Developmental time and size-related traits in Drosophila buzzatii along an altitudinal gradient from Argentina

Clinal analysis for fitness-related traits provides a well-known approach to investigate adaptive evolution. Several fitness-related traits (developmental time, thorax length, wing length and wing loading) were measured at two laboratory generations (G7 and G33) of D. buzzatii from an altitudinal gradient from northwestern Argentina, where significant thermal differences persist. Developmental time (DT) was positively correlated with altitude of origin of population. Further, DT was negatively correlated with maximal mean temperature at the site of origin of population, and this thermal variable decreases with altitude. Wing loading tended to be larger in highland than in lowland populations, suggesting that flight performance is subject to stronger selection pressure in highland populations. Developmental time showed a significant increase with laboratory generation number. There was no significant correlation between developmental time and body size across populations along the altitudinal cline of DT. This result illustrates that developmental time and body size do not always evolve in the same direction, even though both traits are often positively and genetically correlated in a well-known tradeoff in Drosophila.     

Contrasting patterns of intraspecific trait variability in native and non-native plant species along an elevational gradient on Tenerife,Canary Islands

Background and AimsNon-native plant species are not restricted to lowlands, but increasingly are invading high elevations. While for both native and non-native species we expected variability of plant functional traits due to the changing environmental conditions along elevational gradients, we additionally assumed that non-native species are characterized by a more acquisitive growth strategy, as traits reflecting such a strategy have been found to correlate with invasion success. Furthermore, the typical lowland introduction of non-native species coming from multiple origins should lead to higher trait variability within populations of non-native species specifically at low elevations, and they might therefore occupy a larger total trait space.MethodsAlong an elevational gradient ranging from 55 to 1925 m a.s.l. on Tenerife, we collected leaves from eight replicate individuals in eight evenly distributed populations of five native and six non-native forb species. In each population, we measured ten eco-morphological and leaf biochemical traits and calculated trait variability within each population and the total trait space occupied by native and non-native species.Key ResultsWe found both positive (e.g. leaf dry matter content) and negative (e.g. leaf N) correlations with elevation for native species, but only few responses for non-native species. For non-native species, within-population variability of leaf dry matter content and specific leaf area decreased with elevation, but increased for native species. The total trait space occupied by all non-native species was smaller than and a subset of that of native species.ConclusionsWe found little evidence that intraspecific trait variability is associated with the success of non-native species to spread towards higher elevations. Instead, for non-native species, our results indicate that intermediate trait values that meet the requirements of various conditions are favourable across the changing environmental conditions along elevational gradients. As a consequence, this might prevent non-native species from overcoming abruptly changing environmental conditions, such as when crossing the treeline.     

Genetic variation and plasticity of thorax length and wing length in Drosophila aldrichi and D. buzzatii

Reaction norms across three temperatures of development were measured for thorax length, wing length and wing length/thorax length ratio for ten isofemale lines from each of two populations of Drosophila aldrichi and D. buzzatii. Means for thorax and wing length in both species were larger at 24 °C than at either 18 °C or 31 °C, with the reduction in size at 18 °C most likely due to a nutritional constraint. Although females were larger than males, the sexes were not different for wing length/thorax length ratio. The plasticity of the traits differed between species and between populations of each species, with genetic variation in plasticity similar for the two species from one locality, but much higher for D. aldrichi from the other. Estimates of heritabilities for D. aldrichi generally were higher at 18 °C and 24 °C than at 31 °C, but for D. buzzatii they were highest at 31 °C, although heritabilities were not significantly different between species at any temperature. Additive genetic variances for D. aldrichi showed trends similar to that for heritability, being highest at 18 °C and decreasing as temperature increased. For D. buzzatii, however, additive genetic variances were lowest at 24 °C. These results are suggestive that genetic variation for body size characters is increased in more stressful environments. Thorax and wing lengths showed significant genetic correlations that were not different between the species, but the genetic correlations between each of these traits and their ratio were significantly different. For D. aldrichi, genetic variation in the wing length/thorax length ratio was due primarily to variation in thorax length, while for D. buzzatii, it was due primarily to variation in wing length. The wing length/thorax length ratio, which is the inverse of wing loading, decreased linearly as temperature increased, and it is suggested that this ratio may be of greater adaptive significance than either of its components.     

