Patterns Of Local Adaptation Research Articles

Multiple selective events at the PRDM16 functional pathway shaped adaptation of western European populations to different climate conditions.

Several studies highlighted the role of climate in shaping many human evolutionary processes. This occurred even in relatively recent times, having affected various human phenotypic traits, among which metabolic processes that orchestrate absorption and accumulation of substances to maintain energy homeostasis, that is critical for the survival of individuals in high energy-expenditure environments. To date, most researches have focalized on detection of climatic influence on SNPs' frequency in populations exposed to extreme environmental conditions or by comparing variation patterns between populations from different continents. In this study, we instead explored the genetic background of distinct western European human groups at loci involved in nutritional and thermoregulation processes, to test whether patterns of differential local adaptation to environmental conditions could be appreciated also at a lower geographical scale. Taking advantage from the 1000 Genomes Project data, genetic information for 21 genes involved in nutritional and thermoregulation processes was analysed for three western European populations. The applied Anthropological Genetics methods pointed to appreciable differentiation between the examined groups especially for the PRDM16 gene. Moreover, several neutrality tests suggested that balancing selection has acted on different regions of the gene in people from Great Britain, as well as that more recent positive selection could have also targeted some PRDM16 SNPs in Finn and Italian populations. These series of adaptive footprints are plausibly related to climate variability in both ancient and relatively recent times. Since this locus is involved in thermoregulation mechanisms and adipogenesis, local adaptations mediated by a pathway related to the brown adipose tissue activity could have evolved in response to changing cold temperature exposures of such populations.

Connecting genomic patterns of local adaptation and niche suitability in teosintes.

The central abundance hypothesis predicts that local adaptation is a function of the distance to the centre of a species' geographic range. To test this hypothesis, we gathered genomic diversity data from 49 populations, 646 individuals and 33,464 SNPs of two wild relatives of maize, the teosintes Zea mays ssp. parviglumis and Zea. mays. ssp. mexicana. We examined the association between the distance to their climatic and geographic centroids and the enrichment of SNPs bearing signals of adaptation. We identified candidate adaptive SNPs in each population by combining neutrality tests and cline analyses. By applying linear regression models, we found that the number of candidate SNPs is positively associated with niche suitability, while genetic diversity is reduced at the limits of the geographic distribution. Our results suggest that overall, populations located at the limit of the species' niches are adapting locally. We argue that local adaptation to this limit could initiate ecological speciation processes and facilitate adaptation to global change.

Local Adaptive Binary Patterns Using Diamond Sampling Structure for Texture Classification

Local binary pattern (LBP) is sensitive to the noise and suffers from limited discriminative capability, and many LBP variants are reported in the recent literatures. Although a lot of significant progresses have been made, most LBP variants still have limitations of noise sensitivity, high dimensionality, and computational inefficiency. In view of this, we propose a new noise-robust local image descriptor named the diamond sampling structure-based local adaptive binary pattern (DLABP) in this letter, which aims at achieving both efficiency and simplicity at the same time. It mainly features three contributions: 1) an effective diamond sampling structure to decrease the feature dimensionality significantly by fixing the number of sampling neighbors to a constant of 8; 2) a simple and new “average method on the radial direction” to enhance the noise robustness; and 3) an effective adaptive quantization threshold strategy to restore the noise-corrupted nonuniform patterns back to possible uniform patterns. Extensive experiments are conducted on three benchmark texture databases of Outex, UIUC, and CUReT. Compared to state-of-the-art LBP-like methods, the proposed approach consistently demonstrates superior performances both in noise-free conditions and in the presence of high levels of noise, while it has a low complexity and a smaller feature dimension.

Characterizing the roles of changing population size and selection on the evolution of flux control in metabolic pathways

