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3,139 results for “fitting”
Data from: Sexually antagonistic genetic variance for fitness in an ancestral and a novel environment
The intersex genetic correlation for fitness (rwfm), a standardized measure of the degree to which male and female fitness covary genetically, has consequences for important evolutionary processes, but few estimates are available and none have explored how it changes with environment. Using a half-sibling breeding design, we estimated the genetic (co)variance matrix (G) for male and female fitness, and the resulting rwfm,in Drosophila serrata. Our estimates were performed in two environments: the laboratory yeast food to which the population was well adapted and a novel corn food. The major axis of genetic variation for fitness in the two environments, accounting for 51.3 per cent of the total genetic variation, was significant and revealed a strong signal of sexual antagonism, loading negatively in both environments on males but positively on females. Consequently, estimates of rwfm were negative in both environments (-0.34 and -0.73, respectively), indicating that the majority of genetic variance segregating in this population has contrasting effects on male and female fitness. The possible strengthening of the negative rwfm in this novel environment may be a consequence of no history of selection for amelioration of sexual conflict. Additional studies from a diverse range of novel environments will be needed to determine the generality of this finding.
Data from: Epistasis buffers the fitness effects of rifampicin-resistance mutations in Pseudomonas aeruginosa
Epistatic interactions between resistance mutations in antibiotic-free environments potentially play a crucial role in the spread of resistance in pathogen populations by determining the fitness cost associated with resistance. We used an experimental evolution approach to test for epistatic interactions between 14 different pairs of rifampicin mutations in the pathogenic bacterium Pseudomonas aeruginosa in 42 different rifampicin-free environments. First, we show that epistasis between rifampicin-resistance mutations tends to be antagonistic: the fitness effect of having two mutations is generally smaller than that predicted from the effects of individual mutations on the wild type. Second, we show that sign epistasis between resistance mutations is both common and strong; most notably, pairs of deleterious resistance mutations often partially or completely compensate for each others' costs, revealing a novel mechanism for compensatory adaptation. These results suggest that antagonistic epistasis between intragenic resistance mutations may be a key determinant of the cost of antibiotic resistance and compensatory adaptation in pathogen populations.
Data from: Phenological and fitness responses to climate warming depend upon genotype and competitive neighborhood in Arabidopsis thaliana
1. Increasing temperatures during climate change are known to alter the phenology across diverse plant taxa, but the evolutionary outcomes of these shifts are poorly understood. Moreover, plant temperature-sensing pathways are known to interact with competition-sensing pathways, yet there remains little experimental evidence for how genotypes varying in temperature responsiveness react to warming in realistic competitive settings. 2. We compared flowering time and fitness responses to warming and competition for two near isogenic lines (NILs) of <i>Arabidopsis thaliana</i> transgressively segregating temperature-sensitive and -insensitive alleles for major-effect flowering time genes. We grew focal plants of each genotype in intraspecific and interspecific competition in four treatments contrasting daily temperature profiles in summer and fall under contemporary and warmed conditions. We measured phenology and fitness of focal plants to quantify plastic responses to season, temperature, and competition and the dependence of these responses on flowering time genotype. 3. The temperature-insensitive NIL was constitutively early-flowering and less fit, except in a future-summer climate in which its fitness was higher than the later flowering, temperature-sensitive NIL in low competition. The late-flowering NIL showed accelerated flowering in response to intragenotypic competition and to increased temperature in the summer but delayed flowering in the fall. However, its fitness fell with rising temperatures in both seasons, and in the fall its marginal fitness gain from decreasing competition was diminished in the future. 4. Functional alleles at temperature-responsive genes were necessary for plastic responses to season, warming, and competition. However, the plastic genotype was not the most fit in every experimental condition, becoming less fit than the temperature-canalized genotype in the warm summer treatment. 5. Climate change is often predicted to have deleterious effects on plant populations, and our results show how increased temperatures can act through genotype-dependent phenology to decrease fitness. Furthermore, plasticity is not necessarily adaptive in rapidly changing environments since a non-plastic genotype proved fitter than a plastic genotype in a warming climate treatment.
