Redescrição da morfologia externa e fatores que afetam a forma dos girinos de Limnomedusa macroglossa Duméril & Bibron, 1841 no Pampa, RS

Abstract

Limnomedusa (Alsodidae) is a monospecific genus distributed by southern Brazil, Uruguay and parts of Argentina and Paraguay. L. macroglossa is a frog associated with stony streams in forest and grassy areas, has tadpoles that occur in different microhabitats in the riverbed of the streamlets and had external morphology briefly described in the eighties. Many information on external morphology as well as individual variation due to intrinsic and extrinsic factors remain unexplored. Thus, this work has as objectives: (1) redescribing the external morphology of the tadpole of Limnomedusa macroglossa; (2) to analyze the variation in the shape of the individuals (in dorsal and lateral view); (3) to verify if the size of the individuals (allometry) and the depth of the streams interfere in the form. Tadpoles were collected in 13 streamlets distributed in the largest protection area at the Brazilian Pampa biome the (área de Proteção Ambiental do Ibirapuitã) and surroundings, located at the frontier between Rio Grande do Sul and Uruguayan territory. The redescription was based on 20 tadpoles with developing stages ranging from 31 to 37, in which were analyzed 57 and 19 qualitative and quantitative characters, respectively. Morphometric analyzes were performed using photographs of 150 tadpoles with develop stages from 30-37, in dorsal and lateral view. Based on photographies 17 and 14 anatomical landmarks were digitized for lateral and dorsal view, respectively. The morphological characterization presented in the present study differed from that previously reported, mainly in relation to the following aspects: coloration, body shape, nostrils, anal tube, tail, shape and position of nostrils and snout. Unreported characters were added regarding to the spiracle, anal tube, fins and oral disc. Although morphological variation is a result of evolutionary forces and is used to reconstruct phylogenetic relationships, tadpoles of L. macroglossa did not show a marked similarity to tadpoles of the other two genera of the Alsodidae family (Eupsophus and Alsodes), which seens related to unsolved phylogenetic relationships for this group. Among the aspects discussed, we suggested the reclassification of the reproductive mode of L. macroglossa, in order to better reflect the association of tadpoles with lotic ecosystems and the respective morphological adaptations related to facultative rheophilic habits. Allometry was a factor that affected the tadpole shape in lateral view, influencing mainly the body shape, as well as position of eyes and nostrils, structures that are known to undergo changes throughout the larval development toward the metamorphosis. The environmental depth gradient of the streamlets was also responsible for a little part of the variation found in tadpole shape of L. macroglossa. Thus, decrease in streamlet depth resulted in decrease in general height of body, fins and the tail muscles in lateral view, as well as increase of body width in dorsal view. The morphological changes diagnosed suggest the occurrence of adaptations capable of minimizing drag and better enable tadpoles to move in high energy environments (i.e. with intense water flow).