BackgroundUnderstanding the genotype-phenotype map is fundamental to our understanding of genomes. Genes do not function independently, but rather as part of networks or pathways. In the case of metabolic pathways, flux through the pathway is an important next layer of biological organization up from the individual gene or protein. Flux control in metabolic pathways, reflecting the importance of mutation to individual enzyme genes, may be evolutionarily variable due to the role of mutation-selection-drift balance. The evolutionary stability of rate limiting steps and the patterns of inter-molecular co-evolution were evaluated in a simulated pathway with a system out of equilibrium due to fluctuating selection, population size, or positive directional selection, to contrast with those under stabilizing selection.ResultsDepending upon the underlying population genetic regime, fluctuating population size was found to increase the evolutionary stability of rate limiting steps in some scenarios. This result was linked to patterns of local adaptation of the population. Further, during positive directional selection, as with more complex mutational scenarios, an increase in the observation of inter-molecular co-evolution was observed.ConclusionsDifferences in patterns of evolution when systems are in and out of equilibrium, including during positive directional selection may lead to predictable differences in observed patterns for divergent evolutionary scenarios. In particular, this result might be harnessed to detect differences between compensatory processes and directional processes at the pathway level based upon evolutionary observations in individual proteins. Detecting functional shifts in pathways reflects an important milestone in predicting when changes in genotypes result in changes in phenotypes.

Evaluating local adaptation of a complex phenotype: reciprocal tests of pigmy rattlesnake venoms on treefrog prey.

Theory predicts that predator-prey interactions can generate reciprocal selection pressures on species pairs, which can result in local adaptation, yet the presence and pattern of local adaptation is poorly studied in vertebrate predator-prey systems. Here, we used a reciprocal common garden (laboratory) experimental design involving comparisons between local and foreign populations to determine if local adaptation was present between a generalist predator-the pigmy rattlesnake (Sistrurus miliarius)-and a co-occurring prey-the squirrel treefrog (Hyla squirella). We conducted toxicity trials using snake venom from two populations separated by 340km tested on prey from sympatric and allopatric populations, resulting in data from four venom origin-frog origin combinations. We assessed venom effectiveness using two measures (frog mortality at 24h and time to frog death) and then used regression analyses to look for a signal of local adaptation with either measure. We found evidence for local adaptation for one measure (time to death), but not the other (frog mortality). We argue that in this system, the time to death of a prey item is a more ecologically relevant measure of venom effectiveness than is frog mortality at 24h. Our results document an example of local adaptation between two interacting vertebrates using a whole-organism assay and a local versus foreign criteria and provide evidence that population-level variation in snake venom is adaptive.

Water availability drives signatures of local adaptation in whitebark pine (Pinus albicaulis Engelm.) across fine spatial scales of the Lake Tahoe Basin, USA.

Patterns of local adaptation at fine spatial scales are central to understanding how evolution proceeds, and are essential to the effective management of economically and ecologically important forest tree species. Here, we employ single and multilocus analyses of genetic data (n=116231 SNPs) to describe signatures of fine-scale adaptation within eight whitebark pine (Pinus albicaulis Engelm.) populations across the local extent of the environmentally heterogeneous Lake Tahoe Basin, USA. We show that despite highly shared genetic variation (FST =0.0069), there is strong evidence for adaptation to the rain shadow experienced across the eastern Sierra Nevada. Specifically, we build upon evidence from a common garden study and find that allele frequencies of loci associated with four phenotypes (mean=236 SNPs), 18 environmental variables (mean=99 SNPs), and those detected through genetic differentiation (n=110 SNPs) exhibit significantly higher signals of selection (covariance of allele frequencies) than could be expected to arise, given the data. We also provide evidence that this covariance tracks environmental measures related to soil water availability through subtle allele frequency shifts across populations. Our results replicate empirical support for theoretical expectations of local adaptation for populations exhibiting strong gene flow and high selective pressures and suggest that ongoing adaptation of many P.albicaulis populations within the Lake Tahoe Basin will not be constrained by the lack of genetic variation. Even so, some populations exhibit low levels of heritability for the traits presumed to be related to fitness. These instances could be used to prioritize management to maintain adaptive potential. Overall, we suggest that established practices regarding whitebark pine conservation be maintained, with the additional context of fine-scale adaptation.

Long-term growth performance and productivity of Scots pine (Pinus sylvestris L.) populations

