Neutral Expectations Research Articles

Demographic consequences of dispersal-related trait shift in two recently diverged taxa of montane grasshoppers.

Although the pervasiveness of intraspecific wing-size polymorphism and transitions to flightlessness have long captivated biologists, the demographic outcomes of shifts in dispersal ability are not yet well understood and have been seldom studied at early stages of diversification. Here, we use genomic data to infer the consequences of dispersal-related trait variation in the taxonomically controversial short-winged (Chorthippus corsicus corsicus) and long-winged (Chorthippus corsicus pascuorum) Corsican grasshoppers. Our analyses revealed lack of contemporary hybridization between sympatric long- and short-winged forms and phylogenomic reconstructions supported their taxonomic distinctiveness, rejecting the hypothesis of intraspecific wing polymorphism. Statistical evaluation of alternative models of speciation strongly supported a scenario of Pleistocene divergence (<1.5 Ma) with ancestral gene flow. According to neutral expectations from differences in dispersal capacity, historical effective migration rates from the long- to the short-winged taxon were threefold higher than in the opposite direction. Although populations of the two taxa present a marked genetic structure and have experienced parallel demographic histories, our coalescent-based analyses suggest that reduced dispersal has fueled diversification in the short-winged C. c. corsicus. Collectively, our study illustrates how dispersal reduction can speed up geographical diversification and increase the opportunity for allopatric speciation in topographically complex landscapes.

The impact of exercise perceptions and depressive symptoms on polycystic ovary syndrome-specific health-related quality of life.

Background:Studies indicate that women with polycystic ovary syndrome have high depressive symptom scores and more perceived barriers than benefits to exercise, factors that may affect health-related quality-of-life. The purpose of this cross-sectional study was to explore the impact of perceived exercise benefits and barriers, exercise outcome expectations, and depressive symptoms on polycystic ovary syndrome–specific health-related quality-of-life.Methods:A survey link was posted on polycystic ovary syndrome Facebook groups. Women with polycystic ovary syndrome (n = 935) answered questionnaires about demographics, polycystic ovary syndrome–specific health-related quality-of-life, exercise benefits and barriers, exercise outcome expectations, and depressive symptoms. Data were collected using Qualtrics, transferred to SPSS, and statistically analyzed using regression analyses. Mean responses were reported for the questionnaires, with exercise benefits and barriers means divided for a ratio.Results:Respondents were 32 ± 10.6 years of age, mostly White (72%), and employed full-time (65%). The total mean scores were health-related quality-of-life, 2.7 ± 0.1; exercise outcome expectation, 2.4 ± 0.8; and depressive symptoms, 12.4 ± 5.8. The benefit/barrier ratio was 0.9. HRQoL increased 0.32 points for every additional perceived exercise benefit and 0.61 points for every additional exercise outcome expectation (EOE). HRQoL was reduced by 1.19 points for every additional perceived exercise barrier and 2.82 points for every additional one-point increase of the depressive symptoms score.Conclusions:Respondents reported low health-related quality-of-life, greater exercise barriers than benefits, neutral exercise outcome expectations, and high depressive symptoms. These results suggest that promoting exercise benefits, overcoming exercise barriers, and addressing management of depressive symptoms are important foci of future efforts to improve health-related quality-of-life among women with polycystic ovary syndrome.

Tracking Owners’ Sentiments: Subjective Home Values, Expectations and House Price Dynamics

Economic theory predicts that expectations on future house price growth are related to the current price of a house. We test this relationship for the supply side of the secondary housing market using micro data that links individual expectations to a subjective owner estimated value (OEV). We find a strong causal relationship that optimistic expectations indeed imply higher OEVs as compared to neutral or pessimistic expectations. We find qualitatively and quantitatively consistent results for Italy and the US as well as for booming and gloomy years. Our results survive ample robustness checks. Since we use subjective data on house prices, we first show that OEVs are indeed a valid source to study house price dynamics by performing three types of convergent validity tests. We find that price dynamics derived by either combining OEVs and dwelling characteristics, or making use of repeatedly provided OEVs by the same owner over time reproduce objectively measured market trends strikingly well – even over decades. In contrast, OEVs and objective data tend to differ in levels – potentially due to psychological bias. These results hold for a large set of countries. We hence conclude that the wisdom of the home-owner crowd is sufficient to study house price dynamics but OEVs are less suited for measuring the level of market prices.

