Cophylinae, Cope, 1889

Scherz, Mark D., Hutter, Carl R., Rakotoarison, Andolalao, Riemann, Jana C., Rödel, Mark-Oliver, Ndriantsoa, Serge H., Glos, Julian, Roberts, Sam Hyde, Crottini, Angelica, Vences, Miguel & Glaw, Frank, 2019, Morphological and ecological convergence at the lower size limit for vertebrates highlighted by five new miniaturised microhylid frog species from three different Madagascan genera, PLoS ONE 213314, pp. 1-45 : 37-38

Genus-level taxonomy of the Cophylinae

Mini adds a ninth genus to the Cophylinae for a unique clade of miniaturised frogs that falls sister to the large-bodied Plethodontohyla ( Fig 1 ). Although body size is the most obvious character that differentiates these two sister genera, they are also distinguished by a number of osteological features, and can be identified without skeletal analysis by their digital reduction

(present in Mini , absent in Plethodontohyla ) and vomerine teeth (absent in Mini , present in Plethodontohyla ). Despite these differences and consistent recovery of the two genera as being reciprocally monophyletic in genetic analyses, the uncorrected p-distances between these genera in the 3’ fragment of the 16S rRNA mitochondrial gene analysed here are at first glance surprisingly small at 8.3–13.3% (these distances would be distinctly higher if insertions and deletions would be considered in their calculation). Nevertheless, we consider the differences between these clades sufficiently great and robust that we regard them as constituting separate genera. Aside from their morphological and osteological differentiation, a further argument for their classification in distinct genera comes from the strength of support for their sistergroup relationship; while the two clades here seen as genera Plethodontohyla and Mini have been placed sister to each other in most molecular analyses so far, support values for this grouping often were low, and typically lower than the respective support for each of the two clades. The clade stability criterion [ 36] is therefore better served considering both clades as separate genera.

The relationship of Mini to Plethodontohyla is analogous to the relationship of Stumpffia to Rhombophryne : a genus-level sister clade of miniaturised frogs (although Stumpffia also contains several non-miniaturised species), recovered in robust genetic phylogenies as reciprocally monophyletic, and distinguished by several diagnostic characters [ 14, 15, 23]. Peloso et al. [ 19] argued for the lumping of Stumpffia , Rhombophryne , and later also Anilany [ 22] into a single genus, Rhombophryne . In response, we showed that the initial argument for lumping was based on misidentified specimens [ 15], and subsequently incorrectly coded morphology, ignoring various unique diagnostic features of Anilany , and the relationships of particularly unstable taxa (most notably Stumpffia tridactyla) [ 23]. We revised the taxonomy of the genus Stumpffia , describing 26 new species, and providing a more robust phylogeny that resolved the phylogenetic position of Stumpffia tridactyla [ 14]. Despite this progress, the Amphibian Species of the World database (ASW) currently continues to use the lumped taxonomy, in contrast to AmphibiaWeb and other researchers that have adopted our proposed taxonomy (e.g. [ 20, 53]). The newly described Rhombophryne proportionalis , which is the only miniaturised Rhombophryne so far known, is highly distinct from Stumpffia , lacking, for example, the externally obvious digital reduction that is present in all miniaturised species of Stumpffia , and differing in body shape and proportions [ 14]. This demonstrates that even miniaturised Rhombophryne species can be distinguished by external morphology from Stumpffia species, providing still further support for the recognition of Rhombophryne , Stumpffia , and Anilany as separate genera.

Figures

Fig 1. Stylised representation of the latest phylogeny of the microhylid subfamily Cophylinae. Based on the phylogenetic tree of Tu et al. [20] (reconstructed from a concatenated multi-gene DNA sequence data set) with numerous nomenclatural updates. See that paper for support values and phylogenetic context. The sister species of Rhombophryne proportionalis sp. nov. is an undescribed candidate species (R. sp. Ca7) that is not included in this phylogeny; its taxonomy will be treated elsewhere. Taxa highlighted in red are those described herein. Inset photos show a selection of the new species described herein, and representatives of the other small-bodied genera, Stumpffia and Anilany. Inset photos are not to scale. https://doi.org/10.1371/journal.pone.0213314.g001