The phenotypic differentiation of 16 provenances of Scots pine originating from a wide variety of habitats that range from lowland to southern highland locations in Poland was assessed during 47 years of their growth and development in the Carpathian Mountains. The traits, including height, diameter at breast height, stem straightness, and crown width, were used to evaluate the differentiation of the provenances in their juvenile period and at maturity and were examined for patterns of local adaptation. The populations from northern Poland were characterized by the best growth and productivity, whereas provenances from central Poland had the best stem quality. There were some changes in growth between provenances observed during the experiment, but the stand volume (m<sup>3</sup>/ha) in juvenile trees was closely correlated with that in mature trees (<em>r</em> = 0.979). There was a positive relationship between the productivity and the environmental conditions of the geographical origin of provenances with increasing values for the trees’ productivity from south to north. Additionally, the elevation above sea level of the original populations was inversely correlated with the growth achieved by the progeny. In general, most populations from the species distribution range in Poland tested in the severe climate conditions of the Carpathian Mountains showed good growth performance under that environment, characterized by low temperatures and short growing periods. Provenances from climatic zones outside mountain regions demonstrated great growth and productivity, which proved to be the most important for competitively outperforming the local populations. Our study demonstrates good adaptive potential of the tested provenances, as selection will favor fast-growing genotypes under the predicted environmental change scenario.

Evolutionary rescue and local adaptation under different rates of temperature increase: a combined analysis of changes in phenotype expression and genotype frequency in Paramecium microcosms.

Evolutionary rescue (ER) occurs when populations, which have declined due to rapid environmental change, recover through genetic adaptation. The success of this process and the evolutionary trajectory of the population strongly depend on the rate of environmental change. Here we investigated how different rates of temperature increase (from 23 to 32°C) affect population persistence and evolutionary change in experimental microcosms of the protozoan Paramecium caudatum. Consistent with theory on ER, we found that those populations experiencing the slowest rate of temperature increase were the least likely to become extinct and tended to be the best adapted to the new temperature environment. All high-temperature populations were more tolerant to severe heat stress (35, 37°C), indicating a common mechanism of heat protection. High-temperature populations also had superior growth rates at optimum temperatures, leading to the absence of a pattern of local adaptation to control (23°C) and high-temperature (32°C) environments. However, high-temperature populations had reduced growth at low temperatures (5-9°C), causing a shift in the temperature niche. In part, the observed evolutionary change can be explained by selection from standing variation. Using mitochondrial markers, we found complete divergence between control and high-temperature populations in the frequencies of six initial founder genotypes. Our results confirm basic predictions of ER and illustrate how adaptation to an extreme local environment can produce positive as well as negative correlated responses to selection over the entire range of the ecological niche.

Restricted gene flow and local adaptation highlight the vulnerability of high-latitude reefs to rapid environmental change.

Global climate change poses a serious threat to the future health of coral reef ecosystems. This calls for management strategies that are focused on maximizing the evolutionary potential of coral reefs. Fundamental to this is an accurate understanding of the spatial genetic structure in dominant reef-building coral species. In this study, we apply a genotyping-by-sequencing approach to investigate genome-wide patterns of genetic diversity, gene flow, and local adaptation in a reef-building coral, Pocillopora damicornis, across 10 degrees of latitude and a transition from temperate to tropical waters. We identified strong patterns of differentiation and reduced genetic diversity in high-latitude populations. In addition, genome-wide scans for selection identified a number of outlier loci putatively under directional selection with homology to proteins previously known to be involved in heat tolerance in corals and associated with processes such as photoprotection, protein degradation, and immunity. This study provides genomic evidence for both restricted gene flow and local adaptation in a widely distributed coral species, and highlights the potential vulnerability of leading-edge populations to rapid environmental change as they are locally adapted, reproductively isolated, and have reduced levels of genetic diversity.

The coexistence of generalist and specialist clonal lineages in natural populations of the Irish Famine pathogen Phytophthora infestans explains local adaptation to potato and tomato.

Phytophthora infestans, causing late blight on Solanaceae, is a serious threat to potato and tomato crops worldwide. P.infestans populations sampled on either potato or tomato differ in genotypes and pathogenicity, suggesting niche exclusion in the field. We hypothesized that such niche separation can reflect differential host exploitation by different P.infestans genotypes. We thus compared genotypes and phenotypes in 21 isolates sampled on potato (n=11) or tomato (n=10). Typing at 12 microsatellite loci assigned potato isolates to the 13_A2, 6_A1 and 1_A1 lineages, and tomato isolates to the 23_A1, 2_A1 and unclassified multilocus genotypes. Cross-inoculations on potato and tomato leaflets showed that all isolates were pathogenic on both hosts. However, tomato isolates performed much better on tomato than did potato isolates, which performed better on potato than did tomato isolates, thus revealing a clear pattern of local adaptation. Potato isolates were significantly fitter on potato than on tomato, and are best described as potato specialists; tomato isolates appear to be generalists, with similar pathogenicity on both hosts. Niche separation in the field may thus result mainly from the large fitness gap on tomato between generalists and unadapted potato specialists, while the small, but significant fitness difference on potato between both types of isolates may prevent population invasion by generalists. Extreme specialization to potato seems very costly relative to performance loss on the alternative host. This study therefore shows that local adaptation and niche separation, commonly expected to involve and generate specialists, can occur with generalists.