Polygenic Selection within a Single Generation Leads to Subtle Divergence among Ecological NichesINc.

Selection on standing genetic variation may be effective enough to allow for adaptation to distinct niche environments within a single generation. Minor allele frequency changes at multiple, redundant loci of small effect can produce remarkable phenotypic shifts. Yet, demonstrating rapid adaptation via polygenic selection in the wild remains challenging. Here we harness natural replicate populations that experience similar selection pressures and harbor high within-, yet negligible among-population genetic variation. Such populations can be found among the teleost Fundulus heteroclitus that inhabits marine estuaries characterized by high environmental heterogeneity. We identify 10,861 single nucleotide polymorphisms in F. heteroclitus that belong to a single, panmictic population yet reside in environmentally distinct niches (one coastal basin and three replicate tidal ponds). By sampling at two time points within a single generation, we quantify both allele frequency change within as well as spatial divergence among niche subpopulations. We observe few individually significant allele frequency changes yet find that the “number” of moderate changes exceeds the neutral expectation by 10–100%. We find allele frequency changes to be significantly concordant in both direction and magnitude among all niche subpopulations, suggestive of parallel selection. In addition, within-generation allele frequency changes generate subtle but significant divergence among niches, indicative of local adaptation. Although we cannot distinguish between selection and genotype-dependent migration as drivers of within-generation allele frequency changes, the trait/s determining fitness and/or migration likelihood appear to be polygenic. In heterogeneous environments, polygenic selection and polygenic, genotype-dependent migration offer conceivable mechanisms for within-generation, local adaptation to distinct niches.

Articles of Significant Interest In This Issue

Genomic epidemiology studies identify single nucleotide polymorphisms (SNPs). Methods to infer selection using coding sequences are designed for fixed differences rather than polymorphisms. These methods are therefore not suited to outbreak and chronic infection data, in which SNPs are not necessarily fixed. Using models, Loo et al. (e02002-20) quantified the proportion of nonsynonymous SNPs under selection. They developed an approach for comparing SNP data to the neutral expectation and applied these methods to simulation and empirical data. They found that positive selection is generally difficult to detect, but their analysis suggests different underlying mechanisms of evolution in within-host versus between-host data.

Molecular convergent and parallel evolution among four high-elevation anuran species from the Tibetan region

BackgroundTo date, evidence for the relative prevalence or rarity of molecular convergent and parallel evolution is conflicting, and understanding of how these processes contribute to adaptation is limited. We compared four high-elevation anuran species (Bufo tibetanus, Nanorana parkeri, Rana kukunoris and Scutiger boulengeri) from the Tibetan region, and examined convergent and parallel amino acid substitutions between them and how they may have contributed to high-elevation adaptation.ResultsGenomic data of the four high-elevation species and eight of their low-elevation close relatives were gathered. A total of 1098 orthologs shared by all species were identified. We first conducted pairwise comparisons using Zhang and Kumar’s test. Then, the Rconv index was calculated and convergence/divergence correlation plotting was conducted. Furthermore, genes under positive selection and with elevated evolutionary rate were examined. We detected a large number of amino acid sites with convergent or parallel substitutions. Several pairs of high-elevation species, in particular, R. kukunoris vs N. parkeri and B. tibetanus vs S. boulengeri, had excessive amounts of convergent substitutions compared to neutral expectation. Nevertheless, these sites were mostly concentrated in a small number of genes (3–32), and no genome-wide convergence was detected. Furthermore, the majority of these convergent genes were neither under detectable positive selection nor had elevated evolutionary rates, although functional prediction analysis suggested some of the convergent genes could potentially contribute to high-elevation adaptation.ConclusionsThere is a substantial amount of convergent evolution at the amino-acid level among high-elevation amphibians, although these sites are concentrated in a few genes, not widespread across the genomes. This may attribute to the fact that all the target species are from the same environment. The relative prevalence of convergent substitutions among high-elevation amphibians provides an excellent opportunity for further study of molecular convergent evolution.

