Sex-specific changes in gene expression and delayed sex differentiation in response to estrogen pollution in grayling (Salmonidae)

Abstract

26The synthetic 17α-ethinylestradiol (EE2) is an estrogenic compound of oral contraceptives 27 and therefore a common pollutant that has been suspected to affect the demography of river-28 dwelling salmonids. We study a population of European grayling (Thymallus thymallus) that 29 suffers from sex ratio distortions. Here we test how ecologically relevant concentrations of 30 EE2 affect sex-specific gene expression around early stages of sex differentiation. We 31 collected gametes from F1s of wild spawners, used them for in vitro fertilizations, and raised 32 the resulting embryos singly under experimentally controlled conditions. Embryos were either 33 exposed to 1ng/L EE2 or sham-exposed. RNA was collected from samples taken 10 days 34 before hatching, at the day of hatching, and towards the end of the yolk-sac stage, to study 35 gene expression and relate it to genetic sex (sdY genotype). We found that EE2 affects gene 36 expression of a very large number of genes especially at the day of hatching. The effects of 37 EE2 on gene expression is strongly sex-specific. At the day of hatching, EE2 affected about 38 twice as many genes in females than in males, and towards the end of the yolk-sac larval 39 stage, EE2 effects were nearly exclusively observed in females. Among the many effects was, 40 for example, a surprising EE2-induced molecular masculinization in the females' heads. 41Histological examination of gonadal development of EE2-treated or sham-exposed juveniles 42 during the first 4.5 months after hatching revealed a delaying effect of EE2 on sex 43 differentiation. Because grayling sex determination goes through an all-male stage (a rare 44 case of undifferentiated gonochorism), the rate of EE2-induced sex reversal could not be 45 unequivocally determined during the observational period. However, two EE2-treated genetic 46 males had ovarian tissues at the end of the study. We conclude that common levels of EE2 47 pollution affect grayling from very early stages on by interfering with male and female gene 48 expression around the onset of sex differentiation, by delaying sex differentiation, and by 49 feminizing some males. 50 51All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

No additive genetic variance for tolerance to ethynylestradiol exposure in natural populations of brown trout (Salmo trutta)

“…Moreover, Brazzola, Chèvre, and Wedekind (2014) exposed embryos of two species of whitefish (Coregonus palaea and C. albellus) to low concentrations of EE2 (from 1 to 100 ng/L) and found EE2 at all concentrations to delay hatching and to reduce embryo survival and growth. Luca et al (in preparation) confirmed the toxicity of EE2 in whitefish and linked it to changes in the metabolic rates during embryogenesis, and Selmoni et al (2017) found EE2 to delay gonad development in grayling larvae (Thymallus thymallus).…”

“…Moreover, Brazzola, Chèvre, and Wedekind () exposed embryos of two species of whitefish ( Coregonus palaea and C. albellus ) to low concentrations of EE2 (from 1 to 100 ng/L) and found EE2 at all concentrations to delay hatching and to reduce embryo survival and growth. Luca et al (in preparation) confirmed the toxicity of EE2 in whitefish and linked it to changes in the metabolic rates during embryogenesis, and Selmoni et al () found EE2 to delay gonad development in grayling larvae ( Thymallus thymallus ).…”

Toxicity of 2 pg ethynylestradiol in brown trout embryos (Salmo trutta)

“…In accordance, EE2 has been described to change various aspects of development in typical model species (Caldwell et al, 2012, Aris et al, 2014 and to delay early development (Brazzola et al, 2014, Marques da Cunha et al, in prep. ) and sexual differentiation (Selmoni et al, 2017) in salmonids.…”