Comparative Cytogenetics in Four <b><i>Leptodactylus</i></b> Species (Amphibia, Anura, Leptodactylidae): Evidence of Inner Chromosomal Diversification in Highly Conserved Karyotypes

Abstract

With 82 species currently described, the genus &lt;i&gt;Leptodactylus&lt;/i&gt; is the most diverse and representative one in the family Leptodactylidae. Concerning chromosomal organization, this genus represents an interesting and underexplored group since data from molecular cytogenetics are incipient, and little is known about the organization and distribution of repetitive DNA elements in the karyotypes. In this sense, this study aimed at providing a comparative analysis in 4 &lt;i&gt;Leptodactylus&lt;/i&gt; species (&lt;i&gt;L. macrosternum, L. pentadactylus, L. fuscus,&lt;/i&gt; and &lt;i&gt;Leptodactylus&lt;/i&gt; cf&lt;i&gt;. podicipinus&lt;/i&gt;), combining conventional cytogenetics (Giemsa staining, C-banding, and AgNOR staining) and mapping of molecular markers (18S rDNA, telomeric and microsatellite probes), to investigate mechanisms underlying their karyotype differentiation process. The results showed that all species had karyotypes with 2n = 22 and FN = 44, except for &lt;i&gt;Leptodactylus&lt;/i&gt; cf. &lt;i&gt;podicipinus&lt;/i&gt; which presented FN = 36. The 18S rDNA was observed in pair 8 of all analyzed species (corresponding to pair 4 in &lt;i&gt;L. pentadactylus&lt;/i&gt;), coinciding with the secondary constrictions and AgNOR staining. FISH with microsatellite DNA probes demonstrated species-specific patterns, as well as an association of these repetitive sequences with constitutive heterochromatin blocks and ribosomal DNA clusters, revealing the dynamics of microsatellites in the genome of the analyzed species. In summary, our data demonstrate an ongoing process of genomic divergence inside species with almost similar karyotype, driven most likely by a series of pericentric inversions, followed by differential accumulation of repetitive sequences.

Chromosomal Diversification in Pseudacanthicus Species (Loricariidae, Hypostominae) Revealed by Comparative Mapping of Repetitive Sequences

“…In the subfamily Hypostominae, most of the species share the diploid number; however, an extensive variation in karyotypic morphology is observed, suggesting the occurrence of rearrangements such as inversions and translocations [ 10 , 12 , 36 ]. The involvement of repetitive sequences in chromosomal differentiation has been demonstrated in several groups of vertebrates, including mammals [ 37 , 38 ], amphibians [ 23 ] and other fish species of the subfamily Hypostominae [ 9 , 10 , 20 ]. In Pseudacanthicus , variations in the karyotypic formula were not evident; however, the comparative analysis of the distribution of CH blocks, as well as of the rDNA and snDNA genes, suggested the occurrence of microstructural differentiation events among the analyzed karyotypes, including transpositions, CH amplification/deletions and unequal crossing-over.…”

“…These groups of repetitive sequences have been useful as markers in comparative cytogenetic analyses, improving the understanding of mechanisms of karyotypic diversification in different groups of fish [ 9 , 10 , 18 , 19 , 20 , 21 ]. Furthermore, these analyses have been efficient in evidencing mechanisms of chromosomal differentiation between species whose karyotypic constitution appears to be homogeneous, representing an important approach to the study of karyotypic diversification in these groups of organisms, as observed in different lineages of the subfamily Hypostominae [ 10 , 22 , 23 ].…”

Chromosomal Diversification in Ancistrus Species (Siluriformes: Loricariidae) Inferred From Repetitive Sequence Analysis

“…The microsatellites are abundant in eukaryotic genomes, commonly a heterochromatin component, but they could also be found in euchromatic regions ( Martins, 2007 ; Cioffi et al, 2010 ; Santos da Silva et al, 2021 ). They are helpful cytogenetic markers to demonstrate minor chromosomal variations into related species groups, including birds, amphibians, and fish ( Cioffi et al, 2010 ; de Oliveira et al, 2017 ; Da Silva et al, 2021 ). Furthermore, the participation of these sequences in breakpoints regions for chromosomal rearrangements and evolution of sex chromosomes has been shown in many species, including Ancistrus ( Farré et al, 2011 ; Cioffi et al, 2017 ; Favarato et al, 2017 ; Prizon et al, 2017 ).…”

Repetitive DNA Mapping in Five Genera of Tree Frogs (Amphibia: Anura) from the Atlantic Forest: New Highlights on Genomic Organization in Hylidae

“…We conclude that the karyotypes of all species analyzed here show a conservative character regarding the morphology of the chromosomes, as well as the NORs’ localization, despite some observed exceptions. Furthermore, we observed that the use of microsatellites proved to be a helpful cytogenetic marker for some populations of analyzed species, showing interesting patterns since these sequences can detect recent evolutionary events, apparently because of the neutral nature of these genomic regions [51, 52]. In addition, the microsatellites allowed the detection of differences between species that share very similar chromosomal morphologies.…”