Dinâmica evolutiva dos cromossomos sexuais em Coleoptera e marcadores epigenéticos associados

Abstract

Alticini tribe is a big taxon beetles and it has a variety of chromosomal sex determination systems as NeoXY, X0, Xyp, and multiple systems. Particulares systems such as aquiasmatic, asynaptic sex chromosomes and the giant chromosomes are also observed in this group. In this study, five species of Alticini (flea beetles) from Central Amazonia were chromosomally analyzed from meiotic and mitotic cells. In addition, other markers were used (heterochromatin pattern, FISH with rDNA 18S and 5S probes and telomeric sequences - TTAGG) to understand the changes in the karyotype of these species. The functional behavior of the sex chromosomes of different systems during meiosis was analyzed by the patterns of acetylation and methylation in histone and DNA methylation variants. The results evidenced the meiotic formulae 10II+X+y (Omophoita abbreviata), 10II+X+y±3B (Omophoita aequinoctialis), 7II+NeoX1X2y (Omophoita clerica), 7II+Xyp (Diphaulaca diringshofeni), 10II+5X+y (Phenrica diringshofeni), and 10II+X+y (Walterianella sp). Analysis in karyotype of O. aequinoctialis showed variation between individuals in relation to chromosome morphology and number of B chromosomes. This variation observed was interpopulational and interspecific for the genus Omophoita, considered chromosomally conserved. In addition to the questions about the chromosome evolution of the group, the presence of hybridized telomeric sequences on the collochores was first evidenced, raising questions about the functional role of these sequences during chromosome segregation. High amount of heterochromatin in some species may be closely associated with the evolution of these chromosomes. Abundant presence of methylation of the DNA observed, in addition to the difference between the sex chromosomes X and Y, shows dynamicity in this modification, being discussed about the distribution of heterochromatin and the functional role of chromatin in these species. Modified histone pattern indicates a differentiated epigenetic pattern for the sex chromosomes in relation to the autosomes during meiosis I, especially for acetylation.Thus, the results of this work extend the studies on sex chromosomes in Alticini, with descriptions of new diploid number and chromosome systems of sex determination for this taxon.