Evolução cariotípica em espécies da família hirundinidae (aves: passeriformes)

Abstract

Passeriformes is the largest order among the class Aves, comprising a huge diversity with more than 5000 species. Within this order is present the Hirundinidae family, of which the swallows belong, cosmopolitan birds that have substantially homogenous morphological characteristics. Despite the richness of species of Hirudinidae family, little is known about the genome organization of their members. Hence, the aim of this study was to analyze the chromosomal complement of species - Progne tapera, Progne chalybea and Pygochelidon cyanoleuca. The analyses were performed using Giemsa staining, C-banding, Ag-NOR, Fluorescent in situ hybridization (FISH) of eleven microsatellite sequences and two sets of probes (Gallus gallus e Zenaida auriculata). The three species analyzed showed 76 chromosomes with very similar morphologies, presenting differences only in the 5th, 6th and 7th chromosome pairs of P. cyanoleuca. Two chromosomal pairs bearing nucleolar organizer regions (NORs) were identified, showing an apomorphic condition for these species. The pattern of C-banding was the same found in most birds, areas of heterochromatin distributed mainly in the centromeric regions and W chromosome. Microsatellite sequences organization was similar in both species of Progne, while P. cyanoleuca presented a distinct pattern. Except for (CG) 15, all other 10 sequences produced hybridization signals. Repetitive DNA sequences were found in centromeric, pericentromeric, telomeric regions of the macrochromosomes and two interstitial blocks on the W chromosome. Most of the microchromosomes presented telomeric signals. The Z chromosome presented one hybridization signal in P. tapera and none in the other species. In contrast, W chromosome displayed the accumulation of distinct microsatellite sequences. The swallow W chromosome is larger when compared to most Passeriformes. Such high amounts of repetitive sequences may explain the observed chromosome size enlargement. In sum, these data indicate the significant role that microsatellite sequences may play in sex chromosome differentiation. Concerning comparative chromosome painting, it was observed the same hybridization pattern for the two Progne species, which was very similar to the G. gallus karyotype, except for the centric fission in the first pair, as found in other Passeriformes. Although P. cyanoleuca had demonstrated the same fission in the first pair of the ancestral syntenic (GGA1), it also contains a fusion with a microchromosome in the seventh pair, evidencing an extra chromosomal rearrangement for this species. From the analysis on the chromosomal organization of P. tapera, P. chalybea and P. cyanoleuca, it was possible to observe some of the chromosomal changes that occurred during the karyotype evolution of these species, which showed the proximity between the species P. tapera and P. chalybea.