| 1. |
- Kaufmann, Philipp, 1991-, et al.
(författare)
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Assembly of polymorphic Y chromosomes reveals molecular basis of variation in male body size
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Y chromosome of males is theorized to facilitate the evolution of sexual dimorphism by accumulating sexually antagonistic loci, but empirical support is limited. In the seed beetle Callosobruchus maculatus, variation in sexually antagonistic body size is linked to at least two segregating Y haplotypes in males that facilitated rapid laboratory evolution of sexual size dimorphism. Here we assemble previously uncharacterized C. maculatus sex chromosome sequences and identify molecular differences between the two predicted Y haplotypes. The Y chromosome of C. maculatus shows typical hallmarks of degeneration: it is ampliconic and approximately 80% smaller than the X. Nevertheless, the Y harbors over 400 genes with a mixed autosomal and X chromosome ancestry that are enriched with metabolic, developmental and gene regulatory functions. Crucially, we find that besides an autosomal copy of the gene target of rapamycin (TOR), males carry an additional TOR copy on the Y chromosome. TOR is a conserved regulator of growth across taxa, and a Y-linked copy of TOR thus provides a male specific opportunity to alter body size. The two identified Y haplotypes show fixed single nucleotide differences in or in close proximity to over 100 genes, but also copy number variation for TOR, where the more frequent (~95%) Y haplotype that causes increased sexual size dimorphism has two additional TOR copies. These results suggest that part of the sexual conflict over body size has been mitigated by autosome to Y translocation of TOR followed by gene duplications that further increased sexual dimorphism.
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| 2. |
- Kaufmann, Philipp, 1991-, et al.
(författare)
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Sexually antagonistic selection maintains genetic variance when sexual dimorphism evolves
- 2023
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : Royal Society. - 0962-8452 .- 1471-2954. ; 290:1995
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Tidskriftsartikel (refereegranskat)abstract
- Genetic variance (VG) in fitness related traits is often unexpectedly high, evoking the question how VG can be maintained in the face of selection. Sexually antagonistic (SA) selection favouring alternative alleles in the sexes is common and predicted to maintain VG, while directional selection should erode it. Both SA and sex-limited directional selection can lead to sex-specific adaptations but how each affect VG when sexual dimorphism evolves remain experimentally untested. Using replicated artificial selection on the seed beetle Callosobruchus maculatus body size we recently demonstrated an increase in size dimorphism under SA and male-limited (ML) selection by 50% and 32%, respectively. Here we test their consequences on genetic variation. We show that SA selection maintained significantly more ancestral, autosomal additive genetic variance than ML selection, while both eroded sex-linked additive variation equally. Ancestral female-specific dominance variance was completely lost under ML, while SA selection consistently sustained it. Further, both forms of selection preserved a high genetic correlation between the sexes (rm,f). These results demonstrate the potential for sexual antagonism to maintain more genetic variance while fueling sex-specific adaptation in a short evolutionary timescale, and are in line with predicted importance of sex-specific dominance reducing sexual conflict over alternative alleles.
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| 3. |
- Kaufmann, Philipp, 1991-, et al.
(författare)
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Signatures of sex-specific dominance in gene expression
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fitness related traits generally tend to show high levels of dominance. Yet, whether such phenotypic dominance is reflected on the level of gene expression remains controversial and its evolutionary implications have mostly been examined at the theoretical level. Recent theory predicts that sexually antagonistic selection should favour sex-dependent dominance modification, whereby variants encoding relatively high expression are dominant in the sex where high expression is favored by selection and vice versa, to alleviate sexual conflict over the expression of shared genes. Such dominance reversal could contribute importantly to the maintenance of genetic variation in fitness related traits. Here, we explore this possibility by testing for sex-specific dominance in gene expression, using three independent inbred line crosses derived from a single population of the seed beetle Callosobruchus maculatus. In a previous quantitative genetic study, a genome wide signal of dominance variance reversal for fitness between the sexes was detected in these lines. We find that dominance patterns in gene expression are overall strongly correlated between the sexes in all three line crosses, but several hundred genes also show significant dominance differences between the sexes. However, the pattern of sex-specific dominance was contingent upon the cross. Sex-specific dominance disproportionately affected transcripts with sex-biased expression in one cross, but we could not detect any conclusive relationship between the direction of sex-bias and dominance. Gene ontology enrichment analysis revealed that transcripts functionally implicated with traits that are known to be under sexually antagonistic selection in C. maculatus are significantly overrepresented among the genes with sex-specific dominance, including enrichment of genes involved in metabolic and growth regulation as well as male courtship. In line with the tenet that sex-specific dominance modifiers should evolve in response to sexual antagonism, we do find signatures of sex-specific dominance in gene expression associated with enduring sexual antagonism.
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| 4. |
- Kaufmann, Philipp, 1991-
(författare)
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The evolution of sexual dimorphism and its genetic underpinnings
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sexual dimorphism often constitutes the largest phenotypic variance within species but it is puzzling how sexual dimorphisms evolve because most of the genome is shared between the sexes. Sexually antagonistic (SA) selection on a shared genome sets the stage for intralocus sexual conflict. In this thesis, I investigate the genetic basis of sexual size dimorphism (SSD) in the seed beetle Callosobruchus maculatus to understand which mechanisms facilitate sex-specific trait evolution. I combine quantitative genetics with artificial selection to examine how shared and sex-specific genetic variances dictate the evolvability of SSD under different forms of selection and test the hypothesis that SA selection maintains shared genetic variance while fueling the evolution of increased sex differences. Using genomic approaches, I identify the Y chromosome in C. maculatus, investigate how it contributes to SSD, and explore signatures of sex-specific dominance in gene expression as a potential mechanism to alleviate sexual conflict.While both sexes largely share autosomal genetic variance underlying body size, I find significant differences in dominance and sex-linked additive genetic variances that facilitate rapid responses in SSD to male-limited and especially SA selection. Compared to sex-limited directional selection, SA selection maintains more additive and particularly female specific dominance genetic variance. Further, I detect sex-specific dominance in expression of genes associated with SA traits in C. maculatus. These results are compatible with predictions that sex-specific dominance may be central to maintaining genetic variance under, and evolve in response to, SA selection.Despite its degeneration, Y-linked additive genetic variance has a large effect on male size, mirrored in rapid male limited responses to artificial selection, which depleted Y-linked genetic variance. Isolating the effect of the Y chromosome by introgressing different Y lineages into an isogenic background, reveals two distinct Y haplotypes responsible for changing SSD by 30%. Long-read sequencing and assembling the majority of the previously unknown Y chromosome in C. maculatus identified that – while both sexes share an autosomal deeply conserved eukaryotic growth regulator target of rapamycin (TOR) – males carry additional TOR copies on the Y chromosome, which to our knowledge is the first description of TOR on a sex chromosome. This suggests that male specific regulation of growth through a private TOR underlies the overall sexual size dimorphism in C. maculatus. In accordance with this, I identify TOR copy number variation between the Y haplotypes, where the Y haplotype associated with the more pronounced SSD harbors two additional TOR copies.
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