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183 results for “rate variation”
Population-level variation in parasite resistance due to differences in immune initiation and rate of response
<p>Closely related populations often differ in resistance to a given parasite, as measured by infection success or failure. Yet, the immunological mechanisms of these evolved differences are rarely specified. Does resistance evolve via changes to the host's ability to recognize that an infection exists, actuate an effective immune response, or attenuate that response? We tested whether each of these phases of the host response contributed to threespine sticklebacks' recently evolved resistance to their tapeworm <i>Schistocephalus solidus. </i>While marine stickleback and some susceptible lake fish permit fast-growing tapeworms, other lake populations are resistant and suppress tapeworm growth via a fibrosis response. We subjected lab-raised fish from three populations (susceptible marine 'ancestors', a susceptible lake population, a resistant lake population), to a novel immune challenge using an injection of: 1) a saline control, 2) alum, a generalized pro-inflammatory adjuvant that causes fibrosis, 3) a tapeworm protein extract, or 4) a combination of alum and tapeworm protein). With enough time, all three populations generated a robust fibrosis response to the alum treatments. Yet, only the resistant population exhibited a fibrosis response to the tapeworm protein alone. Thus, these populations differed in their ability to respond to the tapeworm protein but shared an intact fibrosis pathway. The resistant population also initiated fibrosis faster in response to alum, and was able to attenuate fibrosis, unlike the susceptible populations' slow but longer-lasting response to alum. As fibrosis has pathological side-effects that reduce fecundity, the faster recovery by the resistant population may reflect an adaptation to mitigate the costs of immunity. Broadly, our results confirm that parasite detection and immune initiation, activation speed, and immune attenuation simultaneously contribute to the evolution of parasite resistance and adaptations to infection in natural populations.</p>
Variation in developmental rates is not linked to environmental unpredictability in annual killifishes
<p>Comparative evidence suggests that adaptive plasticity may evolve as a response to predictable environmental variation. However, less attention has been placed on unpredictable environmental variation, which is considered to affect evolutionary trajectories by increasing phenotypic variation (or bet-hedging). Here, we examine the occurrence of bet-hedging in egg developmental rates in seven species of annual killifish that originate from a gradient of variation in precipitation rates, under three treatment incubation temperatures (21°C, 23°C, and 25°C). In the wild, these species survive regular and seasonal habitat desiccation, as dormant eggs buried in the soil. At the onset of the rainy season embryos must be sufficiently developed in order to hatch and complete their life-cycle. We found substantial differences among species in both the mean and variation of egg development rates, as well as species-specific plastic responses to incubation temperature. Yet, there was no clear relationship between variation in egg development time and variation in precipitation rate (environmental predictability). The exact cause of these differences therefore remains enigmatic, possibly depending on differences in other natural environmental conditions in addition to precipitation predictability. Hence, if species-specific variances are adaptive, the relationship between development and variation in precipitation is complex and does not diverge in accordance with simple linear relationships.</p>
Variations and controlling factors of soil denitrification rate
<p>The denitrification process profoundly affects soil nitrogen (N) availability and generates its byproduct, nitrous oxide, as a potent greenhouse gas. There are large uncertainties in predicting global denitrification because its controlling factors remain elusive. In this study, we compiled 4301 observations of denitrification rates across a variety of terrestrial ecosystems from 214 papers published in the literature. The averaged denitrification rate was 3516.3 ± 91.1 µg N kg<sub>−1</sub> soil day<sub>−1</sub>. The highest denitrification rate was 4242.3 ± 152.3 µg N kg<sub>−1</sub> soil day<sub>−1</sub> under humid subtropical climates, and the lowest was 965.8 ± 150.4 µg N kg−1 under dry climates. The denitrification rate increased with temperature, precipitation, soil carbon and N contents, as well as microbial biomass carbon and N, but decreased with soil clay contents. The variables related to soil N contents (e.g., nitrate, ammonium, and total N) explained the variation of denitrification more than climatic and edaphic variables (e.g., mean annual temperature (MAT), soil moisture, soil pH, and clay content) according to structural equation models. Soil microbial biomass carbon, which was influenced by soil nitrate, ammonium, and total N, also strongly influenced denitrification at a global scale. Collectively, soil N contents, microbial biomass, pH, texture, moisture, and MAT accounted for 60% of the variation in global denitrification rates. The findings suggest that soil N contents and microbial biomass are strong predictors of denitrification at the global scale.</p>
