Comparative analysis based on replication banding reveals the mechanism responsible for the difference in the karyotype constitution of treefrogs and (Arboranae, Hylidae, Scinaxinae).

According to the recent taxonomic and phylogenetic revision of the family Hylidae, species of the former (Boulenger, 1888) clade were included in the resurrected genus Fitzinger, 1843, while species of the (Laurenti, 1768) clade were mostly included in the genus Wagler, 1830, and two were allocated to the newly created genus Duellman et al., 2016. Although all the species of the former genus shared a diploid number of 2n = 24 and the same fundamental number of chromosome arms of FN = 48, two karyotypic constitutions were unequivocally recognized, related mainly to the distinct size and morphology of the first two chromosome pairs. Some possible mechanisms for these differences had been suggested, but without any experimental evidence. In this paper, a comparison was carried out based on replication chromosome banding, obtained after DNA incorporation of 5-bromodeoxiuridine in chromosomes of and . The obtained results revealed that the loss of repetitive segments in chromosome pairs 1 and 2 was the mechanism responsible for karyotype difference. The distinct localization of the nucleolus organizer regions in the species of both genera also differentiates the two karyotypic constitutions.