| 1. |
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| 2. |
- Arnqvist, Göran, 1961-, et al.
(författare)
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Sexual conflict promotes speciation in insects
- 2000
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - Umea Univ, Dept Ecol & Environm Sci, SE-90187 Umea, Sweden. : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 97:19, s. 10460-10464
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Tidskriftsartikel (refereegranskat)abstract
- Speciation rates among extant lineages of organisms vary extensively, but our understanding of the causes of this variation and, therefore, the processes of speciation is still remarkably incomplete. Both theoretical and empirical studies have indicated that sexual selection is important in speciation, but earlier discussions have focused almost exclusively on the potential role of female mate choice. Recent findings of postmating reproductive conflicts of interest between the sexes suggest a quite different route to speciation. Such conflicts may lead to perpetual antagonistic coevolution between males and females and may thus generate rapid evolutionary divergence of traits involved in reproduction. Here, we assess this hypothesis by contrasting pairs of related groups of insect species differing in the opportunity for postmating sexual conflict. Groups where females mate with many males exhibited speciation rates four times as high as in related groups where females mate only once. Our results not only highlight the general importance of postmating sexual selection in speciation, but also support the recent suggestion that sexual conflict is a key engine of speciation.
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| 3. |
- Bailey, Richard I., et al.
(författare)
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Female Drosophila melanogaster Gene Expression and Mate Choice : The X Chromosome Harbours Candidate Genes Underlying Sexual Isolation
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:2, s. e17358-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The evolution of female choice mechanisms favouring males of their own kind is considered a crucial step during the early stages of speciation. However, although the genomics of mate choice may influence both the likelihood and speed of speciation, the identity and location of genes underlying assortative mating remain largely unknown. Methods and Findings: We used mate choice experiments and gene expression analysis of female Drosophila melanogaster to examine three key components influencing speciation. We show that the 1,498 genes in Zimbabwean female D. melanogaster whose expression levels differ when mating with more (Zimbabwean) versus less (Cosmopolitan strain) preferred males include many with high expression in the central nervous system and ovaries, are disproportionately X-linked and form a number of clusters with low recombination distance. Significant involvement of the brain and ovaries is consistent with the action of a combination of pre- and postcopulatory female choice mechanisms, while sex linkage and clustering of genes lead to high potential evolutionary rate and sheltering against the homogenizing effects of gene exchange between populations. Conclusion: Taken together our results imply favourable genomic conditions for the evolution of reproductive isolation through mate choice in Zimbabwean D. melanogaster and suggest that mate choice may, in general, act as an even more important engine of speciation than previously realized.
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| 4. |
- Bilde, Trine, et al.
(författare)
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Sex differences in the genetic architecture of lifespan in a seed beetle : extreme inbreeding extends male lifespan
- 2009
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 9, s. 33-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Sex differences in lifespan are ubiquitous throughout the animal kingdom but the causes underlying this phenomenon remain poorly understood. Several explanations based on asymmetrical inheritance patterns (sex chromosomes or mitochondrial DNA) have been proposed, but these ideas have rarely been tested experimentally. Alternatively, sexual dimorphism in lifespan could result from sex-specific selection, caused by fundamental differences in how males and females optimize their fitness by allocating resources into current and future reproduction. Results: Here we used sex-specific responses to inbreeding to study the genetic architecture of lifespan and mortality rates in Callosobruchus maculatus, a seed beetle that shows sexual dimorphism in lifespan. Two independent assays revealed opposing sex-specific responses to inbreeding. The combined data set showed that inbred males live longer than outbred males, while females show the opposite pattern. Both sexes suffered reduced fitness measured as lifetime reproductive success as a result of inbreeding. Conclusion: No model based on asymmetrical inheritance can explain increased male lifespan in response to inbreeding. Our results are however compatible with models based on sex-specific selection on reproductive strategies. We therefore suggest that sex-specific differences in lifespan in this species primarily result from sexually divergent selection.
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| 5. |
- Bilde, T., et al.
(författare)
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The genetic architecture of fitness in a seed beetle : assessing the potential for indirect genetic benefits of female choice
- 2008
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 8, s. 295-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Quantifying the amount of standing genetic variation in fitness represents an empirical challenge. Unfortunately, the shortage of detailed studies of the genetic architecture of fitness has hampered progress in several domains of evolutionary biology. One such area is the study of sexual selection. In particular, the evolution of adaptive female choice by indirect genetic benefits relies on the presence of genetic variation for fitness. Female choice by genetic benefits fall broadly into good genes (additive) models and compatibility (non-additive) models where the strength of selection is dictated by the genetic architecture of fitness. To characterize the genetic architecture of fitness, we employed a quantitative genetic design (the diallel cross) in a population of the seed beetle Callosobruchus maculatus, which is known to exhibit post-copulatory female choice. From reciprocal crosses of inbred lines, we assayed egg production, egg-to-adult survival, and lifetime offspring production of the outbred F1 daughters (F1 productivity). Results: We used the bio model to estimate six components of genetic and environmental variance in fitness. We found sizeable additive and non-additive genetic variance in F-1 productivity, but lower genetic variance in egg-to-adult survival, which was strongly influenced by maternal and paternal effects. Conclusion: Our results show that, in order to gain a relevant understanding of the genetic architecture of fitness, measures of offspring fitness should be inclusive and should include quantifications of offspring reproductive success. We note that our estimate of additive genetic variance in F-1 productivity (CVA = 14%) is sufficient to generate indirect selection on female choice. However, our results also show that the major determinant of offspring fitness is the genetic interaction between parental genomes, as indicated by large amounts of non-additive genetic variance (dominance and/or epistasis) for F-1 productivity. We discuss the processes that may maintain additive and non-additive genetic variance for fitness and how these relate to indirect selection for female choice.
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| 6. |
- Brengdahl, Martin, et al.
(författare)
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Genetic Quality Affects the Rate of Male and Female Reproductive Aging Differently in Drosophila melanogaster
- 2018
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 192:6, s. 761-772
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Tidskriftsartikel (refereegranskat)abstract
- Males and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive aging. Here we investigate whether reproductive aging and life span respond to condition differently in male and female Drosophila melanogaster, as predicted if sexual selection has shaped male and female resource-allocation patterns. We manipulate condition through genetic quality by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male reproductive output than on female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive aging between the sexes in low condition, but in high condition reproductive aging is relatively faster in males. No corresponding sex-specific change was found for life span. The sex difference in reproductive aging appearing in high condition was specifically due to a decreased aging rate in females rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more toward somatic maintenance than males.
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| 7. |
- Brengdahl, Martin, et al.
(författare)
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Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis
- 2018
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Ingår i: Evolution. - : WILEY. - 0014-3820 .- 1558-5646. ; 72:3, s. 568-577
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Tidskriftsartikel (refereegranskat)abstract
- Life span differs between the sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the heterogametic sex suffers a shortened life span because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (approximate to 20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced life span or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the heterogametic sex appears too small to explain general sex differences in life span.
