@article{3772, author = {Barton, Nicholas H}, journal = {PLoS Genetics}, number = {6}, publisher = {Public Library of Science}, title = {{Understanding adaptation in large populations}}, doi = {10.1371/journal.pgen.1000987}, volume = {6}, year = {2010}, } @article{3773, abstract = {If distinct biological species are to coexist in sympatry, they must be reproductively isolated and must exploit different limiting resources. A two-niche Levene model is analysed, in which habitat preference and survival depend on underlying additive traits. The population genetics of preference and viability are equivalent. However, there is a linear trade-off between the chances of settling in either niche, whereas viabilities may be constrained arbitrarily. With a convex trade-off, a sexual population evolves a single generalist genotype, whereas with a concave trade-off, disruptive selection favours maximal variance. A pure habitat preference evolves to global linkage equilibrium if mating occurs in a single pool, but remarkably, evolves to pairwise linkage equilibrium within niches if mating is within those niches--independent of the genetics. With a concave trade-off, the population shifts sharply between a unimodal distribution with high gene flow and a bimodal distribution with strong isolation, as the underlying genetic variance increases. However, these alternative states are only simultaneously stable for a narrow parameter range. A sharp threshold is only seen if survival in the 'wrong' niche is low; otherwise, strong isolation is impossible. Gene flow from divergent demes makes speciation much easier in parapatry than in sympatry.}, author = {Barton, Nicholas H}, journal = {Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences}, number = {1547}, pages = {1825 -- 1840}, publisher = {Royal Society}, title = {{What role does natural selection play in speciation?}}, doi = {10.1098/rstb.2010.0001}, volume = {365}, year = {2010}, } @article{3774, abstract = {1. Hybridisation with an invasive species has the potential to alter the phenotype and hence the ecology of a native counterpart. 2. Here data from populations of native red deer Cervus elaphus and invasive sika deer Cervus nippon in Scotland is used to assess the extent to which hybridisation between them is causing phenotypic change. This is done by regression of phenotypic traits against genetic hybrid scores. 3. Hybridisation is causing increases in the body weight of sika-like deer and decreases in the body weight of red-like females. Hybridisation is causing increases in jaw length and increases in incisor arcade breadth in sika-like females. Hybridisation is also causing decreases in incisor arcade breadth in red-like females. 4. There is currently no evidence that hybridisation is causing changes in the kidney fat weight or pregnancy rates of either population. 5. Increased phenotypic similarity between the two species is likely to lead to further hybridisation. The ecological consequences of this are difficult to predict.}, author = {Senn, Helen and Swanson, Graeme and Goodman, Simon and Barton, Nicholas H and Pemberton, Josephine}, journal = {Journal of Animal Ecology}, number = {2}, pages = {414 -- 425}, publisher = {Wiley-Blackwell}, title = {{Phenotypic correlates of hybridisation between red and sika deer (genus Cervus)}}, doi = {10.1111/j.1365-2656.2009.01633.x}, volume = {79}, year = {2010}, } @article{3776, abstract = {The prevalence of recombination in eukaryotes poses one of the most puzzling questions in biology. The most compelling general explanation is that recombination facilitates selection by breaking down the negative associations generated by random drift (i.e. Hill-Robertson interference, HRI). I classify the effects of HRI owing to: deleterious mutation, balancing selection and selective sweeps on: neutral diversity, rates of adaptation and the mutation load. These effects are mediated primarily by the density of deleterious mutations and of selective sweeps. Sequence polymorphism and divergence suggest that these rates may be high enough to cause significant interference even in genomic regions of high recombination. However, neither seems able to generate enough variance in fitness to select strongly for high rates of recombination. It is plausible that spatial and temporal fluctuations in selection generate much more fitness variance, and hence selection for recombination, than can be explained by uniformly deleterious mutations or species-wide selective sweeps.