Abstract
The plasticity of the anurans' development is probably related to their great ecological and geographic diversity. Therefore, the understanding of environmental occupation by tadpoles is related to their morphological peculiarities. We evaluated the morphologic development of the larval phases 23, 25, 30, 37, 39 and 42 of Rhinella icterica with the aim of establishing the ratio of growth, the increase in corporal mass in relation to growth and the isometry of the corporal variables for each evaluated stage. We submitted the corporal variables to the Multivariate Allometry and the relation between these variables was evaluated using the Principal Components Analysis. We verified the isometric growth and correlation between the different variables, evaluated the growth according to the body mass and established the proportionality ratio between the corporal regions. Each corporal region evaluated presented a fixed proportionality ratio, regardless of the stage, and the size of this portion was found when its proportionality index was multiplied by the tadpole's total length. This study demonstrates that the larval phase of R. icterica presents an isometric growth with proportional development of the corporal parts regardless of the evaluated stage.
Highlights
The study of anurans, especially in the larval stage, involves knowledge that ranges from the understanding of the environment where they develop, mostly as temporary as their phase, to how they can develop in water courses occupying lentic and lotic environments or even the leaf litter.Using larval characters in taxonomic studies of anurans helps in the phylogenetic knowledge (Cruz, 1990; Duellman and Trueb, 1994; Wild, 1995) making it easier to understand these characters and their morphology in the adult phase (McDiarmid and Altig, 1999)
Each sample corresponded to 50 individuals and the morphometric corresponded to the head length (H.L.), body length (B.L.), tail length, (T.L.), total length (Tt.L.), body height (B.H.), tail height (T.H.) and body mass (M)
The corporal variables were submitted to Multivariate Allometry where the relation between the head length, the body length, the tail length and the total length were evaluated by the Principal Components Analysis (PCA)
Summary
The study of anurans, especially in the larval stage, involves knowledge that ranges from the understanding of the environment where they develop, mostly as temporary as their phase, to how they can develop in water courses occupying lentic and lotic environments or even the leaf litter. Attempting to understand tadpoles’ morphological traits has been studied in-depth: Gosner (1960) studied the development stages; Wilbur and Collins (1973) analysed the ecological aspects associated to tadpoles’ metamorphosis; Wassersug and Seibert (1975) investigated the functional studies associated to abiotic aspects; Wassersug and Hoff (1985) studied the hydrodynamics of tadpoles and McDiarmid and Altig (1999) growth rate models in anuran tadpoles’ adaptation These studies defined some tendencies concerning the understanding between the environment and the biological factors that determine the population structure, they are not sufficient to deplete the studies related to morphology of the various species which present a high plasticity level pressurised by ecological factors. We evaluated the morphological development of six larval stages of Rhinella icterica Spix 1824 with the objective of establishing (1) a probable growth rate, (2) the increase in corporal mass in relation to this growth and (3) the isometry of vector growth of corporal variables between the observed larval stages
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