The curious case of Charles Darwin’s frog, Rana charlesdarwini Das, 1998: Phylogenetic position and generic placement, with taxonomic insights on other minervaryan frogs (Dicroglossidae: Minervarya) in the Andaman and Nicobar Archipelago

Abstract

Since the description of Charles Darwin’s frog asRana charlesdarwiniin 1998, its generic placement has been a taxonomic enigma. Subsequent studies first transferred this species to the dicroglossid genusLimnonectes, and then considered it as a ceratobatrachid of the genusIngerana, which has since been moved to the family Dicroglossidae. However, recent works have doubted this generic placement and also suggested the possibility of its sister relationship with the genusLiurana, within Ceratobatrachidae. Nonetheless, there have been no detailed investigations to ascertain the generic placement of this taxon by confirming its phylogenetic position or using integrative taxonomic approaches. Here, we provide the first molecular assessment ofIngerana charlesdarwinibased on mitochondrial and nuclear DNA and reveal that it is nested in the dicroglossid genusMinervarya. A member of theMinervarya andamanensisspecies group,Minervarya charlesdarwinicomb. nov.is sister taxon toM. andamanensisand shows relatively shallow genetic distances (2.8–3.6%) in the 16S gene. Both species are widely distributed, occur sympatrically, and exhibit high morphological variations, leading to long-standing confusions with other dicroglossid frogs reported from the region. Our combined morphological and molecular studies on dicroglossid frogs sampled across the known ranges of these species suggest that reports ofLimnonectes doriae(Boulenger, 1887) andL. hascheanus(Stoliczka, 1870) from the Andamans are misidentifications of the former two, pointing to the absence of genusLimnonectesfrom the Andaman Islands. Our study also reveals the novel record ofMinervarya agricolafrom the Andamans, a species that appears to have been confused withFejervarya limnocharisandMinervarya keralensisin the literature and misidentified museum specimens, and is found to be widely distributed across these islands. We further find another congener from the Nicobar group of Islands,M. nicobariensis, to be closely related toM. charlesdarwini. Similar to the case of Andaman dicroglossids, our work emphasises on the need for further studies to ascertain the taxonomic identities and generic placement ofMinervaryaandLimnonectesspecies reported from the Nicobars.