}, author = {Barton, Nicholas H}, journal = {Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences}, number = {1552}, pages = {2559 -- 2569}, publisher = {Royal Society}, title = {{Genetic linkage and natural selection}}, doi = {10.1098/rstb.2010.0106}, volume = {365}, year = {2010}, } @article{3777, abstract = {Under the classical view, selection depends more or less directly on mutation: standing genetic variance is maintained by a balance between selection and mutation, and adaptation is fuelled by new favourable mutations. Recombination is favoured if it breaks negative associations among selected alleles, which interfere with adaptation. Such associations may be generated by negative epistasis, or by random drift (leading to the Hill-Robertson effect). Both deterministic and stochastic explanations depend primarily on the genomic mutation rate, U. This may be large enough to explain high recombination rates in some organisms, but seems unlikely to be so in general. Random drift is a more general source of negative linkage disequilibria, and can cause selection for recombination even in large populations, through the chance loss of new favourable mutations. The rate of species-wide substitutions is much too low to drive this mechanism, but local fluctuations in selection, combined with gene flow, may suffice. These arguments are illustrated by comparing the interaction between good and bad mutations at unlinked loci under the infinitesimal model.}, author = {Barton, Nicholas H}, journal = {Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences}, number = {1544}, pages = {1281 -- 1294}, publisher = {Royal Society}, title = {{Mutation and the evolution of recombination}}, doi = {10.1098/rstb.2009.0320}, volume = {365}, year = {2010}, } @article{3779, abstract = {Crosses between closely related species give two contrasting results. One result is that species hybrids may be inferior to their parents, for example, being less fertile [1]. The other is that F1 hybrids may display superior performance (heterosis), for example with increased vigour [2]. Although various hypotheses have been proposed to account for these two aspects of hybridisation, their biological basis is still poorly understood [3]. To gain further insights into this issue, we analysed the role that variation in gene expression may play. We took a conserved trait, flower asymmetry in Antirrhinum, and determined the extent to which the underlying regulatory genes varied in expression among closely related species. We show that expression of both genes analysed, CYC and RAD, varies significantly between species because of cis-acting differences. By making a quantitative genotype-phenotype map, using a range of mutant alleles, we demonstrate that the species lie on a plateau in gene expression-morphology space, so that the variation has no detectable phenotypic effect. However, phenotypic differences can be revealed by shifting genotypes off the plateau through genetic crosses. Our results can be readily explained if genomes are free to evolve within an effectively neutral zone in gene expression space. The consequences of this drift will be negligible for individual loci, but when multiple loci across the genome are considered, we show that the variation may have significant effects on phenotype and fitness, causing a significant drift load. By considering these consequences for various gene-expression-fitness landscapes, we conclude that F1 hybrids might be expected to show increased performance with regard to conserved traits, such as basic physiology, but reduced performance with regard to others. Thus, our study provides a new way of explaining how various aspects of hybrid performance may arise through natural variation in gene activity.}, author = {Rosas, Ulises and Barton, Nicholas H and Copsey, Lucy and Barbier De Reuille, Pierre and Coen, Enrico}, journal = {PLoS Biology}, number = {7}, publisher = {Public Library of Science}, title = {{Cryptic variation between species and the basis of hybrid performance}}, doi = {10.1371/journal.pbio.1000429}, volume = {8}, year = {2010}, } @article{3783, abstract = {MICROSATELIGHT is a Perl/Tk pipeline with a graphical user interface that facilitates several tasks when scoring microsatellites. It implements new subroutines in R and PERL and takes advantage of features provided by previously developed freeware. MICROSATELIGHT takes raw genotype data and automates the peak identification through PeakScanner. The PeakSelect subroutine assigns peaks to different microsatellite markers according to their multiplex group, fluorochrome type, and size range. After peak selection, binning of alleles can be carried out 1) automatically through AlleloBin or 2) by manual bin definition through Binator. In both cases, several features for quality checking and further binning improvement are provided. The genotype table can then be converted into input files for several population genetics programs through CREATE. Finally, Hardy–Weinberg equilibrium tests and confidence intervals for null allele frequency can be obtained through GENEPOP. MICROSATELIGHT is the only freely available public-domain software that facilitates full multiplex microsatellite scoring, from electropherogram files to user-defined text files to be used with population genetics software. MICROSATELIGHT has been created for the Windows XP operating system and has been successfully tested under Windows 7. It is available at http://sourceforge.net/projects/microsatelight/.