Parsimony analysis of the distribution pattern of Japanese primary freshwater fishes, and its application to the distribution of the bagrid catfishes

The geographic distribution of Japanese primary and some secondary freshwater fishes was analyzed using parsimony analysis of endemicity (PAE). Analysis of 73 taxa (species and intraspecific forms) on the four main islands of Japan (divided into 25 geographic areas), produced 44 most parsimonious cladograms. In all of the latter, a total of eight single and compound areas were recognized as endemic areas in nested relationships. The area cladograms showed Japan as comprising a middle-eastern Hokkaido area plus southern areas, the latter containing mainly a northeastern-Honshu endemic area and more heterogeneous southwestern areas, including four endemic areas (western Kyushu, southeastern Chugoku, middle Kinki and Tokai around Ise Bay) and several peripheral areas. Some patterns, e.g., the distinction in fauna across Fossa Magna, noted by previous studies, were supported by these results. Even though the analysis had some problems (e.g., not all geographic ranges of taxa could be included), it provided evidence for the detection of general distribution patterns, because the relationships or similarities among areas were clearly defined by shared taxa. To demonstrate the historical implications of the analysis, the allopatric distribution of, four bagrid catfishes was reconsidered in the area cladogram. The general pattern implied secondary extinction ofPseudobagrus nudiceps around lse Bay, which was in keeping with the fossil record.