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| 8. |
- Burgevin, Lorraine, et al.
(författare)
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Intersexual correlation for same-sex sexual behaviour in an insect
- 2013
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 85:4, s. 759-762
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Tidskriftsartikel (refereegranskat)abstract
- Same-sex sexual behaviour is widespread across taxa and is particularly common in insects, in which up to 50% of copulation attempts by males are directed towards other males in some species. Research effort has focused on male-male same-sex behaviour and the prevailing theory is that benefits of high mating rate combined with poor sex discrimination explain the high incidence of male-male mounting. However, the evolution of female-female mounting is more enigmatic, since females typically do not mount males in order to mate. Using a full-sib design, we found an intersexual correlation for same-sex mounting in the beetle Callosobruchus maculatus. Variation in male-male mounting across families explained over 20% of variation in female-female mounting. Moreover, we found no evidence that same-sex behaviour was related to general activity level in either sex or carried a fitness cost to females. Taken together, our results suggest that female-female mounting is a relatively low-cost behaviour that may be maintained in the population via selection on males.
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| 9. |
- Dowling, Damian K., et al.
(författare)
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A comparison of nuclear and cytoplasmic genetic effects on sperm competitiveness and female remating in a seed beetle
- 2007
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 20:6, s. 2113-2125
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Tidskriftsartikel (refereegranskat)abstract
- It is widely assumed that male sperm competitiveness evolves adaptively. However, recent studies have found a cytoplasmic genetic component to phenotypic variation in some sperm traits presumed important in sperm competition. As cytoplasmic genes are maternally transmitted, they cannot respond to selection on sperm and this constraint may affect the scope in which sperm competitiveness can evolve adaptively. We examined nuclear and cytoplasmic genetic contributions to sperm competitiveness, using populations of Callosobruchus maculatus carrying orthogonal combinations of nuclear and cytoplasmic lineages. Our design also enabled us to examine genetic contributions to female remating. We found that sperm competitiveness and remating are primarily encoded by nuclear genes. In particular, a male's sperm competitiveness phenotype was contingent on an interaction between the competing male genotypes. Furthermore, cytoplasmic effects were detected on remating but not sperm competitiveness, suggesting that cytoplasmic genes do not generally play a profound evolutionary role in sperm competition.
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| 10. |
- Dowling, D. K., et al.
(författare)
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Applying the genetic theories of ageing to the cytoplasm : cytoplasmic genetic covariation for fitness and lifespan
- 2009
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 22:4, s. 818-827
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Tidskriftsartikel (refereegranskat)abstract
- Two genetic models exist to explain the evolution of ageing - mutation accumulation (MA) and antagonistic pleiotropy (AP). Under MA, a reduced intensity of selection with age results in accumulation of late-acting deleterious mutations. Under AP, late-acting deleterious mutations accumulate because they confer beneficial effects early in life. Recent studies suggest that the mitochondrial genome is a major player in ageing. It therefore seems plausible that the MA and AP models will be relevant to genomes within the cytoplasm. This possibility has not been considered previously. We explore whether patterns of covariation between fitness and ageing across 25 cytoplasmic lines, sampled from a population of Drosophila melanogaster, are consistent with the genetic associations predicted under MA or AP. We find negative covariation for fitness and the rate of ageing, and positive covariation for fitness and lifespan. Notably, the direction of these associations is opposite to that typically predicted under AP.
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| 11. |
- Dowling, Damian K., et al.
(författare)
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Evolutionary implications of non-neutral mitochondrial genetic variation
- 2008
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Ingår i: Trends in Ecology & Evolution. - : Cell Press. - 0169-5347 .- 1872-8383. ; 23:10, s. 546-554
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Forskningsöversikt (refereegranskat)abstract
- Sequence variation in mitochondrial DNA (mtDNA) was traditionally considered to be selectively neutral. However, an accumulating body of evidence indicates that this assumption is invalid. Furthermore, recent advances indicate that mtDNA polymorphism can be maintained within populations via selection on the joint mitochondrial-nuclear genotype. Here, we review the latest findings that show mitochondrial and cytoplasmic genetic variation for life-history traits and fitness. We highlight the key importance of the mitochondrial-nuclear interaction as a unit of selection and discuss the consequences of mitochondrially encoded fitness effects on several key evolutionary processes. Our goal is to draw attention to the profound, yet neglected, influence of the mitochondrial genome on the fields of ecology and evolution.
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| 12. |
- Dowling, Damian k., et al.
(författare)
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Intergenomic epistasis for fitness : Within-population interactions between cytoplasmic and nuclear genes in Drosophila melanogaster
- 2007
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 175:1, s. 235-244
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Tidskriftsartikel (refereegranskat)abstract
- The symbiotic relationship between the mitochondrial and nuclear genomes coordinates metabolic energy production and is fundamental to life among eukaryotes. Consequently, there is potential for strong selection to shape interactions between these two genomes. Substantial research attention has focused on the possibility that within-population sequence polymorphism in mitochondrial DNA (mtDNA) is maintained by mitonuclear fitness interactions. Early theory predicted that selection will often eliminate mitochondrial polymorphisms. However, recent models demonstrate that intergenomic interactions can promote the maintenance of polymorphism, especially if the nuclear genes involved are linked to the X chromosome. Most empirical studies to date that have assessed cytonuclear fitness interactions have studied variation across populations and it is still unclear how general and strong such interactions are within populations. We experimentally tested for cytonuclear interactions within a laboratory population of Drosophila melanogaster using 25 randomly sampled cytoplasmic genomes, expressed in three different haploid nuclear genetic backgrounds, while eliminating confounding effects of intracellular bacteria (e.g., Wolbachia). We found sizable cytonuclear fitness interactions within this population and present limited evidence suggesting that these effects were sex specific. Moreover, the relative fitness of cytonuclear genotypes was environment specific. Sequencing of mtDNA (2752 bp) revealed polymorphism within the population, suggesting that the observed cytoplasmic genetic effects may be mitochondrial in origin.
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| 13. |
- Erkosar, Berra, et al.
(författare)
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Host diet mediates a negative relationship between abundance and diversity of Drosophila gut microbiota
- 2018
-
Ingår i: Ecology and Evolution. - : WILEY. - 2045-7758. ; 8:18, s. 9491-9502
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient supply to ecosystems has major effects on ecological diversity, but it is unclear to what degree the shape of this relationship is general versus dependent on the specific environment or community. Although the diet composition in terms of the source or proportions of different nutrient types is known to affect gut microbiota composition, the relationship between the quantity of nutrients supplied and the abundance and diversity of the intestinal microbial community remains to be elucidated. Here, we address this relationship using replicate populations of Drosophila melanogaster maintained over multiple generations on three diets differing in the concentration of yeast (the only source of most nutrients). While a 6.5-fold increase in yeast concentration led to a 100-fold increase in the total abundance of gut microbes, it caused a major decrease in their alpha diversity (by 45-60% depending on the diversity measure). This was accompanied by only minor shifts in the taxonomic affiliation of the most common operational taxonomic units (OTUs). Thus, nutrient concentration in host diet mediates a strong negative relationship between the nutrient abundance and microbial diversity in the Drosophila gut ecosystem.
