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374 results for “Selection: natural”
Genetic diversity and efficacy of natural selection in spiders with pre-copulatory sexual cannibalism
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Data for: Sexual dichromatism may not be a good index of sexual or natural selection in the blue cardinalids (Aves: Passeriformes).
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The MUC19 Gene: An Evolutionary History of Recurrent Introgression and Natural Selection
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Data from: Predator life history and prey ontogeny limit natural selection on the major armour gene, Eda, in threespine stickleback
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The roles of climate, geography and natural selection as drivers of genetic and phenotypic differentiation in a widespread amphibian Hyla annectans (Anura: Hylidae)
The role of geological events and Pleistocene climatic fluctuations as drivers of current patterns of genetic variation in extant species has been a topic of continued interest among evolutionary biologists. Nevertheless, comprehensive studies of widely distributed species are still rare, especially from Asia. Using geographically extensive sampling of many individuals and a large number of nuclear single nucleotide polymorphisms (SNPs), we studied the phylogeography and historical demography of Hyla annectans populations in southern China. Thirty-five sampled populations were grouped into seven clearly defined genetic clusters that closely match phenotype-based subspecies classification. These lineages diverged 2.32–5.23 million years ago, a timing that closely aligns with the rapid and drastic uplifting of the Qinghai-Tibet Plateau and adjacent southwest China. Demographic analyses and species distribution models indicate that different populations of this species have responded differently to past climatic changes. In the Hengduan Mountains, most populations experienced a bottleneck, whereas the populations located outside of the Hengduan Mountains have gradually declined in size since the end of the last glaciation. In addition, the levels of phenotypic and genetic divergence were strongly correlated across major clades. These results highlight the combined effects of geological events and past climatic fluctuations, as well as natural selection, as drivers of contemporary patterns of genetic and phenotypic variation in a widely distributed anuran in Asia.
Density-dependent natural selection mediates harvest-induced trait changes
<p>Rapid life-history changes caused by size-selective harvesting are often interpreted as a response to direct harvest selection against a large body size. However, similar trait changes may result from a harvest-induced relaxation of natural selection for a large body size via density-dependent selection. Here, we show evidence of such density-dependent selection favouring large-bodied individuals at high population densities, in replicated pond populations of medaka fish. Harvesting, in contrast, selected medaka directly against a large body size and, in parallel, decreased medaka population densities. Five years of harvesting were enough for harvested and unharvested medaka populations to inherit the classically-predicted trait differences, whereby harvested medaka grew slower and matured earlier than unharvested medaka. We demonstrate that this life-history divergence was not driven by direct harvest selection for a smaller body size in harvested populations, but by density-dependent natural selection for a larger body size in unharvested populations.</p>
Using ecological context to interpret spatiotemporal variation in natural selection
<p>Spatiotemporal variation in natural selection is expected, but difficult to estimate. Pollinator-mediated selection on floral traits provides a good system for understanding and linking variation in selection to differences in ecological context. We studied pollinator-mediated selection in five populations of <i>Dalechampia scandens</i> (Euphorbiaceae) in Costa Rica and Mexico. Using a nonlinear path-analytical approach, we assessed several functional components of selection, and linked variation in pollinator-mediated selection across time and space to variation in pollinator assemblages. After correcting for estimation error, we detected moderate variation in net selection on two of four blossom traits. Both the opportunity for selection and the mean strength of selection decreased with increasing reliability of cross-pollination. Selection for pollinator attraction was consistently positive and stronger on advertisement than reward traits. Selection on traits affecting pollen transfer from the pollinator to the stigmas was strong only when there was a mismatch between pollinator and blossom size under unreliable cross-pollination. These results illustrate how consideration of trait function and ecological context can facilitate both the detection and the causal understanding of spatiotemporal variation in natural selection.</p>
Combining GWAS and FST-based approaches to identify targets of Borrelia-mediated selection in natural rodent hosts
Recent advances in high-throughput sequencing technologies provide opportunities to gain novel insights into the genetic basis of phenotypic trait variation. Yet to date, progress in our understanding of genotype-phenotype associations in non-model organisms in general and natural vertebrate populations in particular has been hampered by small sample sizes typically available for wildlife populations and a resulting lack of statistical power, as well as a limited ability to control for false positive signals. Here we propose to combine a genome-wide association (GWAS) and FST-based approach with population-level replication to partly overcome these limitations. We present a case study in which we used this approach in combination with Genotyping-by-Sequencing (GBS) SNP data to identify genomic regions associated with Borrelia afzelii resistance or susceptibility in the natural rodent host of this Lyme disease-causing spirochete, the bank vole (Myodes glareolus). Using this combined approach we identified four consensus SNPs located in exonic regions of the genes Slc26a4, Tns3, Wscd1 and Espnl, which were significantly associated with the voles' Borrelia infectious status within and across populations. Functional links between host responses to bacterial infections and most of these genes have previously been demonstrated in other rodent systems, making them promising new candidates for the study of evolutionary host responses to Borrelia emergence. Our approach is applicable to other systems and may facilitate the identification of genetic variants underlying disease resistance or susceptibility, as well as other ecologically relevant traits, in wildlife populations.
