Escherichia coli populations in unpredictably fluctuating environments evolve to face novel stresses through enhanced efflux activity

There is considerable understanding about how laboratory populations respond to predictable (constant or deteriorating environment) selection for single environmental variables such as temperature or pH. However, such insights may not apply when selection environments comprise multiple variables that fluctuate unpredictably, as is common in nature. To address this issue, we grew replicate laboratory populations of Escherichia coli in nutrient broth whose pH and concentrations of salt (NaCl) and hydrogen peroxide (H₂O₂) were randomly changed daily. After ~170 generations, the fitness of the selected populations had not increased in any of the three selection environments. However, these selected populations had significantly greater fitness in four novel environments which have no known fitness‐correlation with tolerance to pH, NaCl or H₂O₂. Interestingly, contrary to expectations, hypermutators did not evolve. Instead, the selected populations evolved an increased ability for energy‐dependent efflux activity that might enable them to throw out toxins, including antibiotics, from the cell at a faster rate. This provides an alternate mechanism for how evolvability can evolve in bacteria and potentially lead to broad‐spectrum antibiotic resistance, even in the absence of prior antibiotic exposure. Given that environmental variability is increasing in nature, this might have serious consequences for public health.     

QTL mapping of freezing tolerance: links to fitness and adaptive trade‐offs

Local adaptation, defined as higher fitness of local vs. nonlocal genotypes, is commonly identified in reciprocal transplant experiments. Reciprocally adapted populations display fitness trade‐offs across environments, but little is known about the traits and genes underlying fitness trade‐offs in reciprocally adapted populations. We investigated the genetic basis and adaptive significance of freezing tolerance using locally adapted populations of Arabidopsis thaliana from Italy and Sweden. Previous reciprocal transplant studies of these populations indicated that subfreezing temperature is a major selective agent in Sweden. We used quantitative trait locus (QTL) mapping to identify the contribution of freezing tolerance to previously demonstrated local adaptation and genetic trade‐offs. First, we compared the genomic locations of freezing tolerance QTL to those for previously published QTL for survival in Sweden, and overall fitness in the field. Then, we estimated the contributions to survival and fitness across both field sites of genotypes at locally adaptive freezing tolerance QTL. In growth chamber studies, we found seven QTL for freezing tolerance, and the Swedish genotype increased freezing tolerance for five of these QTL. Three of these colocalized with locally adaptive survival QTL in Sweden and with trade‐off QTL for overall fitness. Two freezing tolerance QTL contribute to genetic trade‐offs across environments for both survival and overall fitness. A major regulator of freezing tolerance, CBF2, is implicated as a candidate gene for one of the trade‐off freezing tolerance QTL. Our study provides some of the first evidence of a trait and gene that mediate a fitness trade‐off in nature.     

Repeated evolution of local adaptation in swimming performance: population‐level trade‐offs between burst and endurance swimming in Brachyrhaphis freshwater fish

Specialization is fundamentally important in biology because specialized traits allow species to expand into new environments, in turn promoting population differentiation and speciation. Specialization often results in trade‐offs between traits that maximize fitness in one environment but not others. Despite the ubiquity of trade‐offs, we know relatively little about how consistently trade‐offs evolve between populations when multiple sets of populations experience similarly divergent selective regimes. In the present study, we report a case study on Brachyrhaphis fishes from different predation environments. We evaluate apparent within/between population trade‐offs in burst‐speed and endurance at two levels of evolutionary diversification: high‐ and low‐predation populations of Brachyrhaphis rhabdophora, and sister species Brachyrhaphis roseni and Brachyrhaphis terrabensis, which occur in high‐ and low‐predation environments, respectively. Populations of Brachyrhaphis experiencing different predation regimes consistently evolved swimming specializations indicative of a trade‐off between two swimming forms that are likely highly adaptive in the environment in which they occur. We show that populations have become similarly locally adapted at both levels of diversification, suggesting that swimming specialization has evolved rather rapidly and persisted post‐speciation. Our findings provide valuable insight into how local adaptation evolves at different stages of evolutionary divergence.     

