Patterns of genetic diversity vary among shoot and root functional traits in Norway spruce Picea abies along a latitudinal gradient

Roots constitute a major segment of plant biomass, and variation in belowground traits in situ correlates with environmental gradients at large spatial scales. Local adaptation of populations maintains intraspecific genetic variation in various shoot traits, but the contribution of genetic factors to adaptation to soil heterogeneity remains poorly known. I established a common-garden experiment with three Norway spruce Picea abies populations sampled between 60° and 67° N in Finland, each represented by 13 or 15 maternal families, to determine whether belowground traits are as genetically differentiated among populations as those in the shoot along a collective latitudinal gradient of temperature and soil heterogeneity. Two growing season simulations enabled testing for among-population differences in phenotypic plasticity. I phenotyped 777 first-year seedlings from shoot to root to capture functional traits that may influence survival in the wild: autumn phenology, shoot growth, root system size, root architecture, root morphology and growth allocation. All traits exhibited within-population genetic diversity, but among-population differentiation ranged from strong in shoot traits to nonexistent in root system architecture and morphology that are scaled to root system size. However, latitudinal trends characterised root-to-shoot ratio and root tip-to-shoot ratio that account for among-population differences in aboveground growth. Overall trait variability was multidimensional with variable among- versus within-population trends: for example, phenology and shoot growth covaried across populations, but their association within individual populations was variable. Shoot growth correlated positively with root system size, but not with root architecture or morphology. Finally, the two higher-latitude populations exhibited greater phenotypic plasticity in shoot traits and growth allocation. The results demonstrate varying patterns of genetic variation in functional traits of Norway spruce in the boreal zone, suggesting simultaneous adaptation to multiple environmental factors. Functional traits that exhibit phenotypic plasticity, genetic diversity and little covariation will promote long-term survival of populations in fluctuating environments.     

Changes in reproductive investment with altitude in an alpine plant

Aims In perennial species, the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and, therefore, impacts future reproductive success. As a consequence, variation in this trade-off is among the most important driving forces in the life-history evolution of perennial plants and can lead to locally adapted genotypes. In addition to genetic variation, phenotypic plasticity might also contribute to local adaptation of plants to local conditions by mediating changes in reproductive allocation. Knowledge on the importance of genetic and environmental effects on the trade-off between reproduction and vegetative growth is therefore essential to understand how plants may respond to environmental changes.Methods We conducted a transplant experiment along an altitudinal gradient from 425 to 1?921 m in the front range of the Western Alps of Switzerland to assess the influence of both altitudinal origin of populations and altitude of growing site on growth, reproductive investment and local adaptation in Poa alpina .Important findings In our study, the investment in reproduction increased with plant size. Plant growth and the relative importance of reproductive investment decreased in populations originating from higher altitudes compared to populations originating from lower altitudes. The changes in reproductive investment were mainly explained by differences in plant size. In contrast to genetic effects, phenotypic plasticity of all traits measured was low and not related to altitude. As a result, the population from the lowest altitude of origin performed best at all sites. Our results indicate that in P. alpina genetic differences in growth and reproductive investment are related to local conditions affecting growth, i.e. interspecific competition and soil moisture content.     

Phenotypic plasticity and sexual dimorphism in size at post-juvenile metamorphosis: common-garden rearing of an intertidal gastropod with determinate growth

Proximate factors of the intraspecific variation in molluscan shell morphology have long received attention in biology. The intertidal gastropod Monetaria annulus (Mollusca; Gastropoda; Cypraeidae) is particularly suitable for the study of variation in body size, because this species is a determinate grower in the sense that soft-body size shows no further increase after the juvenile stage. Cross-sectional field surveys on post-juvenile individuals have indicated that the mean body size varies widely among populations and is larger in females than in males within populations. To examine whether these patterns are due to genetic differences, we conducted a common-garden rearing experiment with juvenile individuals collected from two populations on Okinawa Island. After adjusting for among-individual differences in initial degree of development, statistical analyses revealed that this species exhibits female-biased sexual size dimorphism mediated by a longer development time rather than by faster growth rates in females. Although wild individuals show a remarkable size difference between populations, no size difference was found between the populations in the individuals reared in a common-garden condition. This result suggests that the among-population size difference does not have a genetic basis and is caused by phenotypic plasticity based on environmental heterogeneity among habitats.     