Variation and covariation among life-history traits in Rumex acetosella from a successional old-field gradient

In this study morphological variation and the potential for competition to affect biomass and seedling selection of the families of five populations of Rumex acetosella L. sampled along a successional old-field gradient have been investigated. Seeds from 25 families were submitted to four competitive regimes: no competition (one plant per pot), medium competition (two plants/ pot taking plants from the same population), high within-population competition (four individuals from the same population in a pot) and high between-population competition (four individuals from two different populations in a pot). Eight traits were analysed after 3 months of growth for variation among families within populations. A significant difference among families within the two older populations was recorded for sexual biomass and related components. High sensitivity of these traits to density was observed in all populations except the youngest, suggesting specialization to particular environmental conditions in late successional populations, and a good adaptive capacity to buffer environmental variation in the pioneer population. Little significant interaction between competitive regimes and families within populations was found, i.e. genotypes within each population showed little variation in their response to environmental variation. Genotypic variance decreased with increasing competitive conditions for the majority of the traits. However, the percentage of variance in sexual reproduction explained by family was stable among treatments. Tradeoffs between vegetative reproduction and sexual reproduction were recorded at the population level along the successional gradient, with increasing competitive conditions. As succession proceeds, we observed a decrease in sexual reproduction and an increase in vegetative reproduction. At the family level, correlation among traits were similar when plants were grown in the absence of competition and at high density, with a significant negative correlation between sexual reproduction and vegetative reproduction. For both sprout number and sexual biomass, the performance of families grown under all the treatments was positively correlated. Together these results indicate allocational constraints on the reproductive biology of R. acetosella that may be favoured by natural selection and have influenced population differentiation along the successional gradient. However, they also revealed that the potential exists for evolutionary specialization through plasticity, in response to variation in environmental conditions.     

Local adaptation and cogradient selection in the alpine plant, Poa hiemata, along a narrow altitudinal gradient

Alpine environments are particularly susceptible to environmental changes associated with global warming but there is potential for alpine plants to adapt to warming if local adaptation occurs and gene flow allows genotypes adapted to low altitudes to colonize higher altitude sites. Here we examine the adaptive potential of a common alpine grass, Poa hiemata, within the restricted alpine habitat of Australian mountains, across a narrow altitudinal gradient replicated in three areas. Grasses at high altitude sites had shorter leaf lengths and larger circumferences than those at lower sites. Transplant experiments with clonal material and plants grown from seed indicated that these differences were partly genetic, with environmental and genetic factors both contributing to the differences between altitudes. Differences in altitudinal forms were also evident in a common garden experiment. Plants showed a home-site advantage in terms of survival. A fitness analysis indicated that at high altitude sites, selection favored plants with short leaves and larger circumferences, whereas these traits were selected in the opposite direction at the low altitude sites. These findings indicate cogradient selection and potential for both plastic and genotypic shifts in response to climate change in P. hiemata.     

Genetic and phenotypic correlations among size-related traits, and heritability variation between body parts in Drosophila buzzatii

Recent studies have shown that body size is a heritable trait phenotypically correlated with several fitness components in wild populations of the cactophilic fly Drosophila buzzatii. To obtain further information on size-related variation, heritabilities as well as genetic and phenotypic correlations among size-related traits of several body parts (head, thorax and wings) were estimated. The study was carried out on an Argentinean natural population in which size-related selection was previously detected. The genetic parameters were estimated using offspring-parent regressions (105 families) in the laboratory G₂ generation of a sample of wild flies. The traits were also scored in Wild-Caught Flies (WCF). Laboratory-Reared Flies (LRF) were larger and less variable than WCF. Although heritability estimates were significant for all traits, heritabilities were higher for thorax-wing traits than for head traits. Phenotypic and genetic correlations were all positive. The highest genetic correlations were found between traits which are both functionally and developmentally related. Genetic and phenotypic correlations estimated in the lab show similar correlation patterns (r = 0.49; TP = 0.02, Mantel's test). However, phenotypic correlations were found to be typically larger in WCF than in LRF. The genetic correlation matrix estimated in the relatively homogeneous lab environment is not simply a constant multiplicative factor of the phenotypic correlation matrix estimated in WCF. This revised version was published online in July 2006 with corrections to the Cover Date.     

