The phylogeography and population demographics of selected freshwater fishes in Taiwan

Unlike most fluvial species, which are usually isolated by geographical barriers, low-elevation wetland fishes have more opportunities to exchange migrants (i.e., higher gene flow). Our phylogeographic analyses revealed that Taiwanese populations of the ricefish (Oryzias latipes), paradise fish (Macropodus opercularis), and a species of the landlocked freshwater goby (Rhinogobius giurinus) are all paraphyletic and clustered with Chinese populations. The 3 ricefish populations known from Taiwan may have been derived from multiple invasion events. We hypothesized that the original ricefish populations distributed throughout northwestern Taiwan significantly declined from their overall range, and the surviving inhabitants were restricted to Shuanglien Pond. This population thereby exhibited high genetic diversity. Alternatively, humans probably unintentionally introduced the other 2 populations. We also found that the abundant freshwater goby and the endangered paradise fish populations in Taiwan had both recently expanded from China. The separation time is insufficient for the Taiwanese populations to have diverged and developed elevated genetic diversity. In other words, the actual genetic homogeneity of paradise fish in Taiwan is not necessarily derived from a recent extinction. The other example of shallow differentiation among Taiwanese fishes is the Formosan masu salmon, Oncorhynchus masou formosanus. Its low genetic diversity may partly have been the result of a founder effect when initial masu salmon populations colonized Taiwan during the last glaciation.