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| 14. |
- Friberg, Urban, et al.
(författare)
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Assessing the potential for an ongoing arms race within and between the sexes : selection and heritable variation
- 2005
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Ingår i: Evolution. - Lawrence, Kans. : John Wiley & Sons. - 0014-3820 .- 1558-5646. ; 59:7, s. 1540-1551
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Tidskriftsartikel (refereegranskat)abstract
- In promiscuous species, sexual selection generates two opposing male traits: offense (acquiring new mates and supplanting stored sperm) and defense (enforcing fidelity on one's mates and preventing sperm displacement when this fails). Coevolution between these traits requires both additive genetic variation and associated natural selection. Previous work with Drosophila melanogaster found autosomal genetic variation for these traits among inbred lines from a mixture of populations, but only nonheritable genetic variation was found within a single outbred population. These results do not support ongoing antagonistic coevolution between offense and defense, nor between either of these male traits and female reproductive characters. Here we use a new method (hemiclonal analysis) to study genomewide genetic variation in a large outbred laboratory population of D. melanogaster. Hemiclonal analysis estimates the additive genetic variation among random, genomewide haplotypes taken from a large, outbred, locally adapted laboratory population and determines the direction of the selection gradient on this variation. In contrast to earlier studies, we found low but biologically significant heritable variation for defensive and offensive offspring production as well as all their components (P1, fidelity, P2, and remating). Genetic correlations between these traits were substantially different from those reported for inbred lines. A positive genetic correlation was found between defense and offense, demonstrating that some shared genes influence both traits. In addition to this common variation, evidence for unique genetic variation for each trait was also found, supporting an ongoing coevolutionary arms race between defense and offense. Reproductive conflict between males can strongly influence female fitness. Correspondingly, we found genetic variation in both defense and offense that affected female fitness. No evidence was found for intersexual conflict in the context of male defense, but we found substantial intersexual conflict in the context of male offensive sperm competitive ability. These results indicate that conflict between competing males also promotes an associated arms race between the sexes.
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| 15. |
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| 16. |
- Friberg, Urban, et al.
(författare)
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Cut thy neighbor : cyclic birth and death of recombination hotspots via genetic conflict.
- 2008
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Ingår i: Genetics. - : Genetics Society of America. - 0016-6731 .- 1943-2631. ; 179:4, s. 2229-2238
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Tidskriftsartikel (refereegranskat)abstract
- Most recombination takes place in numerous, localized regions called hotspots. However, empirical evidence indicates that nascent hotspots are susceptible to removal due to biased gene conversion, so it is paradoxical that they should be so widespread. Previous modeling work has shown that hotspots can evolve due to genetic drift overpowering their intrinsic disadvantage. Here we synthesize recent theoretical and empirical results to show how natural selection can favor hotspots. We propose that hotspots are part of a cycle of antagonistic coevolution between two tightly linked chromosomal regions: an inducer region that initiates recombination during meiosis by cutting within a nearby region of DNA and the cut region itself, which can evolve to be resistant to cutting. Antagonistic coevolution between inducers and their cut sites is driven by recurrent episodes of Hill-Robertson interference, genetic hitchhiking, and biased gene conversion.
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| 17. |
- Friberg, Urban, et al.
(författare)
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Empirical Evidence for Son-Killing X Chromosomes and the Operation of SA-Zygotic Drive
- 2011
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Ingår i: PLOS ONE. - : PlosOne. - 1932-6203. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Background: Diploid organisms have two copies of all genes, but only one is carried by each haploid gamete and diploid offspring. This causes a fundamental genetic conflict over transmission rate between alternative alleles. Single genes, or gene clusters, only rarely code for the complex phenotypes needed to give them a transmission advantage (drive phenotype). However, all genes on a male's X and Y chromosomes co-segregate, allowing different sex-linked genes to code for different parts of the drive phenotype. Correspondingly, the well-characterized phenomenon of male gametic drive, occurring during haploid gametogenesis, is especially common on sex chromosomes. The new theory of sexually antagonistic zygotic drive of the sex chromosomes (SA-zygotic drive) extends the logic of gametic drive into the diploid phase of the lifecycle, whenever there is competition among siblings or harmful sib-sib mating. The X and Y are predicted to gain a transmission advantage by harming offspring of the sex that does not carry them. Results: Here we analyzed a mutant X-chromosome in Drosophila simulans that produced an excess of daughters when transmitted from males. We developed a series of tests to differentiate between gametic and SA-zygotic drive, and provide multiple lines of evidence that SA-zygotic drive is responsible for the sex ratio bias. Driving sires produce about 50% more surviving daughters than sons. Conclusion: Sex-ratio distortion due to genetic conflict has evolved via gametic drive and maternally transmitted endosymbionts. Our data indicate that sex chromosomes can also drive by harming the non-carrier sex of offspring.
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| 18. |
- Friberg, Urban, et al.
(författare)
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Fitness effects of female mate choice : preferred males are detrimental for Drosophila melanogaster females
- 2003
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Ingår i: Journal of Evolutionary Biology. - : John Wiley & Sons. - 1010-061X .- 1420-9101. ; 16, s. 797-811
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.
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| 19. |
- Friberg, Urban
(författare)
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Genetic variation in male and female reproductive characters associated with sexual conflict in Drosophila melanogaster
- 2005
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Ingår i: Behavior Genetics. - New York : Springer. - 0001-8244 .- 1573-3297. ; 35:4, s. 455-462
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that elevated mating, courtship and seminal substances affect female fitness negatively in Drosophila melanogaster. It has also been shown that males vary with respect to these characters and that male harm to females correlates positively with components of male fitness. These results suggest that there is sexual conflict over the effect of such male characters. An important component of this scenario is that females have evolved counteradaptations to male harm, but so far there is limited evidence for this. Here I define female resistance as the ability to withstand an increased exposure to males. Across 10 genetically differentiated lines of D. melanogaster, I found genetic variation among females in the reduction of lifespan that followed from exposure to males of different durations. There was also genetic variation among males with regards to the degree to which they decrease the lifespan of their mates. These results suggest that genetic variation for female ability to endure male sexually antagonistic adaptations exists and may play an important role in male–female coevolution.
