High incidence of a male-specific genetic marker in phenotypic female chinook salmon from the Columbia River.

Abstract

Numerous populations of anadromous salmonids in the northwestern United States have been declining for many years, resulting in Endangered Species Act listings and in some cases extinction. The degradation of river ecosystems has been proposed as one of the major reasons for the inability of salmon to maintain their populations. However, the specific factors interfering with the reproduction and survival of salmon during the freshwater phase of their life cycle have not been fully described. This study was initiated to determine the incidence of phenotypic sex reversal in wild, fall chinook salmon (Oncorhynchus tshawytcha) that returned to spawn in the Columbia River. Fish were sampled at different locations within this watershed to determine whether they were faithfully expressing their genotype. We report a high incidence (84%) of a genetic marker for the Y chromosome in phenotypic females sampled from the wild, which was not observed in female fish raised in hatcheries. It appears likely that female salmon with a male genotype have been sex reversed, creating the potential for an abnormal YY genotype in the wild that would produce all-male offspring and alter sex ratios significantly.

The Evolution of Xy Recombination: Sexually Antagonistic Selection Versus Deleterious Mutation Load

“…If confirmed under other simulation settings, this rarity may explain why sex reversal is only rarely documented in the field (e.g., Crew 1921;Witschi 1929;Aida 1936;Kawamura and Nishioka 1977;Nagler et al 2001;Matsuba et al 2008). In the laboratory, it is easily triggered (as reviewed in Wallace et al 1999;Eggert 2004;Ospina-Álvarez and Piferrer 2008), but usually occurs at extreme temperatures relative to specific natural ranges.…”

“…Sex is easily reversed by temperature in many fish, amphibians, and reptiles, at values likely to be occasionally met in nature (e.g., Wallace and Wallace 2000;Baroiller et al 2009). Sex reversal has been documented from natural populations in a range of species (e.g., Crew 1921;Witschi 1929;Aida 1936;Kawamura and Nishioka 1977;Nagler et al 2001;Matsuba et al 2008). As recombination patterns often depend on phenotypic rather than genotypic sex (e.g., Wallace et al 1997;Kondo et al 2001;Lynn et al 2005;Campos-Ramos et al 2009;Matsuba et al 2010), X and Y are expected to recombine in sex-reversed XY females.…”

Sex Reversal: A Fountain of Youth for Sex Chromosomes?

“…When mated with normal XY males, such females produce male-biased sex ratios of 1:3, including YY males that sire all-male broods. Nagler et al (2001) report an event of mass feminization in a population of Chinook salmon, possibly linked to a temperature increase induced by a dam upstream of the spawning grounds. Sex-reversed XY females were fully fertile, producing YY males.…”

Alterations to gonadal development and reproductive success in japanese medaka (Oryzias latipes) exposed to 17α‐ethinylestradiol

“…In recent years, there has been concern about the release of EDCs and the possible effect that these substances have on aquatic organisms, particularly fish [1,3,8]. Much of this work has focused on biomarker responses in fish, such as induction of vitellogenin [9] and alteration to steroid hormone levels [10].…”