Latitudinal population differentiation in two species of Solidago (Asteraceae) introduced into Europe

Solidago altissima and S. gigantea were introduced from North America to Europe ~250 yr ago and are now considered aggressive weeds in abandoned fields and conservation areas. We studied patterns of genetic differentiation in these two species along their present latitudinal range in Europe (44-61 degrees N). Two generations of clonally propagated ramets from randomly selected genets of 24 populations of each species were grown in a common-garden experiment at latitude 47 degrees N from 1991 to 1992. Both species showed significant variation among populations in morphological and life-history characters: at this southern location, plants from northern populations were smaller and flowered earlier than plants from southern populations. The gradient of clinal variation was more pronounced in the second year of cultivation than in the first and was steeper in S. altissima than in S. gigantea. Within-population variation among genotypes was significant tot most characters in the case of S. altissima. Phenological rate (reciprocal of days to flowering) and size at maturity showed a significant negative correlation among populations bot not among genotypes within populations, indicating that genetic trade-offs may occur at one but not another infraspecific level. We suggest that the pattern of among-population variation reflects rapid adaptive population differentiation after introduction of the species to Europe.     

Comparing indigenous and introduced populations of Melaleuca quinquenervia (Cav.) Blake: response of seedlings to water and pH levels

Melaleuca quinquenervia is a wetland tree species indigenous to eastern Australia. It was separately introduced to east and west Florida as an ornamental, but has since become invasive, dominating several habitat types. We tested the predictions that (1) Australian populations would exhibit more genetic variation than Florida populations, due to founder effect, and (2) high phenotypic plasticity would be found in all populations, due to the wide range of habitats occupied. We compared the phenotypic plasticity and familial variation among three Australian populations, two east Florida, and two west Florida populations in a greenhouse experiment. We grew seedlings collected from different maternal trees in each population under two water levels and three pH levels, reflecting the natural range of water levels and soil pH in Florida and Australian Melaleuca stands. We measured leaf size and shape, growth rate and above-ground biomass of seedlings and determined the components of phenotypic variance (familial, environmental, and their interaction) using univariate and multivariate analysis of variance. All traits showed significant among-population and among-family variation, as well as significant phenotypic plasticity, in response to both water level and pH level changes. Sensitivity to pH was particularly high, presumably because plants were grown under pHs ranging from 4.7 to 7.4, and because pH can influence nutrient availability. Familial variation contains genetic variation, but it may also be confounded with maternal environmental effects. Comparing Australian to Floridian Melaleuca, amounts of familial variation and phenotypic plasticity varied by trait. Overall, Australian Melaleuca had more among-population variation than Floridian Melaleuca, presumably reflecting the wider latitudinal range and longer time for evolutionary change in Australia, but had similar amounts of among-family variation, within any one population. If maternal effects are strong, among-population differences may merely reflect greater environmental differences among Australian sites than Florida sites. Australian Melaleuca had less phenotypic plasticity, possibly due to founder effects in Florida or to subsequent adaptive evolution of phenotypic plasticity in Floridian populations. Floridian Melaleuca shows little loss of familial variation, compared to indigenous Australian populations, and that, in combination with its high phenotypic plasticity, should allow it to continue to colonize new areas successfully.     

