Description of a new music frog (Anura, Ranidae, Nidirana) critically endangered in Taiwan

Nidirana okinavana (Boettger, 1895) is a small-sized ranid species belonging to the East Asian genus Nidirana Dubois, 1992. Previous studies have indicated that this species was exclusively distributed on Ishigaki and Iriomote islands in the southern Ryukyus, as well as two extremely small wetland habitats in central Taiwan. Such a restricted distribution makes it one of the most endangered frog species in both Taiwan and Japan. By using molecular, morphological, and acoustic analyses, our study reveals significant divergence between the Taiwanese and Japanese clades, supporting the recognition of the Taiwanese clade as a distinct species, described herein as Nidirana shyhhuangi sp. nov. Compared to Nidirana okinavana sensu stricto from the southern Ryukyus, the Nidirana shyhhuangi sp. nov. is characterized by a significantly smaller and non-overlapping body size, relatively longer forelimbs and hindlimbs, smaller internostril and interorbital distances, with a higher number of cross bands on thigh and shank. Acoustic analyses reveal that the Nidirana shyhhuangi sp. nov. produces calls with a rapid tempo and higher pulse number, with a higher dominant frequency compared to the Japanese clade. Due to the extremely limited distribution of this species to two small sites on Taiwan, and continuing decline in quality of its habitat, we propose that it should be classified as Critically Endangered (CR) under the IUCN criteria. Immediate and comprehensive in situ and ex situ conservation actions are necessary to ensure the sustainable viability of the population.