ORIGINAL ARTICLE doi:10.1111/evo.13821 Evidence for sympatric speciation in a Wallacean ancient lake Nobu Sutra,1 Junko Kusumi,2 Javier Montenegro,1 Hirozumi Kobayashi,1 Shingo Fujimoto,3 Kawilarang W. A. Masengi,4 Atsushi J. Nagano,5 Atsushi Toyoda,6 Masatoshi Matsunami,3 Ryosuke Kimura,3 and Kazunori Yamahira1,7 1Tropical Biosphere Research Center, University of the Ryukyus, Okinawa 903-0213, Japan 2Faculty of Social and Cultural Studies, Kyushu University, Fukuoka 819-0395, Japan 3Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0125, Japan 4Faculty of Fisheries and Marine Science, Sam Ratulangi University, Manado 95115, Indonesia 5Faculty of Agriculture, Ryukoku University, Otsu 520-2194, Japan 6Comparative Genomics Laboratory, National Institute of Genetics, Mishima 411-8540, Japan 7E-mail:
[email protected] Received March 4, 2019 Accepted August 3, 2019 Sympatric speciation has been demonstrated in few empirical case studies, despite intense searches, because of difficulties in testing the criteria for this mode of speciation. Here, we report a possible case of sympatric speciation in ricefishes of the genus Oryzias on Sulawesi, an island of Wallacea. Three species of Oryzias are known to be endemic to Lake Poso, an ancient tectonic lake in central Sulawesi. Phylogenetic analyses using RAD-seq-derived single nucleotide polymorphisms (SNPs) revealed that these species are monophyletic. We also found that the three species are morphologically distinguishable and clearly separated by population-structure analyses based on the SNPs, suggesting that they are reproductively isolated from each other. A mitochon- drial DNA chronogram suggested that their speciation events occurred after formation of the tectonic lake, and existence of a historical allopatric phase was not supported by coalescent-based demographic inference.