LIFE-HISTORY VARIATION WITHIN A POPULATION OF THE COLONIAL ASCIDIAN BOTRYLLUS SCHLOSSERI. I. THE GENETIC AND ENVIRONMENTAL CONTROL OF SEASONAL VARIATION

Many empirical analyses of life-history tactics are based on the assumption that demographic variation ought to be greatest among populations or species living in different environments. However, in a single population of the sessile colonial sea squirt Botryllus schlosseri, there are two discrete life-history morphs. Semelparous colonies are characterized by a) death immediately following the production of a single clutch, b) early age at first reproduction, c) rapid growth to first reproduction, and d) high reproductive effort. In contrast, iteroparous colonies a) produce at least three clutches before dying, b) postpone sexual reproduction until they are nearly twice the age of semelparous colonies, c) grow at about half the rate of semelparous colonies, and d) invest roughly 75% less in reproductive effort than semelparous colonies. Semelparous colonies numerically dominate the population through midsummer; later in the summer, iteroparous colonies are most numerous. Field and laboratory common-garden experiments, along with breeding studies, indicate that the demographic differences between the morphs are genetically determined. Consequently, the seasonal switch from dominance by semelparous colonies to dominance by iteroparous colonies may be an evolved response to a seasonally changing environment. On theoretical grounds, temporal variation in selection is thought to play a relatively unimportant role in maintaining genetic polymorphism; nonetheless, the seasonally recurrent life-history polymorphism shown in this study indicates that temporal variation in selection can lead to the maintenance of genetic polymorphism for traits strongly affecting fitness.     

Among-population variation in costs of reproduction in the long-lived orchid Gymnadenia conopsea: an experimental study

A cost of reproduction in terms of reduced future performance underlies all life-history models, yet costs have been difficult to detect in short-term experiments with long-lived plants. The likelihood of detecting costs should depend on the range of variation in reproductive effort that can be induced, and also on the shape of the cost function across this range, which should be affected by resource availability. Here, we experimentally examined the effects of both reduced and increased fruit production in two populations of the long-lived orchid Gymnadenia conopsea located at sites that differ in length of the growing season. Plants that were prevented from fruiting produced more flowers in the population with a longer growing season, had higher survival in the other population, and grew larger compared to control plants in both populations. Fruit production was pollen-limited in both populations, and increased reproductive investment after supplemental hand-pollination was associated with reduced fecundity the following year. The results demonstrate that the shape of the cost function varies among fitness components, and that costs can be differentially expressed in different populations. They are consistent with the hypothesis that differences in temporal overlap between allocation to reproduction and other functions will induce among-population variation in reproductive costs.     

Divergent selection on flowering time contributes to local adaptation in Mimulus guttatus populations

The timing of when to initiate reproduction is an important transition in any organism's life cycle. There is much variation in flowering time among populations, but we do not know to what degree this variation contributes to local adaptation. Here we use a reciprocal transplant experiment to examine the presence of divergent natural selection for flowering time and local adaptation between two distinct populations of Mimulus guttatus. We plant both parents and hybrids (to tease apart differences in suites of associated parental traits) between these two populations into each of the two native environments and measure floral, vegetative, life-history, and fitness characters to assess which traits are under selection at each site. Analysis of fitness components indicates that each of these plant populations is locally adapted. We obtain striking evidence for divergent natural selection on date of first flower production at these two sites. Early flowering is favored at the montane site, which is inhabited by annual plants and characterized by dry soils in midsummer, whereas intermediate (though later) flowering dates are selectively favored at the temperate coastal site, which is inhabited by perennial plants and is almost continually moist. Divergent selection on flowering time contributes to local adaptation between these two populations of M. guttatus, suggesting that genetic differentiation in the timing of reproduction may also serve as a partial reproductive isolating barrier to gene flow among populations.     