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| 20. |
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| 21. |
- Friberg, Urban
(författare)
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Male perception of female mating status : its effect on copulation duration and male and female fitness in Drosophila melanogaster
- 2006
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Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 72:6, s. 1259-1268
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Tidskriftsartikel (refereegranskat)abstract
- When females mate with multiple partners, the risk of sperm competition depends on female mating history. To maximize fitness, males should adjust their copulatory investments according to this risk. In the fruit fly, Drosophila melanogaster, the female cuticular hydrocarbon (CH) profile changes when females mate, and males use this to assess female mating status. I tested whether this cue influenced the time males spent copulating with females and if this affected male fertilization success and female fitness. I manipulated female mating status by transferring CHs from either virgin or mated females to virgin females. Males copulated significantly longer with virgin females that had been coated with CHs from mated females (experimental group) than with virgin females coated with CHs from other virgin females (control group). Copulation duration did not differ between females from the experimental group and females that had already mated. To test whether differential investment in copulation affected male sperm defence and female fitness, experimental and control females were mated once to wild-type males and then either housed with males carrying a genetic marker (experiment 1) or alone (experiment 2). In experiment 1 male sperm defence was elevated when males perceived their partner as mated, and this was mainly due to females remating less. Increased male investment in copulation duration also affected female fitness, although this was reversed between experiments 1 and 2. Finally, these results also indicate that copulations are costly to males, since manipulated males copulated for longer with virgin females than they normally would, resulting in higher fertilization success.
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| 22. |
- Friberg, Urban
(författare)
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Male perception of female mating status : its effect on copulation duration, sperm defence and female fitness
- 2006
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 72:6, s. 1259-1268
-
Tidskriftsartikel (refereegranskat)abstract
- When females mate with multiple partners, the risk of sperm competition depends on female mating history. To maximize fitness, males should adjust their copulatory investments according to this risk. In the fruit fly, Drosophila melanogaster, the female cuticular hydrocarbon (CH) profile changes when females mate, and males use this to assess female mating status. I tested whether this cue influenced the time males spent copulating with females and if this affected male fertilization success and female fitness. I manipulated female mating status by transferring CHs from either virgin or mated females to virgin females. Males copulated significantly longer with virgin females that had been coated with CHs from mated females (experimental group) than with virgin females coated with CHs from other virgin females (control group). Copulation duration did not differ between females from the experimental group and females that had already mated. To test whether differential investment in copulation affected male sperm defence and female fitness, experimental and control females were mated once to wild-type males and then either housed with males carrying a genetic marker (experiment 1) or alone (experiment 2). In experiment 1 male sperm defence was elevated when males perceived their partner as mated, and this was mainly due to females remating less. Increased male investment in copulation duration also affected female fitness, although this was reversed between experiments 1 and 2. Finally, these results also indicate that copulations are costly to males, since manipulated males copulated for longer with virgin females than they normally would, resulting in higher fertilization success.
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| 23. |
- Friberg, Urban, et al.
(författare)
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Mechanisms Promoting the Long-Term Persistence of a Wolbachia Infection in a Laboratory-Adapted Population of Drosophila melanogaster
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:1, s. e16448-
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular bacteria of the genus Wolbachia are widespread endosymbionts across diverse insect taxa. Despite this prevalence, our understanding of how Wolbachia persists within populations is not well understood. Cytoplasmic incompatibility (CI) appears to be an important phenotype maintaining Wolbachia in many insects, but it is believed to be too weak to maintain Wolbachia in Drosophila melanogaster, suggesting that Wolbachia must also have other effects on this species. Here we estimate the net selective effect of Wolbachia on its host in a laboratory-adapted population of D. melanogaster, to determine the mechanisms leading to its persistence in the laboratory environment. We found i) no significant effects of Wolbachia infection on female egg-to-adult survival or adult fitness, ii) no reduced juvenile survival in males, iii) substantial levels of CI, and iv) a vertical transmission rate of Wolbachia higher than 99%. The fitness of cured females was, however, severely reduced (a decline of 37%) due to CI in offspring. Taken together these findings indicate that Wolbachia is maintained in our laboratory environment due to a combination of a nearly perfect transmission rate and substantial CI. Our results show that there would be strong selection against females losing their infection and producing progeny free from Wolbachia.
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| 24. |
- Friberg, Urban, et al.
(författare)
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No evidence of mitochondrial genetic variation for sperm competition within a population of Drosophila melanogaster
- 2008
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 21:6, s. 1798-1807
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Tidskriftsartikel (refereegranskat)abstract
- Cytoplasmic, Drosophila melanogaster, genetic variation, mtDNA, offence/k Recent studies have advocated a role for mitochondrial DNA (mtDNA) in sperm competition. This is controversial because earlier theory and empirical work suggested that mitochondrial genetic variation for fitness is low. Yet, such studies dealt only with females and did not consider that variation that is neutral when expressed in females, might be non-neutral in males as, in most species, mtDNA is never selected in males. We measured male ability to compete for fertilizations, at young and late ages, across 25 cytoplasms expressed in three different nuclear genetic backgrounds, within a population of Drosophila melanogaster. We found no cytoplasmic (thus no mtDNA) genetic variation for either male offence or offensive sperm competitiveness. This contrasts with previous findings demonstrating cytoplasmic genetic variation for female fitness and female ageing across these same lines. Taken together, this suggests that mitochondrial genes do not contribute to variation in sperm competition at the within-population level.
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| 25. |
- Friberg, Urban, 1972-
(författare)
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Sexual conflict and male-female coevolution in the fruit fly
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Harmony and cooperation was for long believed to dominate sexual interactions. This view slowly started to change 25 years ago and is today replaced with a view where males and females act based on what is best from a costs-benefits perspective. When sex specific costs and benefits differ, concerning reproductive decision influenced by both sexes, sexual conflict will occur. The basis for discordant reproductive interests between the sexes is that males produce many small gametes, while females’ produce few and large gametes. One result of this difference is that the optimal mating rate differs between the sexes. Males, with their many small sperm, maximize their reproductive output by mating with many females, while females often do best by not mating more frequently than to fertilize their eggs, since mating often entails a cost. Sexual conflict over mating is thus an important factor shaping the interactions between the sexes. In this thesis I study this and related conflicts between the sexes, using mathematical models, fruit flies and comparative methods. Mathematical modelling was used to explore how males and females may coevolve under sexual conflict over mating. This model shows that sexual conflict over mating results in the evolution of costly female mate choice, in terms high resistance to matings, and costly exaggerated male sexual traits, aimed to manipulate females into mating. A key assumption in this model is that males which females find attractive also are more harmful to females. This assumption was tested by housing fruit fly females with either attractive or unattractive males. Females kept with attractive males were courted and mated more, and suffered a 16 percent reduction in lifetime offspring production. In another study I measured genetic variation in two antagonistic male traits used to compete over females; offence - a male’s ability to acquire new mates and supplant stored sperm, and defence - a male’s ability to induce fidelity in his mates and prevent sperm displacement when remating occurs. Independent additive genetic variation and positive selection gradients were found for both these traits, indicating an ongoing arms race between these male antagonistic traits. This arms race also had a negative impact on females, since high values of offence compromised female fitness. Genetic variation in female ability to withstand male harm was also tested for and found, indicating that females evolve counter adaptations to reduce the effect of harmful male traits. Finally, the proposed link between sexual conflict and speciation was tested. Theory suggests that perpetual sexual arms races will cause allopatric populations to evolve along different evolutionary trajectories, resulting in speciation. This theory was tested using comparative methods by contrasting the number of extant species in taxa with high and low opportunity for sexual conflict. The study showed that taxa with high opportunity for sexual conflict, on average, has four times as many species as those with low opportunity, supporting that sexual conflict is a key process in speciation.