Evolutionary rates and shape variation along the anuran vertebral column with attention to phylogeny, body size, and ecology
<p><span>The vertebral column is critical to a vertebrate species' flexibility and skeletal support, making vertebrae a clear target for selection. Anur</span><span>ans (frogs and toads) have a unique, truncated vertebral column that appears constrained to provide axial rigidity for efficient jumping. However, no study has examined how presacral vertebrae shape varies among anuran species at the macroevolutionary scale nor how intrinsic (developmental and phylogenetic) and extrinsic (ecological) factors may have influenced vertebrae shape evolution. We used microCT scans and phylogenetic comparative methods to examine the vertebrae of hundreds of anuran species that vary in body size as well as adult and larval ecology. We found variation in shape and evolutionary rates among anuran vertebrae, dispelling any notion that trunk vertebrae evolve uniformly. We discovered the highest evolutionary rates in the cervical vertebrae and in the more caudal trunk vertebrae. We found little evidence for selection pressures related to adult or larval ecology affecting vertebrae evolution, but we did find body size was highly associated with vertebrae shape and microhabitat (mainly burrowing) affected those allometric relationships. Our results provide an interesting comparison to vertebrae evolution in other clades and a jumping-off point for studies of anuran vertebrae evolution and development.</span></p>
Linked selection, differential introgression and recombination rate variation promote heterogeneous divergence in a pair of yellow croakers
<p><span>Understanding the mechanisms underlying heterogeneous genomic divergence is of particular interest in evolutionary biology. Highly differentiated genomic regions, known as genomic islands, often evolve between diverging lineages. These genomic islands may be related to selection promoting adaptation or reproductive isolation. Based on whole genome assembly and genome-wide RAD sequencing in a pair of yellow croakers (genus: <em>Larimichthys</em>), we investigated the evolutionary processes shaping genomic landscapes of divergence. Demographic modelling indicated that the two species diverged following a secondary contact scenario, where differential introgression and linked selection were suggested to be involved in heterogeneous genomic divergence. We identified reduced recombination rate in genomic islands and a relatively good conservation of both genetic diversity and recombination landscapes between species, which highlight the roles of linked selection and recombination rate variation in promoting heterogeneous divergence in the common ancestral lineage of the two species. In addition, we found a positive correlation between differentiation (F<sub>ST</sub>) and absolute sequence divergence (<em>D</em><sub>xy</sub>), and elevated </span><span><span><em>D</em><sub>xy</sub></span> in genomic islands, which were different from the patterns under linked selection. Restricted gene flow in highly differentiated regions has likely remodeled the landscape of heterogeneous genomic divergence. Moreover, genomic islands showed little evidence of overlapping within and between species, implying that high gene flow and divergent selection when colonizing new habitats have reshaped the patterns of intraspecific divergence. This study highlights that highly differentiated genomic regions can also be from linked selection and variation of recombination rate, and thus are not necessarily related to speciation islands or local adaptation. </span></p>
Widespread variation in functional trait-vital rate relationships in tropical tree seedlings across a precipitation and soil phosphorus gradient
<p>A fundamental assumption of functional ecology is that functional traits are related to interspecific variation in performance. However, the relationship between functional traits and performance is often weak or uncertain, especially for plants. A potential explanation for this inconsistency is that the relationship between functional traits and vital rates (e.g., growth and mortality) is dependent on local environmental conditions, which would lead to variation in trait-rate relationships across environmental gradients. In this study, we examined trait-rate relationships for six functional traits (seed mass, wood density, maximum height, leaf mass per area, leaf area, and leaf dry matter content) using long-term data on seedling growth and survival of woody plant species from eight forest sites spanning a pronounced precipitation and soil phosphorus