| 1. |
- Dowling, Damian K., et al.
(author)
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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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In: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 20:6, s. 2113-2125
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Journal article (peer-reviewed)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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| 2. |
- Dowling, Damian K., et al.
(author)
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Effects of cytoplasmic genes on sperm viability and sperm morphology in a seed beetle : Implications for sperm competition theory?
- 2007
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In: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 20:1, s. 358-368
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Journal article (peer-reviewed)abstract
- Sperm competition theory predicts that sperm traits influencing male fertilizing ability will evolve adaptively. However, it has been suggested that some sperm traits may be at least partly encoded by mitochondrial genes. If true, this may constrain the adaptive evolution of such traits because mitochondrial DNA (mtDNA) is maternally inherited and there is thus no selection on mtDNA in males. Phenotypic variation in such traits may nevertheless be high because mutations in mtDNA that have deleterious effects on male traits, but neutral or beneficial effects in females, may be maintained by random processes or selection in females. We used backcrossing to create introgression lines of seed beetles (Callosobruchus maculatus), carrying orthogonal combinations of distinct lineages of cytoplasmic and nuclear genes, and then assayed sperm viability and sperm length in all lines. We found sizeable cytoplasmic effects on both sperm traits and our analyses also suggested that the cytoplasmic effects varied across nuclear genetic backgrounds. We discuss some potential implications of these findings for sperm competition theory.
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| 3. |
- Dowling, Damian K., et al.
(author)
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Evolutionary implications of non-neutral mitochondrial genetic variation
- 2008
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In: Trends in Ecology & Evolution. - : Cell Press. - 0169-5347 .- 1872-8383. ; 23:10, s. 546-554
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Research review (peer-reviewed)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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| 4. |
- Dowling, Damian k., et al.
(author)
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Intergenomic epistasis for fitness : Within-population interactions between cytoplasmic and nuclear genes in Drosophila melanogaster
- 2007
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In: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 175:1, s. 235-244
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Journal article (peer-reviewed)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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| 5. |
- Dowling, Damian K., et al.
(author)
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Red plumage and its association with reproductive success in red-capped robins
- 2006
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In: Annales Zoologici Fennici. - 0003-455X .- 1797-2450. ; 43:4, s. 311-321
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Journal article (peer-reviewed)abstract
- Red plumage is produced mainly by deposition of carotenoid'pigments into the feathers, and is assumed to be costly. Recent studies suggest red plumage may be a condition-dependent, sexually selected signal. To date, few studies have explored the relationship between carotenoid-based plumage colour and genetic (realised) reproductive success. This is despite the rarity of genetic monogamy among. avian mating systems. We studied. this-relationship. in the red-capped robin (Petroica goodenovii) across two breeding seasons, using spectrophotometric techniques, to score colour and molecular markers to assign paternity. Males with the highest. within-pair. reproductive success during the first season moulted into,the most colourful plumage at the conclusion of that season. We found;no such correlations, when using putative measures of reproductive success, underlining the importance of unambiguous paternity assignment. However, males that moulted into the most, colourful plumage did not go on to attain highest. reproductive success during-the, subsequent breeding season (while displaying this plumage). Instead, variation in male reproductive success was explained by male body condition and age. These results suggest that the information value of male-plumage colour is unpredictable.
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| 6. |
- Dowling, Damian K., et al.
(author)
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Temperature-specific outcomes of cytoplasmic-nuclear interactions on egg-to-adult development time in seed beetles
- 2007
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 61:1, s. 194-201
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Journal article (peer-reviewed)abstract
- The integration of the mitochondrial and nuclear genomes coordinates cellular energy production and is fundamental to life among eukaryotes. Therefore, there is potential for strong selection to shape the interactions between the two genomes. Several studies have now demonstrated that epistatic interactions between cytoplasmic and nuclear genes for fitness can occur both at a "within" and "across" population level. Genotype-by-environment interactions are common for traits that are encoded by nuclear genes, but the effects of environmental heterogeneity on traits that are partly encoded by cytoplasmic genes have received little attention despite the fact that there are reasons to believe that phenotypic effects of cytoplasmic genetic variation may often be environment specific. Consequently, the importance of environmental heterogeneity to the outcomes of cyto-nuclear fitness interactions and to the maintenance of mitochondrial polymorphism is unclear. Here, we assess the influence of temperature on cyto-nuclear effects on egg-to-adult development time in seed beetles (Callosobruchus maculatus). We employed an "across-population" design, sourcing beetles from five distinct populations and using backcrossing to create orthogonal combinations of distinct introgression lines, fixed for their cytoplasmic and nuclear lineages. We then assayed development times at two different temperatures and found sizeable cyto-nuclear effects in general, as well as temperature- and block-specific cyto-nuclear effects. These results demonstrate that environmental factors such as temperature do exert selection on cytoplasmic genes by favoring specific cyto-nuclear genetic combinations, and are consistent with the suggestion that complex genotype-by-environment interactions may promote the maintenance of polymorphism in mitochondrial genes.
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| 7. |
- Maklakov, Alexei A, et al.
(author)
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Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster
- 2006
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In: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 60:10, s. 2081-2086
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Journal article (peer-reviewed)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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| 8. |
- Maklakov, Alexei A., et al.
(author)
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Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster
- 2006
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In: Evolution. - : The Society for the Study of Evolution. - 0014-3820 .- 1558-5646. ; 60:10, s. 2081-2086
-
Journal article (peer-reviewed)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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