Decoupled phenotypic variation between floral and vegetative traits: distinguishing between developmental and environmental correlations

Phenotypic plasticity of growth ring traits in Pinus hartwegii at the ends of its elevational gradient

Introduction

Phenotypic plasticity (PP) could be an important short-term mechanism to modify physiological and morphological traits in response to climate change and global warming, particularly for high-mountain tree species. The objective was to evaluate PP response of growth ring traits to temperature and precipitation in Pinus hartwegii Lindl. populations located at the ends of its elevational gradient on two volcanic mountains in central Mexico (La Malinche and Nevado de Toluca).

Methods

Increment cores collected from 274 P. hartwegii trees were used to estimate their PP through reaction norms (RN), which relate the ring width and density traits with climate variables (temperature and precipitation). We estimated the trees' sensitivity (significant RN) to climatic variables, as well as the relative proportion of RN with positive and negative slope. We also estimated the relationship between the PP of ring width and density traits using correlation and Principal Component (PC) analyses.

Results

Over 70% of all trees showed significant RN to growing season and winter temperatures for at least one growth ring trait, with a similar proportion of significant RN at both ends of the gradient on both mountains. Ring width traits had mostly negative RN, while ring density traits tended to have positive RN. Frequency of negative RN decreased from lower to higher elevation for most traits. Average PP was higher at the lower end of the gradient, especially on LM, both for ring width and ring density traits, although high intrapopulation variation in PP was found on both mountains.

Discussion

Results indicate that P. hartwegii presents spatially differentiated plastic responses in width and density components of radial growth. PP was particularly strong at the lower elevation, which has higher temperature and water stress conditions, putting these populations at risk from the continuing global warming driven by climate change.

Flower morphology and plant-bee pollinator interactions are related to stamen dimorphism in Melastomataceae

Approximately 20,000 species of flowering plant offer mainly pollen to their pollinators, generally bees. Stamen dimorphism, a floral trait commonly present in some pollen flowers, is thought to be associated with exclusive pollen provision for highly effective bee pollinators. Notwithstanding, little is known about how stamen dimorphism is related to other floral morphological traits and, consequently, plant-pollinator interactions at the community scale. Here we investigated the relationship between stamen dimorphism and other floral morphological traits, as well as the interactions with pollinators in plants of Melastomataceae. We characterized each plant species as stamen dimorphic or stamen isomorphic according to differences in size and shape between stamen sets. Data on interactions between the plants and their bee pollinators were analysed as quantitative bipartite networks. We found that petal and style size and shape were correlated to stamen dimorphism. Stamen dimorphic species present larger flowers and less variable style shapes than stamen isomorphic species. Furthermore, stamen dimorphism is associated with higher richness of visiting bees, i.e. higher ecological generalization. During the evolutionary history of Melastomataceae, the dependence on pollinators for fruit set has possibly favoured the evolution of larger flowers with dimorphic stamens, which in turn are able to make use of a larger spectrum of pollen-collecting bees, leading to ecological generalization.

The role of genus and life span in predicting seed and vegetative trait variation and correlation in Lathyrus, Phaseolus, and Vicia

PREMISE

Annual and perennial life history transitions are abundant among angiosperms, and understanding the phenotypic variation underlying life span shifts is a key endeavor of plant evolutionary biology. Comparative analyses of trait variation and correlation networks among annual and perennial plants is increasingly important as new herbaceous perennial crops are being developed for edible seed. However, it remains unclear how seed to vegetative growth trait relationships correlate with life span.

METHODS

To assess the relative roles of genus and life span in predicting phenotypic variation and trait correlations, we measured seed size and shape, germination proportion, and early-life-stage plant height and leaf growth over 3 mo in 29 annual and perennial, herbaceous congeneric species from three legume genera (Lathyrus, Phaseolus, and Vicia).

RESULTS

Genus was the strongest predictor of seed size and shape variation, and life span consistently predicted plant height and leaf number at single time points. Correlation networks revealed that annual species had significant associations between seed traits and vegetative traits, whereas perennials had no significant seed-vegetative associations. Each genus also differed in the extent of integration between seed and vegetative traits, as well as within-vegetative-trait correlation patterns.

