Biology subjects

Wedekind, C.

Publications and source records attributed to Wedekind, C..

5 recordsLinked to original sources

bioRxiv2018

Consumption of carotenoids not increased by bacterial infection in brown trout embryos (Salmo trutta)

Carotenoids are organic pigment molecules that play important roles in signalling, control of oxidative stress, and immunity. Fish allocate carotenoids to their eggs, which gives them the typical yellow to red colouration and supports their resistance against microbial infections. However, it is still unclear whether carotenoids act mainly as a shield against infection or are used up during the embryos immune defence. We investigated this question with experimental families produced from wild-caught brown trout (Salmo trutta). Singly raised embryos were either exposed to the bacterial pathogen Pseudomonas fluorescens or sham-treated at one of two stages during their development. A previous study on these experimental families reported positive effects of egg carotenoids on embryo growth and resistance against the infection. Here, we quantified carotenoid consumption in these infected and sham-infected maternal sib groups. We found that carotenoid contents mostly decreased during embryogenesis. However, these decreases were neither linked to the virulence induced by the pathogen nor dependent on the time point of infection. We conclude that egg carotenoids are not significantly used up by the embryos immune defence.

ecology↗

bioRxiv2018

Comparing methanol-glucose and dimethyl-sulfoxide based extender for milt cryopreservation of brown trout (Salmo trutta)

The potential importance of sperm cryopreservation for aquaculture and conservation management seems still undervalued, probably because the available protocols often lead to reduced fertilization success. We experimentally compared the effectiveness of two different freezing extenders for cryopreservation of brown trout (Salmo trutta) semen, controlling for possible male and female effects. The methanol-glucose based extender that we tested was significantly more effective than a common dimethyl-sulfoxide based extender (a commercial cryopreservation kit). We then studied the effectiveness of the methanol-glucose based extender at different sperm-egg ratios and found no significant differences in fertilization ability of fresh and cryopreserved milt at a sperm-egg ratio of at least 110,000:1. We conclude that brown trout sperm cryopreserved with this extender can be used even at low sperm-egg ratios without significant effects on fertilization rates.

physiology↗

bioRxiv2017

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

Endocrine disrupting chemicals are a threat to natural fish populations in the aquatic environment. Their toxicity is usually discussed relative to concentrations in the water the fish are exposed to. In the case of the synthetic compound 17-alpha-ethynylestradiol (EE2), a common and persistent estrogen, concentrations around 1 ng/L have repeatedly been found to induce toxic effects in fish. Here, we used brown trout (Salmo trutta) from a natural population to study EE2 take up and how it affects early life-history. We collected adults during the spawning season, produced 730 families in vitro (to control for potential maternal and paternal effects on embryo stress tolerance), and singly raised 7,300 embryos (in a 2 mL static system) that were either exposed to one dose of EE2 at 1 ng/L (i.e., 2 pg/embryo) or sham-treated. We found that EE2 concentration did not significantly change over a period of 3 months in control containers without embryos. Embryos took up most of the 2 pg EE2 within about 4 weeks at 4.6{degrees}C. EE2 treated embryos experienced higher mortality, delayed hatching of the survivors, and had reduced size at hatching. Our findings suggest that the toxicity of EE2 is often underestimated when discussed at the level of concentrations in water only.

ecology↗

bioRxiv2017

Sex-Specific Changes In Gene Expression And Delayed Sex Differentiation In Response To Estrogen Pollution In Grayling (Salmonidae)