}, author = {Palero, Ferran and González Candelas, Fernando and Pascual, Marta}, journal = {Journal of Heredity}, number = {2}, pages = {247 -- 249}, publisher = {Oxford University Press}, title = {{Microsatelight – Pipeline to expedite microsatellite analysis}}, doi = {10.1093/jhered/esq111}, volume = {102}, year = {2010}, } @article{3785, abstract = {Most fisheries involving spiny lobsters of the genus Palinurus have been over exploited during the last decades, so there is a raising concern about management decisions for these valuable resources. A total of 13 microsatellite DNA loci recently developed in Palinurus elephas were assayed in order to assess genetic diversity levels in every known species of the genus. Microsatellite markers gave amplifications and showed polymorphism in all species, with gene diversity values varying from 0.65060.077 SD (Palinurus barbarae) to 0.79260.051 SD (Palinurus elephas). Most importantly, when depth distribution was taken into account, shallower waters pecies consistently showed larger historical effective population sizes than their deeper-water counterparts. This could explain why deeper-water species are more sensitive to overfishing, and would indicate that overexploitation may have a larger impact on their long-term genetic diversity.}, author = {Palero, Ferran and Abello, Pere and Macpherson, E. and Matthee, C. and Pascual, Marta}, issn = {1937-240X}, journal = {Journal of Crustacean Biology}, number = {4}, pages = {658 -- 663}, publisher = {Oxford University Press}, title = {{Genetic diversity levels in fishery-exploited spiny lobsters of the Genus Palinurus (Decapoda: Achelata)}}, doi = {10.1651/09-3192.1}, volume = {30}, year = {2010}, } @article{3786, abstract = {Four rare palinurid phyllosoma larvae, one mid-stage and three final stage, were found among the unclassified collections in the Crustacea Section, Natural History Museum, London. Detailed morphological analysis of the larvae indicated that they belong to several Palinustus species given the presence of incipient blunt-horns, length of antennula, length ratio of segments of antennular peduncle, distribution of pereiopod spines, and shape of uropods and telson. Moreover, the size of the final-stage larvae agrees with that expected given the size of the recently described puerulus stage of Palinustus mossambicus. This constitutes the first description of a complete phyllosoma assigned to Palinustus species. The phyllosoma described in the present study include the largest Palinuridae larva ever found.}, author = {Palero, Ferran and Guerao, Guillermo and Clark, Paul and Abello, Pere}, journal = {Zootaxa}, number = {1}, pages = {42 -- 58}, publisher = {Magnolia Press}, title = {{Final-stage phyllosoma of Palinustus A. Milne-Edwards, 1880 (Crustacea: Decapoda: Achelata: Palinuridae)-The first complete description}}, doi = {10.11646/zootaxa.2403.1.4}, volume = {2403}, year = {2010}, } @article{3787, abstract = {DNA samples were extracted from ethanol and formalin-fixed decapod crustacean tissue using a new method based on Tetramethylsilane (TMS)-Chelex. It is shown that neither an indigestible matrix of cross-linked protein nor soluble PCR inhibitors impede PCR success when dealing with formalin-fixed material. Instead, amplification success from formalin-fixed tissue appears to depend on the presence of unmodified DNA in the extracted sample. A staining method that facilitates the targeting of samples with a high content of unmodified DNA is provided.