Data from: Identification of quantitative genetic components of fitness variation in farmed, hybrid and native salmon in the wild
Feral animals represent an important problem in many ecosystems due to interbreeding with wild conspecifics. Hybrid offspring from wild and domestic parents are often less adapted to local environment and ultimately, can reduce the fitness of the native population. This problem is an important concern in Norway, where each year, hundreds of thousands of farm Atlantic salmon escape from fish farms. Feral fish outnumber wild populations, leading to a possible loss of local adaptive genetic variation and erosion of genetic structure in wild populations. Studying the genetic factors underlying relative performance between wild and domesticated conspecific can help to better understand how domestication modifies the genetic background of populations, and how it may alter their ability to adapt to the natural environment. Here, based upon a large-scale release of wild, farm and wild x farm salmon crosses into a natural river system, a genome-wide quantitative trait locus (QTL) scan was performed on the offspring of 50 full-sib families, for traits related to fitness (length, weight, condition factor and survival). Six QTLs were detected as significant contributors to the phenotypic variation of the first three traits, explaining collectively between 9.8 and 14.8% of the phenotypic variation. The seventh QTL had a significant contribution to the variation in survival, and is regarded as a key factor to understand the fitness variability observed among salmon in the river. Interestingly, strong allelic correlation within one of the QTL regions in farmed salmon might reflect a recent selective sweep due to artificial selection.
Data from: Sex-specific fitness consequences of nutrient intake and the evolvability of diet preferences
The acquisition of nutrients is fundamental for the maintenance of bodily functions, growth, and reproduction in animals. As a result, fitness can be maximized only when animals are able to direct their attention to foods that reflect their current nutritional needs. Despite significant literature documenting the fitness consequences of nutrient composition and preference, less is known about the underlying genetic architecture of the dietary preferences themselves, specifically, the degree to which they can respond to selection. We addressed this by integrating evolutionary quantitative genetics and nutritional geometry to examine the shape of the sex-specific fitness surfaces and the availability of genetic variance for macronutrient preferences in the fruit fly Drosophila melanogaster. Combining these analyses, we found that the microevolutionary potential of carbohydrate and protein preference was above average in this population, because the expected direction of selection was relatively well aligned with the major axis of the genetic variance-covariance matrix, G. We also found that potential exists for sexually antagonistic genetic constraint in this system; macronutrient blends maximizing fitness differed between the sexes, and cross-sex genetic correlations for their consumption were positive. However, both sexes were displaced from their feeding optima, generating similar directional selection on males and females, with the combined effect being that minimal sex-specific genetic constraints currently affect dietary preferences in this population.
Data from: The genetic basis of the fitness costs of antimicrobial resistance: a meta-analysis approach
The evolution of antibiotic resistance carries a fitness cost, expressed in terms of reduced competitive ability in the absence of antibiotics. This cost plays a key role in the dynamics of resistance by generating selection against resistance when bacteria encounter an antibiotic-free environment. Previous work has shown that the cost of resistance is highly variable, but the underlying causes remain poorly understood. Here, we use a meta-analysis of the published resistance literature to determine how the genetic basis of resistance influences its cost. We find that on average chromosomal resistance mutations carry a larger cost than acquiring resistance via a plasmid. This may explain why resistance often evolves by plasmid acquisition. Second, we find that the cost of plasmid acquisition increases with the breadth of its resistance range. This suggests a potentially important limit on the evolution of extensive multidrug resistance via plasmids. We also find that epistasis can significantly alter the cost of mutational resistance. Overall, our study shows that the cost of antimicrobial resistance can be partially explained by its genetic basis. It also highlights both the danger associated with plasmidborne resistance and the need to understand why resistance plasmids carry a relatively low cost.