Data from: Climate change shifts natural selection and the adaptive potential of the perennial forb Boechera stricta in the Rocky Mountains
Heritable genetic variation is necessary for populations to evolve in response to anthropogenic climate change. However, antagonistic genetic correlations among traits may constrain the rate of adaptation, even if substantial genetic variation exists. We examine potential genetic responses to selection by comparing multivariate genetic variance-covariances of traits and fitness (multivariate Robertson-Price identities) across different environments in a reciprocal transplant experiment of the forb Boechera stricta in the Rocky Mountains. By transplanting populations into four common gardens arrayed along an elevational gradient, and exposing populations to control and snow removal treatments, we simulated future and current climates and snowmelt regimes. Genetic variation in flowering and germination phenology declined in plants moved downslope to warmer, drier sites, suggesting that these traits may have a limited ability to evolve under future climates. Simulated climate change via snow removal altered the strength of selection on flowering traits, but we found little evidence that genetic correlations among traits are likely to affect the rate of adaptation to climate change. Overall, our results suggest that climate change may alter the evolutionary potential of B. stricta, but reduced expression of genetic variation may be a larger impediment to adaptation than constraints imposed by antagonistic genetic correlations.
Impacts of environmental heterogeneity on natural selection in a wild bird population
<p>Natural selection has been studied for several decades, resulting in the computation of thousands of selection estimates. Although the importance of environmental conditions on selection has often been suggested, published estimates rarely take into account the effects of environmental heterogeneity on selection patterns. Here, we estimated linear and non‐linear viability selection gradients on morphological traits of 12 days‐old nestlings in a wild population of tree swallows (<i>Tachycineta bicolor</i>) across a large‐scale heterogeneous study system in southern Québec, Canada. We assessed the environmental drivers of nestling survival and evaluated their effects on strength and direction of selection gradients. Separate analyses of environmental variables showed that high temperatures and heavy rainfall caused stronger positive linear selection on morphological traits. Weaker linear selection was also measured in more extensively cultivated areas. Both strength and shape of non‐linear quadratic and correlational components of selection were modified by environmental variables. Considering all environmental variables revealed that precipitation since hatching affected patterns of linear selection on traits, while temperatures since hatching shaped nonlinear selection patterns. Our study underlines the importance of quantifying linear and non‐linear natural selection under various environmental conditions and how the evolutionary response of traits may be affected by ongoing human‐induced environmental changes.</p>
Data from: A hurricane alters pollinator relationships and natural selection on an introduced island plant
Novel relationships between the floral morphology of introduced plants and the trophic morphology of native pollinators have been hypothesized to cause strong natural selection on both parties, but evidence for such selection is rare. We capitalized on a natural disturbance to examine selection on an introduced plant, Heliconia wagneriana, on the island of Dominica, before and after Hurricane Maria. Prior to the hurricane, female Anthracothorax jugularis hummingbirds, which have longer bills than males, were the main visitor to H. wagneriana, and directional selection on corolla length was insignificant. After the hurricane, shorter-billed male A. jugularis were the main visitor to H. wagneriana. The absence of trait-matching between a short-billed pollinator and a long-flowered plant resulted in directional selection for shorter flowers because males preferentially visited plants with shorter flowers. The amount of nectar removed by male A. jugularis was negatively associated with flower length, with flowers > 53 mm containing nearly five times the nectar than flowers < 53 mm. We estimate a roughly 75% decrease in the population size of A. jugularis, and results suggest the heaviest mortality occurred among short-billed male hummingbirds and larger-bodied individuals of both sexes, which would have higher nectar requirements and the most difficulty obtaining nectar. Our results indicate that hurricanes may alter relationships between plants and pollinators, and that lack of trait-matching resulting from such disturbances may lead to selection on both plant and pollinator.