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| 26. |
- Friberg, Urban, et al.
(författare)
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Sexually Antagonistic Zygotic Drive: A New Form of Genetic Conflict between the Sex Chromosomes
- 2015
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Ingår i: Cold Spring Harbor Perspectives in Biology. - : COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT. - 1943-0264. ; 7:3, s. a017608-
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Tidskriftsartikel (refereegranskat)abstract
- Sisters and brothers are completely unrelated with respect to the sex chromosomes they inherit from their heterogametic parent. This has the potential to result in a previously unappreciated form of genetic conflict between the sex chromosomes, called sexually antagonistic zygotic drive (SA-ZD). SA-ZD can arise whenever brothers and sisters compete over limited resources or there is brother-sister mating coupled with inbreeding depression. Although theory predicts that SA-ZD should be common and influence important evolutionary processes, there is little empirical evidence for its existence. Here we discuss the current understanding of SA-ZD, why it would be expected to elude empirical detection when present, and how it relates to other forms of genetic conflict.
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| 27. |
- Friberg, Urban, 1972-, et al.
(författare)
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Sexually Antagonistic “Zygotic Drive” of the Sex Chromosomes
- 2008
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Ingår i: PLOS Genetics. - : PLOS Genetics. - 1553-7390 .- 1553-7404. ; 4:12
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Tidskriftsartikel (refereegranskat)abstract
- Genomic conflict is perplexing because it causes the fitness of a species to decline rather than improve. Many diverse forms of genomic conflict have been identified, but this extant tally may be incomplete. Here, we show that the unusual characteristics of the sex chromosomes can, in principle, lead to a previously unappreciated form of sexual genomic conflict. The phenomenon occurs because there is selection in the heterogametic sex for sex-linked mutations that harm the sex of offspring that does not carry them, whenever there is competition among siblings. This harmful phenotype can be expressed as an antagonistic green-beard effect that is mediated by epigenetic parental effects, parental investment, and/or interactions among siblings. We call this form of genomic conflict sexually antagonistic “zygotic drive”, because it is functionally equivalent to meiotic drive, except that it operates during the zygotic and postzygotic stages of the life cycle rather than the meiotic and gametic stages. A combination of mathematical modeling and a survey of empirical studies is used to show that sexually antagonistic zygotic drive is feasible, likely to be widespread in nature, and that it can promote a genetic “arms race” between the homo- and heteromorphic sex chromosomes. This new category of genomic conflict has the potential to strongly influence other fundamental evolutionary processes, such as speciation and the degeneration of the Y and W sex chromosomes. It also fosters a new genetic hypothesis for the evolution of enigmatic fitness-reducing traits like the high frequency of spontaneous abortion, sterility, and homosexuality observed in humans.
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| 28. |
- Friberg, Urban, 1972-
(författare)
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Två kön och många organ : men bara en arvsmassa
- 2016
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Ingår i: Tidskriften för svensk psykiatri. - : Svenska Psykiatriska Föreningen, Svenska Föreningen för Barn- och Ungdomspsykiatri och Svenska Rättspsykiatriska Föreningen. - 1653-8579. ; :4, s. 28-29
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Hos många arter uppvisar könen en rad skillnader.Dessa omfattar vanligtvis deras utseende så väl som beteende. Vad är det egentligen som orsakar evolution av könsskillnader, hur är den möjlig då könen har i princip samma gener, och kan detta tänkas ha konsekvenser för hur vi människor fungerar?
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| 29. |
- Friberg, Urban, et al.
(författare)
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X- and Y-chromosome linked paternal effects on a life-history trait
- 2012
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 8:1, s. 71-73
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Tidskriftsartikel (refereegranskat)abstract
- Males and females usually invest asymmetrically in offspring. In species lacking parental care, females influence offspring in many ways, while males only contribute genetic material via their sperm. For this reason, maternal effects have long been considered an important source of phenotypic variation, while paternal effects have been presumed to be absent or negligible. The recent surge of studies showing trans-generational epigenetic effects questions this assumption, and indicates that paternal effects may be far more important than previously appreciated. Here, we test for sex-linked paternal effects in Drosophila melanogaster on a life-history trait, and find substantial support for both X- and Y-linked effects.
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| 30. |
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| 31. |
- Gavrilets, Sergey, et al.
(författare)
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The evolution of female mate choice by sexual conflict
- 2001
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Ingår i: Proceedings of the Royal Society of London Series B. - London : The Roylal Society. - 0080-4649 .- 0962-8452 .- 1471-2954. ; 268:1466, s. 531-539
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Tidskriftsartikel (refereegranskat)abstract
- Although empirical evidence has shown that many male traits have evolved via sexual selection by female mate choice, our understanding of the adaptive value of female mating preferences is still very incomplete. It has recently been suggested that female mate choice may result from females evolving resistance rather than attraction to males, but this has been disputed. Here, we develop a quantitative genetic model showing that sexual conflict over mating indeed results in the joint evolution of costly female mate choice and exaggerated male traits under a wide range of circumstances. In contrast to traditional explanations of costly female mate choice, which rely on indirect genetic benefits, our model shows that mate choice can be generated as a side–effect of females evolving to reduce the direct costs of mating.
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| 32. |
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| 33. |
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| 34. |
- Griffin, Robert M., et al.
(författare)
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Autosomal and X-Linked Additive Genetic Variation for Lifespan and Aging : Comparisons Within and Between the Sexes in Drosophila melanogaster
- 2016
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Ingår i: G3. - : Oxford University Press (OUP). - 2160-1836. ; 6:12, s. 3903-3911
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Tidskriftsartikel (refereegranskat)abstract
- Theory makes several predictions concerning differences in genetic variation between the X chromosome and the autosomes due to male X hemizygosity. The X chromosome should: (i) typically show relatively less standing genetic variation than the autosomes, (ii) exhibit more variation in males compared to females because of dosage compensation, and (iii) potentially be enriched with sex-specific genetic variation. Here, we address each of these predictions for lifespan and aging in Drosophila melanogaster. To achieve unbiased estimates of X and autosomal additive genetic variance, we use 80 chromosome substitution lines; 40 for the X chromosome and 40 combining the two major autosomes, which we assay for sex-specific and cross-sex genetic (co)variation. We find significant X and autosomal additive genetic variance for both traits in both sexes (with reservation for X-linked variation of aging in females), but no conclusive evidence for depletion of X-linked variation (measured through females). Males display more X-linked variation for lifespan than females, but it is unclear if this is due to dosage compensation since also autosomal variation is larger in males. Finally, our results suggest that the X chromosome is enriched for sex-specific genetic variation in lifespan but results were less conclusive for aging overall. Collectively, these results suggest that the X chromosome has reduced capacity to respond to sexually concordant selection on lifespan from standing genetic variation, while its ability to respond to sexually antagonistic selection may be augmented.