}, author = {Palero, Ferran and Hall, Sally and Clark, Paul and Johnston, David and Mackenzie Dodds, Jackie and Thatje, Sven}, journal = {Scientia Marina}, number = {3}, pages = {465 -- 470}, publisher = {Consejo Superior de Investigaciones Científicas}, title = {{DNA extraction from formalin-fixed tissue: new light from the deep sea}}, doi = {10.3989/scimar.2010.74n3465}, volume = {74}, year = {2010}, } @article{4134, abstract = {All species are restricted in their distribution. Currently, ecological models can only explain such limits if patches vary in quality, leading to asymmetrical dispersal, or if genetic variation is too low at the margins for adaptation. However, population genetic models suggest that the increase in genetic variance resulting from dispersal should allow adaptation to almost any ecological gradient. Clearly therefore, these models miss something that prevents evolution in natural populations. We developed an individual-based simulation to explore stochastic effects in these models. At high carrying capacities, our simulations largely agree with deterministic predictions. However, when carrying capacity is low, the population fails to establish for a wide range of parameter values where adaptation was expected from previous models. Stochastic or transient effects appear critical around the boundaries in parameter space between simulation behaviours. Dispersal, gradient steepness, and population density emerge as key factors determining adaptation on an ecological gradient. }, author = {Bridle, Jon and Polechova, Jitka and Kawata, Masakado and Butlin, Roger}, journal = {Ecology Letters}, number = {4}, pages = {485 -- 494}, publisher = {Wiley-Blackwell}, title = {{Why is adaptation prevented at ecological margins? New insights from individual-based simulations}}, doi = {10.1111/j.1461-0248.2010.01442.x}, volume = {13}, year = {2010}, } @article{4243, abstract = {We investigate a new model for populations evolving in a spatial continuum. This model can be thought of as a spatial version of the Lambda-Fleming-Viot process. It explicitly incorporates both small scale reproduction events and large scale extinction-recolonisation events. The lineages ancestral to a sample from a population evolving according to this model can be described in terms of a spatial version of the Lambda-coalescent. Using a technique of Evans (1997), we prove existence and uniqueness in law for the model. We then investigate the asymptotic behaviour of the genealogy of a finite number of individuals sampled uniformly at random (or more generally `far enough apart') from a two-dimensional torus of sidelength L as L tends to infinity. Under appropriate conditions (and on a suitable timescale) we can obtain as limiting genealogical processes a Kingman coalescent, a more general Lambda-coalescent or a system of coalescing Brownian motions (with a non-local coalescence mechanism).}, author = {Barton, Nicholas H and Etheridge, Alison and Véber, Amandine}, journal = {Electronic Journal of Probability}, number = {7}, pages = {162 -- 216}, publisher = {Institute of Mathematical Statistics}, title = {{A new model for evolution in a spatial continuum}}, doi = {10.1214/EJP.v15-741}, volume = {15}, year = {2010}, } @inbook{3675, abstract = {Sex and recombination have long been seen as adaptations that facilitate natural selection by generating favorable variations. If recombination is to aid selection, there must be negative linkage disequilibria—favorable alleles must be found together less often than expected by chance. These negative linkage disequilibria can be generated directly by selection, but this must involve negative epistasis of just the right strength, which is not expected, from either experiment or theory. Random drift provides a more general source of negative associations: Favorable mutations almost always arise on different genomes, and negative associations tend to persist, precisely because they shield variation from selection. We can understand how recombination aids adaptation by determining the maximum possible rate of adaptation. With unlinked loci, this rate increases only logarithmically with the influx of favorable mutations. With a linear genome, a scaling argument shows that in a large population, the rate of adaptive substitution depends only on the expected rate in the absence of interference, divided by the total rate of recombination. A two-locus approximation predicts an upper bound on the rate of substitution, proportional to recombination rate. If associations between linked loci do impede adaptation, there can be substantial selection for modifiers that increase recombination. Whether this can account for the maintenance of high rates of sex and recombination depends on the extent of selection. It is clear that the rate of species-wide substitutions is typically far too low to generate appreciable selection for recombination. However, local sweeps within a subdivided population may be effective.