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

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