QUANTITATIVE GENETICS OF SIZE,SHAPE, LIFE-HISTORY,AND FRUIT CHARACTERISTICS OF THE SEED-HETEROMORPHIC COMPOSITE HETEROSPERMA PINNATUM. I. VARIATION WITHIN AND AMONG POPULATIONS

We document phenotypic and genetic variation within and among populations of the seed heteromorphic species Heterosperma pinnatum Cav. (Compositae) in the production of seed morphs and in a variety of life-history and morphological characteristics that might be correlated with seed and head traits. Each trait is found to have significant genetic variance in most or, usually, all populations. Significant among-population genetic variation exists for all traits except number of achenes per head and seedling shape, although some traits have much less genetic variation among than within populations. Number and percentage of intermediate achenes per head, total number of achenes per head, and lengths of central and peripheral achenes had little among-population genetic variation compared to within-population variation. Most traits had slightly less genetic variation among than within populations; however, some traits (percentage of central achenes, length of awns, date that the first flowering head opened, date that the first fruiting head opened, and death date) had more among-population genetic variation. The proportions of achene morphs produced had high broad-sense heritabilities and high among-population genetic variance, except in the case of intermediate achenes. All phenological variables had high among-population genetic variation. Within-population heritabilities were high for dates of first flowering head and fruiting head but low for death date and reproductive interval. Family and population means measured in the greenhouse for traits having high broad-sense heritability or among-population genetic variance were closely correlated with field means for the corresponding families or populations. The amounts of phenotypic variation were similar for traits that were measured in both the field and the greenhouse. These lines of evidence suggest that greenhouse results provide reasonable estimates of genetic variation in the field for this species. Numerous studies have reported variation in the proportion of seed morphs for different heteromorphic-seeded species and have discussed adaptive scenarios for the evolution of seed proportions; however, our investigation is one of only a few that have documented the amount of phenotypic and genetic variation within and among populations.     

Experimental evidence for the adaptive evolution of growth rate in the garter snake Thamnophis elegans

The western terrestrial garter snake (Thamnophis elegans) varies significantly in individual growth rates and life-history traits (maturation, reproduction, and survival) among adjacent populations in nature. This study focuses on assessing the genetic and environmental components of the substantial among-population variation in growth rates. Litters of neonates from nine populations inhabiting either mountain meadow or lakeshore habitat were reared for one year in a common-garden experiment with two temperature treatments. Diet, frequency of feeding, light exposure, and daytime temperatures were identical for all individuals. The two different nighttime temperatures (20 degrees C and 25 degrees C) were chosen to mirror field differences in nighttime thermoregulatory constraints for mountain-meadow and lakeshore snakes, respectively. Temperature and source habitat interacted to affect first-year growth rate. Neonates from meadow dams grew fastest in the cooler treatment, whereas those from lakeshore dams grew fastest in the warmer treatment. The observation that naive neonates, which were gestated and raised under identical conditions, grew fastest in environments characteristic of their natal population is evidence both that there are genetic differences among populations for growth and that these differences reflect adaptation to local habitats at a very small geographic scale. In addition, significant directional selection for large birthweight was measured for neonates from all populations. These results are considered in the context of population colonization history, migration and selection, and competing models for growth rate variation.     

Life-history variation in agricultural and wild populations of Erucastrum nasturtiifolium (Brassicaceae)

In the present study we relate the variability in life-history traits (such as flowering time and lifespan) of the herbaceous biennial–perennial Erucastrum nasturtiifolium (Brassicaceae) to habitat type. We studied plant populations from arable fields and from eroded mountain habitats, such as badlands and rocky slopes. Collection sites ranged from low basin to sub-alpine regions in the NE Iberian Peninsula. Plants were grown under common garden conditions to evaluate genetic variation among and within populations. Plants were also subjected to a resource gradient to detect genetic variation in phenotypic plasticity. The populations exhibited differentiation across a number of life-history traits (mainly flowering time and lifespan) and morphological traits related to growth (basal stem diameter, plant height and number of branches). This suggests that life-history differences among populations are genetically based. Moreover, our results show that variation in flowering time and lifespan are affected by habitat type independent of other abiotic factors such as altitude or continentality. Thus, populations from arable fields started flowering in their first year and displayed annual cycles, whereas those from wild habitats generally flowered in their second year and showed biennial or even perennial cycles. Intra-population differences in flowering time were observed in only one population, and were related to nutrient availability. We suggest that early-flowering and shorter lifespan populations of E. nasturtiifolium may have been selected from late-flowering and longer lifespan populations as part of a selective process ensuring survival and future offspring amidst unpredictable and frequently disturbed environments such as exist in many agricultural habitats.     

