Estudo citogenetico e da ultra-estrutura dos espermatozoides de especies da subfamilia Hylodinae (Leptodactylidae) e da familia Dendrobatidae (Amphibia, Anura)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The Dendrobatidae is a large neotropical anuran family for which the evolutionary relationships are still unclear. Affinities with frogs belonging to the Ranoidea neobatrachian lineage, specifically with ranid frogs related to the genus Petropedetes, have been proposed. Alternatively, relationships with hylodine leptodactylids (Bufonoidea) have also been considered. The aim of this work was to examine the relationships between the Hylodinae and Dendrobatidae based on cytogenetic and ultrastructural studies. The karyotypes of foUf dendrobatid species of the genus Epipedobates (E. jlavopictus, E. trivittatus, E. femoralis and E. hahneli), as well as seven Hylodinae species (Hylodes phyllodes, H asper, Crossodactylus sp. n., C. cf. caramaschi, Megaelosia massarti, M boticariana and M lutzae), were analyzed using conventional Giemsa staining, C-banding and Ag-NOR techniques. An ultrastructural analysis of spermatozoa was done for the four species of Epipedobates (listed above) and for Hylodes phyllodes, Crossodactylus sp. n. and Megaelosia massarti. The cytogenetic results showed a conserved chromosome number (2n = 24) in Epipedobates, although there was considerable variation in chromosome morphology, in the amount and distribution of heterochromatin and in the location of the NORs. Within the Hylodinae, the diploid number was the same (2n = 26) in Hylodes and Crossodactylus but varied among the three species of Megaelosia (2n = 28, 30 and 32). Crossodactylus had the most conserved karyotype in terms of chromosome morphology and C-banding pattern, whereas there were differences between the two species of Hylodes. The NOR location did not vary within each genus. On the other hand, all of these parameters varied among the three species of Megaelosia. Ultrastructural analysis showed that Epipedobates femoralis was peculiar in that it possessed biflagellate spermatozoa. The presence of mitochondria within the undulating membrane of the other species also differentiated them from E. femoralis. Despite the great similarity among the spermatozoa of the three genera of Hylodinae, Crossodactylus sp. n. was most similar to other leptodactylids and to most of the remaining bufonoids. In contrast, M massarti and H phyllodes shared a similar shape in their axial and juxtaxonemal fibers. These results elucidated some inter- and intrageneric aspects within each group (Hylodinae and Dendrobatidae) but did not provide much information on the relationships between the two groups. Even with the use of banding techniques, the karyotypical analysis provided no unambiguous homeologies indicative of the possible relationships between the Hylodinae and Dendrobatidae. On the other hand, the karyotypic peculiarities of E. femoralis suggested a unique position within the genus. Within the Hylodinae, the extensive karyotypical variability in Megaelosia, contrasted with the conserved karyotypes of Hylodes and Crossodactylus, and agreed with previously established relationships within the subfamily based on morphological analysis. The peculiarity of the spermatozoa of E. femoralis supported the divergent position of this species within the genus, as already indicated by others. The possible apomorphies shared by the remaining three species of Epipedobates (absence of a juxtaxonemal fiber and the presence of a short, extremely expanded undulating membrane), supported the retention of E. trivittatus in this genus, in agreement with molecular data and contrary to the suggestion of its placement in the genus Phobobates. Base mainly on the structure of the flagellar apparatus and also on similarities in the organization of the acrosomal complex we conc1ude that the spermatozoa of dendrobatids are of the "bufonoid type", and differ strongly from the pattern in ranoid species. Within the Hylodinae, Megaelosia shared flagellar characteristics with Hylodes. These findings together with morphological and biochemical data, reinforce the retention of Megaelosia in the subfamily Hylodinae

ASSUNTO(S)

anuro citogenetica

ACESSO AO ARTIGO

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