CONCLUSIONS

Genus and life span were important for predicting aspects of early-life-stage phenotypic variation and trait relationships. Differences in phenotypic correlation may indicate that selection on seed size traits will impact vegetative growth differently depending on life span, which has important implications for nascent perennial breeding programs.

Phenotypic plasticity of European larch radial growth and wood density along a-1,000 m elevational gradient

Phenotypic plasticity is a key mechanism for sedentary long-living species to adjust to changing environment. Here, we use mature Larix decidua tree-ring variables collected along an elevational transect in the French Alps to characterize the range of individual plastic responses to temperature. Stem cores from 821 mature Larix decidua trees have been collected from four plots distributed along a 1,000-m elevational gradient in a natural forest to build up individual linear reaction norms of tree-ring microdensity traits to temperature. The sign, magnitude and spread of variations of the slopes of the individual reaction norms were used to characterize variation of phenotypic plasticity among plots and traits. Results showed a large range of phenotypic plasticity (with positive and negative slopes) at each elevational plot and for each tree-ring variable. Overall, phenotypic plasticity tends to be larger but positive at higher elevation, negative at the warmer lower sites, and more variable in the center of the elevation distribution. Individual inter-ring reaction norm is a valuable tool to retrospectively characterize phenotypic plasticity of mature forest trees. This approach applied to Larix decidua tree-ring micro-density traits along an elevation gradient showed the existence of large inter-individual variations that could support local adaptation to a fast-changing climate.

Towards the flower economics spectrum

Understanding how floral traits affect reproduction is key for understanding genetic diversity, speciation, and trait evolution in the face of global changes and pollinator decline. However, there has not yet been a unified framework to characterize the major trade-offs and axes of floral trait variation. Here, we propose the development of a floral economics spectrum (FES) that incorporates the multiple pathways by which floral traits can be shaped by multiple agents of selection acting on multiple flower functions. For example, while pollinator-mediated selection has been considered the primary factor affecting flower evolution, selection by nonpollinator agents can reinforce or oppose pollinator selection, and, therefore, affect floral trait variation. In addition to pollinators, the FES should consider nonpollinator biotic agents and floral physiological costs, broadening the drivers of floral traits beyond pollinators. We discuss how coordinated evolution and trade-offs among floral traits and between floral and vegetative traits may influence the distribution of floral traits across biomes and lineages, thereby influencing organismal evolution and community assembly.

Varying Levels of Genetic Control and Phenotypic Plasticity in Timing of Bud Burst, Flower Opening, Leaf Senescence and Leaf Fall in Two Common Gardens of Prunus padus L.

Several phenological phases mark the seasonal growth pattern in temperate woody perennials. To gain further insight into the way these phases react on an altering growth environment, we tested whether vegetative and reproductive phenophases in a shrub species respond differentially among different genetic entities and between two different planting sites. We scored leaf bud burst, flower opening, leaf senescence and leaf fall on 267 ramets of Prunus padus L. belonging to 53 genotypes that were sampled in 9 local populations, and that were planted in 2 common gardens in the northern part of Belgium. The data were processed with cumulative logistic regression. The contribution of genetic and non-genetic components to the total variability varied between the four studied seasonal phenophases. The timing of flower opening displayed the smallest relative amount of intragenotypic variance (between ramets), suggesting a stronger genetic control and a lesser need at the individual plant level for plastic fine tuning to the micro-environment. In addition, whereas leaf bud burst showed the highest relative variance at the interpopulation level among all phenophases, probably at least partly attributable to local adaptation, flower opening displayed the highest intergenotypic variance, which may have been promoted more by assortative mating. Spring phenophases were strongly correlated (r = 0.89) as well as the autumnal phenophases (r = 0.72). Flower opening was not correlated with the autumnal phenophases. Timing of leaf bud burst and leaf senescence were negatively correlated, demonstrating that the length of the growing season enlarged or diminished among the studied genotypes. Although the two planting sites were only 24 km apart, all phenophases were advanced at the less exposed site, indicating a phenotypic plastic response. Together, our results suggest that in P. padus, flowering is less sensitive to environmental variation than leaf bud break and may show a lesser impact of a changing environment on this reproductive phenophase.