A test of island biogeographic theory applied to estimates of gene flow in a Fijian bird is largely consistent with neutral expectations.

Islands were key to the development of allopatric speciation theory because they are a natural laboratory of repeated barriers to gene flow caused by open water gaps. Despite their proclivity for promoting divergence, little empirical work has quantified the extent of gene flow among island populations. Following classic island biogeographic theory, two metrics of interest are relative island size and distance. Fiji presents an ideal system for studying these dynamics, with four main islands that form two large-small pairs. We sequenced thousands of ultraconserved elements (UCEs) of the Fiji bush-warbler Horornis ruficapilla, a passerine distributed on these four Fijian islands, and performed a demographic analysis to test hypotheses of the effects of island size and distance on rates of gene flow. Our demographic analysis inferred low levels of gene flow from each large island to its small counterpart and little or none in the opposite direction. The difference in the distance between these two island pairs manifested itself in lower levels of gene flow between more distant islands. Both findings are generally concordant with classic island biogeography. The amount of reduction in gene flow based on distance was consistent with predictions from island biogeographic equations, while the reduction from small to large islands was possibly greater than expected. These findings offer a hypothesis and framework to guide future study of interisland gene flow in archipelagos as the study of island biogeography progresses into the genomic era.

Assessment of the potential role of natural selection in type 2 diabetes and related traits across human continental ancestry groups: comparison of phenotypic with genotypic divergence.

Prevalence of type 2 diabetes differs among human ancestry groups, and many hypotheses invoke differential natural selection to account for these differences. We sought to assess the potential role of differential natural selection across major continental ancestry groups for diabetes and related traits, by comparison of genetic and phenotypic differences. This was a cross-sectional comparison among 734 individuals from an urban sample (none of whom was more closely related to another than third-degree relatives), including 83 African Americans, 523 American Indians and 128 European Americans. Participants were not recruited based on diabetes status or other traits. BMI was calculated, and diabetes was diagnosed by a 75g oral glucose tolerance test. In those with normal glucose tolerance (n = 434), fasting insulin and 30min post-load insulin, adjusted for 30min glucose, were taken as measures of insulin resistance and secretion, respectively. Whole exome sequencing was performed, resulting in 97,388 common (minor allele frequency ≥ 5%) variants; the coancestry coefficient (FST) was calculated across all markers as a measure of genetic divergence among ancestry groups. The phenotypic divergence index (PST) was also calculated from the phenotypic differences and heritability (which was estimated from genetic relatedness calculated empirically across all markers in 761 American Indian participants prior to the exclusion of close relatives). Under evolutionary neutrality, the expectation is PST = FST, while for traits under differential selection PST is expected to be significantly greater than FST. A bootstrap procedure was used to test the hypothesis PST = FST. RESULTS: With adjustment for age and sex, prevalence of type 2 diabetes was 34.0% in American Indians, 12.4% in African Americans and 10.4% in European Americans (p = 2.9 × 10-10 for difference among groups). Mean BMI was 36.3, 33.4 and 33.0kg/m2, respectively (p =1.9 × 10-7). Mean fasting insulin was 63.8, 48.4 and 45.2pmol/l (p = 9.2 × 10-5), while mean 30min insulin was 559.8, 553.5 and 358.8pmol/l, respectively (p =5.7 × 10-8). FST across all markers was 0.130, while PST for liability to diabetes, adjusted for age and sex, was 0.149 (p = 0.35 for difference with FST). PST was 0.094 for BMI (p = 0.54), 0.095 for fasting insulin (p = 0.54) and 0.216 (p = 0.18) for 30min insulin. For type 2 diabetes and BMI, the maximum divergence between populations was observed between American Indians and European Americans (PST-MAX = 0.22, p = 0.37, and PST-MAX = 0.14, p = 0.61), which suggests that a relatively modest 22% or 14% of the genetic variance, respectively, can potentially be explained by differential selection (assuming the absence of neutral drift). These analyses suggest that while type 2 diabetes and related traits differ significantly among continental ancestry groups, the differences are consistent with neutral expectations based on heritability and genetic distances. While these analyses do not exclude a modest role for natural selection, they do not support the hypothesis that differential natural selection is necessary to explain the phenotypic differences among these ancestry groups. Graphical abstract.