gradient in central Panama. For all traits considered except for leaf mass per area-mortality, leaf mass per area-growth, and leaf area-mortality relationships, we found widespread variation in the strength of trait-rate relationships across sites. For some traits, trait-rate relationships showed no overall trend but displayed wide site-to-site variation. In a small subset of cases, variation in trait-rate relationships was explained by soil phosphorus availability. Our results demonstrate that environmental gradients have the potential to influence how functional traits are related to growth and mortality rates, though much variation remains to be explained. Accounting for site-to-site variation may help resolve a fundamental issue in trait-based ecology – that traits are often weakly related to performance – and improve the utility of functional traits for explaining key ecological and evolutionary processes.</p>
The genetic basis of mutation rate variation in yeast [data and script]
<p>This dataset contains the data and the scripts for the study of exploring the genetic basis of mutation rate in yeast (https://www.biorxiv.org/content/early/2018/06/04/338723). </p> <ul> <li>The genotype folder contains the genotype for 1040 segreants, as well as the genotype for the 843 segregants used for QTL mapping.</li> <li>The mutation_spectrum contains the codes for MiSeq data processing, mutation variants calling, mutation spectrum detection and plotting. </li> <li>The phenotype folder contains the mutations per culture (parameter m) for 843 segreants, as well as the number of cells per culture (parameter N) for the corresponding segregants.</li> <li>The qtl_mapping folder contains the codes for QTL mapping and the codes to plot the correlation between mutation rate and mutagen resistance.</li> </ul>
Natural selection shapes variation in genome-wide recombination rate in Drosophila pseudoobscura
<p>While recombination is widely recognized to be a key modulator of numerous evolutionary phenomena, we have a poor understanding of how recombination rate itself varies and evolves within a species. Here, we performed a comprehensive study of recombination rate (rate of meiotic crossing over) in two natural populations of <i>Drosophila pseudoobscura</i> from Utah and Arizona, USA. We used an amplicon sequencing approach to obtain high-quality genotypes in approximately 8000 individual backcrossed offspring (17 mapping populations with roughly 530 individuals each), for which we then quantified crossovers. Interestingly, variation in recombination rate within and between populations largely manifested as differences in genome-wide recombination rate rather than remodeling of the local recombination landscape. Comparing populations, we discovered individuals from the Utah population displayed on average 8% higher crossover rates than the Arizona population, a statistically significant difference. Using a Q<sub>ST</sub>-F<sub>ST</sub> analysis, we found that this difference in crossover rate was dramatically higher than expected under neutrality, indicating that this difference may have been driven by natural selection. Finally, using a combination of short and long read whole-genome sequencing, we found no significant association between crossover rate and structural variation at the 200-400kb scale. Our results demonstrate that (1) there is abundant variation in genome-wide crossover rate in natural populations, (2) at the 200-400kb scale, recombination rate appears to vary largely genome wide, rather than in specific intervals and (3) interpopulation differences in recombination rate may be the result of local adaptation.</p>
Correlates of substitution rate variation in a robust Procellariiform seabird phylogeny
<p>Molecular substitution rates vary among branches and can lead to inaccurate reconstructions of evolutionary relationships and obscure the true phylogeny of affected clades. Body mass is often assumed to have a major influence on substitution rate, though other factors such as population size, life history traits, and flight demands are also thought to have an influence. Birds of the order Procellariiformes—which encompasses petrels, storm-petrels and albatrosses—show a striking 900-fold difference in body mass between the smallest and largest members, divergent life history traits, and substantial heterogeneity in mitochondrial substitution rates. Here, we used genome-scale nuclear DNA sequence data from 4365 ultraconserved element loci (UCEs) in 51 procellariiform species to examine whether phylogenetic reconstruction using genome-wide datasets is robust to the presence of rate heterogeneity, and to identify predictors of substitution rate variation. Our results provide a backbone phylogeny for procellariiform seabirds and resolves several controversies about the evolutionary history of the order, demonstrating that albatrosses are basal, storm-petrels are paraphyletic and diving petrels nestled within the Procellariidae. We find evidence of rate variation; however, all phylogenetic analyses using both concatenation and multispecies coalescent approaches recovered the same branching topology, including analyses implementing different clock models, and analyses of the most and least clock-like loci. Overall, we find that rate heterogeneity is little impacted by body mass and age at first breeding, but moderately impacted by longevity and hand-wing index, a proxy for wing shape and flight efficiency. Our results indicate that substitution rate may be the product of interactions among many, potentially taxon-specific, variables.</p>