Data from: Local adaptation, phenotypic differentiation and hybrid fitness in diverged natural populations of Arabidopsis lyrata
Selection for local adaptation results in genetic differentiation in ecologically important traits. In a perennial, outcrossing model plant Arabidopsis lyrata, several differentiated phenotypic traits contribute to local adaptation, as demonstrated by fitness advantage of the local population at each site in reciprocal transplant experiments. Here we compared fitness components, hierarchical total fitness and differentiation in putatively ecologically important traits of plants from two diverged parental populations from different continents in the native climate conditions of the populations in Norway and in North Carolina (NC), USA. Survival and number of fruits per inflorescence indicated local advantage at both sites and aster life-history models provided additional evidence for local adaptation also at the level of hierarchical total fitness. Populations were also differentiated in flowering start date and floral display. We also included reciprocal experimental F1 and F2 hybrids to examine the genetic basis of adaptation. Surprisingly, the F2 hybrids showed heterosis at the study site in Norway, likely because of a combination of beneficial dominance effects from different traits. At the NC site, hybrid fitness was mostly intermediate relative to the parental populations. Local cytoplasmic origin was associated with higher fitness, indicating that cytoplasmic genomes also may contribute to the evolution of local adaptation.
Data from: Bacterial motility confers fitness advantage in the presence of phages
Dispersal provides the opportunity to escape harm and colonize new patches, enabling populations to expand and persist. However, the benefits of dispersal associated with escaping harm will be dependent on the structure of the environment and the likelihood of escape. Here, we empirically investigate how the spatial distribution of a parasite influences the evolution of host dispersal. Bacteriophages are a strong and common threat for bacteria in natural environments and offer a good system with which to explore parasite-mediated selection on host dispersal. We used two transposon mutants of the opportunistic bacteria, Pseudomonas aeruginosa, which varied in their motility (a disperser and a nondisperser), and the lytic bacteriophage ФKZ. The phage was distributed either in the central point of colony inoculation only, thus offering an escape route for the dispersing bacteria; or, present throughout the agar, where benefits of dispersal might be lost. Surprisingly, we found dispersal to be equally advantageous under both phage conditions relative to when phages were absent. A general explanation is that dispersal decreased the spatial structuring of host population, reducing opportunities for parasite transmission, but other more idiosyncratic mechanisms may also have contributed. This study highlights the crucial role the parasites can play on the evolution of dispersal and, more specifically, that bacteriophages, which are ubiquitous, are likely to select for bacterial motility.
Data from: The fitness of drug-resistant malaria parasites in a rodent model: multiplicity of infection
Malaria infections normally consist of more than one clonally-replicating lineage. Within-host interactions between sensitive and resistant parasites can have profound effects on the evolution of drug resistance. Here, using the Plasmodium chabaudi mouse malaria model, we ask whether the costs and benefits of resistance are affected by the number of co-infecting strains competing with a resistant clone. We found strong competitive suppression of resistant parasites in untreated infections and marked competitive release following treatment. The magnitude of competitive suppression depended on competitor identity. However, there was no overall effect of the diversity of susceptible parasites on the extent of competitive suppression or release. If these findings generalize, then transmission intensity will impact on resistance evolution because of its effect on the frequency of mixed infections, not because of its effect on the distribution of clones per host. This would greatly simplify the computational problems of adequately capturing within-host ecology in models of drug resistance evolution in malaria.
Data from: Environmental stress increases the magnitude of nonadditive genetic variation in offspring fitness in the frog Crinia georgiana
When organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog Crinia georgiana, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low-water) late in larval development. We estimated the contribution of additive and non-additive sources of genetic variation to early offspring fitness under both environments. Our results revealed a marked decline in larval fitness under the stressful (low-water) rearing environment, but also that additive genetic variation was negligible for all traits. However, in most cases we found significant sire-by-dam interactions, indicating the importance of non-additive genetic variation for offspring fitness. Moreover, sire-by-dam interactions were modified by the treatment, indicating that patterns of non-additive genetic variance depend on environmental context. For all traits, we found higher levels of non-additive genetic variation (relative to total phenotypic variation) when larvae were reared under stressful conditions, suggesting that the fitness costs associated with incompatible parental crosses (e.g. homozygous deleterious recessive alleles) will only be expressed when water availability is low. Taken together, our results highlight the need to consider patterns of non-additive genetic variation under contrasting selective regimes when considering the resilience of species to environmental change.
