Giant dwarfs: discovery of a radiation of large‐bodied ‘stump‐toed frogs’ from karstic cave environments of northern Madagascar

Abstract

The endemic Malagasy microhylid genus Stumpffia usually comprises small-bodied terrestrial frogs with snout–vent lengths of 16 mm or less, with some miniaturized species as small as 10 mm in their adult stage, and only two described species reaching over 20 mm in snout–vent length. Previous studies have provided evidence for parallel miniaturization in Malagasy microhylids, with several species and candidate species previously assigned to Stumpffia probably belonging to other, still undescribed genera. Here, conversely, we report on the discovery of four new species of microhylids from northern Madagascar, of which two are larger than all previously known Stumpffia, but all clearly belong to this genus based on molecular phylogenetic relationships. All four species have fully developed digits, are closely related and occur in karstic limestone environments, with most specimens collected in caves, a habitat formerly unknown for cophylines. This newly discovered radiation of large-bodied and supposedly cave-dwelling Stumpffia contains one species from Nosy Hara, one from Ankarana, one from Ampombofofo and one from Montagne des Français, respectively. In the latter species, specimens can reach up to 28 mm snout–vent length. These new species are genetically differentiated from each other by 3.8–8.6% pairwise divergence in the 16S rRNA gene and furthermore by differences in coloration, extension of terminal finger discs, relative eye diameter and relative head width. We discuss the status of Stumpffia madagascariensisMocquard, 1895 and consider it a valid species referable to one of the two small-bodied species identified from Montagne d'Ambre National Park. Furthermore, our results support that cophylines are highly microendemic and we provide support for a miniaturized ancestor of the large-bodied species described here, thus demonstrating that miniaturization is evolutionarily reversible.