Abstract
Treefrogs of the genus Pithecopus Cope, 1866 exhibit expressive chromosomal homogeneity which contrasts with a high variation frequency of the nucleolus organizer region (NOR) related to the group. Currently, the genus contains eleven species and no chromosomal data are available on P. palliatus Peters, 1873, P. ayeaye Lutz, 1966 and P. megacephalus Miranda-Ribeiro, 1926. Here, we describe the karyotypes of these three species based on Giemsa staining, C-banding, silver impregnation and in situ hybridization (FISH). We were also analyze the evolutionary dynamic of the NOR-bearing chromosome in species of genus under a phylogenetic view. The results indicate that P. palliatus, P. ayeaye, and P. megacephalus have similar karyotypes, which are typical of the genus Pithecopus. In P. palliatus the NOR was detected in the pericentromeric region of pair 9p whereas in P. ayeaye and P. megacephalus we report cases of the multiple NOR sites in karyotypes. In P. ayeaye the NOR was detected in the pericentromeric region of pair 9p in both homologues and additional sites was detected in pairs 3q, 4p, and 8q, all confirmed by FISH experiments. Already in P. megacephalus the NOR sites were detected in pericentromeric region homologues of pair 8q and additionally in one chromosome of pair 13q. A comparative overview of all the Pithecopus karyotypes analyzed up to now indicates the recurrence of the NOR-bearing chromosome pairs and the position of the NORs sites on these chromosomes. We hypothesized that this feature is a result of a polymorphic condition present in the common ancestor of Pithecopus. In such case, the lineages derived from polymorphic ancestor have reached fixation independently after divergence of lineages, resulting in a high level of homoplasy observed in this marker. Our findings help to fill the gaps in the understanding of the karyotype of the genus Pithecopus and reinforce the role of the evolutionary dynamics of the rDNA genes in karyotype diversification in this group.
Highlights
Duellman et al (2016) recognized the genus Pithecopus Cope, 1986 as a distinct taxon from the genus Phyllomedusa Wagler, 1930, with which it had previously been synonymized, and Frost (2019) concluded that the genus contains 11 valid species
A secondary constriction was detected in the pericentromeric region of the short arm of the homologs of pair 9 in P. ayeaye and P. palliatus, in the P. megacephalus karyotype, the secondary constriction was observed in the pericentromeric region of the long arm of the homologs of pair 8
In P. ayeaye karyotype C-banded chromosomes were sequentially stained with DAPI and MM fluorochromes to reveal the A:T and C:G richness and resulted in brilliant signals in regions coincident with heterochromatic blocks detected by C-banding (Fig. 1C)
Summary
Duellman et al (2016) recognized the genus Pithecopus Cope, 1986 (the monkey frogs) as a distinct taxon from the genus Phyllomedusa Wagler, 1930, with which it had previously been synonymized, and Frost (2019) concluded that the genus contains 11 valid species. Molecular inferences (Faivovich et al 2010; Bruschi et al 2014; Duellman et al 2016; Haga et al 2017) have recovered two well-supported clades in Pithecopus with a strong biogeographic component. High levels of endemism (Magalhães et al 2018) and cryptic diversity (Faivovich et al 2010, Ramos et al 2019) have been reported in the “highland” clade. Population genetic divergence was recently confirmed by a molecular analysis using nuclear and mitochondrial markers (Ramos et al 2019), which emphasizes the potential contribution of karyotype data as complementary evidence for the identification of cryptic diversity
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