Data from: A quantitative survey of local adaptation and fitness trade-offs
The long history of reciprocal transplant studies testing the hypothesis of local adaptation has shown that populations are often adapted to their local environments. Yet many studies have not demonstrated local adaptation, suggesting that sometimes native populations are no better adapted than are genotypes from foreign environments. Local adaptation may also lead to trade-offs, in which adaptation to one environment comes at a cost of adaptation to another environment. I conducted a survey of published studies of local adaptation to quantify its frequency and magnitude and the costs associated with local adaptation. I also quantified the relationship between local adaptation and environmental differences and the relationship between local adaptation and phenotypic divergence. The overall frequency of local adaptation was 0.71, and the magnitude of the native population advantage in relative fitness was 45%. Divergence between home site environments was positively associated with the magnitude of local adaptation, but phenotypic divergence was not. I found a small negative correlation between a population's relative fitness in its native environment and its fitness in a foreign environment, indicating weak trade-offs associated with local adaptation. These results suggest that populations are often locally adapted but stochastic processes such as genetic drift may limit the efficacy of divergent selection.
Data from: Genomewide association analyses of fitness traits in captive-reared Chinook salmon: applications in evaluating conservation strategies
A novel application of genome-wide association analyses is to use trait-associated loci to monitor the effects of conservation strategies on potentially adaptive genetic variation. Comparisons of fitness between captive- and wild-origin individuals, for example, do not reveal how captive rearing affects genetic variation underlying fitness traits or which traits are most susceptible to domestication selection. Here, we used data collected across four generations to identify loci associated with six traits in adult Chinook salmon (Oncorhynchus tshawytscha), and then determined how two alternative management approaches for captive rearing affected variation at these loci. Loci associated with date of return to freshwater spawning grounds (return timing), length and weight at return, age at maturity, spawn timing, and daily growth coefficient were identified using 9108 restriction site-associated markers and Random Forest, an approach suitable for polygenic traits. Mapping of trait-associated loci, gene annotations, and integration of results across multiple studies revealed candidate regions involved in several fitness-related traits. Genotypes at trait-associated loci were then compared between two hatchery populations that were derived from the same source but are now managed as separate lines, one integrated with and one segregated from the wild population. While no broad scale change was detected across four generations, there were numerous regions where trait-associated loci overlapped with signatures of adaptive divergence previously identified in the two lines. Many regions, primarily with loci linked to return and spawn timing, were either unique to, or more divergent in, the segregated line, suggesting that these traits may be responding to domestication selection. This study is one of the first to utilize genomic approaches to demonstrate the effectiveness of a conservation strategy, managed gene flow, on trait-associated – and potentially adaptive – loci. The results will promote the development of trait-specific tools to better monitor genetic change in captive and wild populations.
Data from: Ectoparasites and fitness of female Columbian ground squirrels
Parasites play an important role in the evolution of host traits via natural selection, coevolution and sexually selected ornaments used in mate choice. These evolutionary scenarios assume fitness costs for hosts. To test this assumption, we conducted an ectoparasite removal experiment in free-living Columbian ground squirrels (Urocittelus columbianus) in four populations over three years. Adult females were randomly chosen to be either experimentally treated with anti-parasite treatments (spot-on solution and flea powder, N = 61) or a sham treatment (control, N = 44). We expected that experimental females would show better body condition, increased reproductive success and enhanced survival. Contrary to our expectations, body mass was not significantly different between treatments at mating, birth of litter or weaning of young. Further, neither number nor size of young at weaning differed significantly between the two treatments. Survival to the next spring for adult females and juveniles was not significantly different between experimental and control treatments. Finally, annual fitness was not affected by the treatments. We concluded that females and their offspring were able compensate for the presence of ectoparasites, suggesting little or no fitness costs of parasites for females in the different colonies and during the years of our experiments.
