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Phylogenetic Systematics of the Supragenus Rasbora (Teleostei: Cyprinidae) Open Access

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The fishes of the supragenus Rasbora, with 104 valid species, comprise among the most species-rich and widespread lineages of cyprinids that live throughout a vast expanse from the subcontinent India through Southeast Asia as far south as Sundaland. Despite its remarkable diversity, high abundance, and broad distribution, the systematics of Rasbora is highly problematic primarily due to the conflicting phylogenetic hypotheses among previous studies. A multifaceted systematic study incorporating more taxa and characters of Rasbora, which encompasses the alpha-taxonomic work of Rasbora as well as phylogenetic analyses using both morphology and molecules, was conducted to resolve the current systematic disagreement and taxonomic problems of the group. The alpha-taxonomic study in the present study results in the description of eight new species of Rasbora from northern Sumatra: Rasbora api, R. kluetensis, R. nodulosa, R. truncata, Rasbora n. sp. 1, Rasbora n. sp. 2, Rasbora n. sp. 3, and Rasbora n. sp. 4. In addition, a new set of characters useful to diagnose for two rasborin groups, the Reticulata and Sumatrana groups, were described (i.e., the microstructure of the cephalic tubercles and the body pigmentations). Given the allopatric distribution of three of the aforementioned new species, three areas of endemism in northwestern Sumatra are recognized. Cladistic analysis of Rasbora was performed using a dataset containing 274 morphological characters coded for 97 taxa (70 ingroups, 27 outgroups) under the maximum parsimony algorithm, which resulted in a total of 3,411 most parsimonious trees with 1,111 steps length (CI = 0.42; RI 0.57; RI = 0.88; RC = 0.37). The topology of the consensus tree recovered the monophyly of the supragenus Rasbora with high nodal support and five unique synapomorphies. Twelve major monophyletic lineages corresponding to the previously recognized supraspecific groups of Rasbora were recovered in the topology, each of which with moderate to strong nodal support and with a set of unreversed synapomorphies. Moreover, the monophyly of several featured cyprinid taxa is supported with a series of novel unreversed synapomorphies: (1) the subfamily Danioninae; (2) the clade Danionini+Rasborini; (3) the tribe Chedrini; (4) the tribe Danionini; and (5) the tribe Rasborini. Seven genetic markers, which are four nuclear genes (EPIC 55305, EPIC 35692, RAG1, and Rhodopsin) and three mitochondrial regions (16S rRNA, COI, and cytochrome b) sequenced from 93 taxa (80 ingroups, 13 outgroups) were used in the present molecular analyses. The phylogenetic trees were reconstructed based on several different datasets (i.e., individual markers, concatenated datamatrix with different partitioning scenarios) under three general phylogenetic algorithms (maximum parsimony, maximum likelihood, and Bayesian inference). Overall, the three different phylogenetic approaches result in trees with similar topologies of the backbone, in which two major clades of the tribe Rasborini are recovered consistently with high support values: (1) the Indian lineage (12 species), and (2) the Sundaland-Indochinese lineage (92 species). Similar to results from previous molecular studies, Rasbora is inferred to be paraphyletic because the genus Pectenocypris is embedded in the large, Sundaland-Indochinese lineage. The validity of five rasborin genera is corroborated: Boraras, Brevibora, Kottelatia, Rasbosoma, and Trigonostigma. Two formerly monotypic genera, Kottelatia and Rasbosoma, need to be expanded through species transfer and generic synonymization. The validity of the genus Trigonopoma cannot be confirmed in this study due to the rejection of its monophyly as indicated by molecular data. Four major groups are still without valid taxonomic status: the Daniconius group; the Trifasciata group; the Reticulata group; and the Sumatrana group. Considering the inconsistent placement of R. cephalotaenia, the type species of Rasbora, either in the Einthovenii group or the Argyrotaenia group, the more exclusive definition of Rasbora s. s. is reserved to either of these two groups.

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