Detecting canalization and intra-floral modularity in triggerplant (Stylidium) flowers: correlations are only part of the story

BACKGROUND AND AIMS

The Berg hypothesis proposes that specialized-flower traits experience stronger stabilizing selection than non-floral structures and predicts that variation in specialized-flower traits will be mostly uncorrelated with variation in non-floral traits. Similarly, adaptive-accuracy theory predicts lower variation (as a proportion of the mean) in floral traits than in non-floral ones. Both hypotheses can be extended to comparisons between floral traits, where different parts of the flower can be expected to experience different strengths of stabilizing selection, resulting in contrasting patterns of variation. The present study tests these ideas by analysing variation/covariation in those floral traits influencing the location of pollen placement on, and stigma contact with, pollinators ('pollination-mechanics traits', PMTs) in relation to variation/covariation in non-floral traits and floral traits not directly involved in the mechanics of pollination. The prediction was that PMTs are canalized (buffered against genetic and environmental variation) relative to attraction traits, as manifested in lower variances and modular independence.

METHODS

Floral and inflorescence structures of ten species of triggerplants (Stylidium, Stylidiaceae) in south-western Australia were measured; the data were analysed using multivariate and bivariate approaches to detect modular structure of floral and non-floral traits and assess evidence for canalization of PMTs.

KEY RESULTS

Only six of the ten species had PMTs with smaller correlation coefficients than attraction traits, in contrast to the Berg expectation. However, allometric and variance patterns were generally consistent with the predictions of an extended Berg hypothesis and adaptive accuracy. There was modular separation of most floral traits from non-floral traits and clear intra-floral modular structure. PMTs showed lower proportional variation and shallower allometric slopes than pollinator-attraction traits in nine and eight, respectively, of ten species.

CONCLUSIONS

This study demonstrates the value of allometric and variance analyses (in addition to correlation) in assessing the evolutionary significance of floral-trait stability and plasticity.

Evolutionary dynamics of the leaf phenological cycle in an oak metapopulation along an elevation gradient

It has been predicted that environmental changes will radically alter the selective pressures on phenological traits. Long-lived species, such as trees, will be particularly affected, as they may need to undergo major adaptive change over only one or a few generations. The traits describing the annual life cycle of trees are generally highly evolvable, but nothing is known about the strength of their genetic correlations. Tight correlations can impose strong evolutionary constraints, potentially hampering the adaptation of multivariate phenological phenotypes. In this study, we investigated the evolutionary, genetic and environmental components of the timing of leaf unfolding and senescence within an oak metapopulation along an elevation gradient. Population divergence, estimated from in situ and common-garden data, was compared to expectations under neutral evolution, based on microsatellite markers. This approach made it possible (1) to evaluate the influence of genetic correlation on multivariate local adaptation to elevation and (2) to identify traits probably exposed to past selective pressures due to the colder climate at high elevation. The genetic correlation was positive but very weak, indicating that genetic constraints did not shape the local adaptation pattern for leaf phenology. Both spring and fall (leaf unfolding and senescence, respectively) phenology timings were involved in local adaptation, but leaf unfolding was probably the trait most exposed to climate change-induced selection. Our data indicated that genetic variation makes a much smaller contribution to adaptation than the considerable plastic variation displayed by a tree during its lifetime. The evolutionary potential of leaf phenology is, therefore, probably not the most critical aspect for short-term population survival in a changing climate.

Nutrient availability affects floral scent much less than other floral and vegetative traits in Lithophragma bolanderi

Background and Aims

Many plant-pollinator interactions are mediated by floral scents that can vary among species, among populations within species and even among individuals within populations. This variation could be innate and unaffected by the environment, but, because many floral volatiles have amino-acid precursors, scent variation also could be affected by differences in nutrient availability among environments. In plants that have coevolved with specific pollinators, natural selection is likely to favour low phenotypic plasticity in floral scent even under different conditions of nutrient availability if particular scents or scent combinations are important for attracting local pollinators.

Methods

Clonal pairs of multiple seed-families of two Lithophragma bolanderi (Saxifragaceae) populations were subjected to a high and a low nutrient treatment. These plants are pollinated primarily by host-specific Greya moths. It was evaluated how nutrient treatment affected variation in floral scent relative to other vegetative and reproductive traits.

Key Results

Floral scent strength (the per-flower emission rate) and composition were unaffected by nutrient treatment, but low-nutrient plants produced fewer and lighter leaves, fewer scapes and fewer flowers than high-nutrient plants. The results held in both populations, which differed greatly in the number and composition of floral scents produced.

