 |
Family : MICROHYLIDAE
Species : Microhyla borneensis (Microhyla nepenthicola)
Size (snout to vent) : Female 1.9 cm, Male 1.3 cm
The Bornean Chorus Frog,
or Bornean Narrow-mouthed Frog, is one of a handful of species of the genus
Microhyla which inhabits parts of the island of Borneo. Likes its
cousin the Pothole Chorus Frog
Microhyla petrigena it is endemic to the island i.e. it is not known to
occur on other islands or on the mainland of Southeast Asia.
This tiny frog reaches a maximum length of 19 mm, and is thus considered the
smallest frog in Southeast Asia. It occurs in moist, humid lowlands and
appears largely restricted to undisturbed primary forest, but can also
thrive in forest edge settings.
It has long been known to breed in temporary rain pools and wallows made by
the
Bearded Pig Sus barbatus.
In 2010, however, unusual breeding behaviour of this species was described
(Das & Haas, 2010): tadpoles were found thriving inside water-filled
pitchers of the Flask-shaped Pitcher Plant Nepenthes ampullaria.
These tadpoles were assigned to a newly described species, namely
Microhyla nepenthicola, however other researchers treat the latter as
being one and the same as the Bornean Chorus Frog (Microhyla borneensis).
Regardless of taxonomic placement, to find tadpoles living inside pitcher
plants (and successfully metamorphosing into young frogs) is remarkable, but
not unique. For example, in Singapore, tadpoles of another member of the
Microhylid family, namely Kalophrynus limbooliati, have been found
inside pitchers of the same species of pitcher plant (Lim & Ng, 1991, as
Kalophrynus pleurostigma).
In the field, adult frogs are most easily distinguished from other members of the genus
Microhyla by the colour and patterning on the back which comprises a
dark brown (or purplish ?) patch with broad bands extending onto the flank: this
is edged with a pale line.
The tadpoles reach 11 mm in length: a metamorph, with well developed hind
legs, is illustrated in Figures 2 and 3. The tadpoles lack specialised
mouthparts, but gain their nutrition wholly from their store of egg yolk.
(Reference can be made to Das & Haas (2010) for a full description of the
tadpoles).
Within Borneo, this small frog is known from Sarawak, Sabah and northeastern
Kalimantan (the Indonesian province in Borneo).
Fig 1 : Adult frog found at Kubah National Park, Sarawak. Photo thanks to Law Ing Sind.
Figs 2 and 3 : Metamorph, with well developed hind legs, found inside a
terrestrial pitcher of Nepenthes ampullaria. Photos thanks to Law Ing Sind.
Fig 4 : A cluster of pitchers of Nepenthes ampullaria, of various sizes.
Typically these pitchers are found on the forest floor amongst leaf
litter and may measure up to 10 cm tall.
References : H19
Das, I., & Haas, A. (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(1), 37-52.
Lim, K.K.P. & Ng, P.K.L. (1991) Nepenthiphilous larvae and breeding
habits of the sticky frog, Kalophrynus pleurostigma Tschudi
(Amphibia: Microhylidae). Raffles Bulletin of Zoology, 39,
209–214.
|
