Thursday 13 November 2014

Breeding behaviour in a Fanged Frog from Vietnam.

Fanged Frogs of the genus Limnonectes are found across southern China and Japan, as well as the Philippines, Southeast Asia and much of Indonesia. They are unusual in that the males are considerably larger than the females (the reverse of the situation found in most Frogs), with greatly enlarged heads and powerful jaws. The name of the group comes from the fang-like odontoid processes on the lower jaws of both sexes. Mating behaviour seems to vary considerably within the group, with some species giving birth to live young, while others lay eggs, sometimes in nests, and sometimes provide parental care to nestlings. The males often lack vocal sacs and in many species have been seen to fight over territory.

In a paper published in the journal Zootaxa on 4 November 2014, JodiRowley of the Australian Museum Research Institute, Doung Thi Thuy Li and Huy Doc Huang of the Faculty of Biology at the University of Science-Ho Chi Minh City and Ronald Altig of the Department of Biological Sciences at Mississippi StateUniversity, describe the mating behaviour of the Fanged Frog Limnonectes dabanus for the first time.

Males of Limnonectes dabanus show the most extreme enlargement of the head of any species of Fanged Frog, with a head that comprises almost half the body length. The species is found on the Langbian Plateau in Lam Dong Province, Vietnam, and around tributaries of the Mekong and Krong No rivers in Cambodia and southern Vietnam. The species lives in forested areas, and its biology is not well understood.

Adult male Limnonectes dabanus. Rowley et al. (2014). 

Rowley et al. observed the Frogs at the Nui Ong Nature Reserve in Binh Thuan Province, Vietnam, where they were able to observe the mating, and collect specimens of the eggs and tadpoles. Males of Limnonectes dabanus were observed calling from beside a rivulet beneath a rock overhang, from a drainage line in mixed forest, and at the base of a Pandanus plant in a large but shallow temporary pond. Despite lacking vocal sacs they were able to produce a short monotonal chirp, which sounded to human listeners like a drip falling into water; Rowley et al. suggest that if other species of Fanged Frogs make similar noises then this might have been overlooked by herpetologists. One male was observed with two females in close attendance while none of the calling males had another male nearby, suggesting that the males secure and defend territories, mating with any female that comes to its territory (though combat between males was not observed).

Adult female Limnonectes dabanus. Rowley et al. (2014).

Eggs within the rock overhang territory were found on the underside of the overhang (about 40 cm above the water surface), on the adjacent rockface and in the water beneath the overhang (which was mostly only a few millimetres deep). This distribution is difficult to understand, as it appears the female Frogs were relatively unconcerned as to where their eggs were deposited. Rowley et al. suggest that the female Frogs may be exhibiting behaviour similar to that seen in Frogs of the genus Mixophyes, who lay eggs they kick them onto a nearby moist surface, with some eggs subsequently falling to the floor.

Adult male, M, and female, F, in seep area beneath an overhanging boulder with eggs on the ceiling (yellow up arrow) and floor (yellow down arrow). Rowley et al. (2014).

Tadpoles were collected from a muddy, leaf-litter filled pool on the forest floor. The largest was 21.2 mm in length, with coarsely placed teeth and an upper jaw sheath with fine serrations, and a v-shaped lower sheath. The tail fin was clear with speckles.

Limnonectes dabanus (A) eggs grouped for photography, (B) tadpole in lateral view 21.2 mm, tail tip damaged). (C) Oral apparatus of same tadpole (stained with crystal violet to reveal translucent structures) and (D) dorsal view of same tadpole. Rowley et al. (2014).

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