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.
Highlights
The Indonesian island Sulawesi lies at the heart of the IndoAustralian Archipelago (IAA), one of the world’s most species-rich areas and arguably the one with the most complex geography and geology [1]
An ancient continental core in the West that has been emergent since the Mesozoic – comprising Indochina and Sundaland – is sharply set apart from an area of predominantly young (Miocene to Pleistocene) oceanic islands including Sulawesi in the East bordered by the Australian continental margin [5]
Phylogeny of Tylomelania The molecular phylogeny based on MP, ML and BI analyses of the concatenated mtDNA dataset (COI and 16S) reveals eight major lineages of Tylomelania on Sulawesi (Figures 1–3; Table 1)
Summary
The Indonesian island Sulawesi lies at the heart of the IndoAustralian Archipelago (IAA), one of the world’s most species-rich areas and arguably the one with the most complex geography and geology [1]. An ancient continental core in the West that has been emergent since the Mesozoic – comprising Indochina and Sundaland – is sharply set apart from an area of predominantly young (Miocene to Pleistocene) oceanic islands including Sulawesi in the East bordered by the Australian continental margin [5]. Several faunal boundaries, including the famous ‘Wallace Line’ [6], were proposed to account for the observation that the western or eastern distribution limits of many animal groups are located within the oceanic island region of the IAA (see e.g., [7]). The transitional region Wallacea, which comprises all islands between the Sunda and Australian shelves, was proposed as one attempt to avoid the designation of a single faunal boundary [8]. The fauna of the Wallacean islands is generally characteristic of oceanic islands [12], e.g., being ‘‘disharmonic’’, i.e., depauperate at a higher taxonomic level, and having a high proportion of endemic species [9,13]
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