Spiny tree frog (Nyctixalus spinosus)

GenusNyctixalus (1)
SizeMale snout-vent length: 3.0 - 3.7 cm (2)
Female snout-vent length: 3.6 - 3.9 cm (2)

Classified as Vulnerable (VU) on the IUCN Red List (1).

In stark contrast to the greens and browns of many other frogs, the spiny tree frog (Nyctixalus spinosus) is a reddish-tan, covered with small, white-tipped spines. It is from these spines that the species derives both its common and scientific names. There is a large white spot on either side of the head next to the ear drum, and the snout is pointed (2).

Two pairs of spiny crests run above the spiny tree frog’s ear drum and down the centre of the head. The hind limbs are longer than the whole of the rest of the body, and are lightly banded with white. The toes are heavily webbed for propulsion in water, and each toe ends in a large, sticky pad, which enables the spiny tree frog to climb smooth, vertical surfaces such as leaves (2) (3).

Like many other amphibians, the spiny tree frog passes through a tadpole stage. In contrast to the adult frog, tadpoles lack legs, are elongated and have a tail (4). The spiny tree frog tadpole is more flattened in comparison to related species (2), and its body has a purplish tinge (4). The tadpole of this species does not need to feed (2) (5) and so has reduced mouthparts (2). It develops the colour and proportions of the mature frog through the process of metamorphosis (4).

The spiny tree frog is only found in the Philippines (6), where it occurs on four of the major islands: Mindanao, Leyte, Bohol and Basilan (1). Its range appears to be patchy, with isolated populations, but this is likely to be due to a lack of data rather than being a reflection of the true distribution (1).

A tropical forest specialist, the spiny tree frog is found in lowland and upland forest at elevations of 500 to 1,100 metres (2). It also occurs in disturbed areas bordering forest (1).

Almost all adult amphibians are carnivorous, feeding on insects, spiders and other small invertebrates (7). Frogs of the genus Nyctixalus emerge after dark to hunt small insects and spend most of their lives in vegetation off the ground (5).

The spiny tree frog breeds in small pools of water and seems to prefer holes in tree trunks, roughly 1.5 metres above the ground (5). During mating, the male grasps the female around the waist using rough pads on the inside of his thumbs, while the female clings onto the side of the hollow above the water. Each female is likely to distribute her eggs between four or five different sites, producing 30 to 40 large, dark eggs at a time (2).

Newly laid spiny tree frog eggs stick to the inside of the hollow tree trunk (2) (6) about 30 centimetres above the water, and the tadpoles drop into the water after hatching (8). As several different females may use the same pool to lay their eggs, tadpoles of different ages can be found living together (2). The tadpoles of the spiny tree frog develop without feeding, getting all the nutrients and energy they require from a generous store of yolk (5).

The spiny tree frog is known only from a few islands in the Philippines and is principally threatened by habitat destruction. Human activity is clearing and converting land for housing and farming, leaving isolated pockets of forest (1).

Amphibians in the Philippines are also threatened by the devastating fungal disease chytridiomycosis, which is causing high amphibian death rates worldwide (9).

There are no specific conservation measures in place for the spiny tree frog, but some populations occur within national parks where land and water resources are managed and damaged habitat is being restored. Populations of spiny tree frogs on Mindanao and Bohol would benefit from improved protection of forest habitat (1).

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More information on the Philippines and its conservation:

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  1. IUCN Red List (July, 2011)
  2. Brown, W.C. and Alcala, A.C. (1994) Philippine frogs of the family Rhacophoridae. Proceedings of the California Academy of Sciences, 48(9): 185-220.
  3. Li, J., Rao, D., Murphy, R.W. and Zhang, Y. (2011) The systematic status of Rhacophorid frogs. Asian Herpetology Research, 2(1): 1-11.
  4. McDiarmid, R.W. and Altig, R. (Eds.) (1997) Tadpoles: The Biology of Anuran Larvae. The University of Chicago Press, Chicago.
  5. Wells, K.D. (2007) The Ecology and Behaviour of Amphibians. The University of Chicago Press, Chicago.
  6. Inger, R.F. (1999) Distribution of amphibians in southern Asia and adjacent islands. In: Duellman, W.E. (Ed.) Patterns of Distribution of Amphibians: A Global Perspective. The Johns Hopkins University Press, Baltimore and London.
  7. Vitt, L.J. and Caldwell, J.P. (2009) Third Edition Herpetology. An Introductory Biology of Amphibians and Reptiles. Academic Press, London.
  8. Grosjean, S., Delorme, M., Dubois, A. and Ohler, A. (2008) Evolution of reproduction in the Rhacophoridae (Amphibia, Anura). Journal of Zoological Systematics and Evolutionary Research, 46(2): 169-176.
  9. Rowley, J., Brown, R., Bain, R., Kusrini, M., Inger, R., Stuart, B., Wogan, G., Thy, N., Chan-ard, T., Trung, C.T., Diesmos, A., Iskandar, D.T., Lau, M., Ming, L.T., Makchai, S., Truong, N.Q. and Phimmachak, S. (2010) Impending conservation crisis for Southeast Asian amphibians. Biological Letters, 6(4): 336-338.