| 1. |
- Alavioon, Ghazal, 1986-, et al.
(författare)
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Sperm performance traits exhibit low additive genetic component and strong parental effects in external fertilizer
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Despite their key role in determining reproductive success and with that Darwinian fitness, the heritability and underlying additive genetic variance of reproductive traits is still not fully understood. While some traits show relatively high genetic variance, others show very low genetic variance, which is particularly true for complex non-morphological traits. In line with these general patterns, morphological sperm traits show surprisingly high heritability, whereas heritability reported for sperm quality and performance traits generally is lower. A possible explanation for this is the general notion that more fitness related traits show lower levels of additive genetic variance and heritability. We investigated the additive genetic variance and heritability of sperm swimming velocity, the percentage of motile sperm, sperm concentration in the ejaculate and sperm longevity in the externally fertilizing zebrafish Danio rerio. All sperm traits showed low but significant additive genetic variance and high parental components. While the additive genetic variance was significant it was lower than reported in many other studies. A possible explanation for this is that in externally fertilizing species, sperm traits are the prime determinant of fertilization success and high plasticity is crucial for swift adaptations to changes in the environmental conditions such as competition but also water temperature and currents. Given that this is the first study looking into the heritability of sperm traits in an external fertilizer it will be interesting to understand, whether this is true for other externally fertilizing species and taxa.
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| 2. |
- Backström, Niclas, et al.
(författare)
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The recombination landscape of the zebra finch Taeniopygia guttata genome
- 2010
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Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 20:4, s. 485-495
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the causes and consequences of variation in the rate of recombination is essential since this parameter is considered to affect levels of genetic variability, the efficacy of selection, and the design of association and linkage mapping studies. However, there is limited knowledge about the factors governing recombination rate variation. We genotyped 1920 single nucleotide polymorphisms in a multigeneration pedigree of more than 1000 zebra finches (Taeniopygia guttata) to develop a genetic linkage map, and then we used these map data together with the recently available draft genome sequence of the zebra finch to estimate recombination rates in 1 Mb intervals across the genome. The average zebra finch recombination rate (1.5 cM/Mb) is higher than in humans, but significantly lower than in chicken. The local rates of recombination in chicken and zebra finch were only weakly correlated, demonstrating evolutionary turnover of the recombination landscape in birds. The distribution of recombination events was heavily biased toward ends of chromosomes, with a stronger telomere effect than so far seen in any organism. In fact, the recombination rate was as low as 0.1 cM/Mb in intervals up to 100 Mb long in the middle of the larger chromosomes. We found a positive correlation between recombination rate and GC content, as well as GC-rich sequence motifs. Levels of linkage disequilibrium (LD) were significantly higher in regions of low recombination, showing that heterogeneity in recombination rates have left a footprint on the genomic landscape of LD in zebra finch populations.
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| 3. |
- Bolund, Elisabeth, et al.
(författare)
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Correlates of male fitness in captive zebra finches : a comparison of methods to disentangle genetic and environmental effects
- 2011
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 11, s. 327-
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Tidskriftsartikel (refereegranskat)abstract
- Backgound: It is a common observation in evolutionary studies that larger, more ornamented or earlier breeding individuals have higher fitness, but that body size, ornamentation or breeding time does not change despite of sometimes substantial heritability for these traits. A possible explanation for this is that these traits do not causally affect fitness, but rather happen to be indirectly correlated with fitness via unmeasured non-heritable aspects of condition (e. g. undernourished offspring grow small and have low fitness as adults due to poor health). Whether this explanation applies to a specific case can be examined by decomposing the covariance between trait and fitness into its genetic and environmental components using pedigree-based animal models. We here examine different methods of doing this for a captive zebra finch population where male fitness was measured in communal aviaries in relation to three phenotypic traits (tarsus length, beak colour and song rate). Results: Our case study illustrates how methods that regress fitness over breeding values for phenotypic traits yield biased estimates as well as anti-conservative standard errors. Hence, it is necessary to estimate the genetic and environmental covariances between trait and fitness directly from a bivariate model. This method, however, is very demanding in terms of sample sizes. In our study parameter estimates of selection gradients for tarsus were consistent with the hypothesis of environmentally induced bias (beta(A) = 0.035 +/- 0.25 (SE), beta(E) = 0.57 +/- 0.28 (SE)), yet this differences between genetic and environmental selection gradients falls short of statistical significance. Conclusions: To examine the generality of the idea that phenotypic selection gradients for certain traits (like size) are consistently upwardly biased by environmental covariance a meta-analysis across study systems will be needed.
