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Abstract

Triportheus is a neotropical freshwater Characidae fish that has a well-differentiated ZZ/ZW sex chromosome system. The W chromosome of this genus contains a large amount of heterochromatin and is smaller than the Z chromosome. This contrasts with other ZW fish systems where the W chromosome is larger in size due to increased heterochromatin. All species of Triportheus that have been studied cytologically (about 50% of the known species for this genus, from some of the major South American hydrographic basins) share this sex chromosome system, indicating a probable synapomorphic condition not present in other genera of the large Characidae family. However, while the Z chromosome appears to be largely conserved, the W chromosome shows a differential evolution with morphological differentiations not only among species, but also among populations from the same hydrographic basin, and with some species presenting a greater homology between the W and the Z chromosomes than others.

Evolutionary Dynamics of Multigene Families in Triportheus (Characiformes, Triportheidae): A Transposon Mediated Mechanism?

“…The karyotype and 5S rDNA-FISH results agreed with previous studies (Artoni et al, 2001;Diniz et al, 2009;Marquioni et al, 2013;Yano et al, 2016Yano et al, , 2017b. In all species, the double-FISH results demonstrate that U1 snRNA and 5S rRNA are colocalized in the ninth chromosome pair (Figure 3), including T. auritus, which belongs to the first lineage that diverged from the ancestor of the genus (Mariguela et al, 2016).…”

“…According to a recent phylogenetic study established for this genus, Triportheus originated at 26.2 ± 6.5 Myr and represents a monophyletic group in which T. auritus is the oldest living species within the genus (Mariguela et al, 2016). Triportheus has stood out in many cytogenetics studies, mainly because all species studied so far have a ZW sex chromosomes system well characterized (Artoni et al, 2001;Diniz et al, 2009;Yano et al, 2016Yano et al, , 2017a. In addition, the rDNAs (Diniz et al, 2009;Marquioni et al, 2013;Yano et al, 2017b) and the U2 snRNA genes (Yano et al, 2017b) have been also investigated, highlighting the variability in the syntenic configuration as well as in the number of sites of these multigene families, mainly regarding the 5S rDNAs (Yano et al, 2017b).…”

Chromosomal location of 18S and 5S rDNA sites in Triportheus fish species (Characiformes, Characidae)

“…signatus , followed by reports for T. guentheri, T. cf. auritus and distinct populations of T. nematurus (Bertollo and Cavallaro, 1992; Sánchez and Jorge, 1999; Artoni et al , 2001; Artoni and Bertollo, 2002; Diniz et al , 2008) and T. venezuelensis (Nirchio et al , 2007). All of these species and populations share a common diploid number, 2n = 52, and a very similar karyotypic macrostructure composed mainly of meta/submetacentric chromosomes and a ZZ/ZW sex chromosome system.…”

“…cit. ; Bertollo and Cavallaro, 1992; Sánchez and Jorge, 1999; Artoni et al , 2001; Artoni and Bertollo, 2002; Nirchio et al , 2007). …”

Contributions to the cytogenetics of the Neotropical fish fauna

“…Usually, sex chromosomes occur as a particular feature for some species within a specific fish group, as exemplified in the Erythrinidae, Parodontidae, Anostomidae and Crenuchidae families (Galetti Jr. et al 1981, 1995; Moreira-Filho et al 1985, 1993; Molina et al 1998; Centofante et al 2001, 2003; Bertollo et al 2000; Bertollo 2007; Vicari et al 2008; Cioffi et al 2013). As a singular exception, all species of the Triportheus genus (Triportheidae) share a same ZZ/ZW sex chromosome system (Artoni et al 2001, 2002; Diniz et al 2008), constituting a special model to investigate the evolution of the sex chromosomes among lower vertebrates. The modern molecular cytogenetics was a key step for understanding the evolutionary process of the sex chromosomes among fishes.…”