Low concordance of short-term and long-term selection responses in experimental Drosophila populations.

Experimental evolution is becoming a popular approach to study the genomic selection response of evolving populations. Computer simulation studies suggest that the accuracy of the signature increases with the duration of the experiment. Since some assumptions of the computer simulations may be violated, it is important to scrutinize the influence of the experimental duration with real data. Here, we use a highly replicated Evolve and Resequence study in Drosophila simulans to compare the selection targets inferred at different time points. At each time point, approximately the same number of SNPs deviates from neutral expectations, but only 10% of the selected haplotype blocks identified from the full data set can be detected after 20 generations. Those haplotype blocks that emerge already after 20 generations differ from the others by being strongly selected at the beginning of the experiment and display a more parallel selection response. Consistent with previous computer simulations, our results demonstrate that only Evolve and Resequence experiments with a sufficient number of generations can characterize complex adaptive architectures.

The geographic mosaic of arms race coevolution is closely matched to prey population structure.

Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co‐occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of “trait remixing” in the geographic mosaic theory, the process by which non‐adaptive forces dictate spatial variation in the interactions among species.

What Do Men with Lower Urinary Tract Symptoms Expect from a Urologist in Secondary Care?

PurposeTo identify the expectations of men with LUTS referred to a urologist and to study the association between those expectations and satisfaction with the care provided.MethodsIn this prospective cohort study, adult men with LUTS completed a questionnaire before their first outpatient appointment, and again at 6 and 12 weeks. The questionnaires included IPSS and OABq-SF, and self-constructed questions on patient expectations, outcome of expectations and satisfaction.ResultsData from 182 participants showed positive expectations about the urologist performing examinations, providing explanations and finding the underlying cause, but mostly neutral expectations for treatment plans and outcomes. Positive treatment expectations were associated with positive expectations about outcomes after physiotherapy, drug treatment and surgery. Higher symptom scores and age were associated with higher expectations about drug treatment. Expectations were subjectively and objectively fulfilled for 66.4% and 27.3%, respectively. Symptom improvement (decrease in IPSS scores) was significantly more in men with objectively fulfilled expectations than in men with no unfulfilled expectations. No significant difference was present between men with subjectively fulfilled expectations and men with unfulfilled expectations. However, satisfaction was significantly higher for patients with subjectively fulfilled expectations at 6 and 12 weeks compared with those who had unfulfilled expectations.ConclusionMost men referred to a urologist with LUTS do express clear expectations about treatment in secondary care. Patients with higher expectations for treatment outcomes are more likely to expect to receive that treatment. Satisfaction with the care of a urologist is also higher when patients self-report that they receive the treatment they expected.

Is the Interest Rate Channel still working? Post-Crisis Evidence from German SMEs

Abstract Using a unique dataset from German small and medium-sized enterprises (SMEs), we test whether pessimistic business expectations have impeded the functioning of the interest rate channel during the post-crisis period. We estimate firms’ user cost elasticity of capital for the period 2008–2015, and test whether this elasticity differs for firms that hold pessimistic business expectations compared with those that hold positive expectations. Our results show that SMEs have significantly responded to changes in the user cost of capital during the post-crisis period. However, the results are mainly driven by SMEs that hold positive business expectations. Firms having neutral or negative expectations depict a much smaller user cost elasticity, which is not statistically different from zero. Our results reveal the limitations of an expansionary monetary policy and confirm the important role that expectations play for firms’ investment decisions.

