RESUMEN
Four Neotropical tiger beetle species, three from the genus Megacephala and one from the genus Oxycheila, currently assigned to the tribe Megacephalini were examined cytogenetically. All three Megacephala species showed simple sex chromosome systems of the X0/XX type but different numbers of autosomal pairs (15 in M. cruciata, 14 in M. sobrina and 12 in M. rutilans), while Oxycheila tristis was inferred to have a multiple sex chromosome system with four X chromosomes (2n = 24 + X1X2X3X4Y/X1X1X2X2X3X3X4X4). Fluorescence in situ hybridization (FISH) using a PCR-amplified 18S rDNA fragment as a probe revealed the presence of rDNA clusters located exclusively on the autosomes in all the Megacephala species (five clusters in M. cruciata, eight in M. sobrina and three in M. rutilans), indicating variability in the number of clusters and the presence of structural polymorphisms. The same methodology showed that O. tristis had six rDNA clusters, apparently also located on the autosomes. Although our data also show cytogenetic variability within the genus Megacephala, our findings support the most accepted hypothesis for chromosome evolution in the family Cicindelidae. The description of multiple sex chromosomes in O. tristis along with phylogenetic analyses and larval morphological characters may be assumed as an additional evidence for the exclusion of the genus Oxycheila and related taxa from the tribe Megacephalini.
Asunto(s)
Animales , Escarabajos/genética , Bandeo Cromosómico , ADN Ribosómico , Hibridación Fluorescente in Situ , Cariotipificación , Cromosomas SexualesRESUMEN
In this work, the first cytogenetic data on Neotropical Collyrinae is provided, by way of their karyotypes, C-banding and ribosomal genes (rDNA) localization using fluorescence in situ hybridization (FISH). The two species analysed, Ctenostoma (Procephalus) ornatum ornatum (male) and Ctenostoma (Euctenostoma) rugosum (female) showed, respectively, a diploid number of 17 and 18 chromosomes. C. ornatum ornatum has a multiple sex chromosome system (n = 7 + X1X2Y), and mitotic and meiotic metaphase cells showed rDNA gene labelling in the smallest autosomal pair. In this species, no C-bands were obtained, while C. rugosum seems to exhibit centromeric and/or interstitial C-bands in almost all chromosomes. The observation of a multiple sex chromosome system in Ctenostomini ensured the appearance of this characteristic in the hypothetical ancestral of Collyrinae and Cicindelini. The subfamily Collyrinae is not uniform in what concerns diploid chromosome number and rDNA gene localization, because C. ornatum ornatum possesses a lower chromosome number and autosomal rDNA genes when compared with the other Collyrinae species studied (Neocollyris spp.). Independent events leading to the reduction in chromosome number might have taken place during the split of the Collyrinae into the tribes Ctenostomini and Collyrini.
Asunto(s)
Escarabajos/genética , ADN Ribosómico , Animales , Colorantes Azulados , Bandeo Cromosómico , Femenino , Hibridación Fluorescente in Situ , Masculino , Meiosis , MitosisRESUMEN
Three tiger beetle species from the Cicindelini tribe were examined cytogenetically and found to have the following karyotypes: Cicindela argentata, 2n = 18 + X1X2Y/X1X1X2X 2; Cicindela aurulenta, 2n=18 + X1X2X3Y/X1X1X 2X2X3X3 and Cicindela suturalis, 2n = 18 + X1X2X3X4Y/X1X 1X2X2X3X3X4X 4. Fluorescence in situ hybridization (FISH) using a PCR-amplified 18S rDNA fragment as a probe showed the presence of ribosomal clusters in two autosomes in C. argentata, two autosomes and two heterosomes in C. aurulenta and in two heterosomes in C. suturalis (male configuration), revealing two new patterns of rDNA localization. Such results are representative of the cytogenetic variability observed in the species rich genus Cicindela (sensu lato) mainly as regards the localization of rDNA genes and the number and morphology of the heterosomes, in spite of the stability of autosome numbers. Changes in the localization and number of rDNA clusters were independent of changes in the number of sex chromosomes, indicating that several processes might have contributed to the great karyotypic diversity found within this speciose Coleopteran group.