Data from: The rate and effects of spontaneous mutation on fitness traits in the social amoeba, Dictyostelium discoideum
We performed a mutation accumulation (MA) experiment using the social amoeba Dictyostelium discoideum to estimate the rate and distribution of effects of spontaneous mutations affecting eight putative fitness traits. We found that the per generation mutation rate for most fitness components is 0.0019 mutations per haploid genome per generation, or larger. This rate is an order of magnitude higher than estimates for fitness components in the unicellular eukaryote Saccharomyces cerevisiae, even though the base-pair substitution rate is two orders of magnitude lower. The high rate of fitness-altering mutations observed in this species may be partially explained by a large mutational target relative to Saccharomyces cerevisiae. Also, fitness-altering mutations may occur primarily at simple sequence repeats, which are common throughout the genome, including in coding regions, and may represent a target that is particularly likely to give fitness effects upon mutation. The majority of mutations had deleterious effects on fitness, but there was evidence for a substantial fraction, up to 40%, being beneficial for some of the putative fitness traits. Competitive ability within the multicellular slug appears to be under weak directional selection, perhaps reflecting the fact that slugs are sometimes, but not often, comprised of multiple clones in nature. Evidence for pleiotropy among fitness components across MA lines was absent, suggesting that mutations tend to act on single fitness components.
Data from: Fisher's geometrical model of fitness landscape and variance in fitness within a changing environment
The fitness of an individual can be simply defined as the number of its offspring in the next generation. However, it is not well understood how selection on the phenotype determines fitness. In accordance with Fisher's fundamental theorem, fitness should have no or very little genetic variance, whereas empirical data suggest that is not the case. To bridge these knowledge gaps, we follow Fisher's geometrical model and assume that fitness is determined by multivariate stabilizing selection towards an optimum that may vary among generations. We assume random mating, free recombination, additive genes, and uncorrelated stabilizing selection and mutational effects on traits. In a constant environment, we find that genetic variance in fitness under mutation-selection balance is a U-shaped function of the number of traits (i.e. of the so-called "organismal complexity"). Because the variance can be high if the organism is of either low or high complexity, this suggests that complexity has little direct costs. Under a temporally varying optimum, genetic variance increases relative to a constant optimum and increasingly so when the mutation rate is small. Therefore mutation and changing environment together can maintain high genetic variance. These results therefore lend support to Fisher's geometric model of a fitness landscape.
Data from: Joint allelic effects on fitness and metric traits
Theoretical explanations of empirically observed standing genetic variation, mutation, and selection suggest that many alleles must jointly affect fitness and metric traits. However, there are few direct demonstrations of the nature and extent of these pleiotropic associations. We implemented a mutation accumulation (MA) divergence experimental design in Drosophila serrata to segregate genetic variants for fitness and metric traits. By exploiting naturally occurring MA line extinctions as a measure of line-level total fitness, manipulating sexual selection, and measuring productivity we were able to demonstrate genetic covariance between fitness and standard metric traits, wing size and shape. Larger size was associated with lower total fitness and male sexual fitness, but higher productivity. Multivariate wing shape traits, capturing major axes of wing shape variation among MA lines, evolved only in the absence of sexual selection, and to the greatest extent in lines that went extinct, indicating that mutations contributing wing shape variation also typically had deleterious effects on both total fitness and male sexual fitness. This pleiotropic covariance of metric traits with fitness will drive their evolution, and generate the appearance of selection on the metric traits even in the absence of a direct contribution to fitness.