Local adaptation of stress related traits in Drosophila buzzatii and Drosophila simulans in spite of high gene flow

We addressed the question if local adaptation to a thermal gradient is possible in spite of a high gene flow among closely spaced populations of two species of Drosophila from the island of La Gomera (Canary Islands). Variation in multiple traits related to stress resistance in different life stages was measured in both species in flies collected from five localities at different altitudes and thereby with different climatic conditions. Based on microsatellite loci, the populations were not genetically differentiated. However, 18 of the 24 independent traits measured showed significant differentiation among populations of Drosophila buzzatii, but only nine of 25 for Drosophila simulans. This difference in the number of traits might reflect higher habitat specificity and thus higher potential for local adaptation of D. buzzatii than D. simulans. We found clinal variation, as some traits showed significant linear regressions on altitude, but more on altitude cubed.     

Predictability rather than amplitude of temperature fluctuations determines stress resistance in a natural population of Drosophila simulans

The adaptability of organisms to novel environmental conditions depends on the amount of genetic variance present in the population as well as on the ability of individuals to adjust their phenotype through phenotypic plasticity. Here, we investigated the phenotypic plasticity induced by a single generation's exposure to three different temperature regimes with respect to several life‐history and stress‐resistance traits in a natural population of Drosophila simulans. We studied a constant as well as a predictably and an unpredictably fluctuating temperature regime. We found high levels of phenotypic plasticity among all temperature regimes, suggesting a strong influence of both temperature fluctuations and their predictability. Increased heat tolerance was observed for flies developed in both types of fluctuating thermal environments compared with flies developed in a constant environment. We suggest that this was due to beneficial hardening when developing in either fluctuating temperature environment. To our surprise, flies that developed in constant and predictably changing environments were similar to each other in most traits when compared to flies from the unpredictably fluctuating environment. The unpredictably changing thermal environment imposed the most stressful condition, resulting in the lowest performance for stress‐related traits, even though the absolute temperature changes never exceeded that of the predictably fluctuating environment. The overall decreased stress resistance of flies in the unpredictably fluctuating environment may be the consequence of maladaptive phenotypic plasticity in this setting, indicating that the adaptive value of plasticity depends on the predictability of the environment.     

红池坝草地常见物种叶片性状沿海拔梯度的响应特征

叶片性状是决定植物光合能力和羧化能力的关键因素,研究叶片性状在海拔梯度上的变化特征是解释植物对于环境变化的适应策略的重要手段。本文以分布于红池坝(10958′E, 3130′ N)草地的5个常见物种红三叶(Trifolium pratense)、老鹳草(Geranium wilfordii)、紫菀(Aster tataricus)、火绒草(Leontopodium leontopodioides)和绣线菊(Spiraea prunifolia)为研究对象,分析了所有物种(n=56)和不同物种的叶片比叶重(LMA)、叶氮含量(单位面积氮含量Narea、单位重量氮含量Nmass)以及叶片δ13C含量沿海拔梯度(815-2545m)的变化趋势及叶片性状之间的关系。研究结果表明：所有物种样品(n=56)的比叶重(LMA)、Narea和δ13C含量沿海拔梯度的增加呈显著增加趋势;Nmass沿海拔梯度的变化趋势不明显;δ13C含量与LMA、Narea呈现极显著正相关关系;不同物种的叶片性状沿着海拔梯度的响应特征有所不同,绣线菊(S. prunifolia)和老鹳草(G. wilfordii)的叶片性状沿海拔梯度的分布规律与所有物种(n=56)样品分布规律一致,红三叶(T. pratense)、紫菀(A. tataricus)、火绒草(L. leontopodioides)的各叶片性状沿海拔梯度的分布特征有所不同。     

