The tadpole of Chiasmocleis altomontana (Anura: Microhylidae)

Describing the morphology of anuran larvae contributes towards filling gaps in taxonomy and natural history. This is especially relevant for explosive breeders, in which adults remain at the reproduction site for only a short period, while tadpoles may be more conspicuous. Here, we describe the larval external morphology and internal oral anatomy of the microhylid frog Chiasmocleis altomontana from near its type locality in southeastern Brazil.

We took 13 linear morphometric measurements of 11 tadpoles between stages 35 and 39 from four ponds. To compare the larval external morphology of the genus, we also built a morphospace based on the log-shape ratio of linear measurements provided by the original descriptions. To impute missing data, we used a trait imputation method that considered the phylogenetic relationships and a Brownian Motion model of multivariate trait evolution. Finally, we provide novel quantitative and qualitative data on the tadpole of Chiasmocleis anatipes based on museum specimens.

The tadpole of C. altomontana is the largest among the Atlantic Forest species and the second largest of the genus, after C. anatipes. Like all species of the genus, the tadpole of C. altomontana is exotrophic, suspension feeder, Orton type II, and occurs in lentic temporary environments. Overall, C. altomontana shows subtle differences in dorsal fin height, dorsal fin insertion, tail tip, and snout in lateral view from its congeners. The spiracle of C. anatipes is ventral, single, covering the vent tube, as in all other microhylids. The species has a larger tail and interorbital distance than its congeners. All species of the Atlantic Forest clade are clustered together in the morphospace, suggesting little disparity, while those of the Amazonian clade are more spread, suggesting higher morphological disparity. Chiasmocleis altomontana was close to its sister species, Chiasmocleis mantiqueira, while C. anatipes differs greatly in terms of shape from the remaining species of the genus. Our results can improve our understanding of the morphological diversity of microhylid tadpoles and reduce the diversity shortfall in anuran larval forms.