It fits on a fingertip: Noblella pygmaea is a midget frog, the smallest ever found in the Andes and among the smallest amphibians in the world. Only its croaking was to be heard from the leaves on the mossier ground of the 'elfin forests' in the highlands of Manu National Park, before German and Peruvian herpetologists discovered the tiny little thing in south-eastern Peru.
The popular name of the new species is fitting: Noble's Pygmy Frog has an average length of 11.4 millimetres. It was introduced in a paper recently published in the journal Copeia by Edgar Lehr, a German herpetologist at the Senckenberg Natural History Collection Dresden, and the Swiss-Peruvian ecologist Alessandro Catenazzi from the University of California at Berkeley, USA.
The pygmy that fits on a fingertip, was discovered during field work in the Wayqecha Research Station. Not only its small size left it undiscovered for so long. Its predominantly brown colour camougflages Noblella perfectly. But Noble's Pygmy Frog could be spotted with the assistance of the members of the native communities adjacent to the Manu National Park.
Manu National Park is well known as 'hotspot' in the lowland rainforests, a place of exuberant diversity; however the biosphere reserve also preserves vast areas of montane cloud forests, where the sempiternal mists envelop and often conceal plants and animals. In the countless ecological niches many of them were able to evolve undisturbed and are highly adapted to the cold and permanently humidity at a daily average temperature of 11 Celsius. Genetic studies show that the diversity of amphibians in general and especially in this region is highly underestimated. That is why Edgar Lehr and Alessandro Catenazzi think that Noblella pygmaea is only one of many undiscovered amphibians in the Andes mountain area. The scientists expect to find other new species during the next few years.
Currently the midget frog is one of the smallest vertebrates ever found above 3000 metres, where most species tend to be larger than congeneric or similar species in lowland areas. Noblella pygmaea inhabits the cloud forest, the montane scrub and the high-elevation grasslands at a height from 3025 to 3190 metres above sea level. Beside its size the remarkably long forefinger is a notable distinguishing feature that was not found at other pygmy frogs in the mountains of Peru. The females lay only two eggs of approximately four millimetre in diameter. In contrast to most amphibian species these eggs are laid in moist, terrestrial microhabitats, such as in moss or leave litter, and are protected from insect predators by the mother frog. It is noteworthy also that embryos do not change into aquatic tadpoles, but immediately after the hatching lead a fully terrestrial life.
Whilst the scientists cannot give a reason for Noblella's minute size, it is apparently advantageous. Maybe it is perfectly adopted to its special niche. The fact, that the species is not forced to leave its habitat - not even for egg deposition - might protect it from natural enemies. Despite living in the Manu Biosphere Reserve the survival of the midget frog and of other amphibians is uncertain. Several adverse influences such as anthropogenic habitat changes and the effects of global warming, which among other things facilitates the dispersal of the highly virulent pathogenic fungus Batrachochytrium dendrobatidis threaten amphibians of the Andean region. Fortunately the fungus, which has become epidemic, has not been noticed on Noblella so far. Possibly because of its terrestrial life Noblella is less exposed to the fungus than stream-dwelling frogs.
Batrachochytrium dendrobatidis is suspected to be the cause of the extinction of many frog species in Ecuador and northern Peru and is currently decimating populations of high-elevation frogs in southern Peru. Up to now no effective means are known for stopping the expansion of fungal infections in the region. Researchers hope that the large topographic heterogeneity of the Andes cordilleras will provide refugia where the fungus is unable to cause massive population declines in amphibian species, thus ensuring the survival of the dwarf in the Andean 'elfin forests.'