No patterns in thermal plasticity along a latitudinal gradient in Drosophila simulans from eastern Australia

Phenotypic plasticity may be an important initial mechanism to counter environmental change, yet we know relatively little about the evolution of plasticity in nature. Species with widespread distributions are expected to have evolved higher levels of plasticity compared with those with more restricted, tropical distributions. At the intraspecific level, temperate populations are expected to have evolved higher levels of plasticity than their tropical counterparts. However, empirical support for these expectations is limited. In addition, no studies have comprehensively examined the evolution of thermal plasticity across life stages. Using populations of Drosophila simulans collected from a latitudinal cline spanning the entire east coast of Australia, we assessed thermal plasticity, measured as hardening capacity (the difference between basal and hardened thermal tolerance) for multiple measures of heat and cold tolerance across both adult and larval stages of development. This allowed us to explicitly ask whether the evolution of thermal plasticity is favoured in more variable, temperate environments. We found no relationship between thermal plasticity and latitude, providing little support for the hypothesis that temperate populations have evolved higher levels of thermal plasticity than their tropical counterparts. With the exception of adult heat survival, we also found no association between plasticity and ten climatic variables, indicating that the evolution of thermal plasticity is not easily predicted by the type of environment that a particular population occupies. We discuss these results in the context of the role of plasticity in a warming climate.     

Plasticity of functional traits varies clinally along a rainfall gradient in Eucalyptus tricarpa

Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in south‐eastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ¹³C and δ¹⁸O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.     

Variation in genetic architecture of olfactory behaviour among wild-derived populations of Drosophila melanogaster

Odour-guided behaviour is a quantitative trait determined by many genes that are sensitive to gene-environment interactions. Different natural populations are likely to experience different selection pressures on the genetic underpinnings of chemosensory behaviour. However, few studies have reported comparisons of the quantitative genetic basis of olfactory behaviour in geographically distinct populations. We generated isofemale lines of Drosophila melanogaster from six populations in Argentina and measured larval and adult responses to benzaldehyde. There was significant variation within populations for both larval and adult olfactory behaviour and a significant genotype x sex interaction (GSI) for adult olfactory behaviour. However, there is substantial variation in the contribution of GSI to the total phenotypic variance among populations. Estimates of evolvability are orders of magnitude higher for larvae than for adults. Our results suggest that the potential for evolutionary adaptation to the chemosensory environment is greater at the larval feeding stage than at the adult reproductive stage.     

太白山栎属树种气孔特征沿海拔梯度的变化规律

气孔是植物与外界环境进行水分和气体交换的主要通道,调节植物碳同化和水分散失的平衡关系,在一定程度上反映植物对外界环境变化的适应。沿太白山北坡1100—2300 m海拔,测定4种栎属树种的气孔性状,分析气孔性状沿海拔的变化规律和其对环境因子的响应。结果表明:(1)气孔密度与气孔长度间的负相关在4个树种间均显著存在(P0.05);除栓皮栎(Quercus variabilis)外,气孔密度与潜在气孔导度指数的正相关关系均达显著水平;而气孔宽度与气孔长度之间只在栓皮栎和锐齿栎(Q. aliena var. acuteserrata)达到显著水平。(2)栓皮栎和槲栎(Q. aliena)的气孔长度和宽度随海拔升高而下降,气孔密度、潜在气孔导度指数增加,辽东栎(Q. wutaishansea)变化形式则相反;锐齿栎气孔宽度减小,其余性状沿海拔呈单峰变化,在约1600 m处气孔长度达到最小值,气孔密度和潜在气孔导度指数达到最大值。(3)与土壤因子相比,气孔性状主要受气候因素的影响。潜在气孔导度指数与大气温度、空气湿度成极显著正相关(P0.01),与降水量显著负相关(P0.05)。其中,空气相对湿度是影响潜在气孔导度指数的主要因素,能够解释气孔变异的22.9%。本研究结果对于深入认识秦岭太白山地区栎属树种对环境变化的响应和适应提供理论证据。     

