Following the Pathway of W Chromosome Differentiation in Triportheus (Teleostei: Characiformes)

Abstract

In this work, we trace the dynamics of satellite DNAs (SatDNAs) accumulation and elimination along the pathway of W chromosome differentiation using the well-known Triportheus fish model. Triportheus stands out due to a conserved ZZ/ZW sex chromosome system present in all examined species. While the Z chromosome is conserved in all species, the W chromosome is invariably smaller and exhibits differences in size and morphology. The presumed ancestral W chromosome is comparable to that of T. auritus, and contains 19 different SatDNA families. Here, by examining five additional Triportheus species, we showed that the majority of these repetitive sequences were eliminated as speciation was taking place. The W chromosomes continued degeneration, while the Z chromosomes of some species began to accumulate some TauSatDNAs. Additional species-specific SatDNAs that made up the heterochromatic region of both Z and W chromosomes were most likely amplified in each species. Therefore, the W chromosomes of the various Triportheus species have undergone significant evolutionary changes in a short period of time (15-25 Myr) after their divergence.

Keywords: FISH; cytogenomics; satellite DNA; sex chromosomes.

Figure 1

Female metaphase plates of Triportheus guentheri (TGU), T. nematurus (TNE), T. pantanensis (TPA), T. rotundatus (TRO), and T. trifurcatus (TTR) highlighting the chromosomal location of TauSatDNAs. While TauSat07 and TauSat08 showed positive hybridization signals in all species, TauSat17 and TauSat22 were exclusively mapped in TTR and TRO. The SatDNA family names are indicated on the right bottom, in green (Atto488 labeled) or red (Atto550 labeled). The ZW sex chromosomes are indicated. Bar = 5 μm.

Figure 2

Female metaphase plates of Triportheus guentheri (TGU), T. nematurus (TNE), T. pantanensis (TPA), T. aff. rotundatus (TRO), and T. trifurcatus (TTR) highlighting the chromosomal location of TauSat29 in red (Atto550 labeled). The ZW sex chromosomes are indicated. Bar = 5 μm.

Figure 3

Detailed comparison of different TauSatDNAs that hybridized on the Z and/or W chromosomes of Triportheus guentheri (TGU), T. nematurus (TNE), T. pantanensis (TPA), Triportheus aff. rotundatus (TRO), and T. trifurcatus (TTR). The ZW chromosomes were extracted from Figure 1, Figure 2 and Figure S1.

Figure 4

Phylogenetic relationships among the analyzed Triportheus species based on Mariguela et al. [10] and Melo et al. [53] with the representative ideograms highlighting the distribution of the TauSatDNAs on the Z (on the left) and W (on the right) chromosomes of Triportheus. Some data came from Kretschmer et al. [37].