A new framework for ethical creation and evaluation of multi-perspective knowledge organization systems

PurposeThis study aims to present a new framework for ethical creation and evaluation of multi-perspective knowledge organization systems.Design/methodology/approachApplying Held's understanding of the ethics of care, this paper proposes five operative criteria for ethical building and evaluation of multi-perspective knowledge representation and organization systems.FindingsThis paper argues that a carefully designed multipoint view of representation and organization conforms to the proposed ethical criteria and shifts concerns associated with the expectation of neutrality of library information professionals to the necessity to humanize and diversify the representation and organization of knowledge to build inclusive and equitable systems.Originality/valueThis paper presents multi-perspectiveness as key to ethical knowledge organization. The paper proposes a generic taxonomy of the main stages in the creation of multi-perspective knowledge representation and organization systems and demonstrates how to apply the proposed framework in each stage to ensure ethical outcomes.

S141. REWARD PROCESSING IN CHILDREN WITH PSYCHOTIC-LIKE EXPERIENCES

BackgroundIndividuals with psychosis display an attenuated response to reward. However, it has not yet been established whether individuals with psychotic-like experiences (PLEs) also exhibit alterations in reward anticipation.MethodsThe present study examined whether non-distressing and distressing PLEs were associated with functional activity in the nucleus accumbens during reward anticipation. The sample consisted of 10313 children from the ABCD study aged 9–10 who had participated in the Monetary Incentive Delay task. PLEs were measured using the Prodromal Questionnaire Brief Child version and functional activity was measured using regional fMRI summary statistics for reward anticipation activation (data release 2.0, contrast of expected large reward versus neutral expectation). Linear mixed-effects models were used to investigate the relationship between reward anticipation and PLEs (distressing and non-distressing), whilst controlling for gender, household income, ethnicity, BMI and affective symptoms. The analyses were weighted by the average standard error of the mean activation in the accumbens. Separate linear mixed-effects models were conducted for the right and left hemisphere.Results6169 (59.8%) of the children did not report any PLEs, compared to 2270 (22.0%) with non-distressing PLEs and 1874 (18.2%) with distressing PLEs. We ran a regression to examine the association between reward anticipation and PLEs (distressing or non-distressing) and found that non-distressing PLEs were related to reduced reward anticipation in the right nucleus accumbens (P = 0.009). However, there was no significant association between reward anticipation and PLEs when adjusting for potential confounders.DiscussionIn the present study of 9–10 year olds, reward anticipation was not associated with PLEs. As previous research has found reductions in reward anticipation in individuals with schizophrenia, further follow-up studies of the ABCD cohort are needed to explore whether these associations emerge during adolescence.

Recessive Z-linked lethals and the retention of haplotype diversity in a captive butterfly population.

Sex chromosomes are predicted to harbour elevated levels of sexually antagonistic variation due to asymmetries in the heritability of recessive traits in the homogametic versus heterogametic sex. This evolutionary dynamic may manifest as high recessive load specifically affecting the homogametic sex, and the retention of haplotype diversity in small populations. We tested the hypothesis that the Z chromosome in the butterfly Bicyclus anynana carries a high inbred load for male fertility and viability. Homozygosity of Z chromosome blocks was produced by daughter-father backcrosses, and inferred from marker loci positioned via a linkage map. Male sterility was, in general, unrelated to homozygosity in any region of the Z, but there was an extreme deficit of homozygous males within a 2 cM interval in all families. In contrast, no corresponding skew in Z genotype was detected in their (hemizygous) sisters. The same pattern was observed in historically inbred lines, indicating a high frequency of recessive lethals in the ancestral population. Allele-frequency changes between 1993 and 2006 (70 generations at Ne ~ 160) show that, despite the loss of many haplotypes, diversity was retained significantly above the neutral expectation. Effective overdominance in the lethal region can account for this effect locally but not in other parts of the chromosome, that are also associated with persistent linkage disequilibrium. These unexpected patterns suggest the operation of other factors, such as epistatic selection, recombination suppression, assortative mating and meiotic drive. Our results highlight the role of balancing selection in maintaining the inbred load and linked genetic diversity.

Ecological and Ontogenetic Components of Larval Lake Sturgeon Gut Microbiota Assembly, Successional Dynamics, and Ecological Evaluation of Neutral Community Processes.