High intraspecific phenotypic variation, but little evidence for local adaptation in Geum reptans populations in the Central Swiss Alps

The Alpine landscape is characterized by high spatiotemporal heterogeneity in environmental variables, such as climate and soil characteristics. This may lead to divergent selection pressures across plant populations and to local adaptation. Geum reptans, a widespread high-alpine clonal herb, has been the subject of several studies investigating phenotypic variation in populations across the Swiss Alps, yet so far, there is only little knowledge about local adaptation in this species from reciprocal transplantations across original field sites. Here, we reciprocally transplanted three populations of Geum reptans in the Central Swiss Alps, growing at close or far geographical distance from each other, and compared growth- and reproduction-related traits to investigate patterns of local adaptation. We further measured leaf morphological traits to assess potential selection at field sites, and quantified the relative importance of genetic vs. environmental variation (i.e., phenotypic plasticity) for all traits. Additionally, among and within population genetic differentiation was analyzed using microsatellite markers. Molecular diversity was high within populations, and molecular differentiation increased with geographic distance among populations, suggesting that gene flow is maintained at close range, but decreased with distance. Although extensive phenotypic variation was found across site × population transplant combinations, our study revealed little evidence for local adaptation in G. reptans populations. Plant traits also showed strong plasticity, as revealed by pronounced site effects, yet no direct linear selection was detected on leaf trait values within field sites. We suggest that the glacier forelands studied here, which are representative of the habitat of large G. reptans populations, are too similar in environmental conditions to lead to among population intraspecific differentiation in line with local adaptation. As G. reptans showed a great capacity to respond plastically to environmental conditions, we cautiously advocate that the evolution of phenotypic plasticity might have prevailed over genetic differentiation for the adaptation to the relatively narrow niche of this species.

Spatial variation in soil biota mediates plant adaptation to a foliar pathogen.

Theory suggests that below-ground spatial heterogeneity may mediate host-parasite evolutionary dynamics and patterns of local adaptation, but this has rarely been tested in natural systems. Here, we test experimentally for the impact of spatial variation in the abiotic and biotic soil environment on the evolutionary outcome of the interaction between the host plant Plantago lanceolata and its specialist foliar pathogen Podosphaera plantaginis. Plants showed no adaptation to the local soil environment in the absence of natural enemies. However, quantitative, but not qualitative, plant resistance against local pathogens was higher when plants were grown in their local field soil than when they were grown in nonlocal field soil. This pattern was robust when extending the spatial scale beyond a single region, but disappeared with soil sterilization, indicating that soil biota mediated plant adaptation. We conclude that below-ground biotic heterogeneity mediates above-ground patterns of plant adaptation, resulting in increased plant resistance when plants are grown in their local soil environment. From an applied perspective, our findings emphasize the importance of using locally selected seeds in restoration ecology and low-input agriculture.

Can local adaptation explain varying patterns of herbivory tolerance in a recently introduced woody plant in North America?

Patterns of woody-plant mortality have been linked to global-scale environmental changes, such as extreme drought, heat stress, more frequent and intense fires, and episodic outbreaks of insects and pathogens. Although many studies have focussed on survival and mortality in response to specific physiological stresses, little attention has been paid to the role of genetic heritability of traits and local adaptation in influencing patterns of plant mortality, especially in non-native species. Tamarix spp. is a dominant, non-native riparian tree in western North America that is experiencing dieback in some areas of its range due to episodic herbivory by the recently introduced northern tamarisk leaf beetle (Diorhabda carinulata). We propose that genotype × environment interactions largely underpin current and future patterns of Tamarix mortality. We anticipate that (i) despite its recent introduction, and the potential for significant gene flow, Tamarix in western North America is generally adapted to local environmental conditions across its current range in part due to hybridization of two species; (ii) local adaptation to specific climate, soil and resource availability will yield predictable responses to episodic herbivory; and (iii) the ability to cope with a combination of episodic herbivory and increased aridity associated with climate change will be largely based on functional tradeoffs in resource allocation. This review focusses on the potential heritability of plant carbon allocation patterns in Tamarix, focussing on the relative contribution of acquired carbon to non-structural carbohydrate (NSC) pools versus other sinks as the basis for surviving episodic disturbance. Where high aridity and/or poor edaphic position lead to chronic stress, NSC pools may fall below a minimum threshold because of an imbalance between the supply of carbon and its demand by various sinks. Identifying patterns of local adaptation of traits related to resource allocation will improve forecasting of Tamarix population susceptibility to episodic herbivory.

