Aplocheilus dayi phenotype (a) male and (b) female, Aplocheilus werneri phenotype (c) male and (d) female, Aplocheilus parvus (e) male and (f) female. in Sudasinghe, Ranasinghe, Wijesooriya, Rüber et Meegaskumbura, 2024. DOI: 10.1111/jfb.15792 facebook.com/HiranyaSud Researchgate.net/publication/380732853 Abstract Three nominal species of the killifish genus Aplocheilus are reported from the lowlands of Sri Lanka. Two of these, Aplocheilus dayi and Aplocheilus werneri, are considered endemic to the island, whereas Aplocheilus parvus is reported from both Sri Lanka and Peninsular India. Here, based on a collection from 28 locations in Sri Lanka, also including a dataset of Asian Aplocheilus downloaded from GenBank, we present a phylogeny constructed from the mitochondrial cytochrome b (cytb), mitochondrial cytochrome c oxidase subunit 1 (cox1), and nuclear recombination activating protein 1 (rag1), and investigate the interrelationships of the species of Aplocheilus in Sri Lanka. The endemic Sri Lankan aplocheilid clade comprising A. dayi and A. werneri is recovered as the sister group to the clade comprising A. parvus from Sri Lanka and Aplocheilus blockii from Peninsular India. The reciprocal monophyly of A. dayi and A. werneri is not supported in our molecular phylogeny. A. dayi and A. werneri display strong sexual dimorphism, but species-level differences are subtle, explained mostly by pigmentation patterns. Their phenotypes exhibit a parapatric distribution and may represent locally adapted forms of a single species. Alternatively, the present study does not rule out the possibility that A. dayi and A. werneri may represent an incipient species pair or that they have undergone introgression or hybridization in their contact zones. We provide evidence that the Nilwala-Gin region of southwestern Sri Lanka may have acted as a drought refugium for these fishes. Keywords: Aplocheilus, Cyprinodontiformes, phylogeography, sexual dichromatism Diversity of Sri Lankan aplocheilids. Aplocheilus dayi phenotype (a) male, Kandumulla, Attanagalu basin; and (b) female, Gilimale, Kalu basin. Aplocheilus werneri phenotype (c) male, Ampanagala, Nilwala basin; and (d) female, Bambarawana, Bentara basin. Aplocheilus parvus (e) male, Kandumulla, Attanagalu basin; and (f) female, Mannar, Malwathu basin. (a) Molecular phylogenetic relationships of Aplocheilus killifishes based on maximum likelihood inference of the (3168 bp) concatenated mitochondrial + nuclear dataset for 347 individuals. Node support above and below represents ultrafast bootstrapping for 1000 iterations and Bayesian posterior probabilities. Node support below 70 is not labeled. Newly generated sequences of Sri Lankan species of Aplocheilus are denoted by color, their identity inferred from external morphology. Scale bar represents number of changes per site. Numbers in parentheses represent the sampling localities listed in Table 1. LK, Sri Lanka; IN, India. The alternating light and dark‐gray bars indicate the results of the mPTP molecular species delimitation analysis. (b) Live color pattern of male aplocheilid killifishes. (a) Geographical origin of Sri Lankan samples of the Dayi‐Werneri group used in the molecular analysis. Numbers on the map represent the sampling localities listed in Table 1. Median‐joining haplotype networks for the Dayi‐Werneri group group, based on the analysis of (b) a 621 bp fragment of the cox1 gene, (c) a 1081 bp fragment of the cytb gene, and (d) a 1466 bp fragment of the rag1 gene. The number of mutational steps &gt;1 is shown. Legend colors correspond to river basins. The 50 m isobath (dark blue) is that derived by GEBCO Compilation Group (2020). Major river basins in Sri Lanka are labeled in black. The geographic distribution of the Aplocheilus dayi and Aplocheilus werneri phenotypes are represented by orange and blue overlays on the map, respectively. Hiranya Sudasinghe, Tharindu Ranasinghe, Kumudu Wijesooriya, Lukas Rüber and Madhava Meegaskumbura. 2024. Phylogenetic and Phylogeographic insights into Sri Lankan Killifishes (Teleostei: Aplocheilidae). Journal of Fish Biology. DOI: 10.1111/jfb.15792 facebook.com/Tharindu2010ac/posts/8468383033188002 facebook.com/KumuduWijesooriya90/posts/3806986412912229 facebook.com/HiranyaSud/posts/470590205478609 Researchgate.net/publication/380732853_Phylogenetic_phylogeographic_SriLankan_Aplocheilidae