The synthetic 17-ethinylestradiol (EE2) is an estrogenic compound of oral contraceptives and therefore a common pollutant that has been suspected to affect the demography of river-dwelling salmonids. We study a population of European grayling (Thymallus thymallus) that suffers from sex ratio distortions. Here we test how ecologically relevant concentrations of EE2 affect sex-specific gene expression around early stages of sex differentiation. We collected gametes from F1s of wild spawners, used them for in vitro fertilizations, and raised the resulting embryos singly under experimentally controlled conditions. Embryos were either exposed to 1ng/L EE2 or sham-exposed. RNA was collected from samples taken 10 days before hatching, at the day of hatching, and towards the end of the yolk-sac stage, to study gene expression and relate it to genetic sex (sdY genotype). We found that EE2 affects gene expression of a very large number of genes especially at the day of hatching. The effects of EE2 on gene expression is strongly sex-specific. At the day of hatching, EE2 affected about twice as many genes in females than in males, and towards the end of the yolk-sac larval stage, EE2 effects were nearly exclusively observed in females. Among the many effects was, for example, a surprising EE2-induced molecular masculinization in the females heads. Histological examination of gonadal development of EE2-treated or sham-exposed juveniles during the first 4.5 months after hatching revealed a delaying effect of EE2 on sex differentiation. Because grayling sex determination goes through an all-male stage (a rare case of undifferentiated gonochorism), the rate of EE2-induced sex reversal could not be unequivocally determined during the observational period. However, two EE2-treated genetic males had ovarian tissues at the end of the study. We conclude that common levels of EE2 pollution affect grayling from very early stages on by interfering with male and female gene expression around the onset of sex differentiation, by delaying sex differentiation, and by feminizing some males.\n\nAuthor contributionMRR and CW initiated the project. OS, DM, LW, LMC, and CW sampled the adult fish, did the experimental in vitro fertilizations, and prepared the embryos for experimental rearing in the laboratory. All further manipulations on the embryos and the larvae were done by OS, DM, LW, and LMC. The RNA-seq data were analyzed by OS, JR, and MRR, the histological analyses were done by DM, supervised by SK, the molecular genetic sexing was performed by OS and DM, and EV supervised the EE2 analytics. OS and CW performed the remaining statistical analyses and wrote the first version of the manuscript that was then critically revised by all other authors.

ecology↗

bioRxiv2017

Sex Differentiation In Grayling (Salmonidae) Goes Through An All-Male Stage And Is Delayed In Genetic Males Who Instead Grow Faster

Fish can be threatened by distorted sex ratios that arise during sex differentiation. It is therefore important to understand sex determination and differentiation, especially in river-dwelling fish that are often exposed to environmental factors that may interfere with sex differentiation. However, sex differentiation is not sufficiently understood in keystone taxa such as the Thymallinae, one of the three salmonid subfamilies. Here we study a wild grayling (Thymallus thymallus) population that suffers from distorted sex ratios. We found sex determination in the wild and in captivity to be genetic and linked to the sdY locus. We therefore studied sex-specific gene expression in embryos and early larvae that were bred and raised under different experimental conditions, and we studied gonadal morphology in five monthly samples taken after hatching. Significant sex-specific changes in gene expression (affecting about 25,000 genes) started around hatching. Gonads were still undifferentiated three weeks after hatching, but about half of the fish showed immature testes around seven weeks after hatching. Over the next few months, this phenotype was mostly replaced by the \"testis-to-ovary\" or \"ovaries\" phenotypes. The gonads of the remaining fish, i.e. approximately half of the fish in each sampling period, remained undifferentiated until six months after fertilization. Genetic sexing of the last two samples revealed that fish with undifferentiated gonads were all males, who, by that time, were on average larger than the genetic females (verified in 8-months old juveniles raised in another experiment). Only 12% of the genetic males showed testicular tissue six months after fertilization. We conclude that sex differentiation starts around hatching, goes through an all-male stage for both sexes (which represents a rare case of \"undifferentiated\" gonochoristic species that usually go through an all-female stage), and is delayed in males who, instead of developing their gonads, grow faster than females during these juvenile stages.\n\nAuthor contributionMRR and CW initiated the project. DM, OS, AU, LMC, LW, and CW sampled the adult fish, did the experimental in vitro fertilizations, and prepared the embryos for experimental rearing in the laboratory. All further manipulations on the embryos and the larvae were done by DM, OS, AU, LMC, and LW. The RNA-seq data were analyzed by OS, JR, and MRR, the histological analyses were done by DM, supervised by SK, and the molecular genetic sexing was performed by DM, OS, AU, and KBM. DM, OS, and CW performed the remaining statistical analyses and wrote the first version of the manuscript that was then critically revised by all other authors.

developmental biology↗