Evolution of Drosophila resistance against different pathogens and infection routes entails no detectable maintenance costs

Pathogens exert a strong selective pressure on hosts, entailing host adaptation to infection. This adaptation often affects negatively other fitness‐related traits. Such trade‐offs may underlie the maintenance of genetic diversity for pathogen resistance. Trade‐offs can be tested with experimental evolution of host populations adapting to parasites, using two approaches: (1) measuring changes in immunocompetence in relaxed‐selection lines and (2) comparing life‐history traits of evolved and control lines in pathogen‐free environments. Here, we used both approaches to examine trade‐offs in Drosophila melanogaster populations evolving for over 30 generations under infection with Drosophila C Virus or the bacterium Pseudomonas entomophila, the latter through different routes. We find that resistance is maintained after up to 30 generations of relaxed selection. Moreover, no differences in several classical life‐history traits between control and evolved populations were found in pathogen‐free environments, even under stresses such as desiccation, nutrient limitation, and high densities. Hence, we did not detect any maintenance costs associated with resistance to pathogens. We hypothesize that extremely high selection pressures commonly used lead to the disproportionate expression of costs relative to their actual occurrence in natural systems. Still, the maintenance of genetic variation for pathogen resistance calls for an explanation.     

Fitness costs of herbicide resistance across natural populations of the common morning glory,Ipomoea purpurea

Although fitness costs associated with plant defensive traits are widely expected, they are not universally detected, calling into question their generality. Here, we examine the potential for life‐history trade‐offs associated with herbicide resistance by examining seed germination, root growth, and above‐ground growth across 43 naturally occurring populations of Ipomoea purpurea that vary in their resistance to RoundUp ® , the most commonly used herbicide worldwide. We find evidence for life‐history trade‐offs associated with all three traits; highly resistant populations had lower germination, shorter roots, and smaller above‐ground size. A visual exploration of the data indicated that the type of trade‐off may differ among populations. Our results demonstrate that costs of adaptation may be present at stages other than simply the production of progeny in this agricultural weed. Additionally, the cumulative effect of costs at multiple life cycle stages can result in severe consequences to fitness when adapting to novel environments.     

Experimental evolution for generalists and specialists reveals multivariate genetic constraints on thermal reaction norms

Theory predicts the emergence of generalists in variable environments and antagonistic pleiotropy to favour specialists in constant environments, but empirical data seldom support such generalist–specialist trade‐offs. We selected for generalists and specialists in the dung fly Sepsis punctum (Diptera: Sepsidae) under conditions that we predicted would reveal antagonistic pleiotropy and multivariate trade‐offs underlying thermal reaction norms for juvenile development. We performed replicated laboratory evolution using four treatments: adaptation at a hot (31 °C) or a cold (15 °C) temperature, or under regimes fluctuating between these temperatures, either within or between generations. After 20 generations, we assessed parental effects and genetic responses of thermal reaction norms for three correlated life‐history traits: size at maturity, juvenile growth rate and juvenile survival. We find evidence for antagonistic pleiotropy for performance at hot and cold temperatures, and a temperature‐mediated trade‐off between juvenile survival and size at maturity, suggesting that trade‐offs associated with environmental tolerance can arise via intensified evolutionary compromises between genetically correlated traits. However, despite this antagonistic pleiotropy, we found no support for the evolution of increased thermal tolerance breadth at the expense of reduced maximal performance, suggesting low genetic variance in the generalist–specialist dimension.     