}, author = {Barton, Nicholas H}, booktitle = {Cold Spring Harbor Symposia on Quantitative Biology}, pages = {187 -- 195}, publisher = {Cold Spring Harbor Laboratory Press}, title = {{Why sex and recombination? }}, doi = {10.1101/sqb.2009.74.030}, volume = {74}, year = {2009}, } @article{3775, abstract = {There is a close analogy between statistical thermodynamics and the evolution of allele frequencies under mutation, selection and random drift. Wright's formula for the stationary distribution of allele frequencies is analogous to the Boltzmann distribution in statistical physics. Population size, 2N, plays the role of the inverse temperature, 1/kT, and determines the magnitude of random fluctuations. Log mean fitness, View the MathML source, tends to increase under selection, and is analogous to a (negative) energy; a potential function, U, increases under mutation in a similar way. An entropy, SH, can be defined which measures the deviation from the distribution of allele frequencies expected under random drift alone; the sum View the MathML source gives a free fitness that increases as the population evolves towards its stationary distribution. Usually, we observe the distribution of a few quantitative traits that depend on the frequencies of very many alleles. The mean and variance of such traits are analogous to observable quantities in statistical thermodynamics. Thus, we can define an entropy, SΩ, which measures the volume of allele frequency space that is consistent with the observed trait distribution. The stationary distribution of the traits is View the MathML source; this applies with arbitrary epistasis and dominance. The entropies SΩ, SH are distinct, but converge when there are so many alleles that traits fluctuate close to their expectations. Populations tend to evolve towards states that can be realised in many ways (i.e., large SΩ), which may lead to a substantial drop below the adaptive peak; we illustrate this point with a simple model of genetic redundancy. This analogy with statistical thermodynamics brings together previous ideas in a general framework, and justifies a maximum entropy approximation to the dynamics of quantitative traits.}, author = {Barton, Nicholas H and Coe, Jason}, journal = {Journal of Theoretical Biology}, number = {2}, pages = {317 -- 324}, publisher = {Elsevier}, title = {{On the application of statistical physics to evolutionary biology}}, doi = {10.1016/j.jtbi.2009.03.019}, volume = {259}, year = {2009}, } @article{3780, abstract = {Why are sinistral snails so rare? Two main hypotheses are that selection acts against the establishment of new coiling morphs, because dextral and sinistral snails have trouble mating, or else a developmental constraint prevents the establishment of sinistrals. We therefore used an isolate of the snail Lymnaea stagnalis, in which sinistrals are rare, and populations of Partula suturalis, in which sinistrals are common, as well as a mathematical model, to understand the circumstances by which new morphs evolve. The main finding is that the sinistral genotype is associated with reduced egg viability in L. stagnalis, but in P. suturalis individuals of sinistral and dextral genotype appear equally fecund, implying a lack of a constraint. As positive frequency-dependent selection against the rare chiral morph in P. suturalis also operates over a narrow range (< 3%), the results suggest a model for chiral evolution in snails in which weak positive frequency-dependent selection may be overcome by a negative frequency-dependent selection, such as reproductive character displacement. In snails, there is not always a developmental constraint. As the direction of cleavage, and thus the directional asymmetry of the entire body, does not generally vary in other Spiralia (annelids, echiurans, vestimentiferans, sipunculids and nemerteans), it remains an open question as to whether this is because of a constraint and/or because most taxa do not have a conspicuous external asymmetry (like a shell) upon which selection can act.}, author = {Davison, Angus and Barton, Nicholas H and Clarke, Bryan}, journal = {Journal of Evolutionary Biology}, number = {8}, pages = {1624 -- 1635}, publisher = {Wiley}, title = {{The effect of chirality phenotype and genotype on the fecundity and viability of Partula suturalis and Lymnaea stagnalis: Implications for the evolution of sinistral snails}}, doi = {10.1111/j.1420-9101.2009.01770.x}, volume = {22}, year = {2009}, } @article{4136, abstract = {Populations living in a spatially and temporally changing environment can adapt to the changing optimum and/or migrate toward favorable habitats. Here we extend previous analyses with a static optimum to allow the environment to vary in time as well as in space. The model follows both population dynamics and the trait mean under stabilizing selection, and the outcomes can be understood by comparing the loads due to genetic variance, dispersal, and temporal change. With fixed genetic variance, we obtain two regimes: (1) adaptation that is uniform along the environmental gradient and that responds to the moving optimum as expected for panmictic populations and when the spatial gradient is sufficiently steep, and (2) a population with limited range that adapts more slowly than the environmental optimum changes in both time and space; the population therefore becomes locally extinct and migrates toward suitable habitat. We also use a population‐genetic model with many loci to allow genetic variance to evolve, and we show that the only solution now has uniform adaptation.