Abstract
Miniaturised frogs form a fascinating but poorly understood amphibian ecomorph and have been exceptionally prone to taxonomic underestimation. The subfamily Cophylinae (family Microhylidae), endemic to Madagascar, has a particularly large diversity of miniaturised species which have historically been attributed to the single genus Stumpffia largely based on their small size. Recent phylogenetic work has revealed that several independent lineages of cophyline microhylids evolved towards highly miniaturised body sizes, achieving adult snout–vent lengths under 16 mm. Here, we describe five new species belonging to three clades that independently miniaturised and that are all genetically highly divergent from their relatives: (i) a new genus (Mini gen. nov.) with three new species from southern Madagascar, (ii) one species of Rhombophryne, and (iii) one species of Anodonthyla. Mini mum sp. nov. from Manombo in eastern Madagascar is one of the smallest frogs in the world, reaching an adult body size of 9.7 mm in males and 11.3 mm in females. Mini scule sp. nov. from Sainte Luce in southeastern Madagascar is slightly larger and has maxillary teeth. Mini ature sp. nov. from Andohahela in southeast Madagascar is larger than its congeners but is similar in build. Rhombophryne proportionalis sp. nov. from Tsaratanana in northern Madagascar is unique among Madagascar’s miniaturised frogs in being a proportional dwarf, exhibiting far less advanced signs of paedomorphism than other species of similar size. Anodonthyla eximia sp. nov. from Ranomafana in eastern Madagascar is distinctly smaller than any of its congeners and is secondarily terrestrial, providing evidence that miniaturisation and terrestriality may be evolutionarily linked. The evolution of body size in Madagascar’s microhylids has been more dynamic than previously understood, and future studies will hopefully shed light on the interplay between ecology and evolution of these remarkably diverse frogs.
Highlights
Miniaturisation is a common phenomenon in amphibians [1,2,3,4], and is especially widespread and extreme in frogs [4,5,6]
The miniaturised members of the subfamily Cophylinae, considering the described diversity and the undescribed lineages outlined in the Introduction, are morphologically, ecologically, and bioacoustically highly similar: they are terrestrial, leaf-litter dwelling frogs that predominantly emit their advertisement calls during the day
Eye size is rather small, but relatively larger compared to head length (ED up to 57% of Herpetologists’ League (HL); Table 1) than in non-miniaturised cophylines. They are all inconspicuous in colour dorsally, with only a few larger species of Stumpffia possessing red on the hidden surfaces of their legs and on their venters [14]
Summary
Miniaturisation is a common phenomenon in amphibians [1,2,3,4], and is especially widespread and extreme in frogs [4,5,6]. Microhylid frogs exhibit high degrees of osteological variation, especially in the morphology of elements of the skull, hands, feet, and pectoral girdle [9]. The smallest species among the microhylids do not belong to a single clade but rather occur in various different subfamilies spread across the tropics, including New Guinea [5, 6, 8], Borneo [10, 11], South America [12, 13], and Madagascar [14, 15]. One of the best examples is the subfamily Cophylinae, endemic to Madagascar [15]
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