SIGN EPISTASIS LIMITS EVOLUTIONARY TRADE‐OFFS AT THE CONFLUENCE OF SINGLE‐ AND MULTI‐CARBON METABOLISM IN METHYLOBACTERIUM EXTORQUENS AM1

Adaptation of one set of traits is often accompanied by attenuation of traits important in other selective environments, leading to fitness trade‐offs. The mechanisms that either promote or prevent the emergence of trade‐offs remain largely unknown, and are difficult to discern in most systems. Here, we investigate the basis of trade‐offs that emerged during experimental evolution of Methylobacterium extorquens AM1 to distinct growth substrates. After 1500 generations of adaptation to a multi‐carbon substrate, succinate (S), many lineages had lost the ability to use one‐carbon compounds such as methanol (M), generating a mixture of M⁺ and M^? evolved phenotypes. We show that trade‐offs in M^? strains consistently arise via antagonistic pleiotropy through recurrent selection for loss‐of‐function mutations to ftfL (formate‐tetrahydrofolate ligase), which improved growth on S while simultaneously eliminating growth on M. But if loss of FtfL was beneficial, why were M trade‐offs not found in all populations? We discovered that eliminating FtfL was not universally beneficial on S, as it was neutral or even deleterious in certain evolved lineages that remained M⁺. This suggests that sign epistasis with earlier arising mutations prevented the emergence of mutations that drove trade‐offs through antagonistic pleiotropy, limiting the evolution of metabolic specialists in some populations.     

Rainbow trout in seasonal environments: phenotypic trade‐offs across a gradient in winter duration

Survival through periods of resource scarcity depends on the balance between metabolic demands and energy storage. The opposing effects of predation and starvation mortality are predicted to result in trade‐offs between traits that optimize fitness during periods of resource plenty (e.g., during the growing season) and those that optimize fitness during periods of resource scarcity (e.g., during the winter). We conducted a common environment experiment with two genetically distinct strains of rainbow trout to investigate trade‐offs due to (1) the balance of growth and predation risk related to foraging rate during the growing season and (2) the allocation of energy to body size prior to the winter. Fry (age 0) from both strains were stocked into replicate natural lakes at low and high elevation that differed in winter duration (i.e., ice cover) by 59 days. Overwinter survival was lowest in the high‐elevation lakes for both strains. Activity rate and growth rate were highest at high elevation, but growing season survival did not differ between strains or between environments. Hence, we did not observe a trade‐off between growth and predation risk related to foraging rate. Growth rate also differed significantly between the strains across both environments, which suggests that growth rate is involved in local adaptation. There was not, however, a difference between strains or between environments in energy storage. Hence, we did not observe a trade‐off between growth and storage. Our findings suggest that intrinsic metabolic rate, which affects a trade‐off between growth rate and overwinter survival, may influence local adaptation in organisms that experience particularly harsh winter conditions (e.g., extended periods trapped beneath the ice in high‐elevation lakes) in some parts of their range.     

No apparent cost of evolved immune response in Drosophila melanogaster

Maintenance and deployment of the immune system are costly and are hence predicted to trade‐off with other resource‐demanding traits, such as reproduction. We subjected this longstanding idea to test using laboratory experimental evolution approach. In the present study, replicate populations of Drosophila melanogaster were subjected to three selection regimes—I (Infection with Pseudomonas entomophila), S (Sham‐infection with MgSO₄), and U (Unhandled Control). After 30 generations of selection flies from the I regime had evolved better survivorship upon infection with P. entomophila compared to flies from U and S regimes. However, contrary to expectations and previous reports, we did not find any evidence of trade‐offs between immunity and other life history related traits, such as longevity, fecundity, egg hatchability, or development time. After 45 generations of selection, the selection was relaxed for a set of populations. Even after 15 generations, the postinfection survivorship of populations under relaxed selection regime did not decline. We speculate that either there is a negligible cost to the evolved immune response or that trade‐offs occur on traits such as reproductive behavior or other immune mechanisms that we have not investigated in this study. Our research suggests that at least under certain conditions, life‐history trade‐offs might play little role in maintaining variation in immunity.     

