Estudo cromossômico em espécies do gênero Boana (Hylidae, Anura): diversidade cariotípica e distribuição de DNAs repetitivos

Abstract

The anura order, composed of the popularly known frogs, toads and treefrogs, has been suffering a strong threat to its conservation, with reports of recent extinctions. Hylidae is the most diverse family of the order, composed of three subfamilies: Hylinae, Pelodryadinae and Phyllomedusinae. The Cophomantini tribe (one of the tribes of Hylinae) is a diverse clade of neotropical anurans composed of five genus, among which, Boana, originally taken from the Hyla synonymy and later called Hypsiboas, changes that reflect the intense phylogenetic reorganizations undergone by genus. Knowing the wide diversity of the group, studies that combine molecular markers along with other characters have been important to understand the evolution of the clade looking like this better group them. In addition, cytogenetic studies have been widely used to enrich the scenario and to better solve taxonomic and systematic uncertainties, given the ecological importance that the group presents. Therefore, the objective of this work was to use classical cytogenetic markers and repetitive DNA mapping in three species of the genus Boana, located in three different taxonomic groups, all from the Mata Atlântica paranaense. The studied karyotypes showed differences between them, B. faber and B. prasina presented 2n = 24 chromosomes invariably, and B. albopunctata presented 2n = 22 chromosomes with possible presence of chromosome B. Heterochromatic bands were predominant founds in pericentromeric regions in all species, although additional C bands on telomeric and / or interstitial regions showed to be partially species specific. The nucleoli organizing regions (NORs) were restricted in only one pair of the complement, a pattern well conserved in anurans as a whole. U2 snDNA was located in situ in B. albopunctata (pairs 3 and 7) and in B. prasina (pairs 4 and 10). Nucleotide sequencing of the U2 snDNA genes showed a 92% similarity to the U2 snDNA gene of Xenopus laevis. The Tc1- Mariner transposable element (TE) showed scattered markers on all chromosomes of the three species studied. The karyotype 2n = 24 chromosomes is a characteristic of the genus Boana, which may present some oscillations. This diploid number (2n) would have originated from 2n = 26 chromosomes, from chromosomal fusions, these fusions, which together with other types of rearrangements, like pericentric inversions or even centromeric repositions, may explain the variation in the location and quantity of chromosomal markers. The structure and origin of repetitive sequences may explain the current organization of genomes, with the occurrence of a portion of the genes in multiple copies. In eukaryotes, the TEs are mostly the result of degenerative processes, which accumulate mutations and lose their identity when inactivated. It is worth remembering that the in situ mapping of the repetitive sequences presented here is unheard of for the Hylidae family, being another tool to question the idea of karyotype preserved in anurans, given the variations presented here.