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| 35. |
- Griffin, Robert M., et al.
(författare)
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The Shared Genome Is a Pervasive Constraint on the Evolution of Sex-Biased Gene Expression
- 2013
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Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 30:9, s. 2168-2176
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Tidskriftsartikel (refereegranskat)abstract
- Males and females share most of their genomes, and differences between the sexes can therefore not evolve through sequence divergence in protein coding genes. Sexual dimorphism is instead restricted to occur through sex-specific expression and splicing of gene products. Evolution of sexual dimorphism through these mechanisms should, however, also be constrained when the sexes share the genetic architecture for regulation of gene expression. Despite these obstacles, sexual dimorphism is prevalent in the animal kingdom and commonly evolves rapidly. Here, we ask whether the genetic architecture of gene expression is plastic and easily molded by sex-specific selection, or if sexual dimorphism evolves rapidly despite pervasive genetic constraint. To address this question, we explore the relationship between the intersexual genetic correlation for gene expression (r(MF)), which captures how independently genes are regulated in the sexes, and the evolution of sex-biased gene expression. Using transcriptome data from Drosophila melanogaster, we find that most genes have a high r(MF) and that genes currently exposed to sexually antagonistic selection have a higher average r(MF) than other genes. We further show that genes with a high r(MF) have less pronounced sex-biased gene expression than genes with a low r(MF) within D. melanogaster and that the strength of the r(MF) in D. melanogaster predicts the degree to which the sex bias of a gene's expression has changed between D. melanogaster and six other species in the Drosophila genus. In sum, our results show that a shared genome constrains both short- and long-term evolution of sexual dimorphism.
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| 36. |
- Griffin, Robert
(författare)
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The genetic architecture of sexual dimorphism
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phenotypic differences between the sexes evolve largely because selection favours a different complement of traits in either sex. Theory suggests that, despite its frequency, sexual dimorphism should be generally constrained from evolving because the sexes share much of their genome. While selection can lead to adaptation in one sex, correlated responses to selection can be maladaptive in the other. In this thesis I use Drosophila to examine the extent to which the shared genome constrains the evolution of sexual dimorphism and whether the sex chromosomes might play a special role in resolving intralocus sexual conflict.Gene expression data shows that intersexual genetic correlations are generally high, suggesting that genes often affect both sexes. The intersexual genetic correlation is negatively associated with sex-bias in expression in D. melanogaster, and the rate of change in sex-bias between D. melanogaster and six closely related species, showing that a sex-specific genetic architecture is a prerequisite for the evolution of sex difference. In further studies I find that genetic variance affecting lifespan is found in the male-limited Y chromosome within a population, which could offer a route to the evolution of further sexual dimorphism in lifespan, though the amount of variance was small suggesting adaptive potential from standing genetic variance is limited. Genetic variance on the X chromosome is also expected to be depleted once the sex chromosomes evolve, but here I find no evidence of depletion in either sex. Dosage compensation does not appear to double the male X-linked genetic variance, but this effect may be complex to detect. Finally, the X chromosome appears to be enriched for sex-specific genetic variance, and the consequences of this are explored using a variety of analytical methods to test biologically meaningful aspects of G-matrix structure.In summary, this thesis suggests that the evolution of sexual dimorphism is generally constrained by the shared genome, but intralocus sexual conflict could be resolved by novel mutations on the Y chromosomes, and by standing sex-specific genetic variance on the X chromosome. It highlights a special role for the X chromosome in the evolution of sexual dimorphism.
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| 37. |
- Griffin, Robert, 1989-, et al.
(författare)
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Within-population Y-linked genetic variation for lifespan in Drosophila melanogaster
- 2015
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 28:11, s. 1940-1947
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The view that the Y chromosome is of little importance for phenotypic evolution stems from early studies of Drosophila melanogaster. This species’ Y chromosome contains only 13 protein coding genes, is almost entirely heterochromatic, and is not necessary for male viability. Population genetic theory further suggests that non-neutral variation can only be maintained at the Y chromosome under special circumstances. Yet, recent studies suggest that the D. melanogaster Y chromosome trans-regulates hundreds to thousands of X and autosomal genes. This finding suggests that the Y chromosome may play a far more active role in adaptive evolution than has previously been assumed. To evaluate the potential for the Y chromosome to contribute to phenotypic evolution from standing genetic variation, we test for Y-linked variation in lifespan within a population of D. melanogaster. Assessing variation for lifespan provides a powerful test because lifespan i) shows sexual dimorphism, which the Y is primarily predicted to contribute to, ii) is influenced by many genes, which provides the Y with many potential regulatory targets, and iii) is sensitive to heterochromatin remodelling, a mechanism through which the Y chromosome is believed to regulate gene expression. Our results show a small but significant effect of the Y chromosome, and thus suggest that the Y chromosome has the potential to respond to selection from standing genetic variation. Despite its small effect size, Y-linked variation may still be important, in particular when evolution of sexual dimorphism is genetically constrained elsewhere in the genome.
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| 38. |
- Hellquist, Alexander, 1980-, et al.
(författare)
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Taxonomic status of grey-headed Yellow Wagtails breeding in western China
- 2021
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Ingår i: Avian Research. - : Elsevier BV. - 2053-7166. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Field studies from 2011 onwards have demonstrated the presence of a breeding population of Yellow Wagtails (Motacilla flava) in the Xinjiang Uygur Autonomous Region, China that is phenotypically distinct from known subspecies occurring in Asia. Here we describe the plumages and vocalisations of this population and discuss its taxonomic status. Methods The analysis of plumage is based on field studies and photos available online. Recordings of vocalisations are compared with recordings from other Yellow Wagtail populations, and differences are analysed based on sonograms. Mitochondrial DNA from one individual is compared to other Yellow Wagtail taxa. Results Unlike M. flava subspecies breeding in or near Xinjiang, males in the studied population show a blue-grey head without prominent white supercilium, being most similar to the widely disjunct M. f. cinereocapilla. They differ from the similarly widely allopatric M. f. thunbergi, which might occur as a migrant or vagrant in Xinjiang, by on average cleaner yellow breast and more extensive white on the throat, and from the widely disjunct M. f. plexa and M. f. macronyx, which might also occur on migration in that area, by softer contact calls and slower pace of song. Females are similar to female M. f. feldegg in plumage. The mitochondrial ND2 tree shows the single sample from Xinjiang to be nested in the clade of western Yellow Wagtail taxa. Conclusion We discuss whether the Xinjiang breeding population could represent an intergrade between subspecies breeding nearby, or whether it is better regarded as a separate as yet unrecognized subspecies. We argue that the localization of its apparent range in relation to other subspecies along with fairly consistent male and female plumages suggest that it is more likely to represent an undescribed taxon, but conclude that more research is needed to firmly establish its status.