The relationship between the freshwater pearl mussel (Margaritifera margaritifera) and its hosts

Endangered freshwater pearl mussels Margaritifera margaritifera reveal a complex life cycle with an obligate host-dependent phase. Only two species, Atlantic salmon Salmo salar and brown trout S. trutta, are important hosts in Europe, indicating a high degree of specialization. Whilst freshwater pearl mussels with their filtering activity can provide important ecosystem services and indirectly improve the habitat quality for their salmonid hosts, their direct effects on physiological stress, reduced swimming performance, and increased mortality at high rates of infestation all support a parasitic character of the mussel during its hostdependent phase. From an evolutionary perspective, both the much greater generation time of the parasite compared to the host, as well as the great distribution ranges of M. margaritifera and its hosts should favour local adaptation patterns. The variable suitability of different salmonid strains and species as hosts for M. margaritifera and the resulting differences in the performance of larvae during the host-dependent phase indicate that host-management strategies should focus on maintaining high quality hosts at a regional scale to avoid selection or genetic drift effects which could erode the genetic and evolutionary potential for adaptation to changing environmental conditions.

Adaptive patterns of phenotypic plasticity in laboratory and field environments in Drosophila melanogaster.

Identifying mechanisms of adaptation to variable environments is essential in developing a comprehensive understanding of evolutionary dynamics in natural populations. Phenotypic plasticity allows for phenotypic change in response to changes in the environment, and as such may play a major role in adaptation to environmental heterogeneity. Here, the plasticity of stress response in Drosophila melanogaster originating from two distinct geographic regions and ecological habitats was examined. Adults were given a short-term, 5-day exposure to combinations of temperature and photoperiod to elicit a plastic response for three fundamental aspects of stress tolerance that vary adaptively with geography. This was replicated both in the laboratory and in outdoor enclosures in the field. In the laboratory, geographic origin was the primary determinant of the stress response. Temperature and the interaction between temperature and photoperiod also significantly affected stress resistance. In the outdoor enclosures, plasticity was distinct among traits and between geographic regions. These results demonstrate that short-term exposure of adults to ecologically relevant environmental cues results in predictable effects on multiple aspects of fitness. These patterns of plasticity vary among traits and are highly distinct between the two examined geographic regions, consistent with patterns of local adaptation to climate and associated environmental parameters.

Local adaptation at higher trophic levels: contrasting hyperparasite-pathogen infection dynamics in the field and laboratory.

Predicting and controlling infectious disease epidemics is a major challenge facing the management of agriculture, human and wildlife health. Co‐evolutionarily derived patterns of local adaptation among pathogen populations have the potential to generate variation in disease epidemiology; however, studies of local adaptation in disease systems have mostly focused on interactions between competing pathogens or pathogens and their hosts. In nature, parasites and pathogens are also subject to attack by hyperparasitic natural enemies that can severely impact upon their infection dynamics. However, few studies have investigated whether this interaction varies across combinations of pathogen–hyperparasite strains, and whether this influences hyperparasite incidence in natural pathogen populations. Here, we test whether the association between a hyperparasitic fungus, Ampelomyces, and a single powdery mildew host, Podosphaera plantaginis, varies among genotype combinations, and whether this drives hyperparasite incidence in nature. Laboratory inoculation studies reveal that genotype, genotype × genotype interactions and local adaptation affect hyperparasite infection. However, observations of a natural pathogen metapopulation reveal that spatial rather than genetic factors predict the risk of hyperparasite presence. Our results highlight how sensitive the outcome of biocontrol using hyperparasites is to selection of hyperparasite strains.

Co-evolutionary dynamics between a defensive microbe and a pathogen driven by fluctuating selection.

