Genetic Variability of Hymenoscyphus pseudoalbidus on Ash Leaf Rachises in Leaf Litter of Forest Stands in Poland

Two hundred and thirty cultures of Hymenoscyphus pseudoalbidus were obtained from ascospores created in apothecia on the previous years' ash leaf rachises in the stand floor. Fruiting bodies of the pathogen were collected in four regions of Poland differing by geographical location, the altitude above sea level and climatic conditions. Isolates were identified based on the sequences of ribosomal DNA (ITS1‐5.8S‐ITS2) and the calmodulin gene. Only the presence of H. pseudoalbidus was identified in the decaying ash stands in Poland; morphologically similar, saprotrophic species of H. albidus was absent. Intrapopulation and interpopulation genetic variability of isolates was determined based on 84 RAMS markers obtained using four primers. Genetic variability of the fungus populations, measured by the Dice coefficient of genetic similarity and the Shannon coefficient of genetic diversity, decreased along with a decrease in the location of isolate collection area above sea level. A significant dependency was shown between intrapopulation genetic variability of isolates and altitude of regions above sea level. The Mantel test excluded existence of dependence between geographical and genetic distance among populations (r = ?0.038, P = 0.55). A significant correlation was found between the genetic distances of individuals within populations and locations above sea level. Based on PCA and geographical location of populations, it was shown that populations create four distinct groups. amova showed that a majority of total genetic variability (65.80%) constitutes intrapopulation variability. Variability between populations was high (28.7%), and individual regions had a smallest influence (5.5%) on the level of total variability.     

内蒙古高原甘蒙锦鸡儿的遗传分化研究

对分布于内蒙古和林格尔和阿拉善的甘蒙锦鸡儿(Caragana opulens Kom)种群的叶片形态特性和遗传结构进行了比较研究。结果发现:从叶厚度、面积、长/宽、生物量及SLA来看,阿拉善种群与和林格尔种群之间存在明显变异,阿拉善种群比和林格尔种群保水能力强,对干旱的适应能力好。遗传结构比较研究发现,甘蒙锦鸡儿种群间发生明显的遗传分化(遗传相似度为0.711),表明生物对环境的适应是有分子基础的、是以遗传变异为基础的种群分化适应。     

Divergence of functional traits at early stages of development in Stipa tenacissima populations distributed along an environmental gradient of the Mediterranean

Assessing differences in plant functional traits (PFTs) along climatic gradients is potentially useful for understanding variation within and across populations, and for predicting their responses to climate change. This study investigates the intraspecific variability of several PFTs in Stipa tenacissima (Alpha grass) seedlings from different populations distributed across a climatic gradient. Seven populations from Tunisia to Spain within a 100–600 mm/year rainfall range were selected. Seedlings from each population were grown in a common garden. We expected the functional characteristics to differ among seedling populations according to their climatic gradient. The response patterns were helpful to predict acclimation and fitness under future climatic conditions in these populations. The seedling development analysis showed differences in PFTs among S. tenacissima populations. The biomass traits analysis revealed that higher above-ground biomass was related to higher below-ground development. The leaf traits proved that seedlings with longer leaf length would have less sclerophyllous leaves, a trade-off between productivity and drought resistance. The root traits analysis reflects seedling strategies to maximize resource uptake efficiency. PFTs showed several significant relationships with climatic conditions. The less rainfall, the higher plant allocation to root systems exploring soil. Higher mean temperatures were related to reduced root/plant development. The PFT analysis proves that species followed the ‘optimal partitioning theory’, in that plants preferentially allocate biomass to acquire the resource that most limits their development. However, both the environmental conditions and genetic diversity in S. tenacissima populations influenced seedling growth and behaviour to face ongoing climate change.

     

Quantitative variation within and among populations of Arabis serrata Fr. & Sav. (Brassicaceae)