Data from: Population genomics of rapid evolution in natural populations: polygenic selection in response to power station thermal effluents
Background: Examples of rapid evolution are common in nature but difficult to account for with the standard population genetic model of adaptation. Instead, selection from the standing genetic variation permits rapid adaptation via soft sweeps or polygenic adaptation. Empirical evidence of this process in nature is currently limited but accumulating. Results: We provide genome-wide analyses of rapid evolution in two Fundulus heteroclitus populations subjected to recently elevated temperatures due to coastal power station thermal effluents. Bayesian and multivariate analyses of population genomic structure reveal a substantial portion of genetic variation that is most parsimoniously explained by selection at the site of thermal effluents. An FST outlier approach in conjunction with additional conservative requirements identify significant allele frequency differentiation that exceeds neutral expectations among exposed and closely related reference populations. Genomic variation patterns near these candidate loci reveal that individuals living near thermal effluents have rapidly evolved from the standing genetic variation through small allele frequency changes at many loci in a pattern consistent with polygenic selection on the standing genetic variation. Conclusions: While the ultimate trajectory of selection in these populations is unknown, our findings suggest that polygenic models of adaptation may play important roles in large, natural populations experiencing recent selection due to environmental changes that cause broad physiological impacts.
Natural selection drives genome-wide evolution via chance genetic associations
<p>Understanding selection's impact on the genome is a major theme in biology. Functionally-neutral genetic regions can be affected indirectly by natural selection, via their statistical association with genes under direct selection. The genomic extent of such indirect selection, particularly across loci not physically linked to those under direct selection, remains poorly understood, as does the time scale at which indirect selection occurs. Here we use field experiments and genomic data in stick insects, deer mice and stickleback fish to show that widespread statistical associations with genes known to affect fitness cause many genetic loci across the genome to be impacted indirectly by selection. This includes regions physically distant from those directly under selection. Then, focusing on the stick insect system, we show that statistical associations between SNPs and other unknown, causal variants result in additional indirect selection in general and specifically within genomic regions of physically linked loci. This widespread indirect selection necessarily makes aspects of evolution more predictable. Thus, natural selection combines with chance genetic associations to affect genome-wide evolution across linked and unlinked loci and even in modest-sized populations. This process has implications for the application of evolutionary principles in basic and applied science.</p>
Selection against individuals from genetic introgression of escaped farmed salmon in a natural population of Atlantic salmon
<p>The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of geneflow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life-stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of two years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population-level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort) . This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity.The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of geneflow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life-stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of two years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population-level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort) . This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity.</p>
The stabilising impact of natural selection on the allometry of sexual ornaments: Fish that escape locomotor constraints exhibit extravagant ornamentation
<p>1. Positive allometry has been considered a hallmark of sexual selection whereby larger males of superior condition develop disproportionately larger ornaments for their body size compared to smaller males of poorer condition.</p> <p>2. Yet many structures known to be sexually selected often exhibit other allometric patterns. This has led to controversy over the utility of allometry in adequately capturing the signature of sexual selection, particularly if static (within population) and evolutionary (across species) allometries are functionally constrained by stabilising natural selection.</p> <p>3. To investigate this, we evaluated the allometries of ornamental head crests and dorsal fins across multiple species of blenny fish. In particular, we compared species that occupied an aquatic environment—where swimming performance was expected to have constrained ornament size—with species that have transitioned onto land where such biomechanical constraints on ornament size have been removed.