Matamatas Chelus spp. (Testudines, Chelidae) have a remarkable evolutionary history of sex chromosomes with a long-term stable XY microchromosome system

Abstract

The genus Chelus, commonly known as Matamata is one of the most emblematic and remarkable species among the Neotropical chelids. It is an Amazonian species with an extensive distribution throughout Negro/Orinoco and Amazonas River basins. Currently, two species are formally recognized: Chelus orinocensis and Chelus fimbriata and although it is still classified as "Least Concern" in the IUCN, the Matamatas are very appreciated and illegally sold in the international pet trade. Regardless, little is known regarding many aspects of its natural history. Chromosomal features for Chelus, for instance, are meagre and practically restricted to the description of the diploid number (2n = 50) for Chelus fimbriata, and its sex determining strategies are yet to be fully investigated. Here, we examined the karyotype of Chelus fimbriata and the newly described Chelus orinocensis, applying an extensive conventional and molecular cytogenetic approach. This allowed us to identify a genetic sex determining mechanism with a micro XY sex chromosome system in both species, a system that was likely present in their most common recent ancestor Chelus colombiana. Furthermore, the XY system found in Chelus orinocensis and Chelus fimbriata, as seen in other chelid species, recruited several repeat motifs, possibly prior to the split of South America and Australasian lineages, indicating that such system indeed dates back to the earliest lineages of Chelid species.

Karyotypic variation of two populations of the small freshwater stingray Potamotrygon wallacei Carvalho, Rosa & Araújo 2016: A classical and molecular approach

“…These sequences are often associated with regulatory function in the genome architecture, structural organization of DNA, chromatin organization and gene activity [59]. SSRs are also associated with sex chromosomes in many taxa [24,25,51]. In our analyses, we also found differences in the distribution pattern of the SSRs used.…”

“…Although the association of SSRs motifs with sex chromosomes has been documented in many vertebrate groups [24,25,27,51,61,62], unfortunately, data about the distribution of SSRs in Potamotrygoninae species are limited to the present study. While most of SSRs used here showed amplification in several chromosomes, (GATA) 4 motif was associated with the X chromosome in P. wallacei (two sites in the female and one in males).…”

“…These differences between the homologous may be a result of the dynamic behavior of these sequences, together with its expansion and contraction in the genomes due to slippage during DNA replication and high mutation rates [57,58,60]. Those characteristics make SSRs a useful tool to investigate chromosomal variations in closely related species or even in different populations [24,57,59]. Moreover, the differences in the patterns of SSRs (especially the (GT) 15 detected solely in one population) could be related to different landscapes impacting the distribution of these sequences in P. wallacei, thus SSRs might provide important information about chromosomal rearrangements in different populations.…”

“…Molecular cytogenetics approaches using repetitive sequences, such as 18S and 5S rDNAs and simple short repeats (SSRs or microsatellites), surely provides important information about chromosome evolution and sex chromosome origin [24][25][26][27]. Unfortunately, most cytogenetic studies in freshwater stingrays, including Potamotrygon wallacei, are scant (only 11 species were karyotyped-see Table 1 of Cruz et al [28]) and limited to classical techniques (Giemsa staining, C-banding, and Ag-NOR) [22,23,29,30] and only recently, Cruz and colleagues [28] applied molecular tools in their analyses.…”

Estado sanitario de tortugas dulceacuícolas de la familia <i>Chelidae</i> en arroyos pampásicos de llanura y serranos con distinto impacto de contaminación

“…Por otro lado, al tratarse de la población más austral de la especie, la temperatura podría ser un factor a tener en cuenta para explicar la desviación de sexos observada, ya que en muchas especies de tortugas la determinación del sexo depende de la temperatura de los nidos (Ewert et al 1994, Janzen 1994, Valenzuela y Lance 2004. Sin embargo, la mayoría de los chélidos, incluso géneros cercanos a Hydromedusa (Mazzoleni et al 2020, Viana et al 2022, tienen determinación genética del sexo (Valenzuela y Lance 2004). A pesar de que en H. tectifera no se observaron cromosomas sexuales heteromórficos (Noleto et al 2006), probablemente sea necesario aplicar técnicas citogenéticas de mayor resolución debido a la muy baja diferenciación de los cromosomas sexuales en esta familia (Thépot 2021).…”