Phenotypic and genetic variation within and among eight populations of Arabis serrata are documented in this study. This species shows great morphological variation throughout its geographical distribution in Japan. Plants are located in habitats with different types of soils and degree of disturbance. Half-sibs progenies from eight populations were collected and cultivated in a garden experiment. Nine morphological traits representing size and shape of rosette leaves were recorded. Univariate analyses of measured traits showed that phenotypic means differed among populations for all characters. Leaves of plants from disturbed habitats had the longest petioles (lanceolate) and plants from limestone habitats showed the most roundness in leaf shape (ovate). The northernmost populations always revealed the smallest leaves. Multivariate principal component analyses also showed that leaf shape and size varied among populations. The first three principal components explained 98.5% of the variation. Coefficients of variation had a very wide range and differed from one population to another. Some traits (e.g. leaf width/leaf length ratio) were consistently less variable while others (e.g. leaf area and petiole length) were more plastic. All traits had significant genetic variance in all populations. Intra-class correlation coefficients differed for most of the traits and each population presented a different range of values. Most of the leaf traits were intercorrelated in all the populations studied, although some populations were integrated more tightly for some traits. Populations of A. serrata are differentiated in phenotypic means but they display a mosaic of traits with slight morphological differences in each locality (i.e. a quantitative genetic variation). Some traits can be correlated to the habitats that they occupy but for some of them it is difficult to assign an actual adaptive value.     

PERSISTENCE OF AMBROSIA TRIFIDA POPULATIONS IN OLD FIELDS AND RESPONSES TO SUCCESSIONAL CHANGES

A population of Ambrosia trifida L. (Asteraceae) in an annually ploughed field and an adjacent 15-year old population in an old field were compared to determine how plant responses, genotypic composition, and genetic variability change in populations over successional time. The two populations were originally part of a large contiguous population in an annually ploughed field. When individuals from the two populations were grown from seed in a common garden, they showed several significant differences in characteristics indicating different genotypic compositions in the two populations. Individuals from the old field population showed earlier emergence, lower leaf mortality, and greater numbers of leaves, biomass, seed production, and reproductive allocation relative to plants from the annually ploughed field. When sown in the field in a reciprocal transplant experiment, individuals from the two populations also differed in patterns of emergence, survivorship, yield, and fecundity. When grown together in a pairwise competition experiment, individuals from the old field population showed competitive superiority with respect to growth and seed production. This genetic differentiation between populations of different successional ages may be explained by natural selection imposed by the changing environment over successional time. However, the history and characteristics of these populations are such that founder effects may also be important in explaining the differences between them. A comparison of levels of variability in 14 different characters of individuals of the two populations showed no evidence that genetic variability in A. trifida populations declined over successional time.     

Reproductive strategy and ploidy determine the genetic variability of Sorbus aria

Sorbus aria (L.) Crantz (common whitebeam) from the Canary Islands has not been characterised genetically. We analysed the genetic variability of 184 individuals belonging to seven natural populations of S. aria from the Canarian Archipelago and the Iberian Peninsula. Our main aims were to obtain essential information to enable the exploration of the genetic relationship between populations from the Canary Islands and the Iberian Peninsula; to establish the existence of a spatial genetic structure and formulate appropriate management and conservation genetics strategies. Genetic variation was analysed using nine polymorphic microsatellite loci. The Canary Island populations (triploids) were found to have very low genetic variability and to be considerably differentiated from the populations from the peninsula (diploid and triploid), although with a connection to the Sierra Nevada population in the south of the Peninsula. This population, in turn, had many different genotypes, which is indicative of the existence of various origins. The level of genetic diversity was higher in all-diploid populations, which, in addition, presented a greater interpopulation gene flow, possibly the result of a prevalence of sexual reproduction. On the other hand, the triploid populations presented lower levels of genetic variability, with a significant degree of fixed heterozygosity, possibly due to asexual reproduction, mainly by apomixis. The reproductive biology and ploidy appear to be responsible for the levels of genetic variability in S. aria.     

The importance of genetic variability and population differentiation in the Eurasian lynx Lynx lynx for conservation,in the context of habitat and climate change

• 1 The Eurasian lynx Lynx lynx occupies a variety of environmental and climatic conditions, and the majority of present‐day European populations have either recovered from severe demographic bottlenecks, or are living in fragmented habitat. These factors may have affected the genetic variability of lynx populations. We summarize available data on genetics, population status and ecology of these felids to shed light on the pattern and mechanisms behind their genetic variability and population differentiation in Europe.
• 2 Genetic studies conducted so far, based on mtDNA and microsatellites, have shown that the Eurasian lynx has low to moderate genetic variability. Variability is lowest in the north (Scandinavian bottlenecked population), but is also low in the Carpathian region. A trend towards loss of genetic variation has been noted in fragmented and reintroduced populations. Genetically, the populations are highly differentiated from each other.
• 3 There are clear relationships between the pattern of lynx genetic variability, differentiation between the populations, and such factors as population history (demographic bottlenecks), social interactions and habitat fragmentation. The genetic divergence between lynx populations is also strongly correlated with the depth and duration of snow cover.
• 4 Our review provides evidence that the lynx is undergoing significant genetic differentiation, due to several factors. To enable better planning of conservation programmes for the Eurasian lynx, researchers should identify the Evolutionarily Significant Units among its populations, using different classes of molecular markers.

