Evidence for Sex Chromosome Turnover in Proteid Salamanders

Abstract

A major goal of genomic and reproductive biology is to understand the evolution of sex determination and sex chromosomes. Species of the 2 genera of the Salamander family Proteidae - Necturus of eastern North America, and Proteus of Southern Europe - have similar-looking karyotypes with the same chromosome number (2n = 38), which differentiates them from all other salamanders. However, Necturus possesses strongly heteromorphic X and Y sex chromosomes that Proteus lacks. Since the heteromorphic sex chromosomes of Necturus were detectable only with C-banding, we hypothesized that we could use C-banding to find sex chromosomes in Proteus. We examined mitotic material from colchicine-treated intestinal epithelium, and meiotic material from testes in specimens of Proteus, representing 3 genetically distinct populations in Slovenia. We compared these results with those from Necturus. We performed FISH to visualize telomeric sequences in meiotic bivalents. Our results provide evidence that Proteus represents an example of sex chromosome turnover in which a Necturus-like Y-chromosome has become permanently translocated to another chromosome converting heteromorphic sex chromosomes to homomorphic sex chromosomes. These results may be key to understanding some unusual aspects of demographics and reproductive biology of Proteus, and are discussed in the context of models of the evolution of sex chromosomes in amphibians.

Shedding Light on a Secretive Tertiary Urodelean Relict: Hynobiid Salamanders (Paradactylodon persicus s.l.) from Iran, Illuminated by Phylogeographic, Developmental, and Transcriptomic Data

“…This might facilitate future studies in the genus Paradactylodon and other Hynobiidae. Sex chromosomes of most salamanders are homomorphic [50,51], and in most species, mainly the observation of balanced sex ratios from clutches is interpreted as indication for genetic sex determination but has remained essentially without genetic evidence [52]. In Hynobiidae, gene expression in context to sexual development has been studied using histology and qPCR of a single gene (P450) in Hynobius retardus by Sakata et al [53].…”

Repeated Evolution Versus Common Ancestry: Sex Chromosome Evolution in the Haplochromine CichlidPseudocrenilabrus philander

“…Sex chromosome turnovers have indeed been shown in, for example, fishes and amphibians (Miura 2007; Volff et al. 2007; Kitano and Peichel 2012; Sessions et al. 2016; Jeffries et al.…”

Miniscule differences between sex chromosomes in the giant genome of a salamander

“…Among most amphibians that have been investigated, homomorphy is prevalent 17–19 . It has been suggested that a majority of salamanders have homomorphic sex chromosomes 18,20 , however, evidence for genetic sex determination in most species is largely based on the observation of 1:1 sex ratios from clutches without thorough demonstration of Mendelian inheritance.…”