Abstract
Species boundaries and patterns of gene flow in Dwarf toads, Duttaphrynus scaber and D. atukoralei, were assessed using mitochondrial DNA markers. Samples from four populations in Sri Lanka (Mihintale, Ampara, Yala, Galle) were analyzed for three mitochondrial gene fragments (16S rRNA, COI and Cyt b) along with four Genbank sequences of 16S rRNA from Indian samples (Thiruvananthapuram, Maharashtra, Mudigere). Phylogenetic trees and haplotype networks were generated, and morphology was assessed. Analyses suggest a single species (Duttaphrynus scaber) with three major clades: a widespread clade shared between India and Northern Sri Lanka, an Eastern and Southeastern Sri Lankan clade (previously referred to as D. atukoralei, the validity of which, however, our analysis disputes), and a distinct Southern wet-zone clade from Galle (referred previously to as D. atukoralei). Duttaphrynus atukoralei (topotypes from Yala, Sri Lanka) is genetically too close to D. scaber (Indian and northern Sri Lankan clade) to be distinguished as a species; these two clades have a genetic distance of 0.95 – 1.55% for the 16S rRNA fragment. The haplotype networks for the 16S rRNA gene suggest incomplete lineage sorting between the Ampara and Yala populations; COI and Cyt b show complete sorting for all populations analyzed, suggesting strong population structure. All analyses suggest substantially restricted gene flow to the southern wet-zone population (Galle). This population also assumes a basal phylogenetic position, suggesting that D. scaber first evolved in southern Sri Lanka’s wet zone and dispersed across the lowland areas of the island and to India. Here, we provisionally recognize this population (Galle) as an evolutionarily significant unit of D. scaber; future analyses using multiple criteria may indicate this to be a new Dwarf toad species. External morphology is largely uninformative as the Yala, Ampara and Galle populations cannot be distinguished from each other; the morphological distinction between Yala, Ampara, Galle versus Mihintale is restricted to only the shape of the parotid glands – slightly oval versus rounded – a minor difference. Both genetic and morphological evidence so far suggest that there is only a single Dwarf toad species in Sri Lanka, which is also shared with India, namely Duttaphrynus scaber; however, with strong population structure, including an evolutionarily significant unit (Southern wet-zone population).
Highlights
Sri Lanka is a global amphibian hotspot with many unique and threatened taxa, especially of the genus Pseudophilautus, which have undergone a large endemic radiation resulting in some 100 species (Meegaskumbura et al, 2002). Bossuyt et al (2004), in an analysis of several vertebrate and invertebrate groups representing a diversity of lifehistory strategies showed that the wet-adapted taxa are characterized by clade level endemism
Sequence data for 467 bp of 16S rRNA were obtained for a total of 38 species of Adenominae, including D. scaber and D. atukoralei. jModelTest results shows that GTR+I+G is the best fit model for the data set
Our molecular phylogeny suggests a single species of Dwarf toad (D. scaber) with three closely related clades: a widespread clade shared between India and Northern dry zone of Sri Lanka, a clade restricted to the Eastern and Southeastern dry zone of Sri Lankan, and a clade known from the southern wet zone of Sri Lanka (Galle population), which is the most distinct form from all currently recognized taxa
Summary
Sri Lanka is a global amphibian hotspot with many unique and threatened taxa, especially of the genus Pseudophilautus (shrub frogs), which have undergone a large endemic radiation resulting in some 100 species (Meegaskumbura et al, 2002). Bossuyt et al (2004), in an analysis of several vertebrate (shrub frogs, caecilians, earth snakes and freshwater fish) and invertebrate (freshwater crabs and shrimps) groups representing a diversity of lifehistory strategies showed that the wet-adapted taxa are characterized by clade level endemism. For wet-adapted frogs, this notion was reinforced with the recognition of a Sri Lankan endemic genus, Taruga, (Meegaskumbura et al, 2010), delineation of reciprocal endemicity of Hylarana species of India and Sri Lanka (Biju et al, 2014), endemicity of Nannophrys (which exhibits several unique features (Senevirathne & Meegaskumbura, 2015), and the endemicity of the genus Adenomus (Meegaskumbura et al, 2015; Van Bocxlaer et al, 2009) It is not known if this pattern is representative of the other anuran taxa, especially for some of the dry-adapted species, which are putatively shared with India. The Dwarf Toads, according to published work (Van Bocxlaer et al, 2009; Meegaskumbura et al, 2015) form a well-supported clade
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