     

Leaf trait associations with environmental variation in the wide‐ranging shrub Dodonaea viscosa subsp. angustissima (Sapindaceae)

Intra‐species variation in specific leaf area (SLA) and leaf area (LA) provides mechanistic insight into the persistence and function of plants, including their likely success under climate change and their suitability for revegetation. We measured SLA and LA in 101 Australian populations of the perennial shrub Dodonaea viscosa (L.) Jacq. subsp. angustissima (narrow‐leaf hop‐bush) (Sapindaceae). Populations were located across about a 1000 km north–south gradient, with climate grading from arid desert to mesic Mediterranean. We also measured leaves from 11 populations across an elevational gradient (300–800 m asl), where aridity and temperature decrease with elevation. We used regression and principal component analyses to relate leaf traits to the abiotic environment. SLA displayed clinal variation, increasing from north to south and correlated with latitude and the first principal component of joint environmental variables. Both SLA and LA correlated positively with most climatic and edaphic variables. Across latitude, LA showed more variability than SLA. Changes in leaf density and thickness may have caused the relative stability of SLA. Only LA decreased with elevation. The absence of a SLA response to elevation could be a consequence of abiotic conditions that favour low SLA at both ends of the elevational gradient. We demonstrated that the widely distributed narrow‐leaf hop‐bush shows considerable variability in LA and SLA, which allows it to persist in a broad environmental envelope. As this shrub is widely used for revegetation in Australia, South America and the Asia‐Pacific region, our results are consistent with the notion that seed used to revegetate mesic environments could be sourced from more arid areas to increase seed suitability to future climate change.     

First Report on RAPDs Patterns Able to Differentiate Some Argentinean Species of Section Algarobia (Prosopis, Leguminosae)

Prosopis species constitute a very important resource in arid and semiarid regions. Some species of section Algarobia hybridise and introgress naturally in areas of sympatry. According to previous isoenzymatic studies these species have high variability within populations. However, the genetic differentiation among species was very low, and these markers failed to provide diagnostic loci for species recognition. Here we analysed by the RAPD technique natural populations of Prosopis alba, P. ruscifolia, P. nigra, P. flexuosa, and P. vinalillo with the purpose of obtaining markers for species and hybrid identification, by analysing the distribution of genetic diversity within and among species. Genetic variability (H = 0.12-0.26) was similar in all populations. Genetic differentiation among populations (FST = 0.39) was highly significant. Hierarchical analysis of genetic structure performed by Wright (1978) method and analysis of molecular variance (AMOVA) indicated that the diversity among populations within species is low (4-13%) and most genetic diversity (54-61%) occurs within populations. The differentiation among species is intermediate (26-42%) between the previous components but highly significant. Five bands provided a tool for identifying any of the species studied, with the exception of P. vinalillo. The difficulty in diagnosing this species is discussed in reference to the hypothesis of its hybrid origin.     

Temporal variation in genetic diversity and effective population size of Mediterranean and subalpine Arabidopsis thaliana populations

Currently, there exists a limited knowledge on the extent of temporal variation in population genetic parameters of natural populations. Here, we study the extent of temporal variation in population genetics by genotyping 151 genome-wide SNP markers polymorphic in 466 individuals collected from nine populations of the annual plant Arabidopsis thaliana during 4 years. Populations are located along an altitudinal climatic gradient from Mediterranean to subalpine environments in NE Spain, which has been shown to influence key demographic attributes and life cycle adaptations. Genetically, A. thaliana populations were more variable across space than over time. Common multilocus genotypes were detected several years in the same population, whereas low-frequency multilocus genotypes appeared only 1 year. High-elevation populations were genetically poorer and more variable over time than low-elevation populations, which might be caused by a higher overall demographic instability at higher altitudes. Estimated effective population sizes were low but also showed a significant decreasing trend with increasing altitude, suggesting a deeper impact of genetic drift at high-elevation populations. In comparison with single-year samplings, repeated genotyping over time captured substantially higher amount of genetic variation contained in A. thaliana populations. Furthermore, repeated genotyping of populations provided novel information on the genetic properties of A. thaliana populations and allowed hypothesizing on their underlying mechanisms. Therefore, including temporal genotyping programmes into traditional population genetic studies can significantly increase our understanding of the dynamics of natural populations.     

