Diversity, phylogeny and biogeography of Systomus (Teleostei, Cyprinidae) in Sri Lanka

Abstract

The South and SouthEast Asian freshwater fish genus Systomus (Cyprinidae) comprises 17 valid species. Six nominal species, including three endemics, have been reported from Sri Lanka, a continental island separated from India by a shallow-shelf sea. The species diversity of Systomus on the island has until now not been assessed; neither has an evaluation been made of their phylogenetic history. Here, based on an analysis of the nuclear recombination activating protein 1 (rag1), and mitochondrial cytochrome c oxidase subunit 1 (cox1) and cytochrome b (cytb) gene markers, and a morphological examination of 143 specimens from 49 locations in Sri Lanka, we reassess the diversity of Systomus on the island and analyse patterns of their evolution and biogeography. Divergence-time estimates, based on a substitution rate calibration, date the basal split between Systomus and its sister group, the Afrotropical small barbs, to 30.0 Ma (95% highest posterior density: 25.4-35.2 Ma). The species of Systomus belong to two distinct clades. The first includes the Sri Lankan endemics S. asoka, S. martenstyni and S. pleurotaenia, which comprise an insular diversification following the immigration of a common ancestor during the Oligocene. The second, which includes the remaining species of Indian, Sri Lankan and SouthEast Asian Systomus, has a crown age dating to the Late Miocene. Morphological and molecular species delimitation analyses failed to validate the two nominal species, S. spilurus and S. timbiri, previously reported from Sri Lanka: both are considered synonyms of S. sarana, as are the nomina S. chryseus, S. chrysopoma, S. laticeps, S. rufus, S. pinnauratus and S. subnasutus. Four genetically and geographically discrete lineages of S. sarana occur in the island, and three in India. Molecular species delimitation analysis suggests these all belong to a single species, S. sarana. The genetically distinct Sri Lankan populations of S. sarana result from Plio-Pleistocene dispersal or vicariance events between India and Sri Lanka-as a result of emergence and inundation of the now submerged isthmus connecting the two landmasses-as well as autochthonous insular diversification.

Molecular phylogeny and phylogeography of the freshwater-fish genus Pethia (Teleostei: Cyprinidae) in Sri Lanka

“…4) recovered P. nigrofasciata as two well-supported, sympatric subclades, one spanning the distribution of the species in Sri Lanka, from the Attanagalu to the Walawe basins, and the other confined to the region between the Kalu and Gin basins, inclusive. Such a pattern has not been observed in the other phylogeographic studies of Sri Lankan cyprinids published so far [5,11,14,15,39]. Given that our genetic dataset is limited, it is difficult to offer an explanation for this observation.…”

“…An alternative scenario would be two colonization events from mainland India, being the common ancestors of P. melanomaculata and P. nigrofasciata, P. bandula, P. cumingii and P. reval, followed by a back-migration to India. This is noteworthy because, despite having been connected by a broad isthmus during episodes of low sea level, post-Miocene biotic exchanges of forest-adapted taxa between India and Sri Lanka have been infrequent [5,10,11]. Though subaerial for most of the Plio-Pleistocene, the Palk Isthmus appears, because it was too arid, to have acted more of a filter than a conduit for the dispersal of forest-adapted taxa [5,8,10].…”

“…Following the recognition of the genus by Pethiyagoda et al [16], several studies confirmed the monophyly of Pethia [e.g., 10,11,18,25,26]. Nevertheless, about half of the 43 species included in the genus since 2012 are yet to be represented in a molecular phylogenetic framework.…”

“…Members of the genus are united by a suite of characters (none of them exclusive) that include small size (standard length up to about 5 cm), a posteriorly serrated last unbranched dorsal-fin ray, having the lateral line (usually) incomplete, and exhibiting between one and three black blotches, bars or spots on the side of the body, usually including one in the humeral-cleithral region and another above the anal fin or on the caudal peduncle [16]. Although the phylogenetic relationships of Pethia to the genera formerly referred to Puntius sensu lato, in which the genus was subsumed prior to Pethiyagoda et al [16], remain only weakly supported, several molecular studies have shown Pethia to be monophyletic [10,11,[23][24][25][26]. Phylogenetic relationships within the genus, however, remain to be elucidated.…”

On the freshwater fish fauna of Krishna River, Sangli District, Maharashtra, India

“…Assuming that the fishing effort for a given type of net was constant, the relative abundance of the fish was grossly categorized following Dahanukar et al (2012), namely abundant (76-100 % of total catch), common (51-75 % of total catch), moderate (26-50 % of total catch), and rare (1-25 % of total catch). Samples were preserved in 10% formalin and identified using the available literature (Menon 1987(Menon , 1992 Jayaram 1991Jayaram , 2006Jayaram , 2010 and relevant recent taxonomic literature related to different groups Keskar et al 2015;Katawate et al 2016;Lavoué et al 2020;Sudasinghe et al 2020). All identified specimens are deposited at the Department of Zoology, Arts, Commerce and Science College, Palus, Sangli District, Maharashtra, with accession numbers from ZID 01-73.…”