Plant population differentiation and climate change: responses of grassland species along an elevational gradient

Mountain ecosystems are particularly susceptible to climate change. Characterizing intraspecific variation of alpine plants along elevational gradients is crucial for estimating their vulnerability to predicted changes. Environmental conditions vary with elevation, which might influence plastic responses and affect selection pressures that lead to local adaptation. Thus, local adaptation and phenotypic plasticity among low and high elevation plant populations in response to climate, soil and other factors associated with elevational gradients might underlie different responses of these populations to climate warming. Using a transplant experiment along an elevational gradient, we investigated reproductive phenology, growth and reproduction of the nutrient‐poor grassland species Ranunculus bulbosus, Trifolium montanum and Briza media. Seeds were collected from low and high elevation source populations across the Swiss Alps and grown in nine common gardens at three different elevations with two different soil depths. Despite genetic differentiation in some traits, the results revealed no indication of local adaptation to the elevation of population origin. Reproductive phenology was advanced at lower elevation in low and high elevation populations of all three species. Growth and reproduction of T. montanum and B. media were hardly affected by garden elevation and soil depth. In R. bulbosus, however, growth decreased and reproductive investment increased at higher elevation. Furthermore, soil depth influenced growth and reproduction of low elevation R. bulbosus populations. We found no evidence for local adaptation to elevation of origin and hardly any differences in the responses of low and high elevation populations. However, the consistent advanced reproductive phenology observed in all three species shows that they have the potential to plastically respond to environmental variation. We conclude that populations might not be forced to migrate to higher elevations as a consequence of climate warming, as plasticity will buffer the detrimental effects of climate change in the three investigated nutrient‐poor grassland species.     

Genetic architecture and phenotypic plasticity of thermally-regulated traits in an eruptive species, <Emphasis Type="Italic">Dendroctonus ponderosae</Emphasis>

Phenotypic plasticity in thermally-regulated traits enables close tracking of changing environmental conditions, and can thereby enhance the potential for rapid population increase, a hallmark of outbreak insect species. In a changing climate, exposure to conditions that exceed the capacity of existing phenotypic plasticity may occur. Combining information on genetic architecture and trait plasticity among populations that are distributed along a latitudinal cline can provide insight into how thermally-regulated traits evolve in divergent environments and the potential for adaptation. Dendroctonus ponderosae feed on Pinus species in diverse climatic regimes throughout western North America, and show eruptive population dynamics. We describe geographical patterns of plasticity in D. ponderosae development time and adult size by examining reaction norms of populations from multiple latitudes. The relative influence of additive and non-additive genetic effects on population differences in the two phenotypic traits at a single temperature is quantified using line-cross experiments and joint-scaling tests. We found significant genetic and phenotypic variation among D. ponderosae populations. Simple additive genetic variance was not the primary source of the observed variation, and dominance and epistasis contributed greatly to the genetic divergence of the two thermally-regulated traits. Hybrid breakdown was also observed in F₂ hybrid crosses between northern and southern populations, further indication of substantial genetic differences among clinal populations and potential reproductive isolation within D. ponderosae. Although it is unclear what maintains variation in the life-history traits, observed plasticity in thermally-regulated traits that are directly linked to rapid numerical change may contribute to the outbreak nature of D. ponderosae, particularly in a changing climate.     