</p> <p>4. Static allometries of both head crest and dorsal fin ornaments were found to be positive in males, but less so in females, across all species examined. This was consistent with the allometric theory of sexual selection that predicts positive allometry specifically in male ornamentation. Nevertheless, male allometric slopes were constrained in aquatic species whereas males of terrestrial species were free to exaggerate the size of their ornaments. Natural selection therefore appears to suppress ornament size in aquatics because of the biomechanical constraints associated with swimming. These differences in within-population static allometry between aquatic and terrestrial species in turn manifested in a greater across-species evolutionary allometric intercept, but not slope, for terrestrial species relative to aquatic and species.</p> <p>5. These findings indicate that the study of ornament allometries can provide useful insights into the role of sexual selection on ornament elaboration and also help reveal the presence of opposing natural selection that might result in alternative allometric patterns. The relationship between static and evolutionary allometries remains complex, and our results caution against the interpretation of evolutionary allometry in the absence of a clear understanding of the underlying static allometries associated with it.</p>
Recent natural variability in global warming weakened phenological mismatch and selection on seasonal timing in great tits (Parus major)
<p></p><p> Climate change has led to phenological shifts in many species, but with large variation in magnitude among species and trophic levels. The poster child example of the resulting phenological mismatches between the phenology of predators and their prey is the great tit (Parus major), where this mismatch led to directional selection for earlier seasonal breeding. Natural climate variability can obscure the impacts of climate change over certain periods, weakening phenological mismatching and selection. Here, we show that selection on seasonal timing indeed weakened significantly over the past two decades as increases in late spring temperatures have slowed down. Consequently, there has been no further advancement in the date of peak caterpillar food abundance, while great tit phenology has continued to advance, thereby weakening the phenological mismatch. We thus show that the relationships between temperature, phenologies of prey and predator, and selection on predator phenology are robust, also in times of a slowdown of warming. Using projected temperatures from a large ensemble of climate simulations that take natural climate variability into account, we show that prey phenology is again projected to advance faster than great tit phenology in the coming decades, and therefore that long-term global warming will intensify phenological mismatches. </p><p></p>
Determination of Natural Radioactivity Levels and Associated Radiation Hazard Indices of Wheat Flour Samples From Selected Ethiopian Markets.
<p>Wheat flour is a nutrient-dense food that is commonly consumed by various age groups in Ethiopia. In this study, natural radioactivity levels of <sup>226</sup>Ra, <sup>232</sup>Th, and <sup>40</sup>K, as well as the related dangerous radiological characteristics, were successfully measured on 10 different brands of wheat flour samples using high-purity germanium (HPGe) gamma-ray spectrometry. Average activity concentrations of <sup>226</sup>Ra, <sup>232</sup>Th, and <sup>40</sup>K in wheat flour are found to be 0.26<strong> ±</strong>0.07 Bq.kg<sup>-1</sup>, 1.54<strong> ± </strong>0.43 Bq.kg<sup>-1</sup>, and 59.79<strong>±</strong>3.65 Bq.kg<sup>-1</sup>, respectively. Moreover, the average values of the corresponding radiological parameters, Ra<sub>eq</sub>, H<sub>int</sub>, and annual effective dose (E<sub>ave</sub>) (sum), were also found to be 7.07±0.96 Bq.kg<sup>-1</sup>, 0.019±0.003, and 0.109±0.019 mSvy<sup>-1</sup>, respectively. When the obtained results for all of the samples were compared to the internationally accepted norms, they were found to be below the permissible world average values. Furthermore, the lifetime cancer risk was discovered to be substantially below the permissible limit. According to the study, the risk of absorbing natural radionuclides from wheat flour consumption is negligible. The findings can be used to develop radiation protection rules and regulations for the use of wheat flour in food production and processing.</p>
Signatures of natural selection in a foundation tree along Mediterranean climatic gradients
