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The karyotype of Zingel zingel from the Morava River (Czech Republic) was analyzed. The diploid chromosome number was 2n=48 in females and 2n=47 in males, however, one large unpaired metacentric chromosome was present in males. This proves to be the X1X1X2X2/X1X2Y multiple sex chromosome system developed from the fusion of two sub- or acrocentric c...
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... substantial sexual dimorphism was ob- served in the karyotype of the Zingels. The female karyotype consisted of 48 chromosomes (2n = 4 metacentrics (m) + 16 submetacentrics (sm) + 28 subtelo to acrocentrics (st-a)). This number of chromosomes corresponds to a figure stated in lit- erature for this species. The number of chromo- somes in all the 7 males was 47 (2n = 5m + 16 sm + 26 st-a). The number of st-a chromosomes was lower by one pair in males compared to females. However, one big unpaired metacentric chromo-some was present in males, whereas in females it was not (Fig. 2). Numbers of sm chromosomes were in both sexes ...
Citations
Despite decades of cytogenetic and genomic research of dynamic sex chromosome evolution in teleost fishes, multiple sex chromosomes have been largely neglected. In this review, we compiled available data on teleost multiple sex chromosomes, identified major trends in their evolution and suggest further trajectories in their investigation. In a compiled dataset of 440 verified records of fish sex chromosomes, we counted 75 multiple sex chromosome systems with 60 estimated independent origins. We showed that male-heterogametic systems created by Y-autosome fusion predominate and that multiple sex chromosomes are over-represented in the order Perciformes. We documented a striking difference in patterns of differentiation of sex chromosomes between male and female heterogamety and hypothesize that faster W sex chromosome differentiation may constrain sex chromosome turnover in female-heterogametic systems. We also found no significant association between the mechanism of multiple sex chromosome formation and percentage of uni-armed chromosomes in teleost karyotypes. Last but not least, we hypothesized that interaction between fish populations, which differ in their sex chromosomes, can drive the evolution of multiple sex chromosomes in fishes. This underlines the importance of broader inter-population sampling in studies of fish sex chromosomes.
This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.
Closely related species of fishes often have different sex chromosome systems. Such rapid turnover of sex chromosomes can
occur by several mechanisms, including fusions between an existing sex chromosome and an autosome. These fusions can result
in a multiple sex chromosome system, where a species has both an ancestral and a neo-sex chromosome. Although this type of
multiple sex chromosome system has been found in many fishes, little is known about the mechanisms that select for the formation
of neo-sex chromosomes, or the role of neo-sex chromosomes in phenotypic evolution and speciation. The identification of closely
related, sympatric species pairs in which one species has a multiple sex chromosome system and the other has a simple sex
chromosome system provides an opportunity to study sex chromosome turnover. Recently, we found that a population of threespine
stickleback (Gasterosteus aculeatus) from Japan has an X1X2Y multiple sex chromosome system resulting from a fusion between the ancestral Y chromosome and an autosome, while a sympatric
threespine stickleback population has a simple XY sex chromosome system. Furthermore, we demonstrated that the neo-X chromosome
(X
2) plays an important role in phenotypic divergence and reproductive isolation between these sympatric stickleback species
pairs. Here, we review multiple sex chromosome systems in fishes, as well as recent advances in our understanding of the evolutionary
role of sex chromosome turnover in stickleback speciation.
KeywordsMultiple sex chromosomes–Neo-sex chromosome–X1X2Y–Stickleback–Sexual conflict–Speciation