Reproductive strategies and body shape in the European pond turtle (Emys orbicularis) from contrasting habitats in Italy

Comparisons within and among populations offer important insights into variation in life-history traits and possible adaptive patterns to environmental conditions. We present the results of observed differences in body size, body shape and patterns of reproduction in four separate populations of the European pond turtle Emys orbicularis in central and southern Italy – coastal ( n =3) and mountainous ( n =1) sites and pond ( n =2) and canal ( n= 2) habitats – to determine whether phenotypic plasticity affects reproductive output. Although we did not find any significant latitudinal variation in body size, we observed significant differences in body shape between canal (rounded body shape) and pond (elongated body shape) systems and smaller size with rounded shape in the mountainous population. Reproductive output is similar among populations (median=5 eggs per clutch), whereas reproductive investment (relative clutch mass to maternal body mass) is higher in the mountain population (one clutch per year) than in coastal populations (two clutches per year), suggesting differential trade-offs between geographic locality, elevation and habitat type. Turtle shell shape and geographic location together affect reproductive output in E. orbicularis in Italy.     

Correlation between time of flowering and phenotypic plasticity in Arabidopsis thaliana (Brassicaceae)

We observed substantial variation in the time of flowering among 13 populations of Arabidopsis thaliana (Brassicaceae) from an extensive latitudinal range when grown under uniform experimental conditions. The later the onset of flowering, the greater was potential reproduction. Later flowering plants also had greater plasticity in a host of morphological and physiological traits measured in nutrient-rich vs. nutrient-poor test environments. This relationship between flowering time and overall plasticity was only apparent for traits measured at the time of seed production, not at the time of flowering or earlier. At the time of seed production in this short-lived annual, the regression of a multivariate measure of overall plasticity on the time of flowering was linear and highly significant (r² = 0.90, P < 0.0001). These correlations among time of flowering, reproductive fitness, and plasticity support the idea that selection for late-flowering genotypes would select concomitantly for greater plasticity.     

Seasonality determines patterns of growth and age structure over a geographic gradient in an ectothermic vertebrate

Environmental variation connected with seasonality is likely to affect the evolution of life-history strategies in ectotherms, but there is no consensus as to how important life-history traits like body size are influenced by environmental variation along seasonal gradients. We compared adult body size, skeletal growth, mean age, age at first reproduction and longevity among 11 common frog (Rana temporaria) populations sampled along a 1,600-km-long latitudinal gradient across Scandinavia. Mean age, age at first reproduction and longevity increased linearly with decreasing growth season length. Lifetime activity (i.e. the estimated number of active days during life-time) was highest at mid-latitudes and females had on average more active days throughout their lives than males. Variation in body size was due to differences in lifetime activity among populations??individuals (especially females) were largest where they had the longest cumulative activity period??as well as to differences between populations in skeletal growth rate as determined by skeletochronological analyses. Especially, males grew faster at intermediate latitudes. While life-history trait variation was strongly associated with latitude, the direction and shape of these relationships were sex- and trait-specific. These context-dependent relationships may be the result of life-history trade-offs enforced by differences in future reproductive opportunities and time constraints among the populations. Thus, seasonality appears to be an important environmental factor shaping life-history trait variation in common frogs.     

Variable salinity tolerance in ascidian larvae is primarily a plastic response to the parental environment