Analysis of genetic diversity and structure in Ethiopian populations of Phytolacca dodecandra using RAPD

The genetic diversity and structure in 17 wild populations (249 individuals) of Phytolacca dodecandra (endod) sampled along altitudinal gradients of 1600-3000 meters above sea level (m.a.s.l.) in Ethiopia was studied using random amplified polymorphic DNA (RAPD). A total of 70 polymorphic loci (P) scored from 12 RAPD primers were used to calculate different diversity indices within and between populations, habitats, geographical regions, climatic zones and altitude groups. The number of polymorphic loci and overall Shannon information measure (H) in the populations varied from 30 to 55 and from 0.228 to 0.418, respectively. In general, differences in population variability were found significantly correlated to effective population size. Both P and H were significantly higher in an undisturbed than in a disturbed habitat, and in the lowland and central-highland than in the highland altitude group. However, for both parameters the differences were not statistically significant between regions and climatic zones. Genetic distance between populations varied from 0.301 to 0.628. Cluster analysis performed using the genetic distance matrix revealed a clear separation of the highland populations (2501-3000 m.a.s.l.) from those of the lowland/central-highlands (1600-2500 m.a.s.l.) irrespective of their geographical regions and climatic zones. Analysis of molecular variance (AMOVA) indicated that differences in habitat, geographical regions and climatic zones explained 4.6%, 2.5% and 4.6%, respectively. But none of these differences were significant. Altitude explained 17.2% of the total variance and was highly significant. The data, therefore, clearly indicated the association of genetic structure in endod with altitude. The proportion of RAPD variation found among populations (21.2-35.0%) was somewhat intermediate between values reported for selfing and outcrossing species. The fixation index (FST) values (0.350 to 0.384) indicated very high genetic differentiation among populations.     

Is the genetic diversity of small scattered forest tree populations at the southern limits of their range more prone to stochastic events? A wild cherry case study by microsatellite-based markers

Wild cherry (Prunus avium L.) is a widespread, partially asexual, noble hardwood European species characterized by a scattered distribution, small population sizes, and human exploitation for its valuable wood. These characteristics, especially at the southern limits of the species natural distribution where additional varying stresses may occur, render P. avium populations prone to potential stochastic, genetic, and demographic events. In this study, we used dominant inter simple sequence repeat (ISSR) and codominant simple sequence repeat (SSR) markers to infer the genetic structure of P. avium. Five populations from northern Greece were evaluated based on 46 ISSR and 11 SSR loci. Populations presented a relatively high level of genetic variation, with a mean genetic diversity of H _e?=?0.166 and H _e?=?0.740 regarding ISSR and SSR analysis, respectively. We observed moderate population differentiation for ISSR (G _ST?=?0.113) and SSR (F _ST?=?0.097) markers. AMOVA also detected significant differentiation among populations for ISSRs (?? _ST?=?0.338) and SRRs (?? _ST?=?0.162). According to linkage disequilibrium analysis, estimates of effective population size were generally sufficient for maintaining extant genetic variability and evolutionary potential. A possible bottleneck was detected for only one population. In general, it appears that despite the particular characteristics of the P. avium populations studied, genetic stochasticity events were not apparent. The studied populations, located at the rear edge of the species European distribution, reveal a wealth of genetic variation that is very valuable for the genetic conservation of local adaptive gene complexes, especially under contemporary climatic change scenarios.     

In situ marker‐based assessment of leaf trait evolutionary potential in a marginal European beech population

Evolutionary processes are expected to be crucial for the adaptation of natural populations to environmental changes. In particular, the capacity of rear edge populations to evolve in response to the species limiting conditions remains a major issue that requires to address their evolutionary potential. In situ quantitative genetic studies based on molecular markers offer the possibility to estimate evolutionary potentials manipulating neither the environment nor the individuals on which phenotypes are measured. The goal of this study was to estimate heritability and genetic correlations of a suite of leaf functional traits involved in climate adaptation for a natural population of the tree Fagus sylvatica, growing at the rear edge of the species range. Using two marker‐based quantitative genetics approaches, we obtained consistent and significant estimates of heritability for leaf phenological (phenology of leaf flush), morphological (mass, area, ratio mass/area) and physiological (δ¹³C, nitrogen content) traits. Moreover, we found only one significant positive genetic correlation between leaf area and leaf mass, which likely reflected mechanical constraints. We conclude first that the studied population has considerable genetic diversity for important ecophysiological traits regarding drought adaptation and, second, that genetic correlations are not likely to impose strong genetic constraints to future population evolution. Our results bring important insights into the question of the capacity of rear edge populations to evolve.     