Conclusions

The results reveal a strong genetic component both to scent composition and emission level, and partly contrasts with the only previous study that has assessed the susceptibility of floral volatile signals to variation in the abundance of nutrients. These results, and the tight coevolutionary relationship between Lithophragma plants and their specialized Greya moth pollinators, indicate that reproductive traits important to coevolving interactions, such as the floral scent of L. bolanderi, may be locally specialized and more canalized than other traits important for plant fitness.

Genetic and environmental integration of the hawkmoth pollination syndrome in Ruellia humilis (Acanthaceae)

BACKGROUND AND AIMS

The serial homology of floral structures has made it difficult to assess the relative contributions of selection and constraint to floral integration. The interpretation of floral integration may also be clouded by the tacit, but largely untested, assumption that genetic and environmental perturbations affect trait correlations in similar ways. In this study, estimates of both the genetic and environmental correlations between components of the hawkmoth pollination syndrome are presented for chasmogamous flowers of Ruellia humilis , including two levels of control for serial homology.

METHODS

A greenhouse population for quantitative genetic analysis was generated by a partial diallel cross between field-collected plants. An average of 634 chasmogamous flowers were measured for each of eight floral traits that contribute to the hawkmoth syndrome. Genetic correlations (across parents) and environmental correlations (across replicate flowers) were estimated by restricted maximum likelihood.

KEY RESULTS

Stigma height, anther height and floral tube length were very tightly integrated in their responses to both genetic and environmental perturbations. The inclusion of floral disc width as a control for serial homology suggests this integration is an adaptive response to correlational selection imposed by pollinators. In contrast, integration of non-homologous traits was low. Furthermore, when comparisons between the dimensions of serially homologous structures were excluded, the genetic and environmental correlation matrices showed little congruence.

CONCLUSIONS

The results suggest that hawkmoths have imposed strong correlational selection on floral traits involved in the deposition and removal of pollen, and that this is a consequence of stabilizing selection on the relative positions of stigmas and anthers in the face of substantial flower size variation. Low integration of other floral traits, and conflicting patterns of genetic and environmental correlations among these traits, suggest weak or no correlational selection within the range of variability expressed within a population.

Support Vector Machine and Artificial Neural Network Models for the Classification of Grapevine Varieties Using a Portable NIR Spectrophotometer

The identification of different grapevine varieties, currently attended using visual ampelometry, DNA analysis and very recently, by hyperspectral analysis under laboratory conditions, is an issue of great importance in the wine industry. This work presents support vector machine and artificial neural network’s modelling for grapevine varietal classification from in-field leaf spectroscopy. Modelling was attempted at two scales: site-specific and a global scale. Spectral measurements were obtained on the near-infrared (NIR) spectral range between 1600 to 2400 nm under field conditions in a non-destructive way using a portable spectrophotometer. For the site specific approach, spectra were collected from the adaxial side of 400 individual leaves of 20 grapevine (Vitis vinifera L.) varieties one week after veraison. For the global model, two additional sets of spectra were collected one week before harvest from two different vineyards in another vintage, each one consisting on 48 measurement from individual leaves of six varieties. Several combinations of spectra scatter correction and smoothing filtering were studied. For the training of the models, support vector machines and artificial neural networks were employed using the pre-processed spectra as input and the varieties as the classes of the models. The results from the pre-processing study showed that there was no influence whether using scatter correction or not. Also, a second-degree derivative with a window size of 5 Savitzky-Golay filtering yielded the highest outcomes. For the site-specific model, with 20 classes, the best results from the classifiers thrown an overall score of 87.25% of correctly classified samples. These results were compared under the same conditions with a model trained using partial least squares discriminant analysis, which showed a worse performance in every case. For the global model, a 6-class dataset involving samples from three different vineyards, two years and leaves monitored at post-veraison and harvest was also built up, reaching a 77.08% of correctly classified samples. The outcomes obtained demonstrate the capability of using a reliable method for fast, in-field, non-destructive grapevine varietal classification that could be very useful in viticulture and wine industry, either global or site-specific.

