Sex Determination and Male Differentiation in Southern Swordtail Fishes: Evaluation from an Evolutionary Perspective

Abstract

Southern swordtail fishes, which belong to the viviparous teleosts called Xiphophorus, are unique models for studies of evolution of sex chromosomes. Monofactorial sex-determining systems, with either the male or the female being the heterogametic sex, as well as sex determination involving more than two sex chromosomes, are found in swordtails and related species. Some swordtail species seem to have originated by crossing between two closely related species. Although the sword has disappeared in many Xiphophorus species during evolution, females of non-sworded species still prefer sworded males, demonstrating a discrepancy between natural and sexual selection. Natural sex change has not been documented sufficiently convincingly in swordtails, but, at least in some subspecies, two or more male phenotypes exist. In a laboratory experiment performed for over 30 years, it has been observed that sex-determining genes may be translocated from one chromosome to another in hybrids of these evolutionary young species. While the factors suggested to play central roles in sex determination and differentiation, e.g., Dmrt1 and AMH, are highly conserved during evolution, several master determining factors have been detected in teleosts. Endocrine-induced sex reversal has been demonstrated in the guppy Poecilia reticulata, another viviparous fish. In swordtails (X. helleri), endocrine disruptors such as nonylphenol and bisphenol A may cause testis cell degeneration and the inhibition of spermatogenesis. Furthermore, swordtails are very easy to breed in freshwater aquaria and, therefore, may be good models for studying the factors influencing sex determination and male differentiation.

Feeding Habits and Reproductive Biology of Newly Discovered Endemic Glassfish, Parambassis waikhomi Geetakumari & Basudha, 2012 of Manipur

“…Females of the same age group are comparatively larger in size than male also support the previous studies conducted in different species of fishes [18].…”

Complete or partial loss of the Y chromosome in an unselected cohort of 865 non-vasectomized, azoospermic men

“…One possible explanation for this apparently lack in SRY may be due to lack in access due to the vast variation in SRY between species [ 3 ]. If SRY is absent in these few mammal species, another master sex determining factor may be present [ 41 , 42 ].…”

In Silico Chromosome Mapping of the Male-Specific/Linked Loci in the Jade Perch (Scortum barcoo) Suggests Chromosome 19 as the Putative Y Sex Chromosome

“…Teleosts display a large diversity in SDSs, including genetic sex determination (GSD), environmental sex determination, and interactions between the two systems [10][11][12][13][14]. Different systems of GSD have been identified in a particular species with one system (XX/XY or ZZ/ZW), or both XX/XY and ZZ/ZW systems existing within the same genus, species, and even at the population level [15][16][17][18][19][20][21]. Because of this variability, several genes and SDRs might initiate SDS in a species, known as a polygenic sex determination (PSD) system [22].…”