By Dr. Tan Heok Hui
Raffles Museum of Biodiversity Research, Department of Biological Sciences,
National University of Singapore, Kent Ridge, Singapore 117600.
Barbourula kalimantanensis was first described by Djoko T. Iskandar (1978 ) based on a single male specimen collected by two ichthyologists (Soetikno Wirjoatmodjo and Tyson R. Roberts, whose collections contributed to Roberts’ 1989 monograph on the freshwater fishes of western Borneo) from the Pinoh River at Nanga Sayan, Kapuas basin of West Kalimantan in 1976. The next specimen of B. kalimantanensis, a female, was again collected by an ichthyologist – Maurice Kottelat, from near to type location in 1993 (Iskandar, 1995).
The habitat was the main river at low water level, exposing the rock strewn bottom. The holotype of B. kalimantanensis was collected in a seine net set across a series of large rocks in the main river when an ichthyocide was used to survey that river section (T. R. Roberts, pers. comm.). The second specimen was collected using a push net placed downstream of a large submerged rock (M. Kottelat, pers. comm.).
The type habitat is today a scene of human exploitation, the Melawi River is dotted regularly along its bank and shallow stretches with illegal make-shift gold panning structures spewing black smoke from generators and silt from the filtered river substrate. The waters are muddied not only from the illegal gold panning but also from logging activities located further upstream. All these activities, had no doubt forced the bornean lungless frog further upstream into cleaner headwater streams or locally extirpated in the main river.
I had been invited to participate in this field expedition to assist in the fish surveys. Due to earlier work commitments, I could only join the main party one week later. When I arrived in the interior of Kalimantan, it was after more than 2 days’ travel from Pontianak (main town in West Kalimantan) across the border into Central Kalimantan. It was disheartening to travel across rolling fields of grassland and denuded landscape, evidence of earlier logging activities; and polluted rivers. The main party had been in active survey, but yet to collect any Barbourula. Coincidentally, with the arrival of an ichthyologist (myself), we surveyed a new site at night and hit pay dirt.
With whoops of delight, Djoko was overjoyed, punching the air and dancing around despite the uneven ground due to the rock-filled river bank. We passed the prize catch carefully around and examined in wonder at the small flat black frog at the bottom of the plastic bag. Subsequently, we managed to catch another juvenile Barbourula that same night. We had definitely uncovered the hiding place of this most elusive aquatic frog, more than 50 km distant from the type location and more than 31 years after its first capture into the scientific world. We celebrated later that night without proper aplomb but a box of raisins.
Barbourula kalimantanensis belongs to one of the most primitive groups of frogs (Inger & Stuebing, 1997). It is a fully aquatic frog, adapted to the fast flowing waters of hill streams and rivers. It is well adapted to the aquatic medium, with fully webbed fingers on both fore and hind limbs. It has no external ear drum nor a protrusible tongue. It has an extremely dorso-ventrally flattened body profile with skin folds along the lateral of the body, and a pair of almost stereoscopic eyes; probably further adaptations to its riparian habitat.
In life, it is mainly black with occasional specks of brown and yellow. Its dorsum is darker than its ventrum. Although, it is a fully aquatic frog, it can leap and creep along the river bank.
Its habitus is very similar to that of other fully aquatic frogs (e.g. Xenopus), sometimes remaining stationary in the water with head pointing upwards, and foraging/digging movements with its fore limbs. On the hand, Barbourula kalimantanensis has a soft and slippery texture, leaving mucous trails. In its habitat, juveniles were obtained from the shallow waters at the river bank. I almost caught an adult in the middle of the torrent stream but it was way too quick in water and literally bounced off the push net. The fishes obtained from this habitat were typical of torrent hill streams, with many balitorid loaches (e.g. Borneo Suckers – Gastromyzon).
Barbourula kalimantanensis is a creature with strange distribution pattern. Its nearest cousin, B. busuangensis is located in Palawan and Busuang Islands, in the vast Philippine archipelago. The rest of its cousins are in Southern China and Central Europe, the likes of Bombina, more commonly known as fire-belly toads. With such an unusual disjunct distribution pattern, there must have been curious origins. This disjunct distribution of aquatic vertebrates is evident in the Sunda shelf, in which elements are found to skip certain Sunda Islands, despite relatively thorough sampling for the last few decades. The disjunct distribution shows its presence in Indochina, Borneo and/or northern Malay Peninsula; but absence in Malaysia, Sumatra and Java.
It was only later with the capture of more specimens, that with careful dissection, the absence of lungs was noted. This was later confirmed in the laboratory with proper equipment (D. Bickford, pers. comm.).
I thank Peter Ng and Navjot Sodhi, for allowing my participation in the expedition; David Bickford and Djoko Iskandar, for field logistics and wonderful field companionship; LIPI, for scientific research permit. Funding for the fieldwork came from R-154-000-270-112, from the National University of Singapore.
Inger, R. F. & R. B. Stuebing, 1997. A field guide to the frogs of Borneo. Natural History Publications, Kota Kinabalu, Sabah, i-x, 205 pp.
Iskandar, D. T., 1978. A new species of Barbourula: First record of a discoglossid anuran in Borneo. Copeia, 1978 (4): 564-566.
Iskandar, D. T., 1995. Note on the second specimen of Barbourula kalimantanensis (Amphibia: Anura: Discoglossidae). Raffles Bulletin of Zoology, 43 (2): 309-311.
Kottelat, M., A. J. Whitten, S. N. Kartikasari & S. Wirjoatmodjo, 1993. Freshwater Fishes of Western Indonesia and Sulawesi. Hong Kong, Periplus Editions. 221 pp. + 84 pl.
Roberts, T. R., 1989. The freshwater fishes of Western Borneo (Kalimantan Barat, Indonesia). Memoirs of the California Academy of Sciences, San Francisco, 14: 1-210.
All photos and text by Tan Heok Hui.