Tadpoles of the Tobago Glass Frog

A metamorph of the Tobago Glass Frog.

The Tobago glass frog, Hyalinobatrachium orientale tobagoense is endemic to the island of Tobago. They reproduce by laying a clutch of gelatinous eggs on the underside of broad leaves overhanging streams, a mode of reproduction which is characteristic of all Hyalinobatrachium. The embryos develop on the leaf until hatching when they drop into the stream below where they develop further, eventually emerging as metamorphs.

Previous authors have reported on embryonic development, hatching, and tadpole growth and morphology in this frog. The tads initially lacking pigmentation, but with age develop pigment over much of the body, darker on the dorsal side, but lacking on the tail fins and ventral body. The tadpoles’ eyes are small and dorsally oriented.  They have very long tails, 64% of total length. In the lab, growth, is very slow. After six weeks, tadpoles had tripled in mass, increased in length by a little under 40%, but were still at Gosner stage 25, with no sign of limb buds. Previous authors have reported very slow growth and development in two glass frog species which took more than  200 days to reach metamorphosis.

Tadpoles hide in sediment and among rocks, gravel, and fallen leaves, and escape with bursts of fast swimming when disturbed. Given their secretive nature, it is not surprising that the behavior of these tadpoles is poorly known.

In a recent paper, Byrne et al. (2018) collected egg clutches of the Tobago Glass Frog and allowed them to hatch into tanks of native stream water.  Observations were made through a series of tests for substrate preference (gravel, rocks or leaves), shelter or open water preference, and surfacing behavior under different depths and turbulence levels. Tests found that tadpoles showed a preference for stream substrates over plastic tank floor, with the highest percentage of tadpoles found in gravel. Tadpoles preferred sheltered areas of the tank and surfaced significantly less when water was turbulent, with depth having no significant effect on surfacing behavior.

Byrne I, Judge C, Downie JR. 2018. The behaviour of recently hatched Tobago glass frog tadpoles. Herpetological Bulletin. 2018 Jun 1(144).