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| 39. |
- Iinatti Brengdahl, Martin, 1990-, et al.
(författare)
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Age-specific effects of deletions: Implications for ageing theories
- 2022
-
Annan publikationabstract
- Evolution of ageing requires mutations with late-life deleterious effects. Classic theories assume these mutations either have neutral (Mutation Accumulation) or beneficial (Antagonistic Pleiotropy) effects early in life, but it is also possible that they start out as mildly harmful and gradually become more deleterious with age. Despite a wealth of studies on the genetics of ageing, we still have a poor understanding of how common mutations with age-specific effects are and what ageing theory they support. To advance our knowledge on this topic we measure a set of genomic deletions for their heterozygous effects on juvenile performance, fecundity at three ages, and adult survival. Most deletions have age-specific effects, and these are commonly harmful late in life. Many of the deletions assayed here would thus contribute to ageing if present in a population. Taking only age-specific fecundity into account, some deletions support Antagonistic Pleiotropy, but the majority of them better fit a scenario where their negative effects on fecundity become progressively worse with age. Most deletions have a negative effect on juvenile performance, a fact which strengthens the conclusion that deletions primarily contribute to ageing through negative effects that amplify with age.
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| 40. |
- Iinatti Brengdahl, Martin, et al.
(författare)
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Age-specific effects of deletions: implications for aging theories
- 2023
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Ingår i: Evolution. - : OXFORD UNIV PRESS. - 0014-3820 .- 1558-5646. ; 77:1, s. 254-263
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of aging requires mutations with late-life deleterious effects. Classic theories assume these mutations either have neutral (mutation accumulation) or beneficial (antagonistic pleiotropy) effects early in life, but it is also possible that they start out as mildly harmful and gradually become more deleterious with age. Despite a wealth of studies on the genetics of aging, we still have a poor understanding of how common mutations with age-specific effects are and what aging theory they support. To advance our knowledge on this topic, we measure a set of genomic deletions for their heterozygous effects on juvenile performance, fecundity at 3 ages, and adult survival. Most deletions have age-specific effects, and these are commonly harmful late in life. Many of the deletions assayed here would thus contribute to aging if present in a population. Taking only age-specific fecundity into account, some deletions support antagonistic pleiotropy, but the majority of them better fit a scenario where their negative effects on fecundity become progressively worse with age. Most deletions have a negative effect on juvenile performance, a fact that strengthens the conclusion that deletions primarily contribute to aging through negative effects that amplify with age.
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| 41. |
- Iinatti Brengdahl, Martin, 1990-, et al.
(författare)
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Data from: Sex differences in lifespan: females homozygous for the X chromosome do not suffer the shorter lifespan predicted by the unguarded X hypothesis
- 2018
-
Annan publikationabstract
- Lifespan differs between the sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the heterogametic sex suffers a shortened lifespan because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (~20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced lifespan or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the heterogametic sex appears too small to explain general sex differences in lifespan.
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| 42. |
- Iinatti Brengdahl, Martin, et al.
(författare)
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Deleterious mutations show increasing negative effects with age in Drosophila melanogaster
- 2020
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Ingår i: BMC Biology. - : BMC. - 1741-7007. ; 18:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background In order for aging to evolve in response to a declining strength of selection with age, a genetic architecture that allows for mutations with age-specific effects on organismal performance is required. Our understanding of how selective effects of individual mutations are distributed across ages is however poor. Established evolutionary theories assume that mutations causing aging have negative late-life effects, coupled to either positive or neutral effects early in life. New theory now suggests evolution of aging may also result from deleterious mutations with increasing negative effects with age, a possibility that has not yet been empirically explored. Results To directly test how the effects of deleterious mutations are distributed across ages, we separately measure age-specific effects on fecundity for each of 20 mutations inDrosophila melanogaster. We find that deleterious mutations in general have a negative effect that increases with age and that the rate of increase depends on how deleterious a mutation is early in life. Conclusions Our findings suggest that aging does not exclusively depend on genetic variants assumed by the established evolutionary theories of aging. Instead, aging can result from deleterious mutations with negative effects that amplify with age. If increasing negative effect with age is a general property of deleterious mutations, the proportion of mutations with the capacity to contribute towards aging may be considerably larger than previously believed.
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| 43. |
- Iinatti Brengdahl, Martin, 1990-
(författare)
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The effects of deleterious mutations on ageing
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ageing is defined as the deterioration of an individual's physiological performance with advancing age, which leads to a decrease in reproduction and/or survival. The question why most organisms age has preoccupied humans for millennia and, over the last decades, resulted in an ever-increasing research effort to understand this phenomenon. The full explanation for why we age has, however, remained elusive. Evolutionary theories of ageing are based on two assumptions, which together inevitably result in organismal ageing, that the strength of selection declines with age and that mutations have age-specific effects. While a declining strength of selection with age naturally follows from external sources of death, the age-specific properties of mutations is a topic we only have a rudimentary understanding of. Established theories of ageing predict that mutations either have a beneficial or neutral effect early in life, and a deleterious effect later in life. New theory suggests that mutations with a small negative effect already early in life can also contribute to the evolution of ageing, a possibility that potentially explains empirical results that have been difficult to reconcile with current theories. Deleterious mutations may also directly or indirectly explain the sex differences in ageing and lifespan that are observed in many species.In this thesis, I investigate the age-specificity of deleterious mutations and test if they contribute to sex differences in ageing and lifespan. In paper I and II, I investigate the age-specificity of a set of supposedly deleterious mutations, by estimating their effect on fecundity in young, middle-aged and moderately old Drosophila melanogaster females. The majority of tested mutations show age-specific effects, with a detrimental effect that gradually increases with advancing age. These results thus support that mutations expressing a small negative effect already at an early age also can contribute to the evolution of ageing.In paper III, I manipulate the expression of autosomal deleterious mutations in D. melanogaster through inbreeding, and test if this has different effects on male and female ageing as predicted if sexual selection has shaped sex differences in ageing through condition-dependent investment in current reproduction. I find a sex difference in ageing in high condition, but not in low condition flies, suggesting that sexual selection indeed has shaped how resources are allocated between reproduction and somatic maintenance in relation to condition. I did not find a corresponding response for lifespan.In paper IV, I investigate if sex differences in lifespan are partly explained by the unconditional expression of recessive deleterious mutations on the single X-chromosome in males (the Unguarded X hypothesis). I test this hypothesis by forcing D. melanogaster females to express recessive mutations on the X-chromosome to the same extent as males do and assess their effect on female lifespan. This direct test did not show the expected reduction in female lifespan and thus fails to support the Unguarded X hypothesis as a major explanation of sex differences in lifespan.
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| 44. |
- Johnsson, Martin, et al.
(författare)
-
Feralisation targets different genomic loci to domestication in the chicken.
