Microhyla borneensis (junior synonym Microhyla nepenthicola), also known as the Mantang narrow-mouthed frog, is a species of microhylid frog found in the Matang Range in Sarawak, Borneo. It was once the smallest known frog from the Old World (the current record holder is Paedophryne amauensis from New Guinea). Adult males of this species have a snout-vent length (SVL) of 10.6–12.8 mm. Tadpoles measure just 3 mm. It is one of 30 species in the genus Microhyla, 5 others of which live in Borneo. It is endemic to Borneo. Its natural habitats are subtropical or tropical moist lowland forests and intermittent freshwater marshes. The International Union for Conservation of Nature does not consider it threatened.
Frogs of the species that was eventually described as Microhyla nepenthicola had been known for at least 100 years prior to its description in 2010. However, scientists had always assumed that the frogs were juveniles of another species. Researchers Indraneil Das and Alexander Haas recognized that they were actually adults when they heard the frogs calling in Kubah National Park, since only adult frogs make calls. Adult males call from the pitcher plants at dusk.
Microhyla borneensis is a very small species with a snout to vent length of about 18 millimetres (0.71 in)for females and around two thirds of this for males. It has a broadly triangular body that is flattened dorso-ventrally. The snout is obtusely pointed, the eyes are small and have round pupils and there are no visible tympani. The skin on the dorsal surface may be smooth or bear tubercles and that of the ventral surface is always smooth. The limbs are short. The hands are unwebbed and the outer digits are spatulate. The digits of the feet are partially webbed. The dorsal surface of this frog is reddish-brown, the throat is mottled brown and the ventral surface is pale.
Distribution and habitat
Microhyla borneensis is native to Borneo and is probably present over much of the island wherever the habitat is suitable. It lives among leaf litter on the forest floor in lowland areas of primary rainforest, in secondary rainforest and along the forest fringe. Its altitudinal range is from 70 to 550 metres (230 to 1,800 ft) above sea level.
M. nepenthicola is found near Mount Serapi in Kubah National Park, Sarawak, Borneo. It spends much of its lifecycle in the traps of the pitcher plant Nepenthes ampullaria, after which it is named. It is therefore considered a nepenthebiont. This is not particularly unusual; in fact, it shares this environment with a species of crab spider, Misumenops nepenthicola, which is also commonly found in Nepenthes pitchers, and is similarly named for this reason. Microhyla nepenthicola has less webbing on its feet than most frogs, which may be beneficial when trying to climb the sides of the pitcher plants, which can be slippery.
Microhyla borneensis breeds in the water-filled pitchers of Nepenthes ampullaria, a pitcher plant that is a feature of the floor of the Borneo rainforest. Multiple clutches may be laid in the same pitcher which may contain tadpoles of different ages. Metamorphosis takes place about a fortnight after the eggs are laid.
This frog is seldom seen, perhaps because of its small size and inconspicuous appearance. Its numbers are thought to be in slow decline but the IUCN rates it as being of "Least Concern" as it considers that the rate of decline is insufficient to justify listing it in a more threatened category. No particular threats to this species have been identified.
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- Das, I. & A. Haas. (2010). "New species of Microhyla from Sarawak: Old World’s smallest frogs crawl out of miniature pitcher plants on Borneo (Amphibia: Anura: Microhylidae)". Zootaxa 2571: 37–52.
- "Tiny, New, Pea-Sized Frog Is Old World's Smallest". Science Daily. 2010-08-25.
- Gururaja, K.V. 2010. PDF Current Science 99(8): 1000.
- "World's smallest frog is size of a pea". New York Post. 2006-08-26. Retrieved 2010-08-26.
- Muessig, Ben. "Scientists Discover Pea-Sized Frog in Borneo". aol. Retrieved 2010-08-26.
- "Microhyla nepenthicola sp. nov.". Conservation International. Retrieved 2010-08-27.
- Kellie Whittaker (2011-05-26). "Microhyla borneensis ". AmphibiaWeb. Retrieved 2013-12-10.