Gastrointestinal (GI) or gut microbiotas play essential roles in host development and physiology. These roles are influenced partly by the microbial community composition. During early developmental stages, the ecological processes underlying the assembly and successional changes in host GI community composition are influenced by numerous factors, including dispersal from the surrounding environment, age-dependent changes in the gut environment, and changes in dietary regimes. However, the relative importance of these factors to the gut microbiota is not well understood. We examined the effects of environmental (diet and water sources) and host early ontogenetic development on the diversity of and the compositional changes in the gut microbiota of a primitive teleost fish, the lake sturgeon (Acipenser fulvescens), based on massively parallel sequencing of the 16S rRNA gene. Fish larvae were raised in environments that differed in water source (stream versus filtered groundwater) and diet (supplemented versus nonsupplemented Artemia fish). We quantified the gut microbial community structure at three stages (prefeeding and 1 and 2 weeks after exogenous feeding began). The diversity declined and the community composition differed significantly among stages; however, only modest differences associated with dietary or water source treatments were documented. Many taxa present in the gut were over- or underrepresented relative to neutral expectations in each sampling period. The findings indicate dynamic relationships between the gut microbiota composition and host gastrointestinal physiology, with comparatively smaller influences being associated with the rearing environments. Neutral models of community assembly could not be rejected, but selectivity associated with microbe-host GI tract interactions through early ontogenetic stages was evident. The results have implications for sturgeon conservation and aquaculture production specifically and applications of microbe-based management in teleost fish generally.IMPORTANCE We quantified the effects of environment (diet and water sources) and host early ontogenetic development on the diversity of and compositional changes in gut microbial communities based on massively parallel sequencing of the 16S rRNA genes from the GI tracts of larval lake sturgeon (Acipenser fulvescens). The gut microbial community diversity declined and the community composition differed significantly among ontogenetic stages; however, only modest differences associated with dietary or water source treatments were documented. Selectivity associated with microbe-host GI tract interactions through early ontogenetic stages was evident. The results have implications for lake sturgeon and early larval ecology and survival in their natural habitat and for conservation and aquaculture production specifically, as well as applications of microbe-based management in teleost fish generally.

Proteomic similarity of the Littorinid snails in the evolutionary context.

BackgroundThe introduction of DNA-based molecular markers made a revolution in biological systematics. However, in cases of very recent divergence events, the neutral divergence may be too slow, and the analysis of adaptive part of the genome is more informative to reconstruct the recent evolutionary history of young species. The advantage of proteomics is its ability to reflect the biochemical machinery of life. It may help both to identify rapidly evolving genes and to interpret their functions.MethodsHere we applied a comparative gel-based proteomic analysis to several species from the gastropod family Littorinidae. Proteomes were clustered to assess differences related to species, geographic location, sex and body part, using data on presence/absence of proteins in samples and data on protein occurrence frequency in samples of different species. Cluster support was assessed using multiscale bootstrap resampling and the stability of clustering—using cluster-wise index of cluster stability. Taxon-specific protein markers were derived using IndVal method. Proteomic trees were compared to consensus phylogenetic tree (based on neutral genetic markers) using estimates of the Robinson–Foulds distance, the Fowlkes–Mallows index and cophenetic correlation.ResultsOverall, the DNA-based phylogenetic tree and the proteomic similarity tree had consistent topologies. Further, we observed some interesting deviations of the proteomic littorinid tree from the neutral expectations. (1) There were signs of molecular parallelism in two Littoraria species that phylogenetically are quite distant, but live in similar habitats. (2) Proteome divergence was unexpectedly high between very closely related Littorina fabalis and L. obtusata, possibly reflecting their ecology-driven divergence. (3) Conservative house-keeping proteins were usually identified as markers for cryptic species groups (“saxatilis” and “obtusata” groups in the Littorina genus) and for genera (Littoraria and Echinolittorina species pairs), while metabolic enzymes and stress-related proteins (both potentially adaptively important) were often identified as markers supporting species branches. (4) In all five Littorina species British populations were separated from the European mainland populations, possibly reflecting their recent phylogeographic history. Altogether our study shows that proteomic data, when interpreted in the context of DNA-based phylogeny, can bring additional information on the evolutionary history of species.

