The choice of external morphological characters and developmental stages for tadpole-based anuran taxonomy: a case study in Rana (Sylvirana) nigrovittata (Blyth, 1855) (Amphibia, Anura, Ranidae)

Abstract

The morphology of tadpoles has long received too little attention in taxonomic and phylogenetic contexts, beyond the use of Orton’s general tadpole types, despite the potential of larval characters for resolving problems in systematics. A possible explanation for this neglect is the ontogenetic variation of external morphology. In order to understand the value of larval characters in taxonomy and systematics, it is necessary to determine the developmental stage at which characters reach their definitive size, form and colour before meaningful comparisons can be made within and between species. Here I use the tadpole of Rana (Sylvirana) nigrovittata as a model organism to assess ontogenetic character variation. Morphometric measurements were taken, and external oral and internal buccal characters were assessed separately for each developmental stage from 26 to 38. Coefficients of variation were calculated for each morphometric character at each stage of development to test the character’s efficiency in reflecting the morphology of the tadpole. Most morphometric characters taken from the body described the shape of the animal well and varied little among individuals, whereas those taken from the tail were less reliable and those of the oral disk were quite variable due to contraction during fixation. A developmental 'climax' for most characters was reached by specimens between stages 32-40, indicating that they are best suited for morphological intra- and interspecific comparisons.

Intraspecific and interspecific trait variability in tadpole meta‐communities from the Brazilian Atlantic rainforest

“…This variability was not simply driven by ontogeny, because all the stages presented similar variability in the different traits (Supporting information Figure ). This is in agreement with the literature on tadpoles, which suggests that morphological characters are highly variable within species because anuran larvae are highly adaptive to their environment (Grosjean, ). Grosjean () also found tail traits to be more variable than body traits, as we did.…”

“…This is in agreement with the literature on tadpoles, which suggests that morphological characters are highly variable within species because anuran larvae are highly adaptive to their environment (Grosjean, ). Grosjean () also found tail traits to be more variable than body traits, as we did. Here, the tail compression index (TCI) presented high levels (69%) of intraspecific variability in both datasets (Atlantic forest and Amazonia).…”

“…This variability was not simply driven by ontogeny, because all the stages presented similar variability in the different traits (Supporting information Figure S2). This is in agreement with the literature on tadpoles, which suggests that morphological characters are highly variable within species because anuran larvae are highly adaptive to their environment (Grosjean, 2005 Baldo et al, 2014), and even single species (Zhao et al, 2017). Interestingly, our results are overall in agreement with decompositions of trait variation performed in plants, as most studies have found between 25% and 33% of trait variation to occur within species (Albert et al, 2010;Messier et al, 2010;Siefert et al, 2015).…”

Effect of hydric stress on locomotion and morphology of tadpoles from temporary ponds

“…For each species, all euthanized tadpoles were positioned between two glass slides with a known scale inside a Petri dish containing alcohol (70%) and were photographed (Canon SX50 HS) in lateral and dorsal views. Following Grosjean (), seven morphological measurements (BH, maximum body height; BW, maximum body width; SU, distance from tip of snout‐insertion of upper tail fin; VT, distance from opening of the vent until the tip of tail; HT, maximum tail height; TMH; tail muscles height; TL, total length) were taken using the ImageJ Software version 1.49.…”

Morphology, natural history and molecular identification of tadpoles of three endemic frog species ofNyctibatrachusBoulenger, 1882 (Anura: Nyctibatrachidae) from Central Western Ghats, India

“…Morphological characters were selected based on Altig and McDiarmid (1999), Grosjean (2005) and Schmidt et al (2009). Morphological terminology follows that of Altig and McDiarmid (1999).…”