Studying morphological integration and modularity at multiple levels: concepts and analysis

Although most studies on integration and modularity have focused on variation among individuals within populations or species, this is not the only level of variation for which integration and modularity exist. Multiple levels of biological variation originate from distinct sources: genetic variation, phenotypic plasticity resulting from environmental heterogeneity, fluctuating asymmetry from random developmental variation and, at the interpopulation or interspecific levels, evolutionary change. The processes that produce variation at all these levels can impart integration or modularity on the covariance structure among morphological traits. In turn, studies of the patterns of integration and modularity can inform about the underlying processes. In particular, the methods of geometric morphometrics offer many advantages for such studies because they can characterize the patterns of morphological variation in great detail and maintain the anatomical context of the structures under study. This paper reviews biological concepts and analytical methods for characterizing patterns of variation and for comparing across levels. Because research comparing patterns across level has only just begun, there are relatively few results, generalizations are difficult and many biological and statistical questions remain unanswered. Nevertheless, it is clear that research using this approach can take advantage of an abundance of new possibilities that are so far largely unexplored.

Phenotypic integration in style dimorphic daffodils (Narcissus, Amaryllidaceae) with different pollinators

Different pollinators can exert different selective pressures on floral traits, depending on how they fit with flowers, which should be reflected in the patterns of variation and covariation of traits. Surprisingly, empirical evidence in support of this view is scarce. Here, we have studied whether the variation observed in floral phenotypic integration and covariation of traits in Narcissus species is associated with different groups of pollinators. Phenotypic integration was studied in two style dimorphic species, both with dimorphic populations mostly visited by long-tongued pollinators (close fit with flowers), and monomorphic populations visited by short-tongued insects (loose fit). For N. papyraceus, the patterns of variation and correlation among traits involved in different functions (attraction and fit with pollinators, transfer of pollen) were compared within and between population types. The genetic diversity of populations was also studied to control for possible effects on phenotypic variation. In both species, populations with long-tongued pollinators displayed greater phenotypic integration than those with short-tongued pollinators. Also, the correlations among traits involved in the same function were stronger than across functions. Furthermore, traits involved in the transfer of pollen were consistently more correlated and less variable than traits involved in the attraction of insects, and these differences were larger in dimorphic than monomorphic populations. In addition, population genetic parameters did not correlate with phenotypic integration or variation. Altogether, our results support current views of the role of pollinators in the evolution of floral integration.

Geographical differentiation in floral traits across the distribution range of the Patagonian oil-secreting Calceolaria polyrhiza: do pollinators matter?

BACKGROUND AND AIMS

The underlying evolutionary processes of pollinator-driven floral diversification are still poorly understood. According to the Grant-Stebbins model speciation begins with adaptive local differentiation in the response to spatial heterogeneity in pollinators. Although this crucial process links the micro- and macroevolution of floral adaptation, it has received little attention. In this study geographical phenotypic variation was investigated in Patagonian Calceolaria polyrhiza and its pollinators, two oil-collecting bee species that differ in body size and geographical distribution.

METHODS

Patterns of phenotypic variation were examined together with their relationships with pollinators and abiotic factors. Six floral and seven vegetative traits were measured in 45 populations distributed across the entire species range. Climatic and edaphic parameters were determined for 25 selected sites, 2-16 bees per site of the most frequent pollinator species were captured, and a critical flower-bee mechanical fitting trait involved in effective pollination was measured. Geographical patterns of phenotypic and environmental variation were examined using uni- and multivariate analyses. Decoupled geographical variation between corolla area and floral traits related to the mechanical fit of pollinators was explored using a Mantel test.

KEY RESULTS

The body length of pollinators and the floral traits related to mechanical fit were strongly correlated with each other. Geographical variation of the mechanical-fit-related traits was decoupled from variation in corolla size; the latter had a geographical pattern consistent with that of the vegetative traits and was mainly affected by climatic gradients.

CONCLUSIONS

The results are consistent with pollinators playing a key role in shaping floral phenotype at a geographical scale and promoting the differentiation of two floral ecotypes. The relationship between the critical floral-fit-related trait and bee length remained significant even in models that included various environmental variables and an allometric predictor (corolla area). The abiotic environment also has an important role, mainly affecting floral size. Decoupled geographical variation between floral mechanical-fit-related traits and floral size would represent a strategy to maintain plant-pollinator phenotypic matching in this environmentally heterogeneous area.