| 1. |
- Mank, Judith E, et al.
(författare)
-
Are sex-biased genes more dispensable?
- 2009
-
Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 5:3, s. 409-412
-
Tidskriftsartikel (refereegranskat)abstract
- Many genes show different expression levels in males and females, and these form the basis of sexually dimorphic phenotypes. Sex-biased genes experience accelerated rates of protein evolution, which has been attributed to sexual selection. However, it is possible that the increased rates of molecular evolution, and more importantly the sex-biased gene expression pattern itself, are due to decreased selective constraint. This notion may explain many of the patterns associated with sex-biased gene expression, and changes how we should view the role of natural and sexual selection in relation to these genes.
|
|
| 2. |
- Mank, Judith E., et al.
(författare)
-
Fast-X on the Z : Rapid evolution of sex-linked genes in birds
- 2007
-
Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 17:5, s. 618-624
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical work predicts natural selection to be more efficient in the fixation of beneficial mutations in X-linked genes than in autosomal genes. This “fast-X effect” should be evident by an increased ratio of nonsynonymous to synonymous substitutions (dN/dS) for sex-linked genes; however, recent studies have produced mixed support for this expectation. To make an independent test of the idea of fast-X evolution, we focused on birds, which have female heterogamety (males ZZ, females ZW), where analogous arguments would predict a fast-Z effect. We aligned 2.8 Mb of orthologous protein-coding sequence of zebra finch and chicken from 172 Z-linked and 4848 autosomal genes. Zebra finch data were in the form of EST sequences from brain cDNA libraries, while chicken genes were from the draft genome sequence. The dN/dS ratio was significantly higher for Z-linked (0.110) than for all autosomal genes (0.085; P = 0.002), as well as for genes linked to similarly sized autosomes 1–10 (0.0948; P = 0.04). This pattern of fast-Z was evident even after we accounted for the nonrandom distribution of male-biased genes. We also examined the nature of standing variation in the chicken protein-coding regions. The ratio of nonsynonymous to synonymous polymorphism (pN/pS) did not differ significantly between genes on the Z chromosome (0.104) and on the autosomes (0.0908). In conjunction, these results suggest that evolution proceeds more quickly on the Z chromosome, where hemizygous exposure of beneficial nondominant mutations increases the rate of fixation.
|
|
| 3. |
- Mank, Judith E.
(författare)
-
Mating preferences, sexual selection and patterns of cladogenesis in ray-finned fishes
- 2007
-
Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 20:2, s. 597-602
-
Tidskriftsartikel (refereegranskat)abstract
- Evolutionary theory predicts that sexual selection may increase taxonomic diversity when emergent mating preferences result in reproductive isolation and therefore speciation. This theory has been invoked to explain patterns of diversity in ray-finned fishes (most notably in the cichlids), but the theory has not been tested comparatively in fish. Additionally, several other unrelated factors have been identified as promoters of cladogenesis, so it is unclear how important sexual selection might be in diversification. Using sister-clade analysis, I tested the relationship between the presence of sexually selected traits and taxonomic diversification in actinopterygiian fishes, a large clade that shows substantial diversity in mating preferences and related sexually selected traits. In all identified sister-families that differed with regard to the proportion of species manifesting sexually selected traits, sexual selection was correlated with increased diversification, and this association was significant across all sister clades (P = 0.02). This suggests that sexual selection, when present, is a substantial driver of diversification in the ray-finned fishes, and lends further empirical support to the theoretical link between mating preferences and accelerated cladogenesis.
|
|
| 4. |
- Mank, Judith E., et al.
(författare)
-
Parallel divergence and degradation of the avian W sex chromosome
- 2007
-
Ingår i: Trends in Ecology & Evolution. - : Elsevier BV. - 0169-5347 .- 1872-8383. ; 22:8, s. 389-391
-
Tidskriftsartikel (refereegranskat)abstract
- Sex chromosomes are ubiquitous in birds but our understanding of how they originated and evolved has remained incomplete. Recent work by Tsuda et al. on tinamou and ratite birds suggests that, although all bird sex chromosomes evolved from the same pair of autosomes, the Z and W sex chromosomes have diverged from one another several times independently. This parallel evolution of the avian W presents a means for comparison in studies of sex chromosome evolution, which could help us understand more about the general forces that shape the development of all types of sex chromosome.
|
|
| 5. |
- Mank, Judith E, et al.
(författare)
-
Pleiotropic constraint hampers the resolution of sexual antagonism in vertebrate gene expression
- 2008
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 171:1, s. 35-43
-
Tidskriftsartikel (refereegranskat)abstract
- The numerous physiological and phenotypic differences between the sexes, as well as the disparity between male and female reproductive interests, result in sexual conflicts, which are often manifested at the genomic level. Sexually antagonistic genes benefit one sex at the expense of the other and experience strong pressure to evolve male- and female-specific expression patterns to resolve sexual conflicts and maximize fitness for both sexes. Sex-biased gene expression has recently been demonstrated for much of the metazoan transcriptome, suggesting that many loci are sexually antagonistic. However, many coding regions function in multiple processes throughout the organism. This pleiotropy increases the complexity of selection for any given gene, which in turn may obscure sex-specific selective pressures and hamper the evolution of sex-biased gene expression. Here we use microarray gene expression data, in conjunction with data on transcript abundance from expressed sequence tag libraries, to demonstrate that loci with sex-biased gene expression are significantly less pleiotropic than unbiased genes. This relationship was independent of sex chromosome gene dosage effects, and the results were concordant across two study organisms, chicken and mouse. These results suggest that the resolution of sexually antagonistic gene expression is determined by the evolutionary constraints acting on any given antagonistic locus.
|
|
| 6. |
- Mank, Judith E., et al.