Both phenotypic plasticity and local genetic adaptation may contribute to a species’ ability to inhabit different environmental conditions. While phenotypic plasticity is usually considered costly, local adaptation takes generations to respond to environmental change and may be constrained by strong gene flow. The majority of marine species have complex life-cycles with pelagic stages that might be expected to promote gene flow and plastic responses, and yet several notable examples of local adaptation have been found in species with broadcast larvae. In the ascidian, Ciona intestinalis (Linnaeus, 1767),—a common marine species with broadcast spawning and a short larval stage—previous studies have found marked differences in salinity tolerance of early life-history stages among populations from different salinity regimes. We used common-garden experiments to test whether observed differences in salinity tolerance could be explained by phenotypic plasticity. Adult ascidians from two low salinity populations [2–5 m depth, ~25 practical salinity units (PSU)], and two full salinity populations (25–27 m depth, ~31 PSU) were acclimated for 2–4 weeks at both 25 and 31 PSU. Gametes were fertilized at the acclimation salinities, and the newly formed embryos were transferred to 10 different salinities (21–39 PSU) and cultured to metamorphosis. Adult acclimation salinity had an overriding and significant effect on larval metamorphic success: tolerance norms for larvae almost fully matched the acclimation salinity of the parents, independent of parental origin (deep or shallow). However we also detected minor population differences that could be attributed to either local adaptation or persistent environmental effects. We conclude that differences in salinity tolerance of C. intestinalis larvae from different populations are driven primarily by transgenerational phenotypic plasticity, a strategy that seems particularly favourable for an organism living in coastal waters where salinity is less readily predicted than in the open oceans.     

A trade-off between reproduction and a condition-dependent sexually selected ornament in the house sparrow Passer domesticus

Reproductive effort was manipulated in a free-living population of house sparrows (Passer domesticus) to investigate the trade-off between reproductive investment and the expression of a condition-dependent sexually selected ornament. Phenotypic plasticity in the expression of this trait was related to the experimentally manipulated size of the brood reared by a male. Males that invested more in current reproduction subsequently became more attractive to females in this population as they showed a preference for males with smaller badges. This supports the argument that direct benefits are a primary focus for mate choice by females. Trade-offs between reproductive effort and the expression of sexual ornaments are a potentially important source of phenotypic variation in both sexual ornaments and life-history traits.     

Host responses in life-history traits and tolerance to virus infection in Arabidopsis thaliana

Knowing how hosts respond to parasite infection is paramount in understanding the effects of parasites on host populations and hence host-parasite co-evolution. Modification of life-history traits in response to parasitism has received less attention than other defence strategies. Life-history theory predicts that parasitised hosts will increase reproductive effort and accelerate reproduction. However, empirical analyses of these predictions are few and mostly limited to animal-parasite systems. We have analysed life-history trait responses in 18 accessions of Arabidopsis thaliana infected at two different developmental stages with three strains of Cucumber mosaic virus (CMV). Accessions were divided into two groups according to allometric relationships; these groups differed also in their tolerance to CMV infection. Life-history trait modification upon virus infection depended on the host genotype and the stage at infection. While all accessions delayed flowering, only the more tolerant allometric group modified resource allocation to increase the production of reproductive structures and progeny, and reduced the length of reproductive period. Our results are in agreement with modifications of life-history traits reported for parasitised animals and with predictions from life-history theory. Thus, we provide empirical support for the general validity of theoretical predictions. In addition, this experimental approach allowed us to quantitatively estimate the genetic determinism of life-history trait plasticity and to evaluate the role of life-history trait modification in defence against parasites, two largely unexplored issues.     

Local adaptation in brown trout early life-history traits: implications for climate change adaptability

Knowledge of local adaptation and adaptive potential of natural populations is becoming increasingly relevant due to anthropogenic changes in the environment, such as climate change. The concern is that populations will be negatively affected by increasing temperatures without the capacity to adapt. Temperature-related adaptability in traits related to phenology and early life history are expected to be particularly important in salmonid fishes. We focused on the latter and investigated whether four populations of brown trout (Salmo trutta) are locally adapted in early life-history traits. These populations spawn in rivers that experience different temperature conditions during the time of incubation of eggs and embryos. They were reared in a common-garden experiment at three different temperatures. Quantitative genetic differentiation (QST) exceeded neutral molecular differentiation (FST) for two traits, indicating local adaptation. A temperature effect was observed for three traits. However, this effect varied among populations due to locally adapted reaction norms, corresponding to the temperature regimes experienced by the populations in their native environments. Additive genetic variance and heritable variation in phenotypic plasticity suggest that although increasing temperatures are likely to affect some populations negatively, they may have the potential to adapt to changing temperature regimes.