Correlated changes in thermotolerance traits and body color phenotypes in montane populations of Drosophila melanogaster: analysis of within- and between-population variations

Thermotolerance traits vary across geographical gradients but there is a lack of clinal variation in some Drosophila species. Thus, it is not clear whether thermotolerance or other correlated traits are the target of natural selection. In order to test selection responses, we investigated body melanization and thermotolerance traits in six altitudinal populations of Drosophila melanogaster . Based on rearing different geographical populations under uniform growth conditions at 21 °C (common garden experiments), clinal variations for cold resistance are in the direction opposite to heat resistance along an altitudinal gradient, that is darker flies from highland populations evidenced higher levels of cold resistance while lowland populations showed higher heat resistance. Phenotypic plastic responses for body melanization at 17–28 °C showed significant correlations with thermotolerance traits. At 17 °C, regression coefficients as a function of altitude are highly significant and positive for cold resistance but negative for heat knockdown. However, for flies reared at 28 °C, there is no elevational change in melanization as well as thermotolerance traits. Thus, both genetic and plastic changes of body melanization and thermotolerance traits suggest a correlated selection response. Further, within-population analyses of body melanization (based on dark, intermediate and light color phenotypes) showed significant associations with thermotolerance traits. Correlated variations in body melanization and thermal tolerances are associated with climatic thermal variability ( T _cv) but not with T _min. or T _max. along an altitudinal gradient.     

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.     

Variation in P-content in aquatic plant tissues offers an efficient tool for determining plant growth strategies along a resource gradient

1. The application of functional ecology models to aquatic plants often relies on morphological and life‐history traits which may reflect, in part, the phenotypic plasticity displayed by aquatic plants. The present study was designed to evaluate the use of physiological traits, such as nutrition patterns, to describe aquatic plant strategies along a gradient of increasing resource availablity. 2. Taking phosphorus (P) as an example, nutrition‐use efficiencies were evaluated in five species, through the P‐content in plant tissues, the variations in P‐content according to nutrient availability and the perenniality of P‐storage. Plasticity in P‐storage was also investigated in Ranunculus peltatus, a morphologically highly plastic species. 3. In 2001, P‐content was analysed in Callitriche hamulata, C. obtusangula, C. platycarpa, Elodea nuttallii and R. peltatus tissue samples. These five species were sampled at nine different sites in streams along an increasing resource gradient in the Northern Vosges Biosphere Reserve (NE France). Variations of P‐content in the roots, stems and dissected and floating leaves of R. peltatus were also studied. 4. Only C. platycarpa and R. peltatus were found to occur in low nutrient availability conditions. Callitriche hamulata, C. obtusangula and E. nuttallii were restricted to mesotrophic and eutrophic sites. The highest nutrient‐use efficiency was found for E. nuttallii which was able to adapt its P‐storage to varying resource availabilities. Ranunculus peltatus was able to store high concentrations of P, but its P‐integration within the vegetative structure was less efficient under eutrophic conditions. Callitriche spp. appeared to have relatively low nutrient‐use efficiencies, although C. obtusangula displayed a high P‐content. While P was stored preferentially in roots in R. peltatus populations occurring in nutrient‐rich sites, there was no particular P‐storage organ for populations from nutrient‐poor sites. 5. On the basis of P‐usage, R. peltatus and E. nuttallii presented competitor traits, C. hamulata and C. platycarpa displayed stress‐tolerant nutrient signatures and for C. obtusangula, ruderal or competitor characteristics dominated. The use of physiological traits, such as nutrition patterns, may provide valuable, complementary information about aquatic plant strategies, independent from the influence of morphological trait plasticity often displayed by these plants.