Sex Determination Diversity and Sex Chromosome Evolution in Poeciliid Fish

Abstract

Poeciliids, a family of live-bearing freshwater fish, including among others platyfish, swordtails and guppies, fully illustrate the diversity of genetic sex determination mechanisms observed in teleosts. Besides unisexuality, a variety of sex-determining systems has been described in this group of fish, including male and female heterogamety with or without autosomal influence, as well as more complicated situations such as multichromosomal and polyfactorial sex determination. Due to the presence of different mechanisms in closely related species or even between populations within a same species, poeciliids are a very attractive model to study the evolutionary dynamics of sex determination. For one species, the Southern platyfish Xiphophorus maculatus, positional cloning of the master sex-determining gene has been initiated through the construction and sequencing of bacterial artificial chromosome contigs covering the region differentiating the X from the Y chromosome. Initial analysis revealed a high plasticity of the sex-determining region and the absence of synteny with other fish and vertebrate sex chromosomes, indicating an independent evolutionary origin.

Coexistence of Y, W, and Z sex chromosomes in Xenopus tropicalis

“…Several possibilities exist for the sex chromosome systems in natural populations of this species. The existence of more than two types of sex chromosomes in the same species has been described in fish, amphibians, and even mammals (6,7,(43)(44)(45)(46)(47) and can occur in several forms. In some fish species, the existence of two or more nonhomologous sex pairs allows coexistence of more than two types of sex chromosomes.…”

“…An example is Xiphophorus maculatus, a species with three sex chromosomes (W, Y, and X), in which females can be XX, XW, or YW, and males are YY or XY (43,44). In addition to X. maculatus, several rodent species show three sex chromosomes with different masculinizing/feminizing capacity.…”

The Birds and the Bees and the Flowers and the Trees: Lessons from Genetic Mapping of Sex Determination in Plants and Animals

“…However, the platyfish, Xiphophorus maculatus, also has a ''W'' chromosome carrying a female-determining gene. Xiphophorus species may be changing between female and male heterogamety, and in X. maculatus, like the frog Rana ragosa (see below), the X and W chromosomes are at least partially homologous (reviewed in Schultheis et al 2009). The male color polymorphisms may be maintained by sexual antagonism, being advantageous to males, but disadvantageous to females (Fisher 1931;Kallman 1970;Rice 1984).…”

Karyotype Differentiation between Two Stickleback Species (Gasterosteidae)

“…Studies have documented sex chromosome diversity within species of poeciliid fish [Nanda et al, 2000;Volff and Schartl, 2001;Schultheis et al, 2009] and within several species of neotropical fish, including E. virescens [Almeida-Toledo et al, 2002;Henning et al, 2011], Erythrinus erythrinus [Bertollo et al, 2004;, and Hoplias malabaricus [Bertollo et al, 2000;. Sex chromosome systems also differ among populations of other stickleback species.…”