Taxonomy, Evolution and Phylogeography of Balitoridae in East Asia

• Main Authors: Tzi-Yuan Wang, 王子元
• Other Authors: Chyng-Shyan Tzeng
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/78371631885347983830

博士 === 國立清華大學 === 生命科學系 === 93 === ABSTRACT Stream loaches (Cypriniformes: Balitoridae) are primary freshwater fish. The geographical distributions are in Southern and Eastern Asia, including the south of Yanze River, the north of Borneo, Southwestern Indonesia and Taiwan. There are over 30 genera and 135 species in the world. Among which more than 50% of species are distributed in Mainland China and Taiwan. Balitorid fishes are small benthic and loach-like. They prefer to live in swift streams, where they attach to rocks scraping algae as a food source. Their populations are widespread and numerous among freshwater fishes in East Asia. These fishes can only survive in freshwater streams, thus their colonization routes depend on the changes of flowing river systems, climatic oscillations, and paleogeography. Molecular evolutionary comparison of mitochondrial coding gene and genetic divergence among species and populations revealed that both spatial patterns and temporal implications offered a scenario to understand the taxonomy, evolution and phylogeography of balitorid fish in East Asia. The taxonomy disagreements of stream loaches have been observed among various researches since nineteenth century. The collected samples included 25 genera and 36 species of balitorids, cobitids and cyprinids based on the traditional phylogeny. The analysis of two mitochondrial coding genes, cytochrome b (cytb) and cytochrome c oxyosidase subunit I (COI), helped to reconstruct the higher-level phylogeny of Balitoridae. The results indicated monophyly of Balitorinae, meaning that they do not cluster with the fish of Nemacheilinae and Cobitidae. Neohomaloptera and Homaloptera are two primitive genera in Balitorinae, while Protomyzon and Gastromyzon are two primitive genera in Gastomyzonitinae. Therefore, it is proposed that the Balitoridae is a monophyletic family and includes two subfamilies, Gastromyzontinae and Balitorinae. The Gastromyzontinae only has one monophyletic group (the crossostomoid-group) while others are the paraphyletic groups. The adaptative evolution of balitorid fish shows directional selection in Balitorinae and diversifying selection in Gastromyzontinae. Different forces of selection result in the morphological convergences between two subfamilies to adapt in the habitats of swift streams. Crossostomoid-group containing two major genera, Crossostoma and Vanmanenia, is the one of monophyly in Gastromyzontinae. Many species of this group are distributed in southern China and adjacent islands. Except the widespread distribution of V. pingchowsis, most are endemic species. Species of Crossostoma are restricted in Fujian province and Taiwan. Analyzing the cytb sequences of 4 genera and 15 species to reveal the classification and phylogeography of crossostomoid-group. The molecular phylogeny indicates three monophyletic groups. The primitive group (Vanmanenia) and derived group (Crossostoma) show morphological differences in the arrangement of rostral fold, the uncovered area of ventral parts and the location of anus. However, the gradual development of other morphological changes mixed up the synopsis of genera. The color patterns, the ratio of caudal peduncle length and depth, and the numbers of lateral line scales show no direction in systematics. The temporal estimation indicates that the three monophyletic groups were restricted by the Nan Mountain and Wuyi Mountain since 7 million years ago (mya). Hence, the local subdivisions were then separated by the isolation of river systems from 3 to 6 mya. The derived species of Crossostoma were speciated since 6 mya and restricted in Fujian and eastern Guangdong provinces. During the Pleistocene ice ages, the endemic C. lacustre speciated in central Fujian and colonized into northern and central Taiwan. Subdivisions are closely related to geographic vicariance or populations' migrations. Although phylogeographic studies discovered a similar, deep genetic break between the freshwater fishes in the north-central and southern areas of Taiwan, it is still not clear when the distinct geological events affected the subdivision of these fishes in sympatric area. Fishes can reach a new river basin by forces such as river capture, river confluence in downstream after sea level lowering, and sea dispersal during low-salinity conditions. The evolution of the hydrographic restrictions is the main driving force of dispersion, diversification, and speciation of freshwater fishes. In order to assess the temporal and spatial phylogeography of freshwater fishes, three distinct species of balitorid fishes related to sympatric biogeographical zones in Taiwan were selected to analyze the cytb gene sequences in mitochondrial DNA (mtDNA). Spatial patterns and temporal implications summarized a probale scenario to explain the migration and sequential subdivisions of balitorid fishes. Paleo-climates and geographical changes were the two major influences on the genetic and spatial differences in East Asia. The reconnected passages in the Taiwan Strait led to the sequential fragmentations and secondary contacts within various freshwater species. Because of different reconnected times in northern, central and southern Taiwan, paleogeogrpahical changes caused the complexity of colonization routes and inferred various patterns in genetic differentiation. Northern colonization route transported freshwater fish to Taiwan during different ice ages. The southern colonization seemed to have late contacts since the mid-Pleistocene glaciation. During Last Pleistocene Glaciation, some species crossed southern Central Mountain Range and invaded into the East Rift Valley, in eastern Taiwan. The major contributions of this study can be summarized as follows: (1) It clarifies the higher-level phylogeny between Gastromyzontinae and Balitorinae represent as a monophyly, which is the only two subfamilies in Balitoridae. Directional selection and diversificated selection causes the morphological convergence in Gastromyzontinae. (2) It provides insights on phylogenetic relationship of crossostomoid-group. The rostral folds, position of anus, and uncovered belly were three significant differences between species groups. Three monophylies were revealed by the genetic difference. The Pleistocene geohistory influences on the speciation and genetic divergence. (3) Sea-level lowering of Taiwan Strait reconnected the colonization routes at least three times in northern Taiwan. Some forerunners dispersed into northern Taiwan and become widespread species in the early stage. Secondary contacts occasionally happened in central and southern Taiwan during mid-Pleistocene. Evolutionary histories of freshwater fishes in East Asia serve as good examples in accounting how freshwater species colonies extended, segregated, and diverged from the mainland onto an island.