Selfing rate variation within species is unrelated to life-history traits or geographic range position
<p>Premise: In plants, populations and species vary widely along the continuum from outcrossing to selfing. Life-history traits and ecological circumstances influence among-species variation in selfing rates but their general role in explaining intraspecific variation is unknown. Using a database of plant species, we test whether life-history traits, geographic range position, or abundance predict selfing rate variation among populations. </p> <p>Methods: We identified species where selfing rates were estimated in at least three populations at known locations. Two key life-history traits (generation time and growth form) were used to predict within-species selfing rate variation. Populations sampled within a species' native range were assessed for proximity to the nearest edge and abundance. Finally, we conducted linear and segmented regressions to determine functional relationships between selfing rate and geographic range position within species.</p> <p>Key results: While woody species exhibit lower variation in selfing rates compared to herbs, this is explained by the lower average selfing rate of woody species. Relationships between selfing and peripherality or abundance significantly varied among species in their direction and magnitude. However, there was no general pattern of increased selfing towards range edges. A power analysis shows that tests of this hypothesis require studying many (i.e. 40+) populations.</p> <p>Conclusions: Intraspecific variation in plant mating systems is often substantial yet remains difficult to explain. Beyond sampling more populations, future tests of biogeographic hypotheses will benefit from phylogeographic information concerning specific range edges, the study of traits influencing mating system (e.g. herkogamy), and measures of abundance at local scales (e.g. population density).</p>
Data from: Summary tests of introgression are highly sensitive to rate variation across lineages
<p>The evolutionary implications and frequency of hybridization and introgression are increasingly being recognized across the tree of life. To detect hybridization from multi-locus and genome-wide sequence data, a popular class of methods is based on summary statistics from subsets of 3 or 4 taxa. However, these methods often carry the assumption of a constant substitution rate across lineages and genes, which is commonly violated in many groups. In this work, we quantify the effects of rate variation on the <em>D </em>test (also known as ABBA-BABA test), the <em>D</em><sub>3</sub> test, and HyDe. All three tests are used widely across a range of taxonomic groups, in part because they are very fast to compute. We consider rate variation across species lineages, across genes, their lineage-by-gene interaction, and residual variation across gene-tree edges. We do so by simulating gene trees within species networks according to a birth-death-hybridization process so as to capture a range of realistic species phylogenies. For all three methods tested, we found a marked increase in the false discovery of reticulation (type-1 error rate) when there is rate variation across species lineages. The <em>D</em><sub>3</sub> test was the most sensitive, with around 80% type-1 error, such that <em>D</em><sub>3</sub> appears to be more sensitive to a departure from the clock than to the presence of reticulation. For all three tests, the power to detect hybridization events decreased as the number of hybridization events increased, indicating that multiple hybridization events can obscure one another if they occur within a small subset of taxa. Our study highlights the need to consider rate variation when using site-based summary statistics and points to the advantages of methods that do not require assumptions on evolutionary rates across lineages or across genes.</p>
Open-population SCR model to estimate spatiotemporal variation in individual birth locations, detection rates, and survival
<p>This is an open population SCR model developed by R. Chandler and K. Engebretsen. The full model incorporates 4 spatial covariates in birth location density submodel, 3 location-specific, temporal covariates in the detection submodel, and 4 spatial covariates in the survival submodel. </p> <p>Formatted data is provided for the 2015 and 2016 fawning season in south Florida and the model can be fit using the script fitFawnModel.R.</p>