}, author = {Polechova, Jitka and Barton, Nicholas H and Marion, Glenn}, journal = {American Naturalist}, number = {5}, pages = {E186 -- E204}, publisher = {University of Chicago Press}, title = {{Species' range: Adaptation in space and time}}, doi = {10.1086/605958}, volume = {174}, year = {2009}, } @article{4231, abstract = {The evolution of quantitative characters depends on the frequencies of the alleles involved, yet these frequencies cannot usually be measured. Previous groups have proposed an approximation to the dynamics of quantitative traits, based on an analogy with statistical mechanics. We present a modified version of that approach, which makes the analogy more precise and applies quite generally to describe the evolution of allele frequencies. We calculate explicitly how the macroscopic quantities (i.e., quantities that depend on the quantitative trait) depend on evolutionary forces, in a way that is independent of the microscopic details. We first show that the stationary distribution of allele frequencies under drift, selection, and mutation maximizes a certain measure of entropy, subject to constraints on the expectation of observable quantities. We then approximate the dynamical changes in these expectations, assuming that the distribution of allele frequencies always maximizes entropy, conditional on the expected values. When applied to directional selection on an additive trait, this gives a very good approximation to the evolution of the trait mean and the genetic variance, when the number of mutations per generation is sufficiently high (4Nμ > 1). We show how the method can be modified for small mutation rates (4Nμ → 0). We outline how this method describes epistatic interactions as, for example, with stabilizing selection.}, author = {Barton, Nicholas H and De Vladar, Harold}, journal = {Genetics}, number = {3}, pages = {997 -- 1011}, publisher = {Genetics Society of America}, title = {{Statistical mechanics and the evolution of polygenic quantitative traits}}, doi = {10.1534/genetics.108.099309}, volume = {181}, year = {2009}, } @article{4242, abstract = {Felsenstein distinguished two ways by which selection can directly strengthen isolation. First, a modifier that strengthens prezygotic isolation can be favored everywhere. This fits with the traditional view of reinforcement as an adaptation to reduce deleterious hybridization by strengthening assortative mating. Second, selection can favor association between different incompatibilities, despite recombination. We generalize this “two allele” model to follow associations among any number of incompatibilities, which may include both assortment and hybrid inviability. Our key argument is that this process, of coupling between incompatibilities, may be quite different from the usual view of reinforcement: strong isolation can evolve through the coupling of any kind of incompatibility, whether prezygotic or postzygotic. Single locus incompatibilities become coupled because associations between them increase the variance in compatibility, which in turn increases mean fitness if there is positive epistasis. Multiple incompatibilities, each maintained by epistasis, can become coupled in the same way. In contrast, a single-locus incompatibility can become coupled with loci that reduce the viability of haploid hybrids because this reduces harmful recombination. We obtain simple approximations for the limits of tight linkage, and strong assortment, and show how assortment alleles can invade through associations with other components of reproductive isolation.}, author = {Barton, Nicholas H and De Cara, Maria}, journal = {Evolution; International Journal of Organic Evolution}, number = {5}, pages = {1171 -- 1190}, publisher = {Wiley}, title = {{The evolution of strong reproductive isolation}}, doi = {10.1111/j.1558-5646.2009.00622.x}, volume = {63}, year = {2009}, } @article{517, author = {Barton, Nicholas H}, journal = {Genetics Research}, number = {5-6}, pages = {475 -- 477}, publisher = {Cambridge University Press}, title = {{Identity and coalescence in structured populations: A commentary on 'Inbreeding coefficients and coalescence times' by Montgomery Slatkin}}, doi = {10.1017/S0016672308009683}, volume = {89}, year = {2008}, }