The genetic signature of ecologically different grassland Lepidopterans

The level of genetic diversity found for species is strongly influenced by properties of the species’ ecology, abundance and behaviour (as dispersal). To address this coherence, we selected twenty-two grassland butterfly and burnet moth species, which were previously analysed by allozyme electrophoresis (using 15–25 loci per species) over a study area in western Germany with adjoining areas of Luxembourg and north-eastern France. For this study area, we calculated the species’ specific climatic niche breadths and derived various ecological parameters from literature and own field observations. The obtained parameters of genetic diversity (heterozygosity, number of alleles and percentage of polymorphic loci), genetic differentiation (D _est as well as F _ST and F _IS values as proxis for genetic differentiation among populations and inbreeding within populations), as well as ecological and climatic niche dimensions did not show significant differences among the different Lepidoptera families; therefore taxonomic assignment apparently has a negligible influence on the genetic structure of taxa. Genetic diversity and differentiation showed a significant correlation with the ecological and climatic niche-breadth of species in many cases: generalistic species with rather unspecific ecological characteristics and climatic niche had higher genetic diversities and tend to have lower differentiation and inbreeding, whereas specialist taxa (i.e. with narrow ecological and climatic niches) have lower genetic diversities and higher differentiation and inbreeding. The results might reflect contrasting population structures of specialist species with lower abundances compared with the more common generalists. The more restricted and isolated occurrence of specialists might consequence a reduction in genetic diversity and an increase in genetic differentiation among local populations. In contrast, generalists with unspecific habitat requirements occur in higher abundances and in consequence show a more homogenous genetic structure with higher diversities.     

Phenotypic variability along a climatic gradient in a perennial afrotropical rainforest understorey herb

Plants evolved in response to climatic conditions, which shaped their geographic distribution, functional traits and genetic composition. In the face of climatic changes, plants have to react by either genetic adaptation, phenotypic plasticity or geographic range shift. Their reaction potential depends on their phenotypic and genetic variability which can be evaluated through regional scale trait estimates, however, little is known here about tropical African plants. To start filling this gap of knowledge, the aim of this study was to estimate the phenotypic variability in a widespread perennial herb from the understorey of tropical African rainforests: Sarcophrynium prionogonium (Marantaceae). We surveyed 211 individuals from eight populations distributed across four sites in Cameroon covering largely the climatic range of the study species. Fourteen key functional traits were measured monthly for 18 months (2013–2014). Individuals of the study species persisted under a wide range of environmental conditions and there was considerable intraspecific variability within and across populations. Still, plant vegetative growth decreased with dryness. Productivity was positively related to a combination of high temperatures and precipitation and under these favourable conditions strongly shaped by light. Seasonal patterns of flower and fruit development were strongly associated with seasonal rainfall. Thus, the predicted increased dryness in tropical Africa might be disadvantageous for the study species. In the past, plants reacted to such aridification tendencies (e.g. during the Pleistocene glacial cycles) by retracting to moist refugia. The current climatic changes, however, being much faster and larger might provide new challenges.     

Genetic variability is correlated with population size and reproduction in American wild-rice (Zizania palustris var. palustris, Poaceae) populations

American wild-rice (Zizania palustris var. palustris) has served as a staple for indigenous North Americans for thousands of years, but has had significant habitat losses in recent centuries. We investigated genetic variability among 17 wild-rice populations in northern Wisconsin using 13 isozyme markers. We then compared these genetic patterns to differences in habitat and population characteristics and phenotypic variation in plant growth and reproduction across sites. Wild-rice's mean genetic diversity (0.15) is moderate compared to wind-pollinated outcrossers but lower than the mean (0.20) reported for the Poaceae. Estimated inbreeding coefficients within populations (f) average 0.12 but vary greatly among the populations (from -0.44-0.52), suggesting heterogeneous population histories. Larger populations in larger lakes express higher levels of genetic variability and smaller inbreeding coefficients than smaller or more isolated populations. The number of panicles per plant is also higher in populations with greater genetic variability. Estimated genetic differentiation among the 17 populations (F(ST)) was high (0.30), suggesting limited gene flow among drainages. Wild-rice population size and degree of isolation have opposing effects on its genetic variability, and plant performance is positively associated with genetic variability.     