Chromosome VCF files and 1Mb recombination rate estimations for: Fine-scale recombination rate variation and association with genomic features in a butterfly
<p>Genetic recombination is a key molecular mechanism that has profound implications on both micro- and macro-evolutionary processes. However, the determinants of recombination rate variation in holocentric organisms are poorly understood, in particular in Lepidoptera (moths and butterflies). The wood white butterfly (<em>Leptidea</em> <em>sinapis</em>) shows considerable intraspecific variation in chromosome numbers and is a suitable system for studying regional recombination rate variation and its potential molecular underpinnings. Here, we developed a large whole-genome resequencing data set from a population of wood whites to obtain high-resolution recombination maps using linkage disequilibrium information. The analyses revealed that larger chromosomes had a bimodal recombination landscape, potentially due to interference between simultaneous chiasmata. The recombination rate was significantly lower in subtelomeric regions, with exceptions associated with segregating chromosome rearrangements, showing that fissions and fusions can have considerable effects on the recombination landscape. There was no association between the inferred recombination rate and base composition, supporting a negligible influence of GC-biased gene conversion in butterflies. We found significant but variable associations between the recombination rate and the density of different classes of transposable elements (TEs), most notably a significant enrichment of SINEs in genomic regions with higher recombination rate. Finally, the analyses unveiled significant enrichment of genes involved in farnesyltranstransferase activity in recombination cold-spots, potentially indicating that expression of transferases can inhibit formation of chiasmata during meiotic division. Our results provide novel information about recombination rate variation in holocentric organisms and has particular implications for forthcoming research in population genetics, molecular/genome evolution and speciation.</p>
Data for: Among-species rate variation produces false signals of introgression
<p>The role of interspecific hybridization in the context of diversification dynamics has recently seen increasing attention. Genomic research has now made it abundantly clear that both hybridization and introgression - the exchange of genetic material through hybridization - are far more common than previously thought. Moreover, even highly divergent species were found to hybridize and backcross. These findings raise the question whether commonly used methods for the detection of introgression are applicable to such divergent hybridizing species, given that most of these methods were originally developed for analyses at the level of populations and recently diverged species. In particular, the assumption of constant evolutionary rates, which is implicit in many commonly used approaches, is more likely to be violated as evolutionary divergence increases. To test the limitations of introgression detection methods when being applied to divergent species, we simulated thousands of genomic datasets under a wide range of settings, with varying degrees of among-species rate variation and introgression. Using these simulated datasets, we were able to show that commonly applied statistical methods, including the D-statistic and tests based on sets of phylogenetic trees, produce false-positive signals of introgression between highly divergent taxa when these have different rates of evolution. These misleading signals are caused by the presence of homoplasies that occur at different rates when rate variation is present. To distinguish between the patterns caused by rate variation and genuine introgression, we developed a new test that is based on the expected clustering of introgressed sites and implemented this test in the program Dsuite.</p>
Data from: Species-specific variation in germination rates contributes to spatial coexistence more than adult plant water use in four closely-related annual flowering plants
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Population-level variation in parasite resistance due to differences in immune initiation and rate of response
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Open-population SCR model to estimate spatiotemporal variation in individual birth locations, detection rates, and survival
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Selfing rate variation within species is unrelated to life-history traits or geographic range position
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Data from: A Bayesian approach for inferring the impact of a discrete character on rates of continuous-character evolution in the presence of background-rate variation
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Neighbor effects on population growth rate differ among populations due to variation in demographic rate sensitivities in Sedum lanceolatum
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