- 2016
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Ingår i: Nature Communications. - London : Nature Publishing Group. - 2041-1723. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Feralisation occurs when a domestic population recolonizes the wild, escaping its previous restricted environment, and has been considered as the reverse of domestication. We have previously shown that Kauai Island's feral chickens are a highly variable and admixed population. Here we map selective sweeps in feral Kauai chickens using whole-genome sequencing. The detected sweeps were mostly unique to feralisation and distinct to those selected for during domestication. To ascribe potential phenotypic functions to these genes we utilize a laboratory-controlled equivalent to the Kauai population-an advanced intercross between Red Junglefowl and domestic layer birds that has been used previously for both QTL and expression QTL studies. Certain sweep genes exhibit significant correlations with comb mass, maternal brooding behaviour and fecundity. Our analyses indicate that adaptations to feral and domestic environments involve different genomic regions and feral chickens show some evidence of adaptation at genes associated with sexual selection and reproduction.
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| 45. |
- Lehtovaara, Anne, et al.
(författare)
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Heritability of Life Span Is Largely Sex Limited in Drosophila
- 2013
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 182:5, s. 653-665
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Tidskriftsartikel (refereegranskat)abstract
- Males and females differ with respect to life span and rate of aging in most animal species. Such sexual dimorphism can be associated with a complex genetic architecture, where only part of the genetic variation is shared between the sexes. However, the extent to which this is true for life span and aging is not known, because studies of life span have given contradictory results and aging has not been studied from this perspective. Here we investigate the additive genetic architecture of life span and aging in Drosophila melanogaster. We find substantial amounts of additive genetic variation for both traits, with more than three-quarters of this variation available for sex-specific evolutionary change. This result shows that the sexes have a profoundly different additive genetic basis for these traits, which has several implications. First, it translates into an, on average, three-times-higher heritability of life span within, compared to between, the sexes. Second, it implies that the sexes are relatively free to evolve with respect to these traits. And third, as life span and aging are traits that integrate over all genetic factors that contribute to mortal disease, it also implies that the genetics of heritable disease differs vastly between the sexes.
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| 46. |
- Maklakov, Alexei A., et al.
(författare)
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Ageing : Why Males Curtail the Longevity of Their Mates
- 2016
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 26:20, s. R929-R932
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Male nematodes secrete pheromones that accelerate the somatic senescence of potential mates. A new study shows that this harm most likely is an unintended by-product of the males' aim to speed up sexual maturation and delay reproductive senescence of future partners.
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| 47. |
- Maklakov, Alexei A., et al.
(författare)
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The effect of sexual harassment on lethal mutation rate in female Drosophila melanogaster
- 2013
-
Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - London, UK : The Royal Society. - 0962-8452 .- 1471-2954. ; 280:1750, s. 20121874-
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Tidskriftsartikel (refereegranskat)abstract
- The rate by which new mutations are introduced into a population may have far-reaching implications for processes at the population level. Theory assumes that all individuals within a population have the same mutation rate, but this assumption may not be true. Compared with individuals in high condition, those in poor condition may have fewer resources available to invest in DNA repair, resulting in elevated mutation rates. Alternatively, environmentally induced stress can result in increased investment in DNA repair at the expense of reproduction. Here, we directly test whether sexual harassment by males, known to reduce female condition, affects female capacity to alleviate DNA damage in Drosophila melanogaster fruitflies. Female gametes can repair double-strand DNA breaks in sperm, which allows manipulating mutation rate independently from female condition. We show that male harassment strongly not only reduces female fecundity, but also reduces the yield of dominant lethal mutations, supporting the hypothesis that stressed organisms invest relatively more in repair mechanisms. We discuss our results in the light of previous research and suggest that social effects such as density and courtship can play an important and underappreciated role in mediating condition-dependent mutation rate.
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| 48. |
- Maklakov, Alexei A., et al.
(författare)
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Why organisms age : Evolution of senescence under positive pleiotropy?
- 2015
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Ingår i: Bioessays. - : Wiley. - 0265-9247 .- 1521-1878. ; 37:7, s. 802-807
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Tidskriftsartikel (refereegranskat)abstract
- Two classic theories maintain that aging evolves either because of alleles whose deleterious effects are confined to late life or because of alleles with broad pleiotropic effects that increase early-life fitness at the expense of late-life fitness. However, empirical studies often reveal positive pleiotropy for fitness across age classes, and recent evidence suggests that selection on early-life fitness can decelerate aging and increase lifespan, thereby casting doubt on the current consensus. Here, we briefly review these data and promote the simple argument that aging can evolve under positive pleiotropy between early-and late-life fitness when the deleterious effect of mutations increases with age. We argue that this hypothesis makes testable predictions and is supported by existing evidence.
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| 49. |
- Maklakov, Alexei A, et al.
(författare)
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Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster
- 2006
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 60:10, s. 2081-2086
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that mitochondrial DNA (mtDNA) may play an important role in aging. Yet, few empirical studies have tested this hypothesis, partly because the degree of sequence polymorphism in mtDNA is assumed to be low. However, low sequence variation may not necessarily translate into low phenotypic variation. Here, we report an experiment that tests whether there is within-population variation in cytoplasmic genes for female longevity and senescence. To achieve this, we randomly selected 25 "mitochondrial founders" from a single, panmictic population of Drosophila melanogaster and used these founders to generate distinct "mt" lines in which we controlled for the nuclear background by successive backcrossing. Potential confounding effects of cytoplasmically transmitted bacteria were eliminated by tetracycline treatment. The mt lines were then assayed for differences in longevity, Gompertz intercept (frailty), and demographic rate of change in mortality with age (rate-of-senescence) in females. We found significant cytoplasmic effects on all three variables. This provides evidence that genetic variation in cytoplasmic genes, presumably mtDNA, contributes to variation in female mortality and aging.
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- Maklakov, Alexei A., et al.
(författare)
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Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster
- 2006
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Ingår i: Evolution. - : The Society for the Study of Evolution. - 0014-3820 .- 1558-5646. ; 60:10, s. 2081-2086
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that mitochondrial DNA (mtDNA) may play an important role in aging. Yet, few empirical studies have tested this hypothesis, partly because the degree of sequence polymorphism in mtDNA is assumed to be low. However, low sequence variation may not necessarily translate into low phenotypic variation. Here, we report an experiment that tests whether there is within-population variation in cytoplasmic genes for female longevity and senescence. To achieve this, we randomly selected 25 "mitochondrial founders" from a single, panmictic population of Drosophila melanogaster and used these founders to generate distinct "mt" lines in which we controlled for the nuclear background by successive backcrossing. Potential confounding effects of cytoplasmically transmitted bacteria were eliminated by tetracycline treatment. The mt lines were then assayed for differences in longevity, Gompertz intercept (frailty), and demographic rate of change in mortality with age (rate-of-senescence) in females. We found significant cytoplasmic effects on all three variables. This provides evidence that genetic variation in cytoplasmic genes, presumably mtDNA, contributes to variation in female mortality and aging.
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