Microbes that protect their hosts from pathogenic infection are widespread components of the microbiota of both plants and animals. It has been found that interactions between ‘defensive’ microbes and pathogens can be genotype‐specific and even underlie the variation in host resistance to pathogenic infection. These observations suggest a dynamic co‐evolutionary association between pathogens and defensive microbes, but direct evidence of co‐evolution is lacking. We tested the hypothesis that defensive microbes and pathogens could co‐evolve within host populations by co‐passaging a microbe with host‐defensive properties (Enterococcus faecalis) and a pathogen (Staphylococcus aureus) within Caenorhabditis elegans nematodes. Using both phenotypic and genomic analyses across evolutionary time, we found patterns of pathogen local adaptation and defensive microbe–pathogen co‐evolution via fluctuating selection dynamics. Moreover, co‐evolution with defensive microbes resulted in more rapid and divergent pathogen evolution compared to pathogens evolved independently in host populations. Taken together, our results indicate the potential for defensive microbes and pathogens to co‐evolve, driving interaction specificity and pathogen evolutionary divergence in the absence of host evolution.

Temporal patterns of local adaptation in soil pseudomonads.

Strong divergent selection leading to local adaptation is often invoked to explain the staggering diversity of bacteria in microbial ecosystems. However, examples of specialization by bacterial clones to alternative niches in nature are rare. Here, we investigate the extent of local adaptation in natural isolates of pseudomonads and their relatives to their soil environments across both space and time. Though most isolates grew well in most environments, patchily distributed low-quality environments were found to drive specialization. In contrast to experimental evolution work on microbial adaptation, temporal adaptation was stronger than spatial adaptation among the isolates and environments we sampled. Time-shift analysis of fitness across two seasons of growth revealed an unexpectedly strong effect of preadaptation. This pattern of apparent future adaptation may be caused by unknown abiotic properties of these environments, phages, bacterial competitors or general mechanisms of ecological niche release, and warrants future study.

A Photoreceptor Contributes to the Natural Variation of Diapause Induction in Daphnia magna.

Diapause is an adaptation that allows organisms to survive harsh environmental conditions. In species occurring over broad habitat ranges, both the timing and the intensity of diapause induction can vary across populations, revealing patterns of local adaptation. Understanding the genetic architecture of this fitness-related trait would help clarify how populations adapt to their local environments. In the cyclical parthenogenetic crustacean Daphnia magna, diapause induction is a phenotypic plastic life history trait linked to sexual reproduction, as asexual females have the ability to switch to sexual reproduction and produce resting stages, their sole strategy for surviving habitat deterioration. We have previously shown that the induction of resting stage production correlates with changes in photoperiod that indicate the imminence of habitat deterioration and have identified a Quantitative Trait Locus (QTL) responsible for some of the variation in the induction of resting stages. Here, new data allows us to anchor the QTL to a large scaffold and then, using a combination of a new mapping panel, targeted association mapping and selection analysis in natural populations, to identify candidate genes within the QTL. Our results show that variation in a rhodopsin photoreceptor gene plays a significant role in the variation observed in resting stage induction. This finding provides a mechanistic explanation for the link between diapause and day-length perception that has been suggested in diverse arthropod taxa.

Local adaptation to temperature in populations and clonal lineages of the Irish potato famine pathogen Phytophthora infestans.

Environmental factors such as temperature strongly impact microbial communities. In the current context of global warming, it is therefore crucial to understand the effects of these factors on human, animal, or plant pathogens. Here, we used a common‐garden experiment to analyze the thermal responses of three life‐history traits (latent period, lesion growth, spore number) in isolates of the potato late blight pathogen Phytophthora infestans from different climatic zones. We also used a fitness index (FI) aggregating these traits into a single parameter. The experiments revealed patterns of local adaptation to temperature for several traits and for the FI, both between populations and within clonal lineages. Local adaptation to temperature could result from selection for increased survival between epidemics, when isolates are exposed to more extreme climatic conditions than during epidemics. We also showed different thermal responses among two clonal lineages sympatric in western Europe, with lower performances of lineage 13_A2 compared to 6_A1, especially at low temperatures. These data therefore stress the importance of thermal adaptation in a widespread, invasive pathogen, where adaptation is usually considered almost exclusively with respect to host plants. This must now be taken into account to explain, and possibly predict, the global distribution of specific lineages and their epidemic potential.