Clinal variation along precipitation gradients in Patagonian temperate forests: unravelling demographic and selection signatures in three Nothofagus spp.

Past demographic changes and current selection pressures determine the genetic variation displayed by Nothofagus species along rainfall gradients. Based on the diversity trends observed at candidate genes associated to drought stress, we inferred a differential species’ adaptive potential. Clinal genetic variation in natural populations could reflect either recent demographic history or the evolution of adapted genotypes along heterogeneous environments. We describe genetic variation patterns in three Nothofagus species of South American temperate forests, growing along steep rainfall gradients. Our hypothesis is that the selection pressure along this gradient reinforces the genetic structure previously shaped by Pleistocene climate oscillations. We screened variation along gradients at putative adaptive markers: candidate genes involved in response to drought, and EST-SSRs linked to drought stress genes. Genomic SSRs (gSSRs) were used to decouple the incidence of demographic events in the genetic structure. Genetic diversity at SSRs agreed with the putative location of cryptic Pleistocene refugia in Nothofagus. In addition, each species showed different trends for nucleotide diversity at candidate genes. Unbiased heterozygosity significantly correlated with precipitation at EST-SSRs in Nothofagus nervosa. We found evidences of balancing selection and several SNPs departed from neutral expectations. Nothofagus genetic variability shows a strong imprint of demographic changes that reveals refugia location for the species during Pleistocene. This variability is modelled by environmental conditions across natural gradients, which impose selection pressure at genome regions related to stress response, providing clues about inter-specific differences in adaptive potential to water deficit.

How Puzzling is the Forward Premium Puzzle? A Meta-Analysis

A key theoretical prediction in financial economics is that under risk neutrality and rational expectations, a currency's forward rates should form unbiased predictors of future spot rates. Yet scores of empirical studies report negative slope coefficients from regressions of spot rates on forward rates, which is inconsistent with the forward rate unbiasedness hypothesis. We collect 3,643 estimates from 91 research articles and using recently developed techniques investigate the effect of publication and misspecification biases on the reported results. Correcting for these biases yields slope coefficients of 0.31 and 0.98 for developed and emerging currencies respectively, which implies that empirical evidence is in line with the theoretical prediction for emerging economies and less puzzling than commonly thought for developed economies. Our results also suggest that the coefficients are systematically influenced by the choice of data, numeraire currencies, and estimation methods. The findings can be applied to calibrating carry trade strategies for individual currencies.

Molecular responses to freshwater limitation in the mangrove tree Avicennia germinans (Acanthaceae).

Environmental variation along the geographical space can shape populations by natural selection. In the context of global warming and changing precipitation regimes, it is crucial to understand the role of environmental heterogeneity in tropical trees adaptation, given their disproportional contribution to water and carbon biogeochemical cycles. Here, we investigated how heterogeneity in freshwater availability along tropical wetlands has influenced molecular variations of the black mangrove (Avicennia germinans). A total of 57 trees were sampled at seven sites differing markedly in precipitation regime and riverine freshwater inputs. Using 2,297 genome-wide single nucleotide polymorphic markers, we found signatures of natural selection by the association between variations in allele frequencies and environmental variables, including the precipitation of the warmest quarter and the annual precipitation. Additionally, we found candidate loci for selection based on statistical deviations from neutral expectations of interpopulation differentiation. Most candidate loci within transcribed sequences were functionally associated with central aspects of drought tolerance or plant response to drought. Moreover, our results suggest the occurrence of the rapid evolution of a population, probably in response to sudden and persistent limitations in plant access to soil water, following a road construction in 1974. Observations supporting rapid evolution included the reduction in tree size and changes in allele frequencies and in transcript expression associated with increased drought tolerance through the accumulation of osmoprotectants and antioxidants, biosynthesis of cuticles, protection against protein degradation, stomatal closure, photorespiration and photosynthesis. We describe a major role of spatial heterogeneity in freshwater availability in the specialization of this typically tropical tree.