(författare)
-
Rapid evolution of female-biased, but not male-biased, genes expressed in the avian brain
- 2007
-
Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 24:12, s. 2698-2706
-
Tidskriftsartikel (refereegranskat)abstract
- The powerful pressures of sexual and natural selection associated with species recognition and reproduction are thought to manifest in a faster rate of evolution in sex-biased genes, an effect that has been documented particularly for male-biased genes expressed in the reproductive tract. However, little is known about the rate of evolution for genes involved in sexually dimorphic behaviors, which often form the neurological basis of intrasexual competition and mate choice. We used microarray data, designed to uncover sex-biased expression patterns in embryonic chicken brain, in conjunction with data on the rate of sequence evolution for >4,000 coding regions aligned between chicken and zebra finch in order to study the role of selection in governing the molecular evolution for sex-biased and unbiased genes. Surprisingly, we found that female-biased genes, defined across a range of cutoff values, show a higher rate of functional evolution than both male-biased and unbiased genes. Autosomal male-biased genes evolve at a similar rate as unbiased genes. Sex-specific genomic properties, such as heterogeneity in genomic distribution and GC content, and codon usage bias for sex-biased classes fail to explain this surprising result, suggesting that selective pressures may be acting differently on the male and female brain.
|
|
| 7. |
|
|
| 8. |
- Mank, Judith E., et al.
(författare)
-
SEX-LINKAGE OF SEXUALLY ANTAGONISTIC GENES IS PREDICTED BY FEMALE, BUT NOT MALE, EFFECTS IN BIRDS
- 2009
-
Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 63:6, s. 1464-1472
-
Tidskriftsartikel (refereegranskat)abstract
- Evolutionary theory predicts that sexually antagonistic loci will be preferentially sex-linked, and this association can be empirically testes with data on sex-biased gene expression with the assumption that sex-biased gene expression represents the resolution of past sexual antagonism. However, incomplete dosage compensating mechanisms and meiotic sex chromosome inactivation have hampered efforts to connect expression data to theoretical predictions regarding the genomic distribution of sexually antagonistic loci in a variety of animals. Here we use data on the underlying regulatory mechanism that produce expression sex-bias to test the genomic distribution of sexually antagonistic genes in chicken. Using this approach, which is free from problems associated with the lack of dosage compensation in birds, we show that female-detriment genes are significantly overrepresented on the Z chromosome, and female-benefit genes underrepresented. By contrast, male-effect genes show no over-or underrepresentation on the Z chromosome. These data are consistent with a dominant mode of inheritance for sexually antagonistic genes, in which male-benefit coding mutations are more likely to be fixed on the Z due to stronger male-specific selective pressures. After fixation of male-benefit alleles, regulatory changes in females evolve to minimize antagonism by reducing female expression.
|
|
| 9. |
- Mank, Judith E.
(författare)
-
The evolution of sexually selected traits and antagonistic androgen expression in actinopterygiian fishes
- 2007
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 169:1, s. 142-149
-
Tidskriftsartikel (refereegranskat)abstract
- Many sexually selected traits in male fishes are controlled by testosterone. Directional selection for male ornaments could theoretically increase male testosterone levels over evolutionary time-scales, and when genetically correlated, female testosterone levels as well. Because of the negative fitness consequences of high testosterone, it is plausible that female choice for sexually selected traits in males results in decreased female reproductive fitness. I used comparative analysis to examine the association between male peak testosterone expression and sexually selected ornaments. I also tested for genetic correlation between male and female androgen levels. The presence of sexually selected traits in males was significantly correlated with increased peak androgen levels in males as well as females, and female testosterone levels were significantly correlated with male peak testosterone titers, although the slope was only marginally < 1. This suggests that selection to decouple high male and female testosterone levels is either weak or otherwise ineffective.
|
|
| 10. |
- Mank, Judith E., et al.
(författare)
-
The unique genomic properties of sex-biased genes: insights from avian microarray data
- 2008
-
Ingår i: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 9, s. 148-
-
Tidskriftsartikel (refereegranskat)abstract
- Background: In order to develop a framework for the analysis of sex-biased genes, we present a characterization of microarray data comparing male and female gene expression in 18 day chicken embryos for brain, gonad, and heart tissue. Results: From the 15982 significantly expressed coding regions that have been assigned to either the autosomes or the Z chromosome ( 12979 in brain, 13301 in gonad, and 12372 in heart), roughly 18% were significantly sex- biased in any one tissue, though only 4 gene targets were biased in all tissues. The gonad was the most sex- biased tissue, followed by the brain. Sex- biased autosomal genes tended to be expressed at lower levels and in fewer tissues than unbiased gene targets, and autosomal somatic sex- biased genes had more expression noise than similar unbiased genes. Sex-biased genes linked to the Z- chromosome showed reduced expression in females, but not in males, when compared to unbiased Z- linked genes, and sex- biased Z- linked genes were also expressed in fewer tissues than unbiased Z coding regions. Third position GC content, and codon usage bias showed some sex- biased effects, primarily for autosomal genes expressed in the gonad. Finally, there were several over-represented Gene Ontology terms in the sex- biased gene sets. Conclusion: On the whole, this analysis suggests that sex- biased genes have unique genomic and organismal properties that delineate them from genes that are expressed equally in males and females.
|
|
