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Habitat loss is a primary driver of global biodiversity decline, negatively impacting many species, including native bees. One approach to counteract the consequences of habitat loss is through restoration, which includes the transformation of degraded or damaged habitats to increase biodiversity. In this review, we survey bee habitat restoration literature over the last 14 years to provide insights into how best to promote bee diversity and abundance through the restoration of natural landscapes in North America. We highlight relevant questions and concepts to consider throughout the various stages of habitat restoration projects, categorizing them into pre-, during-, and post-restoration stages. We emphasize the importance of planning speciesand site-specific strategies to support bees, including providing floral and non-floral resources and increasing nest site availability. Lastly, we underscore the significance of conducting evaluations and long-term monitoring following restoration efforts. By identifying effective restoration methods, success indicators, and areas for future research, our review presents a comprehensive framework that can guide land managers during this urgent time for bee habitat restoration. [ABSTRACT FROM AUTHOR]

Summary: Anthropogenetic climate change has caused range shifts among many species. Species distribution models (SDMs) are used to predict how species ranges may change in the future. However, most SDMs rarely consider how climate‐sensitive traits, such as phenology, which affect individuals' demography and fitness, may influence species' ranges.Using > 120 000 herbarium specimens representing 360 plant species distributed across the eastern United States, we developed a novel 'phenology‐informed' SDM that integrates phenological responses to changing climates. We compared the ranges of each species forecast by the phenology‐informed SDM with those from conventional SDMs. We further validated the modeling approach using hindcasting.When examining the range changes of all species, our phenology‐informed SDMs forecast less species loss and turnover under climate change than conventional SDMs. These results suggest that dynamic phenological responses of species may help them adjust their ecological niches and persist in their habitats as the climate changes.Plant phenology can modulate species' responses to climate change, mitigating its negative effects on species persistence. Further application of our framework will contribute to a generalized understanding of how traits affect species distributions along environmental gradients and facilitate the use of trait‐based SDMs across spatial and taxonomic scales. [ABSTRACT FROM AUTHOR]

Restricting seed collecting to local populations is a common practice in restoration because it is assumed that most plants are adapted to local environmental conditions. However, there is still considerable debate about whether local seed collection should be the default seed‐provenancing strategy as the effects of climate change are increasingly considered in restoration planning. It is especially important to explore whether local seed provenance is necessary for dominant species used in restoration because the success of these projects often rests on these species. Stipa pulchra is one such species that is commonly used in grassland restoration projects in California. To explore how different seed‐provenancing strategies affected the establishment and growth of S. pulchra, we established three common garden experiments distributed across a latitudinal gradient in California. We collected seeds from seven wild populations, germinated seeds in a common greenhouse, then planted all populations at the three common gardens. We assessed growth and reproduction for 2 years. We found limited evidence that restricting seed sourcing to local populations increased the establishment of S. pulchra compared to seeds from more distant populations. Instead, we found evidence to support the use of regional admixture seed sourcing to increase resiliency to environmental variation. In particular, we found being sourced from a dry location during the dry 2018 season was a benefit, highlighting the importance of including dry‐adapted populations to increase climate resilience. Our experiment highlights the importance of exploring multiple seed‐provenancing methods when designing a project to improve long‐term success. [ABSTRACT FROM AUTHOR]

Plants interact extensively with their neighbors, but the evolutionary consequences of variation in neighbor identity are not well understood. Seedling traits are likely to experience selection that depends on the identity of neighbors because they influence competitive outcomes. To explore this, we evaluated selection on seed mass and emergence time in two California grasses, the native perennial Stipa pulchra , and the non-native annual Bromus diandrus , in the field with six other native and non-native neighbor grasses in single- and mixed-species treatments. We also quantified characteristics of each neighbor treatment to further investigate factors influencing their effects on fitness and phenotypic selection. Selection favored larger seeds in both focal species and this was largely independent of neighbor identity. Selection generally favored earlier emergence in both focal species, but neighbor identity influenced the strength and direction of selection on emergence time in S. pulchra , but not B. diandrus. Greater light interception, higher soil moisture, and greater productivity of neighbors were associated with more intense selection for earlier emergence and larger seeds. Our findings suggest that changes in plant community composition can alter patterns of selection in seedling traits, and that these effects can be associated with measurable characteristics of the community. [ABSTRACT FROM AUTHOR]

