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Expression profiles of male and female Drosophila melanogaster with X-chromosomes that were subjected to male-limited evolution

ABSTRACT: Due to its hemizygous mode of inheritance and role in sex determination, the X chromosome is expected to play an important role in the evolution of sexual dimorphism, and to be enriched for sexually antagonistic genetic variation. By forcing the X chromosome to only be expressed in males over many generations, we changed the selection pressures on the X to become similar to those experienced by the Y chromosome. This releases the X from any constraints arising from selection in females, and is predicted to lead to specialization for male fitness, including masculinization of phenotypes that normally experience sexually antagonistic selection. Indeed, we found evidence of this via upregulation of male-benefit sexually antagonistic genes, and downregulation of X-linked female benefit genes. Interestingly, we could detect evidence of microevolutionary changes consistent with previously documented patterns of macroevolutionary change, such as changes in expression consistent with previously established patterns of sexual dimorphism, an increase in the expression of metabolic genes related to mitonuclear conflict, and evidence that dosage compensation constitutes a constraint for male-benefit genes. These results confirm the importance of the X in the evolution of sexual dimorphism and as a source for sexually antagonistic genetic variation, and demonstrate that experimental evolution can be a fruitful method for testing theories of sex chromosome evolution. Microarray data was used to detect differences in gene expression as result of experimental evolution.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE123827 | GEO | 2018/12/14

REPOSITORIES: GEO

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Project description:Sexually dimorphic traits are by definition exaggerated in one sex, which may arise from a history of sex-specific selection â in males, females, or both. If this exaggeration comes at a cost, exaggeration is expected to be greater in higher condition individuals (condition-dependent). Although studies using small numbers of morphological traits are generally supportive, this prediction has not been examined at a larger scale. We test this prediction across the trancriptome by determining the condition-dependence of sex-biased (dimorphic) gene expression. We find that high-condition populations are more sexually dimorphic in transcription than low-condition populations. High condition populations have more male-biased genes and more female-biased genes, and a greater degree of sexually dimorphic expression in these genes. Also, condition-dependence in male-biased genes was greater than in a set of unbiased genes. Interestingly, male-biased genes expressed in the testes were not more condition-dependent than those in the soma. By contrast, increased female-biased expression under high condition may be have occurred because of the greater contribution of the ovary-specific transcripts to the entire mRNA pool. We did not find any genomic signatures distinguishing the condition-dependent sex-biased genes. The degree of condition-dependent sexual dimorphism (CDSD) did not differ between the autosomes and the X-chromosome. There was only weak evidence that rates of evolution correlated with CDSD. We suggest that the sensitivity of both female-biased genes and male-biased genes to condition may be akin to the overall heightened sensitivity to condition that life-history and sexually selected traits tend to exhibit. Our results demonstrate that through condition-dependence, early life experience has dramatic effects on sexual dimorphism in the adult transcriptome. There were 8 biologically distinct samples. Each was replicated 6 times for a total of 48 biological samples on 24 arrays. There was no reference or control sample as a loop design was used. Each of the 48 samples are represented separately.

Project description:Despite sharing much of their genomes, males and females are often highly dimorphic, reflecting at least in part the resolution of sexual conflict in response to sexually antagonistic selection. Sexual dimorphism arises owing to sex differences in gene expression, and steroid hormones are often invoked as a proximate cause of sexual dimorphism. Experimental elevation of androgens can lead to masculinization of behavior, physiology, and gene expression, but knowledge of the role of hormones remains incomplete, including how the sexes differ in their gene expression in response to exposure to hormones. We addressed these questions in a bird species with a long history of behavioral endocrinological and ecological study, the dark-eyed junco (Junco hyemalis), using a species-specific microarray. Focusing on two brain regions involved in sexually dimorphic behavior and regulation of hormone secretion, we identified 1,639 genes that differed in expression by sex in the ventromedial telencephalon and 768 in hypothalamus. In response to experimentally elevated testosterone, females exhibited a more “male-like” expression pattern than control females; unexpectedly, male expression patterns became more “female-like” rather than hyper-masculinized when compared to control males. This sex difference in pattern arose both because testosterone altered regulation of different genes in each sex and because testosterone altered regulation of the same genes differentially, i.e., up in one sex, down in the other. Hormonally regulated gene expression is a key genetic and physiological mechanism underlying sexual dimorphism, and further study should help to explain how it relates to the resolution of sexual conflict. Hypothalamus: 24 samples were analyzed, all were biological (not technical) replicates. 6 from males treated with testosterone [MT], 6 from control males [MC], 6 from females treated with testosterone [FT], and 6 from control females [FC]. All hybridizations were paired, and all treatment groups were compared, but no sample was analyzed more than once. Ventromedial telencephalon: 24 samples were analyzed, all were biological (not technical) replicates. 6 from males treated with testosterone [MT], 6 from control males [MC], 6 from females treated with testosterone [FT], and 6 from control females [FC]. All hybridizations were paired, and all treatment groups were compared, but no sample was analyzed more than once.

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Expression profiles of male and female Drosophila melanogaster with X-chromosomes that were subjected to male-limited evolution

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