<p>Temperature and precipitation regimes are rapidly changing, resulting in forest dieback and extinction events, particularly in Mediterranean-type climates (MTC). Forest management that enhance forests' resilience is urgently required, however adaptation to climates in heterogeneous landscapes with multiple selection pressures is complex. For widespread trees in MTC we hypothesized that: patterns of local adaptation are associated with climate; precipitation is a stronger factor of adaptation than temperature; functionally related genes show similar signatures of adaptation; and adaptive variants are independently sorting across the landscape. We sampled 28 populations across the geographic distribution of Eucalyptus marginata (jarrah), in South-west Western Australia, and obtained 13,534 independent single nucleotide polymorphic (SNP) markers across the genome. Three genotype-association analyses that employ different ways of correcting population structure were used to identify putatively adapted SNPs associated with independent climate variables. While overall levels of population differentiation were low (<i>F</i><sub>ST</sub> = 0.04), environmental association analyses found a total of 2,336 unique SNPs associated with temperature and precipitation variables, with 1,440 SNPs annotated to genic regions. Considerable allelic turnover was identified for SNPs associated with temperature seasonality and mean precipitation of the warmest quarter, suggesting that both temperature and precipitation are important factors in adaptation. SNPs with similar gene functions had analogous allelic turnover along climate gradients, while SNPs among temperature and precipitation variables had uncorrelated patterns of adaptation. These contrasting patterns provide evidence that there may be standing genomic variation adapted to current climate gradients, providing the basis for adaptive management strategies to bolster forest resilience in the future.</p>
Data from: Multivariate selection mediated by aridity predicts divergence of drought resistant traits along natural aridity gradients of an invasive weed
<p><span>Geographic variation in the environment underpins selection for local adaptation and evolutionary divergence among populations. Because many environmental conditions vary across species' ranges, identifying the specific environmental variables underlying local adaptation is profoundly challenging. </span></p> <p><span>We tested whether natural selection mediated by aridity predicts clinal divergence among invasive populations of capeweed (<i><span>Arctotheca calendula</span></i>) that established and spread across southern Australia during the last two centuries. </span></p> <p><span>Using common garden experiments with two environmental treatments (wet and dry) that mimic aridity conditions across capeweed's invasive range, we estimated clinal divergence and effects of aridity on fitness and multivariate phenotypic selection in populations sampled along aridity gradients in Australia. We show that: (<i>i</i>) capeweed populations have relatively high fitness in aridity environments similar to their sampling locations; (<i>ii</i>) the magnitude and direction of selection strongly differs between wet and dry treatments, with drought stress increasing the strength of selection; and (<i>iii</i>) differences in directional selection between wet and dry treatments predict patterns of clinal divergence across the aridity gradient, particularly for traits affecting biomass, flowering phenology and putative antioxidant expression. </span></p> <p><span>Our results suggest that aridity-mediated selection contributes to trait diversification among invasive capeweed populations, possibly facilitating the expansion of capeweed across southern Australia. </span></p>
Exploring the interplay between natural and intersexual selection on the evolution of a cognitive trait
<p><span>There has been an increased focus on the role of natural and sexual selection in shaping cognitive abilities, but the importance of the interaction between both forces remain largely unknown. Intersexual selection through female mate choice might be an important driver of the evolution of cognitive traits, especially in monogamous species, where females may obtain direct fitness benefits by choosing mates with better cognitive abilities. However, the importance given by females to male cognitive traits might vary among species and/or populations according to their life-history traits and ecology. To disentangle the effects of natural and sexual selection, here we use an agent-based simulation model and compare the model's predictions when females mate with the first randomly encountered male (i.e. under natural selection) versus when they choose among males based on their cognitive trait values (i.e. under natural and intersexual selection). Males and females are characterized, respectively, by their problem-solving ability and assessment strategy. At each generation, agents go through (1) a choosing phase during which females assess the cognitive abilities of potential mates until eventually finding an acceptable one, and (2) a reproductive phase during which all males compete for limited resources that are exploited at a rate which depends on their cognitive abilities. Because males provide paternal care, the foraging success of mated males determines the breeding success of the pair through its effect on nestling provisioning efficiency. The model predicts that intersexual selection plays a major role in most ecological conditions, by either reinforcing or acting against the effect of natural selection. The latter case occurs under harsh environmental conditions, where intersexual selection contributes to maintaining cognitive diversity. Our findings thus demonstrate the importance of considering the interaction between both selective forces and highlight the need to build a conceptual framework to target relevant cognitive traits.</span></p>
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