Wild plant species provide excellent examples of qualitative traits that evolve in response to environmental challenges (e.g., flower color, heavy metal tolerance, cyanogenesis, and male sterility). In addition to such discrete characters, a dazzling array of continuously distributed, quantitative traits are expressed at every phase of the life cycle. These traits are known or suspected to have evolved by natural selection because they are heritable, differ among populations or closely related taxa occupying distinct habitats, and have individual phenotypes associated with survival and reproductive success. This special issue [American Journal of Botany 109(11)] focuses on the tools and approaches for detecting or inferring the ecological and genetic factors contributing to changes in genetically based variation of quantitative traits within or among populations, or causing their divergence among taxa. The assembled articles use one or more of three primary approaches to detect the process or outcome of natural selection on morphological, life history, reproductive, chemical, and physiological quantitative traits: the analysis of phenotypic or artificially imposed selection to detect direct and indirect selection on traits whose function is well‐understood; common garden experiments, including reciprocal transplants and "resurrection" experiments; and quantitative genetic analyses designed to detect and to estimate the environmental and genetic sources of phenotypic variation or to forecast short‐term evolutionary change. Together, these articles examine and reveal the adaptive capacity of quantitative traits and the genetically based constraints that may limit their directional evolutionary change, thereby informing and testing inferences, hypotheses, and predictions concerning the evolutionary trajectories of wild plant species. [ABSTRACT FROM AUTHOR]

Premise: In many species, seed size influences individual fitness, but its heritability is low, impeding its evolution. In heterogeneous environments, even if heritability of seed size is low, genetic variation in phenotypic plasticity for seed size may provide the opportunity for selection, but this possibility has rarely been investigated in wild species. The evolutionary trajectory of seed size depends on whether additive, maternal, or non‐additive genetic variance dominates; moreover, the expression of any of these sources of variance may be environment‐dependent, reflecting genetic variation in plasticity. In this study, we examined these sources of variation in seed size and their response to drought in Dithyrea californica. Methods: We used a diallel design to estimate variance components for seed size in three greenhouse‐raised populations sampled from California and northern Mexico. We replicated diallels in two watering treatments to examine genetic parameters and genotype × environment interactions affecting seed size. We estimated general (GCA) and specific (SCA) combining ability, reciprocal effects (RGCA and RSCA), and their interactions with water availability, and we sought evidence that sexual conflict influences seed size. Results: Norms of reaction revealed genetic variation in plasticity for seed size in each population. Seed size in D. californica is determined by the combination of watering treatment, GCA and RGCA; parental identity and water availability do not consistently affect seed size, and we detected no evidence for sexual conflict. Conclusions: Multiple sources of genetic variation in phenotypic plasticity for seed size have the potential to influence its evolutionary trajectory in heterogenous environments. [ABSTRACT FROM AUTHOR]

Premise: The study of phenotypic divergence of, and selection on, functional traits in closely related taxa provides the opportunity to detect the role of natural selection in driving diversification. If the strength or direction of selection in field populations differs between taxa in a pattern that is consistent with the phenotypic difference between them, then natural selection reinforces the divergence. Few studies have sought evidence for such concordance for physiological traits. Methods: Herbarium specimen records were used to detect phenological differences between sister taxa independent of the effects on flowering time of long‐term variation in the climate across collection sites. In the field, physiological divergence in photosynthetic rate, transpiration rate, and instantaneous water‐use efficiency were recorded during vegetative growth and flowering in 13 field populations of two taxon pairs of Clarkia, each comprising a self‐pollinating and a outcrossing taxon. Results: Historically, each selfing taxon flowered earlier than its outcrossing sister taxon, independent of the effects of local long‐term climatic conditions. Sister taxa differed in all focal traits, but the degree and (in one case) the direction of divergence depended on life stage. In general, self‐pollinating taxa had higher gas exchange rates, consistent with their earlier maturation. In 6 of 18 comparisons, patterns of selection were concordant with the phenotypic divergence (or lack thereof) between sister taxa. Conclusions: Patterns of selection on physiological traits measured in heterogeneous conditions do not reliably reflect divergence between sister taxa, underscoring the need for replicated studies of the direction of selection within and among taxa. [ABSTRACT FROM AUTHOR]

