CALCARIFER - Andrew Gray: Short notes on neotropical treefrogs of the genus Phyllodytes

Short notes on neotropical treefrogs of the genus Phyllodytes

by Andrew R. Gray

The Department of Zoology, The Manchester Museum, The University of Manchester.

The Golden Tree Frog, Phyllodytes auratus, has a compressed head and a bodyshape which enables it to live deep within giant bromeliads.

Introduction

The genus Phyllodytes (Wagler) consists of seven species which occur in South America. These small arboreal frogs are known to live and breed exclusively in the leaf axils of epiphytic bromeliad plants, although very little is known of their natural history. In this account, it is interesting to note that Phyllodytes luteolus and Phyllodytes melanoystax are two of four species which occur in Brazil and Phyllodytes auratus is considered endemic to Trinidad where it occurs only on the highest peaks.

Description

The Golden Tree Frog, Phyllodytes auratus (Boulenger), is a small to medium sized species which reaches approximately 35 mm in length from snout to vent, although males are somewhat smaller. The dorsum of this frog is chocolate brown and has two iridescent golden-yellow stripes which run from snout to vent. The limbs are a transparent cream colour and the stunning eye colouration consists of a black pupil surrounded by finely reticulated golden irides. All members of this family have a very compressed head and body shape which enables the adult frogs to tuck themselves deep into the narrow leaf axils in which they live. Another unusual feature, which further separates these frogs from most others, is their mouthparts: they have serrated teeth and sharp "fangs" on their jaws.

Habitat

Field work in Trinidad during the summer of 1997 aimed to investigate amphibian diversity in the north of the island and this also involved work on the summit of its second highest mountain, El Tucuche, where the Golden Tree Frog, Phyllodytes auratus was found. This rare species is associated with one particular species of bromeliad, Glomeropitcairnia erectiflora, a large epiphitic bromeliad which grows in Trinidad’s northern mountain range and also at suitable sites in Venezuela and on the Island of Magarita (Beard,1946). Although a number of the bromeliads sought were sighted as the summit was approached, most of these were inaccessible due to the fact that they were growing so high in the tree canopy. However, upon reaching the summit, and travelling still further along the uppermost pinnacle of the main ridge, it was possible to sample several large bromeliad specimens which were growing much closer to the ground.

At its peak, El Tucuche reaches a total height of 936 metres above sea level. At this altitude, the area receives a large amount of rainfall (probably over 5000mm per year) and the elfin woodland in which the giant bromeliads grow is completely shrouded in mist or covered by clouds during much of the day and night. This constant supply of moisture creates extremely high levels of humidity and the unique micro-habitat used by this specialised frog species. Surveying in July, the air temperature averaged about 24 degrees and the water content of the bromeliads, which had a fairly acid Ph of 5.5, had a temperature of 22 degrees centigrade. During the year temperatures vary considerably and readings taken at a similar height on Mount Aripo, the highest mountain in Trinidad (940 m), indicate that temperatures in February may drop at night to as low as 14.4 degrees centigrade (Beard, 1946).

Reproduction

The males of these species have a subgular vocal sac and although it was once thought that P.auratus lacked an audible call, it has apparently been heard calling at dusk. However, at the time of writing, this has not been recorded or described. The call of Phyllodytes melanoystax has been described as being a trill-like call which is emitted intermittently (Caramaschi, 1992). These frogs are known to be highly terratorial and although the "fangs" or "tusks" described above are present, particularly on the bottom jaw, in both sexes of the Brazilian Phyllodytes luteolus, they are much bigger in the males. The males behave very aggressively to one another and use their "fangs" for biting during combat (Weygolt, 1981). These species are known to lay very small egg clutches or as in P. Melonomystax single eggs are deposited onto the bromeliad leaves (Caramaschi et al,1992).

Tadpoles

Feeding primarily on algae or infusora which grows on the surface of the leaves, the almost transparent larvae attach themselves to the surface of the leaves by their mouth-parts and this enables them to suspend themselves, motionless and vertically within the vase. Their thin, almost fin-less tails are incapable of sustaining a swimming motion for long and, detatching themselves by throwing back their heads, the tadpoles beat their tails only long enough for them to take sufficient air from the water’s surface before returning to the leaf for support. It was of particular interest to find that of all the bromeliads sampled, only the larger plants contained tadpoles or a single adult specimen. Tadpoles were mainly found in plants where the adult was present and this suggests that perhaps a certain degree of parental care may take place.

Acknowledgement

I am grateful to Simeon "Patsy" Williams, and thank him for sharing his knowledge of El Tucuche and experience in locating specimens.

Bibliography

Beard, J.S., 1946. The natural vegetation of Trinidad. Oxford Forest Mem. 20. Clarendon Press, Oxford.
Caramaschi, U., Da Silva, H.R., and De Britto-Pereira, M.C., 1992. A new species of Phyllodytes (Anura, Hylidae) from Southern Bahia, Brazil. Copeia 1:187-191.
Murphy J.C., 1997. Amphibians and Reptiles of Trinidad and Tobago. Krieger publishing Co, Malibar, Florida.
Weygoldt, P., 1981. Beobachtungen Zur Fortpflanzungsbiologie von Phyllodytes luteolus (Wied 1824) im Terrarium. Salamandra 17:1 11.