ORIGINAL ARTICLE doi:10.1111/j.1558-5646.2008.00447.x ADAPTIVE SYMPATRIC SPECIATION OF POLYCHROMATIC “ROUNDFIN” SAILFIN SILVERSIDE FISH IN LAKE MATANO (SULAWESI) Fabian Herder,1,2,3 Jobst Pfaender,1,4 and Ulrich K. Schliewen2,5 1Sektion Ichthyologie, Zoologisches Forschungsmuseum Alexander Koenig, Adenauerallee 160, D-53113 Bonn, Germany 2Department of Ichthyology, Bavarian State Collection of Zoology (ZSM), Munchhausenstr.¨ 21, D-81247 Munchen,¨ Germany 3E-mail:
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[email protected] Received December 21, 2007 Accepted June 9, 2008 The significance of sympatric speciation is one of the most controversial topics in evolutionary biology. Theory suggests that different factors can lead to speciation in full geographical contact, including selection and nonrandom mating. Strict criteria have been established for assessing sympatric speciation, which have been met in only a very few cases. Here, we investigate differen- tiation among sympatric morphospecies and color morphs of “roundfin” sailfin silversides (Telmatherinidae), small freshwater fish endemic to ancient Lake Matano in Central Sulawesi (Indonesia). Morphospecies are distinct according to body shape (geometric morphometrics), population structure (population-level amplified fragment length polymorphism [AFLP] markers), ecology, and mating behavior (habitat transects, stomach contents). Explorative genome scans based on AFLPs indicate that divergent selection affects only 1.3–4.2% of the analyzed loci, suggesting an early stage of speciation. Transect data demonstrate strong assortative mating and adaptive niche differentiation. However, we find no restrictions in gene flow among the conspicuous male color morphs. In summary, our data are consistent with a sympatric mode of divergence among three morphospecies under conditions effectively ruling out allopatric scenarios.