Herbarium records provide a broad spatial and temporal range with which to investigate plant responses to environmental change. Research on plant phenology and its sensitivity to climate has advanced with the increasing availability of digitized herbarium specimens, but limitations of specimen‐derived data can undermine the inferences derived from such research. One issue that has received little attention is collection site uncertainty (i.e. error distance), a measure of confidence in the location from which a specimen was collected. We conducted comparative analyses of phenoclimatic models to determine whether spatial deviations of 2, 5, 15 or 25 km between recorded and simulated collection sites, as well as the error distance reported in digitized records, affect estimates of the phenological sensitivity of flowering time to annual temperature and precipitation in a widespread annual California wildflower. In this approach, we considered both spatial and interannual variation in climatic conditions. Simulated site displacements led to increasingly weak estimates of phenological sensitivity to temperature and precipitation anomalies with increasing distances. However, we found no significant effect of reported error distance magnitude on estimates of phenological sensitivity to climate normals or anomalies. These findings suggest that the spatial uncertainty of collection sites among specimens of widely collected plant species may not adversely affect estimates of phenological sensitivity to climate, even though real discrepancies and georeferencing inaccuracy can negatively impact such estimates. Collection site uncertainty merits further attention as a potential source of noise in herbarium data, especially for research on how plant traits respond to spatial and interannual climatic variation. [ABSTRACT FROM AUTHOR]

Understanding the effects of climate change on the phenological structure of plant communities will require measuring variation in sensitivity among thousands of co‐occurring species across regions. Herbarium collections provide vast resources with which to do this, but may also exhibit biases as sources of phenological data. Despite general recognition of these caveats, validation of herbarium‐based estimates of phenological sensitivity against estimates obtained using field observations remains rare and limited in scope. Here, we leveraged extensive datasets of herbarium specimens and of field observations from the USA National Phenology Network for 21 species in the United States and, for each species, compared herbarium‐ and field‐based estimates of peak flowering dates expected under standardized temperature conditions, and of sensitivity of peak flowering time to geographic and interannual variation in mean minimum temperatures (TMIN). We found strong agreement between herbarium‐ and field‐based estimates for standardized peak flowering time (r = 0.91, p < 0.001) and for the direction and magnitude of sensitivity to both geographic TMIN variation (r = 0.88, p < 0.001) and interannual TMIN variation (r = 0.82, p < 0.001). This agreement was robust to substantial differences between datasets in 1) the long‐term TMIN conditions observed among collection and phenological monitoring sites and 2) the interannual TMIN conditions observed in the time periods encompassed by both datasets for most species. Our results show that herbarium‐based sensitivity estimates are reliable among species spanning a wide diversity of life histories and biomes, demonstrating their utility in a broad range of ecological contexts, and underscoring the potential of herbarium collections to enable phenoclimatic analysis at taxonomic and spatiotemporal scales not yet captured by observational data. [ABSTRACT FROM AUTHOR]

Offspring size is a key functional trait that can affect subsequent life history stages; in many species, it exhibits both local adaptation and phenotypic plasticity. Variation among populations in offspring size may be explained by various factors, including local climatic conditions. However, geographic variation in climate may be partitioned into long‐term and interannual sources of variation, which may differ in their effects on population mean offspring size. To assess environmental correlates of offspring size, we evaluated geographic variation in seed mass among 88 populations representing 6 species of Streptanthus (Brassicaceae) distributed across a broad climatic gradient in California. We examined the effects of temperature‐mediated growing season length and precipitation on population mean seed mass to determine whether it is best explained by (1) long‐term mean climatic conditions; (2) interannual climate anomalies (i.e., deviations in climate from long‐term means) during the year of seed development, or (3) interactions between climate variables. Both long‐term mean climate and climate anomalies in the year of collection were associated with population mean seed mass, but their effects differed in direction and magnitude. Relatively large seeds were produced at chronically wet sites but also during drier‐than‐average years. This contrast indicates that these associations may be generated by different mechanisms (i.e., adaptive evolution vs. phenotypic plasticity) and may be evidence of countergradient plasticity in seed mass. In addition, populations occurring in locations characterized by relatively long growing seasons produced comparatively large seeds, particularly among chronically dry sites. This study highlights the need to consider that the responses of seed mass to long‐term versus recent climatic conditions may differ and that climate variables may interact to predict seed mass. Such considerations are especially important when using these patterns to forecast the long‐ and short‐term responses of seed mass to climate change. The results presented here also contribute to our broader understanding of how climate drives long‐term (e.g., local adaptation) and short‐term (e.g., phenotypic plasticity) variation in functional traits, such as offspring size across landscapes. [ABSTRACT FROM AUTHOR]

