Island colonization by a ‘rheophilic’ fish: the phylogeography ofGarra ceylonensis(Teleostei: Cyprinidae) in Sri Lanka

Abstract

Despite exhibiting multiple morphological adaptations to living in swiftly flowing water (rheophily), Garra ceylonensis is one of the most widely distributed freshwater fish in Sri Lanka. It is thus an ideal organism to reconstruct the evolutionary history of a widespread, yet morphologically specialized, freshwater fish in a tropical-island setting. We analysed the phylogenetic and phylogeographic relationships of G. ceylonensis based on two mitochondrial and one nuclear genes. G. ceylonensis is shown to be monophyletic, with a sister-group relationship to the Indian species Garra mullya. Our results suggest a single colonization of Sri Lanka by ancestral Garra, in the late Pliocene. This suggests that the Palk Isthmus, which was exposed for most of the Pleistocene, had a hydroclimate unsuited to the dispersal of fishes such as Garra. G. ceylonensis exhibits strong phylogeographic structure: six subclades are distributed as genetically distinct populations in clusters of contiguous river basins, albeit with two exceptions. Our data reveal one or more Pleistocene extirpation events, evidently driven by aridification, with relict populations subsequently re-colonizing the island. The phylogeographic structure of G. ceylonensis suggests inter-basin dispersal largely through headwater capture, likely facilitated by free-swimming post-larvae. The Peninsular-Indian species G. mullya comprises two genetically distinct parapatric clades, which may represent distinct species.

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].…”

“…4 Naturhistorisches Museum Bern, Bernastrasse, 15, 3005 Bern, Switzerland. 5 Butterfly Conservation Society of Sri Lanka, 762/A, Yatihena, Malwana 11670, Sri Lanka. 6 Guangxi Key Laboratory for Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning 530004, Guangxi, People's Republic of China.…”

“…Isthmus) connecting Sri Lanka and India [4,5]. Despite Sri Lanka's Gondwanan origins [6], its vertebrate fauna lacks a clear Gondwanan signature except in the case of a single lineage of amphibians [7].…”

“…nigrofasciata from the Attanagalu basin in g-n. g DZ5353F, 40.3 mm SL (2). h DZ4452C, 38.8 mm SL (5). i DZ4452A, 36.9 mm SL (5).…”