Insights on repetitive DNA behavior in two species of Ctenus Walckenaer, 1805 and Guasuctenus Polotow and Brescovit, 2019 (Araneae, Ctenidae): Evolutionary profile of H3 histone, 18S rRNA genes and heterochromatin distribution

Ctenidae represents one of the most representative spider families in the tropical forests of Brazil. Its largest genus, Ctenus, has approximately 220 species out of the more than 520 Ctenidae species described, and several authors consider it polyphyletic. Chromosomal data are only available for four species of Ctenus, representing a large gap in the cytogenetic knowledge about the group. This study provided cytogenetic data on two Ctenus species and one Guasuctenus (previously described as Ctenus). All showed 2n♂ = 28 (26+X(1)X(2)0). Guasuctenus longipes presented two chromosome pairs containing 18S rDNA genes and C. medius, however C. ornatus showed only one chromosome pair with the 18S rDNA gene. Hybridization data using histone H3 probe indicated specific profiles: histone H3 genes were found in one chromosome pair in G. longipes, in three pairs in C. medius, and in four pairs in C. ornatus. Furthermore, supernumerary chromosomes were identified in C. ornatus presenting a meiotic behavior similar to that of sex chromosomes; and a trivalent was found in C. medius, formed by the association of one sex chromosome and an autosomal bivalent, indicating the importance of these events for the diversification of sex chromosomes in spiders. The C-banding pattern was similar between C. medius and C. ornatus with regard to the number and locations of heterochromatic bands, suggesting that heterochromatin amplification and dispersion, affect karyotypic evolution in the genus. Cytogenetic data showed similarity between C. medius and C. ornatus, and differentiation of G. longipes congruent with morphological data. Moreover, although more comparative analyses are needed to specify composition of the dispersed heterochromatin in Ctenus, the mapping of heterochromatic bands provided insights about the evolution of the karyotypes in this genus.