There are specific chemical tags on the DNA of the embryo of the fish. The genes can be changed so that the sex of the embryo is determined. It's not just a fundamental scientific interest in this finding. Since an influence of temperature on sex determination could be a recipe for disaster, it's relevant for conservativism.
The first author of the study is a researcher at the Department of Animal Sciences at Gttingen University. The interaction between environment and genotype is thought to be caused by epigenetics.
Sex is determined by genes interacting with environment.
Most of us are familiar with the XX/XY system of mammals. Sex is mostly determined by the environment. The influence of the environment, for example temperature or population density, can affect the susceptibility of genes to one sex over another. The environment may make a mark on the genome of such species.
In the model species of the zebrafish, the answers seem to be the same. They show that high temperature causes methyl groups to be added to the DNA. The expression of downstream genes is usually dialed down there.
There are rudimentary ovary-like gonads in the embryo of the fish. Depending on the "crosstalk" between the many sex-determining genes and the environment, individuals may be able to reabsorb these Proto-ovaries and become males.
Sex reversal occurs when the temperature is higher.
3.5 months later, a single generation was raised for each of the 17 families. Each family had around 200 siblings. Half of the embryos within each family were exposed to 35 C when they were five to 24 hours old. After a brief exposure to 35 C, the percentage of males in a family became higher. It's not possible to determine which male was born male and which was reversed sex at the moment.
Two families were selected for experiments, one male and one female. The testes and ovaries of the two families were separated for the two treatments. They used a technique calledBS-Seq on the DNA in 72 of the gonad samples. They looked at 174 genes that were thought to be involved in sex determination. They looked at the promoter regions of genes in the general.
54 genes that are "hot spots" for crosstalk between environment and genes predisposing to either sex were identified by the team. Male-biased broods can be created here due to higher temperatures in the embryo. Many of the genes found here have been shown to be important for reproduction in other parts of the world.
The co-author says that their results show for the first time that the existence of male-biased and female-biased families is due to differences in the degree of DNA methylation.
Climate warming may cause sex ratios to be abnormal.
The director of the Institute of Veterinary Medicine at Gttingen University concluded that the results show that epigenetic regulatory mechanisms are important in shaping sex in species with different sex determinations.
The researchers think that their results can be generalized to other species with the same sex determination system.
"Because their sex-determining system is sensitive to temperature, such species run a greater risk of becoming extinct when they produce maladaptive, strongly skewed sex ratios under the predicted global warming scenario," said the author.
More information: Shahrbanou Hosseini et al, Epigenetic Regulation of Phenotypic Sexual Plasticity Inducing Skewed Sex Ratio in Zebrafish, Frontiers in Cell and Developmental Biology (2022). DOI: 10.3389/fcell.2022.880779
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