Speciation driven by repeated colonization in a Wallacean ancient lake

*Sutra Nobu（TBRC, Univ. Ryukyus）, Junko Kusumi（Kyushu Univ.）, Atsushi J Nagano（Agriculture, Univ. Ryukoku）, Masatoshi Matsunami（Medicine, Univ. Ryukyus）, Ryosuke Kimura（Medicine, Univ. Ryukyus）, Kazunori Yamahira（TBRC, Univ. Ryukyus）

To demonstrate sympatric speciation, the absence of allopatric phase in the past has to be proved. Moreover, it is also essential to demonstrate that sympatric divergence was not aided by secondary gene flow from outgroup populations. In this study, we examine the possibility of these two historical events during the divergence of three sympatric species of medaka fishes (the genus Oryzias) in an ancient lake on Sulawesi, a Wallacean island, by demographic modeling approaches and tests of differential admixture using genome-wide SNPs. First, our demographic inference did not support a model that assumes a historical allopatric phase during their divergences. Second, the demographic inference also demonstrated that introgressive hybridization from an outgroup population was evident. However, differential admixture among the sympatric species was not supported by any statistical tests. These results satisfy the criteria which are necessary to demonstrate sympatric speciation, but further analyses on functional roles of the introgressed genes and their neutrality are necessary to conclude that these sympatric species in the Wallacean ancient lake diverged without the aid of the secondary gene flow.