Analysis of genotypic diversity inCercospora beticola Sacc. field isolates

Genetic variability and population structure ofCercospora beticola, the causal agent of Cercospora leaf spot in sugarbeet, from four sugarbeet-growing regions of Greece were investigated using growth rate, pathogenicity, and mini- and microsatellite DNA fingerprinting. Mycelial growth and pathogenicity were very diverse within and between groups, and no correlation was found between these features and the geographic origin of the isolates. High diversity was found by micro- and minisatellite fingerprinting, with an average gene diversity of 0.21, and no significant differences among populations. Among the 46 isolates, 45 different genotypes were identified, showing a high degree of genotype diversity. Analysis of the genetic profiles provided no evidence for regional patterns of variation (ΦF_ST=0.01, P=0.261) and the analysis of molecular variation (AMOVA) revealed that genetic variability was due mainly to variations within (99%) rather than between (1%) populations. Such a low level of genetic differentiation is reflected by a migration rate value Nm of 4.7. The high migration rate cannot be referred to splash dispersed conidia. To justify the absence of a regional structure in these C.beticola populations, we must suppose the existence of a long-distance means of dispersal, such as seed transmission and/or man mediated transmission.     

High levels of genetic differentiation and selfing in the Brazilian cerrado fruit tree Dipteryx alata Vog. (Fabaceae)

Dipteryx alata is a native fruit tree species of the cerrado (Brazilian savanna) that has great economic potential because of its multiple uses. Knowledge of how the genetic variability of this species is organized within and among populations would be useful for genetic conservation and breeding programs. We used nine simple sequence repeat (SSR) primers developed for Dipteryx odorata to evaluate the genetic structure of three populations of D. alata located in central Brazil based on a leaf sample analysis from 101 adults. The outcrossing rate was evaluated using 300 open-pollinated offspring from 25 seed-trees. Pollen dispersal was measured by parentage analysis. We used spatial genetic structure (SGS) to test the minimal distance for harvesting seeds in conservation and breeding programs. Our data indicate that the populations studied had a high degree of genetic diversity and population structure, as suggested by the high level of divergence among populations . The estimated outcrossing rate suggested a mixed mating system, and the intrapopulation fixation index was influenced by SGS. We conclude that seed harvesting for genetic conservation and breeding programs requires a minimum distance between trees of 196 m to avoid collecting seeds from related seed-trees.     

Genetic variability, population size and isolation of distinct populations in the freshwater fish Cottus gobio L.

Analysis of allozyme data of the European freshwater fish Cottus gobio showed marked genetic differentiation across drainage basins in northeastern Bavaria, which points to the existence of at least two cryptic taxa. Genetic variability within populations differed significantly between these two taxa, which could be due to historical (bottlenecks) or ecological reasons (population size). To distinguish between these two hypotheses we sampled 12 distinct populations from Rhine, Elbe and Danube drainages. Using allozyme data we examined the influence of population size and isolation on genetic variability within populations. We used spatial extent of populations (patch size) as a measure for population size. To estimate isolation we calculated a compound measure which took into account patch size and distance to all neighbouring populations. Both patch size and isolation were highly correlated with genetic variability, explaining ≈95% of the variance of genetic variability within populations. Furthermore, analysis of covariance suggests that the difference in genetic variability between taxa may be explained by differences in population size.     

VARIATION IN LEAF DISSECTION AND LEAF ENERGY BUDGETS AMONG POPULATIONS OF ACHILLEA FROM AN ALTITUDINAL GRADIENT

The degree of leaf dissection differs dramatically among populations of the Achillea millefolium complex along an altitudinal gradient in the Sierra Nevada. The purpose of this study was to determine whether there was a genetic basis to differences in leaf shape among populations, and also to determine the importance of genetic variability within populations, plastic responses of leaf shape to the growth environment, and genetic differences among populations in plastic response to the environment. A second major goal of the research was to investigate the effects of differences in leaf dissection on the capacity for leaf temperatures to become uncoupled from air temperatures. Greenhouse experiments using clonal replicates of plants collected at different altitudes revealed that there were genetic differences among populations in the degree of dissection, and that other sources of phenotypic variation, such as plasticity, were also significant. Leaves from the highest altitude population had the most compact shape under all conditions, while those from lower altitude populations were always more open and highly dissected. In both simulations and actual measurements the dissected leaves of low altitude plants remained close to air temperatures, while the compact leaves of high altitude plants had the capacity to warm up substantially above air temperatures.