Allopatric, sympatric, and hybrid speciation in a lacustrine medaka species complex

*Ixchel F MANDAGI（TBRC, University of Ryukyus, FPIK, Univ. of Sam Ratulangi, Daniel F Mokodongan（FPIK, Univ.of Halu Oleo, Koji Mochida（Keio University, Nobuyuki Inomata（Fukuoka Women's Univ., Atsushi J Nagano（Ryukoku University, Jun Kitano（Nat. Inst. Genetics, Kazunori Yamahira（TBRC, University of Ryukyus）

In addition to the presence/absence of physical barriers, the role of hybridization due to secondary contact between isolated populations is recently getting more attention in the process of speciation. In this study, we investigated the speciation processes of a medaka species complex in Malili Lake system in Sulawesi Island, where five tectonic lakes are connected with each other by rivers, and therefore historical and ongoing gene flows between isolated lacustrine populations are highly probable. Both mitochondrial and genome-wide SNP analyses revealed that the Malili species complex was basically separated by lakes, indicating that physical isolations into each lake contributed to their divergences. However, hybridizations have repeatedly occurred between lakes. Especially, one lacustrine species was considered to have originated from a hybrid population. We also found that hybridization is still ongoing between a certain pair of lakes, but that inter-lake population structures persist. Interestingly, sympatric speciation was evident in one of the lake where hybrids were found. These findings suggest that hybridizations may have greatly contributed to the speciation of the medaka complex in this lake system.