Interspecific variation and elevated CO2 influence the relationship between plant chemical resistance and regrowth tolerance

To understand how comprehensive plant defense phenotypes will respond to global change, we investigated the legacy effects of elevated CO₂ on the relationships between chemical resistance (constitutive and induced via mechanical damage) and regrowth tolerance in four milkweed species (Asclepias). We quantified potential resistance and tolerance trade‐offs at the physiological level following simulated mowing, which are relevant to milkweed ecology and conservation. We examined the legacy effects of elevated CO₂ on four hypothesized trade‐offs between the following: (a) plant growth rate and constitutive chemical resistance (foliar cardenolide concentrations), (b) plant growth rate and mechanically induced chemical resistance, (c) constitutive resistance and regrowth tolerance, and (d) regrowth tolerance and mechanically induced resistance. We observed support for one trade‐off between plant regrowth tolerance and mechanically induced resistance traits that was, surprisingly, independent of CO₂ exposure. Across milkweed species, mechanically induced resistance increased by 28% in those plants previously exposed to elevated CO_2. In contrast, constitutive resistance and the diversity of mechanically induced chemical resistance traits declined in response to elevated CO₂ in two out of four milkweed species. Finally, previous exposure to elevated CO₂ uncoupled the positive relationship between plant growth rate and regrowth tolerance following damage. Our data highlight the complex and dynamic nature of plant defense phenotypes under environmental change and question the generality of physiologically based defense trade‐offs.     

Idiosyncratic evolution of maternal effects in response to juvenile malnutrition in Drosophila

Maternal effects often affect fitness traits, but there is little experimental evidence pertaining to their contribution to response to selection imposed by novel environments. We studied the evolution of maternal effects in Drosophila populations selected for tolerance to chronic larval malnutrition. To this end, we performed pairwise reciprocal F₁ crosses between six selected (malnutrition tolerant) populations and six unselected control populations and assessed the effect of cross direction on larval growth and developmental rate, adult weight and egg‐to‐adult viability expressed under the malnutrition regime. Each pair of reciprocal crosses revealed large maternal effects (possibly including cytoplasmic genetic effects) on at least one trait, but the magnitude, sign and which traits were affected varied among populations. Thus, maternal effects contributed significantly to the response to selection imposed by the malnutrition regime, but these changes were idiosyncratic, suggesting a rugged adaptive landscape. Furthermore, although the selected populations evolved both faster growth and higher viability, the maternal effects on growth rate and viability were negatively correlated across populations. Thus, genes mediating maternal effects can evolve to partially counteract the response to selection mediated by the effects of alleles on their own carriers’ phenotype, and maternal effects may contribute to evolutionary trade‐offs between components of offspring fitness.     

When do trade‐offs occur? The roles of energy constraints and trait flexibility in bushcricket populations

In many animal species, the expression of sexually selected traits is negatively correlated with traits associated with survival such as immune function, a relationship termed a ‘trade‐off’. But an alternative in which sexually selected traits are positively correlated with survival traits is also widespread. We propose that the nature of intertrait relationships is largely determined by overall energy expenditure, energy availability and trait flexibility, with trade‐offs expected when individuals are subject to energy constraints. We tested this hypothesis in Ephippiger diurnus, a European bushcricket in which males are distinguished by two prominent sexually selected traits, acoustic calls and a large spermatophore transferred to the female at mating, and where immune function may be critical in survival. Ephippiger diurnus are distributed as small, isolated populations that are differentiated genetically and behaviourally. We analysed songs, spermatophores and the immune function in male individuals from eight populations spanning a range of song types. As predicted, we only found trade‐offs in those populations that expended more energy on song and were less flexible in their ability to adjust that expenditure. Ultimately, energy constraints and resulting trade‐offs may limit the evolution of song exaggeration in E. diurnus populations broadcasting long calls comprised of multiple ‘syllables’.     

