The Amazonian Red Side-Necked Turtle Rhinemys rufipes (Spix, 1824) (Testudines, Chelidae) Has a GSD Sex-Determining Mechanism with an Ancient XY Sex Microchromosome System

Abstract

The Amazonian red side-necked turtle Rhynemis rufipes is an endemic Amazonian Chelidae species that occurs in small streams throughout Colombia and Brazil river basins. Little is known about various biological aspects of this species, including its sex determination strategies. Among chelids, the greatest karyotype diversity is found in the Neotropical species, with several 2n configurations, including cases of triploidy. Here, we investigate the karyotype of Rhinemys rufipes by applying combined conventional and molecular cytogenetic procedures. This allowed us to discover a genetic sex-determining mechanism that shares an ancestral micro XY sex chromosome system. This ancient micro XY system recruited distinct repeat motifs before it diverged from several South America and Australasian species. We propose that such a system dates back to the earliest lineages of the chelid species before the split of South America and Australasian lineages.

Heterochromatin and microsatellites detection in karyotypes of four sea turtle species: Interspecific chromosomal differences

“…Usually, microsatellites accumulations were demonstrated in the terminal regions of vertebrate chromosomes, which seems to be a common feature due to different mechanisms that accumulate these sequences in these regions ( Pokorná et al ., 2011b ; Torres et al ., 2011 ; Ruiz-Ruano et al ., 2015 ; Ernetti et al ., 2019 ; Lee et al ., 2019 ; Viana et al ., 2020 ). The (CA) n , (GA) n , (CAG) n and (GATA) n microsatellites were reported for the first time in sea turtle’s karyotypes and demonstrated that most of them possibly make up part of the repetitive units of heterochromatin in C. mydas, C. caretta , L. olivacea and E. imbricata , especially in mc.…”

“…Dmrt1 is a gene that acts during sex determination stages in reptile development ( Kettlewell et al ., 2000 ; Mizoguchi and Valenzuela, 2020 ), in which the sex of the embryos is determined by the incubation temperature of the nest (temperature-dependent sex determination: TSD), the most common mechanism of environmental sex determination (ESD) ( Ferreira Júnior, 2009 ). Although, genotypic sex determination was described to have evolved independently in five families of turtles (Chelidae, Emydidae, Geoemydidae, Kinosternidae and Trionychidae) (Valenzuela and Adams, 2011 , Valenzuela et al , 2014 ; Badenhorst et al ., 2013 ; Rovatsos et al ., 2017 ; Lee et al ., 2019 ; Viana et al ., 2020 ), sea turtles were described as belonging to a TSD lineage ( Bickham et al ., 1980 ; Morreale et al ., 1982 ; Yntema and Mrosovsky, 1982 ; Mrosovsky et al ., 1984 , 1992 ; Valenzuela and Adams, 2011 ; Montiel et al ., 2016 ). Previous in situ localization of (GATA) n in three species of turtles with TSD, using both sexes, detected markers preferably in mc and without evidence of sex-specific chromosomal sites ( Mazzoleni et al ., 2019 ).…”

“…All sea turtle species show different levels of threat of extinction and are considered flag species for the conservation of biodiversity ( IUCN, 2020 ) since numerous threats affect the populations maintenance ( Lara-Ruiz et al ., 2006 ; Proietti et al ., 2014 ; Arantes et al ., 2020 ). In addition, chromosomal studies in turtles demonstrated great karyotypic diversification among evolutionary lineages, making the cytogenetic knowledge important for recognition of species diversity and conservation ( Valenzuela and Adams, 2011 ; Montiel et al ., 2016 ; Rovatsos et al ., 2017 ; Cavalcante et al ., 2018 ; Lee et al ., 2019 ; Deakin and Ezaz, 2019 ; Clemente et al ., 2020 ; Viana et al ., 2020 ).…”

“…In this sense, the characterization of repetitive DNA sequences present in heterochromatin sites allow us to understand chromosomal rearrangements in some species of the group ( Cavalcante et al ., 2018 , 2020a , 2020b ). In turtles, as well as in sister groups, heterochromatin is located in the pericentromeric region of most macrochromosomes and some mc ( Nishida et al ., 2013 ; de Oliveira et al ., 2017 ; Cavalcante et al ., 2018 ; Barcellos et al ., 2019 ; Viana et al ., 2020 ). In crocodilians, which do not have mc, the heterochromatic regions were also preferentially located in the pericentromeric regions ( Amavet et al ., 2003 ; Kawagoshi et al ., 2008 ).…”

“…Although controversy still exists, the term satellite DNA has been applied to any tandem repetitive sequence which is present in blocks of hundreds to thousands of units and which are located in heterochromatin sites regardless of unit size ( Garrido-Ramos, 2015 ). For instance, microsatellites are 1-6 nucleotide units tandemly repeated and can be found accumulated as a part constituent of heterochromatin ( Kubat et al ., 2008 ; Schemberger et al ., 2019 ; Viana et al ., 2020 ; Zattera et al ., 2020 ) or located dispersed in euchromatic chromosomes regions ( Tóth et al ., 2000 ; Ruiz-Ruano et al ., 2015 ). Their location on chromosomes can be species-specific or present a similar distribution pattern in close relationship species groups ( Tóth et al ., 2000 ; Ziemniczak et al ., 2014 ; Pucci et al ., 2016 ).…”