Male Y chromosome facilitates the evolution of sex differences in body size

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Women and men differ in many ways and yet they share the same genome. The only exception is the male Y chromosome. Using beetles as a study system, new research from Uppsala University, now published in Ecology and evolution of nature, shows that despite the Y chromosome containing very few genes, it can radically change the size of the male body and thus facilitate the development of sexual differences.

Females and males generally differ in many ways in their morphology, physiology, and behavior. How such gender differences, known as sexual dimorphism, evolve is a puzzle as women and men share the same set of genes and an evolutionary change in one sex should cause a correlated change even in the other sex. , thus preventing sexual differences from evolving. The new study shows that even small amounts of genetic differences between the sexes can facilitate the evolution of sexual dimorphism as it can evolve in just a few generations.

“Our experiments show that autosomes as well as the two sex chromosomes, the X and the Y, can harbor genetic variation important for sexual dimorphism, but the Y chromosome alone can alter the size difference between the sexes by up to 30 percent. This is remarkable because in these beetles the Y chromosome contains only a handful of genes and is a very small fraction of the genome, just like in humans. Many believe that the Y only affects the genes. most important reproductive processes in males, namely sperm production, suggest that the Y chromosome may have a larger role than previously believed, ”says Philipp Kaufmann, a Ph.D. student in the Department. of Ecology and Genetics from Uppsala University and first author of the study.

The course of sexual dimorphism, however, depends not only on where genetic variation resides in the genome, but also on how natural and sexual selection can act on it. Using evolution in the lab, the research team showed that sexual size dimorphism may evolve when selecting for height in males, but when selection only acts on females, the shared part of the genome elicited a correlated evolutionary response in males preventing dimorphism from evolving.

“The most dramatic change in sexual dimorphism, a 50% increase in just ten generations, occurred when we applied selection in a sexually antagonistic fashion, favoring the opposite body size in both sexes. This shows that with the right kind of selection, sex differences can clearly evolve. quickly, perhaps easier than previously thought, ”says Elina Immonen, assistant professor in the Department of Ecology and Genetics at Uppsala University, and lead investigator of the study.

“Combining information on the type of genetic variation available for selection with different forms of selection is a powerful way to test the determinants of the evolution of sex differences. By isolating the effect of the Y chromosome variation from the rest of the genome, we could directly demonstrate the magnitude of the Y chromosome effect, which we didn’t expect to see when we started labor and it helped to understand how sexual dimorphism evolved in this species. Future work will tell us more about how the Y chromosome can have such an important effect on males and how general its role is in the evolution of sex differences between taxa, ”concludes Immonen.

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In their study, the researchers characterized the genetic architecture of body size in males and females by creating a large pedigree of over 8,000 beetles (the beetle Callosobruchus maculatus). This multigenerational family tree has been used to quantify autosomal and sex chromosome-linked genetic variation in body size. The use of artificial selection made it possible to test how different forms of selection affect the evolution of height dimorphism and included selection acting only on males, only on females, or sexually acting antagonistically (in opposite directions). ) in both sexes. After ten generations of selection, the sexual size dimorphism was compared between the breeding lines and the ancestral pedigree population. These two experiments clearly indicated that the Y chromosome plays an important role in determining the male response to selection. In order to further test the effect of Y-linked variation independently of variation in the rest of the genome, the research team performed a third experiment. They isolated the effect of the Y chromosome on sexual size dimorphism in these beetles by introducing the different Y chromosomes in a genetically identical background. In other words, create beetles that are identical twins except for the Y chromosome.


Experiments show that natural selection is opposed to sexual selection


More information:
Philipp Kaufmann et al, Rapid evolution of sexual size dimorphism facilitated by Y-linked genetic variance, Ecology and evolution of nature (2021). DOI: 10.1038 / s41559-021-01530-z

Provided by Uppsala University

Quote: Male Y Chromosome Facilitates Evolution of Sex Differences in Body Size (2021, August 24) Retrieved October 24, 2021 from https://phys.org/news/2021-08-male-chromosome-evolution- sex-differences.html

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