Predators modify the temperature dependence of life‐history trade‐offs

Although life histories are shaped by temperature and predation, their joint influence on the interdependence of life‐history traits is poorly understood. Shifts in one life‐history trait often necessitate shifts in another—structured in some cases by trade‐offs—leading to differing life‐history strategies among environments. The offspring size–number trade‐off connects three traits whereby a constant reproductive allocation (R) constrains how the number (O) and size (S) of offspring change. Increasing temperature and size‐independent predation decrease size at and time to reproduction which can lower R through reduced time for resource accrual or size‐constrained fecundity. We investigated how O, S, and R in a clonal population of Daphnia magna change across their first three clutches with temperature and size‐independent predation risk. Early in ontogeny, increased temperature moved O and S along a trade‐off curve (constant R) toward fewer larger offspring. Later in ontogeny, increased temperature reduced R in the no‐predator treatment through disproportionate decreases in O relative to S. In the predation treatment, R likewise decreased at warmer temperatures but to a lesser degree and more readily traded off S for O whereby the third clutch showed a constant allocation strategy of O versus S with decreasing R. Ontogenetic shifts in S and O rotated in a counterclockwise fashion as temperature increased and more drastically under risk of predation. These results show that predation risk can alter the temperature dependence of traits and their interactions through trade‐offs.     

Phenotypic constraints and community structure: Linking trade‐offs within and among species

Trade‐offs are central to many topics in biology, from the evolution of life histories to ecological mechanisms of species coexistence. Trade‐offs observed among species may reflect pervasive constraints on phenotypes that are achievable given biophysical and resource limitations. If so, then among‐species trade‐offs should be consistent with trade‐offs within species. Alternatively, trait variation among co‐occurring species may reflect historical contingencies during community assembly rather than within‐species constraints. Here, we test whether a key trade‐off between relative growth rate (RGR) and water‐use efficiency (WUE) among Sonoran Desert winter annual plants is apparent within four species representing different strategies in the system. We grew progeny of maternal families from multiple populations in a greenhouse common garden. One species, Pectocarya recurvata, displayed the expected RGR–WUE trade‐off among families within populations. For other species, although RGR and WUE often varied clinally among populations, among‐family variation within populations was lacking, implicating a role for past selection on these traits. Our results suggest that a combination of limited genetic variation in single traits and negative trait correlations could pose constraints on the evolution of a high‐RGR and high‐WUE phenotype within species, providing a microevolutionary explanation for phenotypes that influence community‐level patterns of abundance and coexistence.     

Is local adaptation in Mimulus guttatus caused by trade‐offs at individual loci?

Local adaptation is considered to be the result of fitness trade‐offs for particular phenotypes across different habitats. However, it is unclear whether such phenotypic trade‐offs exist at the level of individual genetic loci. Local adaptation could arise from trade‐offs of alternative alleles at individual loci or by complementary sets of loci with different fitness effects of alleles in one habitat but selective neutrality in the alternative habitat. To evaluate the genome‐wide basis of local adaptation, we performed a field‐based quantitative trait locus (QTL) mapping experiment on recombinant inbred lines (RILs) created from coastal perennial and inland annual races of the yellow monkeyflower (Mimulus guttatus) grown reciprocally in native parental habitats. Overall, we detected 19 QTLs affecting one or more of 16 traits measured in two environments, most of small effect. We identified 15 additional QTL effects at two previously identified candidate QTLs [DIV ERGENCE (DIV)]. Significant QTL by environment interactions were detected at the DIV loci, which was largely attributable to genotypic differences at a single field site. We found no detectable evidence for trade‐offs for any one component of fitness, although DIV2 showed a trade‐off involving different fitness traits between sites, suggesting that local adaptation is largely controlled by non‐overlapping loci. This is surprising for an outcrosser, implying that reduced gene flow prevents the evolution of individuals adapted to multiple environments. We also determined that native genotypes were not uniformly adaptive, possibly reflecting fixed mutational load in one of the populations.     

