments for several poorly documented limnic lineages (e.g. Melanopsidae, Thiaridae) and comparative data for poorly understood organ systems (e.g. renal system); (3) the addition of poorly known, minute, and/or rare marine taxa, to provide novel character combinations, insight into putative homologies, and to help anchor basal nodes and break up long branches.© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162, 43–89.
    Zoological Journal of the Linnean Society 04/2011; 162(1):43 - 89. · 2.58 Impact Factor
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    American Malacological Bulletin 04/2011; · 1.00 Impact Factor

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