Data from: The direct effects of male-killer infection on fitness of ladybird hosts (Coleoptera: Coccinellidae)
Male-killing bacteria are common in insects, and are thought to persist in host populations primarily by indirect fitness benefits to infected females, while direct fitness effects are generally assumed to be neutral or deleterious. Here, we estimated the effect of male-killer infection on direct fitness (number of eggs laid, as a measure of fecundity, together with survival) and other life-history traits (development time and body size) in seven ladybird host/male-killer combinations. Effects of male-killers on fecundity ranged, as expected, from costly to neutral, however we found evidence of reduced development time and increased survival and body size, in infected strains. Greater body size in Spiroplasma-infected Harmonia axyridis corresponded to greater ovariole number, and therefore higher potential fecundity. To our knowledge, this is the first report of direct benefits of male-killer infection after explicitly controlling for indirect fitness effects. Neutral or deleterious fitness effects of male-killer infection should not therefore be automatically assumed.
Data from: Antagonistic pleiotropy in species with separate sexes, and the maintenance of genetic variation in life-history traits and fitness
Antagonistic pleiotropy (AP) – where alleles of a gene increase some components of fitness at a cost to others – can generate balancing selection, and contribute to the maintenance of genetic variation in fitness traits, such as survival, fecundity, fertility, and mate competition. Previous theory suggests that AP is unlikely to maintain variation unless antagonistic selection is strong, or AP alleles exhibit pronounced differences in genetic dominance between the affected traits. We show that conditions for balancing selection under AP expand under the likely scenario that the strength of selection on each fitness component differs between the sexes. Our model also predicts that the vast majority of balanced polymorphisms have sexually antagonistic effects on total fitness, despite the absence of sexual antagonism for individual fitness components. We conclude that AP polymorphisms are less difficult to maintain than predicted by prior theory, even under our conservative assumption that selection on components of fitness is universally sexually concordant. We discuss implications for the maintenance of genetic variation, and for inferences of sexual antagonism that are based on sex-specific phenotypic selection estimates – many of which are based on single fitness components.
Data from: Irreproducible text-book 'knowledge': the effects of color bands on zebra finch fitness
Many fields of science currently experience a heated debate about the extent of publication bias against null-findings. Here, we show a case where putatively well-established text-book knowledge cannot be confirmed. Across four decades, zebra finch (Taeniopygia guttata) studies have reported effects of bands of certain colors on male or female attractiveness and further on behavior, physiology, life-history and fitness. Only 8 out of 39 publications presented exclusively null-findings. Here, we analyze the results of eight experiments in which we quantified the fitness of 730 color-banded individuals from four captive populations (two domesticated and two recently wild-derived). This sample size exceeds the combined sample size of all 23 publications that clearly support the "color-band effect" hypothesis. In our populations, band color explained no variance in fitness and there were no context- or population-specific band color effects. Analysis of unpublished data from three other laboratories strengthens our null finding. Finally, a meta-analysis of previously published results is indicative of selective reporting and suggests that the effect size approaches zero when sample size is large. We argue that our field would benefit from more effective means to counter confirmation bias and publication bias.
Data from: An advanced shape-fitting algorithm applied to quadrupedal mammals: improving volumetric mass estimates
Body mass is a fundamental physical property of an individual and has enormous bearing upon ecology and physiology. Generating reliable estimates for body mass is therefore a necessary step in many palaeontological studies. Whilst early reconstructions of mass in extinct species relied upon isolated skeletal elements, volumetric techniques are increasingly applied to fossils when skeletal completeness allows. We apply a new 'alpha shapes' (α-shapes) algorithm to volumetric mass estimation in quadrupedal mammals. α-shapes are defined by: (i) the underlying skeletal structure to which they are fitted; and (ii) the value α, determining the refinement of fit. For a given skeleton, a range of α-shapes may be fitted around the individual, spanning from very coarse to very fine. We fit α-shapes to three-dimensional models of extant mammals and calculate volumes, which are regressed against mass to generate predictive equations. Our optimal model is characterized by a high correlation coefficient and mean square error (r 2=0.975, m.s.e.=0.025). When applied to the woolly mammoth (Mammuthus primigenius) and giant ground sloth (Megatherium americanum), we reconstruct masses of 3635 and 3706 kg, respectively. We consider α-shapes an improvement upon previous techniques as resulting volumes are less sensitive to uncertainties in skeletal reconstructions, and do not require manual separation of body segments from skeletons.
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