Use of trade-off theory to advance understanding of herbivore–parasite interactions

• 1 Trade‐off theory has been extensively used to further our understanding of animal behaviour. In mammalian herbivores, it has been used to advance our understanding of their reproductive, parental care and foraging strategies. Here, we detail how trade‐off theory can be applied to herbivore–parasite interactions, especially in foraging environments.
• 2 Foraging is a common mode of uptake of parasites that represent the most pervasive challenge to mammalian fitness and survival. Hosts are hypothesized to alter their foraging behaviour in the presence of parasites in three ways: (i) hosts avoid foraging in areas that are contaminated with parasites; (ii) hosts select diets that increase their resistance and resilience to parasites; and (iii) hosts select for foods with direct anti‐parasitic properties (self‐medication). We concentrate on the mammalian herbivore literature to detail the recent advances made using trade‐off frameworks to understand the mechanisms behind host–parasite interactions in relation to these three hypotheses.
• 3 In natural systems, animals often face complex foraging decisions including nutrient intake vs. predation risk, nutrient intake vs. sheltering and nutrient intake vs. parasite risk trade‐offs. A trade‐off framework is detailed that can be used to interpret mammal behaviour in complex environments, and may be used to advance the self‐medication hypothesis.
• 4 The use of trade‐off theory has advanced our understanding of the contact process between grazing mammalian hosts and their parasites transmitted via the faecal–oral route. Experimental manipulation of the costs and benefits of a nutrient intake vs. parasite risk trade‐off has shown that environmental conditions (forage quality and quantity) and the physiological state (parasitic and immune status) of a mammalian host can both affect the behavioural decisions of foraging animals.
• 5 Naturally occurring trade‐offs and the potential to manipulate their costs and benefits enables us to identify the abilities and behavioural rules used by mammals when making decisions in complex environments and thus predict animal behaviour.

     

Productivity and thallus toughness trade‐off relationship in marine macroalgae from the Japan Sea

Trade‐offs are considered key to understanding mechanisms supporting the coexistence of multiple plant species. Thus, understanding the mechanisms underlying trade‐offs is expected to contribute to conservation and management of macroalgal beds composed of diverse macroalgae of rocky shore ecosystems. To test the occurrence of trade‐offs between productivity and thallus toughness as well as pair‐wise thallus trait relationships that are expected to indirectly relate to any trade‐offs, traits and relationships for 13 species of macroalgae from the central area along the Japan Sea coast of Honshu, Japan were examined. In each species we examined for photosynthetic capacity per unit biomass (as A_mass) and nitrogen (i.e., photosynthetic nitrogen‐use efficiency, PNUE), nitrogen content (as N_mass), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as F_p, a common index of leaf toughness in land plants by punch test). A significant negative correlation indicating a trade‐off between productivity and thallus toughness was found between A_mass or PNUE and F_p. Pair‐wise relationships that were expected to indirectly relate to the trade‐off were as follows. A_mass was positively correlated with N_mass. Thalli with high N_mass extensively utilizing nitrogen in the photosynthetic parts, and consequently exhibiting elevated metabolic rates. Moreover, thalli with high N_mass tended to be associated with low TMA, and N_mass decreased with increasing TMA. A significant negative correlation was observed between TMA and A_mass or PNUE because of the linkage of high A_mass or PNUE with high N_mass and high N_mass associated with low TMA, while a significant positive correlation was observed between TMA and F_p. The two correlations indicate a physiological and structural trade‐off, which underlies the interdependency of thallus traits. Results of multivariate analyses also indicated that the thallus traits interdependently vary across a single axis based on the trade‐off.     