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| 4. |
- Evans, Simon R., et al.
(författare)
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Nonautosomal Genetic Variation in Carotenoid Coloration
- 2014
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 184:3, s. 374-383
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Tidskriftsartikel (refereegranskat)abstract
- Carotenoid-based coloration plays an important role in signaling, is often sexually dimorphic, and is potentially subject to directional and/or sex-specific selection. To understand the evolutionary dynamics of such color traits, it is essential to quantify patterns of inheritance, yet nonautosomal sources of genetic variation are easily overlooked by classical heritability analyses. Carotenoid metabolism has recently been linked to mitochondria, highlighting the potential for color variation to be explained by cytoplasmically inherited factors. In this study, we used quantitative genetic animal models to estimate the importance of mitochondrial and sex chromosome-linked sources of genetic variation in coloration in two songbird populations in which dietary carotenoids are either unmodified (great tit plumage) or metabolized into alternative color forms (zebra finch beak). We found no significant Z-linked genetic variance in great tit plumage coloration, while zebra finch beak coloration exhibited significant W linkage and cytoplasmic inheritance. Our results support cytoplasmic inheritance of color in the zebra finch, a trait based on endogenously metabolized carotenoids, and demonstrate the potential for nonautosomal sources to account for a considerable share of genetic variation in coloration. Although often overlooked, such nonautosomal genetic variation exhibits sex-dependent patterns of inheritance and potentially influences the evolution of sexual dichromatism.
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| 5. |
- Forstmeier, Wolfgang, et al.
(författare)
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Heterozygosity-fitness correlations in zebra finches : microsatellite markers can be better than their reputation
- 2012
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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 21:13, s. 3237-3249
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Tidskriftsartikel (refereegranskat)abstract
- Numerous studies have reported associations between heterozygosity in microsatellite markers and fitness-related traits (heterozygosityfitness correlations, HFCs). However, it has often been questioned whether HFCs reflect general inbreeding depression, because a small panel of microsatellite markers does not reflect very well an individuals inbreeding coefficient (F) as calculated from a pedigree. Here, we challenge this prevailing view. Because of chance events during Mendelian segregation, an individuals realized proportion of the genome that is identical by descent (IBD) may substantially deviate from the pedigree-based expectation (i.e. F). This Mendelian noise may result in a weak correlation between F and multi-locus heterozygosity, but this does not imply that multi-locus heterozygosity is a bad estimator of realized IBD. We examined correlations between 11 fitness-related traits measured in up to 1192 captive zebra finches and three measures of inbreeding: (i) heterozygosity across 11 microsatellite markers, (ii) heterozygosity across 1359 single-nucleotide polymorphism (SNP) markers and (iii) F, based on a 5th-generation pedigree. All 11 phenotypic traits showed positive relationships with measures of heterozygosity, especially traits that are most closely related to fitness. Remarkably, the small panel of microsatellite markers produced equally strong HFCs as the large panel of SNP markers. Both marker-based approaches produced stronger correlations with phenotypes than the pedigree-based F, and this did not seem to result from the shortness of our pedigree. We argue that a small panel of microsatellites with high allelic richness may better reflect an individuals realized IBD than previously appreciated, especially in species like the zebra finch, where much of the genome is inherited in large blocks that rarely experience cross-over during meiosis.
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| 6. |
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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Husby, Arild, et al.
(författare)
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Sex chromosome linked genetic variance and the evolution of sexual dimorphism of quantitative traits
- 2013
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 67:3, s. 609-619
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts that sex chromsome linkage should reduce intersexual genetic correlations thereby allowing the evolution of sexual dimorphism. Empirical evidence for sex linkage has come largely from crosses and few studies have examined how sexual dimorphism and sex linkage are related within outbred populations. Here, we use data on an array of different traits measured on over 10,000 individuals from two pedigreed populations of birds (collared flycatcher and zebra finch) to estimate the amount of sex-linked genetic variance (h2z). Of 17 traits examined, eight showed a nonzero h2Z estimate but only four were significantly different from zero (wing patch size and tarsus length in collared flycatchers, wing length and beak color in zebra finches). We further tested how sexual dimorphism and the mode of selection operating on the trait relate to the proportion of sex-linked genetic variance. Sexually selected traits did not show higher h2Z than morphological traits and there was only a weak positive relationship between h2Z and sexual dimorphism. However, given the relative scarcity of empirical studies, it is premature to make conclusions about the role of sex chromosome linkage in the evolution of sexual dimorphism.
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