Abstract
This study focuses on two subjects by using the mtDNA sequences: (i) molecular systematics of the freshwater prawn genus Macrobrachium Bate, 1868 (Crustacea: Decapoda: Palaemonidae) with emphasis on East Asian species; (ii) phylogeography and the genetic structure of the land-locked freshwater prawn Macrobrachium asperulum on the continental island of Taiwan. Based on mitochondrial DNA fragment of the large subunit (16S) rRNA gene, the monophyletic phylogeny of the genus Macrobrachium, including land-locked and euryhaline species, was supported. There was, however, poor support for the internal structure. Results suggested that the evolution of this group was marked by rapid radiation. The hypotheses that the prawns originated from marine ancestors and have subsequently migrated towards freshwaters in more than one wave of migration, and the abbreviated larval development of land-locked species represents adaptive convergence are supported. It appears that most of the commonly used morphological characters used in the taxonomy of genus evolved independently during the invasion of inland waters. Based on the 16S and fragment of the cytochrome oxidase subunit I (COI) gene, several species groups, including species from different geographic regions and endemic groups could be recognized from various continents (regions). The presence of five cryptic species is indicated and the identity of four supposedly undescribed species are confirmed. Localized speciation events in East Asia can be correlated with morphological similarities, notably members of the M. asperulum species group. Morphological characters tend to be conservative within species-groups but quite variable between geographic distant populations, making species identifications difficult. The present molecular results, combined with morphological datasets, can be used to help reorganize the various species groups in taxonomy. M. asperulum is a land-locked macroinvertebrate species of freshwater prawn and is abundant in fresh waters and has a pan-island distribution in Taiwan. In the phylogeography and the genetic structure study of M. asperulum in Taiwan. Phylogenetic reconstructions revealed four phylogenetic lineages, with significant genetic differentiation, distributed in three geographical regions; analysis of molecular variance (AMOVA) and minimal-spanning network revealed significant genetic structure across all hierarchical levels, indicating that a major proportion of the genetic divergence is geographically subdivided with a strong population structure. Phylogeographical analyses and an estimation of genetic divergence suggest that such spatial divisions could be correlated with two different colonization routes from the Asian mainland, during the glaciation with low sea level, followed by past fragmentation due to the formation of geographical barriers, such as the Central Mountain Range and Miaoli Plateau in Taiwan, which resulted in rare contemporary gene flow. The high diversity of the genetic structure of eastern populations suggests multiple artificial introductions mainly from rivers of west-central Taiwan. The impacts of the introduced populations on the freshwater ecology in eastern Taiwan require further study.