Trade‐offs in osmoregulation and parallel shifts in molecular function follow ecological transitions to freshwater in the Alewife

Adaptation to freshwater may be expected to reduce performance in seawater because these environments represent opposing selective regimes. We tested for such a trade‐off in populations of the Alewife (Alosa pseudoharengus). Alewives are ancestrally anadromous, and multiple populations have been independently restricted to freshwater (landlocked). We conducted salinity challenge experiments, whereby juvenile Alewives from one anadromous and multiple landlocked populations were exposed to freshwater and seawater on acute and acclimation timescales. In response to acute salinity challenge trials, independently derived landlocked populations varied in the degree to which seawater tolerance has been lost. In laboratory‐acclimation experiments, landlocked Alewives exhibited improved freshwater tolerance, which was correlated with reductions in seawater tolerance and hypo‐osmotic balance, suggesting that trade‐offs in osmoregulation may be associated with local adaptation to freshwater. We detected differentiation between life‐history forms in the expression of an ion‐uptake gene (NHE3), and in gill Na⁺/K⁺‐ATPase activity. Trade‐offs in osmoregulation, therefore, may be mediated by differentiation in ion‐uptake and salt‐secreting pathways.     

Finite element modeling of shell shape in the freshwater turtle Pseudemys concinna reveals a trade‐off between mechanical strength and hydrodynamic efficiency

Aquatic species can experience different selective pressures on morphology in different flow regimes. Species inhabiting lotic regimes often adapt to these conditions by evolving low‐drag (i.e., streamlined) morphologies that reduce the likelihood of dislodgment or displacement. However, hydrodynamic factors are not the only selective pressures influencing organismal morphology and shapes well suited to flow conditions may compromise performance in other roles. We investigated the possibility of morphological trade‐offs in the turtle Pseudemys concinna. Individuals living in lotic environments have flatter, more streamlined shells than those living in lentic environments; however, this flatter shape may also make the shells less capable of resisting predator‐induced loads. We tested the idea that “lotic” shell shapes are weaker than “lentic” shell shapes, concomitantly examining effects of sex. Geometric morphometric data were used to transform an existing finite element shell model into a series of models corresponding to the shapes of individual turtles. Models were assigned identical material properties and loaded under identical conditions, and the stresses produced by a series of eight loads were extracted to describe the strength of the shells. “Lotic” shell shapes produced significantly higher stresses than “lentic” shell shapes, indicating that the former is weaker than the latter. Females had significantly stronger shell shapes than males, although these differences were less consistent than differences between flow regimes. We conclude that, despite the potential for many‐to‐one mapping of shell shape onto strength, P. concinna experiences a trade‐off in shell shape between hydrodynamic and mechanical performance. This trade‐off may be evident in many other turtle species or any other aquatic species that also depend on a shell for defense. However, evolution of body size may provide an avenue of escape from this trade‐off in some cases, as changes in size can drastically affect mechanical performance while having little effect on hydrodynamic performance. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Life‐history trade‐offs vary with resource availability across the geographic range of a widespread plant

• Trade‐offs between reproduction, growth and survival arise from limited resource availability in plants. Environmental stress is expected to exacerbate these negative correlations, but no studies have evaluated variation in life‐history trade‐offs throughout species geographic ranges. Here we analyse the costs of growth and reproduction across the latitudinal range of the widespread herb Plantago coronopus in Europe.
• We monitored the performance of thousands of individuals in 11 populations of P. coronopus, and tested whether the effects of growth and reproduction on a set of vital rates (growth, probability of survival, probability of reproduction and fecundity) varied with local precipitation and soil fertility. To account for variation in internal resources among individuals, we analysed trade‐offs correcting for differences in size.
• Growth was negatively affected by previous growth and reproduction. We also found costs of growth and reproduction on survival, reproduction probability and fecundity, but only in populations with low soil fertility. Costs also increased with precipitation, possibly due to flooding‐related stress. In contrast, growth was positively correlated with subsequent survival, and there was a positive covariation in reproduction between consecutive years under certain environments, a potential strategy to exploit temporary benign conditions.
• Overall, we found both negative and positive correlations among vital rates across P. coronopus geographic range. Trade‐offs predominated under stressful conditions, and positive correlations arose particularly between related traits like reproduction investment across years. By analysing multiple and diverse fitness components along stress gradients, we can better understand life‐history evolution across species’ ranges, and their responses to environmental change.