Premise: Forecasting how species will respond phenologically to future changes in climate is a major challenge. Many studies have focused on estimating species‐ and community‐wide phenological sensitivities to climate to make such predictions, but sensitivities may vary within species, which could result in divergent phenological responses to climate change. Methods: We used 743 herbarium specimens of the mountain jewelflower (Streptanthus tortuosus, Brassicaceae) collected over 112 years to investigate whether individuals sampled from relatively warm vs. cool regions differ in their sensitivity to climate and whether this difference has resulted in divergent phenological shifts in response to climate warming. Results: During the past century, individuals sampled from warm regions exhibited a 20‐day advancement in flowering date; individuals in cool regions showed no evidence of a shift. We evaluated two potential drivers of these divergent responses: differences between regions in (1) the degree of phenological sensitivity to climate and (2) the magnitude of climate change experienced by plants, or (3) both. Plants sampled from warm regions were more sensitive to temperature‐related variables and were subjected to a greater degree of climate warming than those from cool regions; thus our results suggest that the greater temporal shift in flowering date in warm regions is driven by both of these factors. Conclusions: Our results are among the first to demonstrate that species exhibited intraspecific variation in sensitivity to climate and that this variation can contribute to divergent responses to climate change. Future studies attempting to forecast temporal shifts in phenology should consider intraspecific variation. [ABSTRACT FROM AUTHOR]

Adaptation to current and future climates can be constrained by trade‐offs between fitness‐related traits. Early seedling emergence often enhances plant fitness in seasonal environments, but if earlier emergence in response to seasonal cues is genetically correlated with lower potential to spread emergence among years (i.e., bet‐hedging), then this functional trade‐off could constrain adaptive evolution. Consequently, selection favoring both earlier within‐year emergence and greater spread of emergence among years—as is expected in more arid environments—may constrain adaptive responses to trait value combinations at which a performance gain in either function (i.e., evolving earlier within‐ or greater among‐year emergence) generates a performance loss in the other. All such trait value combinations that cannot be improved for both functions simultaneously are described as Pareto optimal and together constitute the Pareto front. To investigate how this potential emergence timing trade‐off might constrain adaptation to increasing aridity, we sourced seeds of two grasses, Stipa pulchra and Bromus diandrus, from multiple maternal lines within populations across an aridity gradient in California and examined their performance in a greenhouse experiment. We monitored emergence and assayed ungerminated seeds for viability to determine seed persistence, a metric of potential among‐year emergence spread. In both species, maternal lines with larger fractions of persistent seeds emerged later, indicating a trade‐off between within‐year emergence speed and potential among‐year emergence spread. In both species, populations on the Pareto front for both earlier emergence and larger seed persistence fraction occupied significantly more arid sites than populations off the Pareto front, consistent with the hypothesis that more arid sites impose the strongest selection for earlier within‐year emergence and greater among‐year emergence spread. Our results provide an example of how evaluating genetically based correlations within populations and applying Pareto optimality among populations can be used to detect evolutionary constraints and adaptation across environmental gradients. [ABSTRACT FROM AUTHOR]

In recent decades, the final frost dates of winter have advanced throughout North America, and many angiosperm taxa have simultaneously advanced their flowering times as the climate has warmed. Phenological advancement may reduce plant fitness, as flowering prior to the final frost date of the winter/spring transition may damage flower buds or open flowers, limiting fruit and seed production. The risk of floral exposure to frost in the recent past and in the future, however, also depends on whether the last day of winter frost is advancing more rapidly, or less rapidly, than the date of onset of flowering in response to climate warming. This study presents the first continental‐scale assessment of recent changes in frost risk to floral tissues, using digital records of 475,694 herbarium specimens representing 1,653 angiosperm species collected across North America from 1920 to 2015. For most species, among sites from which they have been collected, dates of last frost have advanced much more rapidly than flowering dates. As a result, frost risk has declined in 66% of sampled species. Moreover, exotic species consistently exhibit lower frost risk than native species, primarily because the former occupy warmer habitats where the annual frost‐free period begins earlier. While reducing the probability of exposure to frost has clear benefits for the survival of flower buds and flowers, such phenological advancement may disrupt other ecological processes across North America, including pollination, herbivory, and disease transmission. [ABSTRACT FROM AUTHOR]

Machine learning (ML) has great potential to drive scientific discovery by harvesting data from images of herbarium specimens—preserved plant material curated in natural history collections—but ML techniques have only recently been applied to this rich resource. ML has particularly strong prospects for the study of plant phenological events such as growth and reproduction. As a major indicator of climate change, driver of ecological processes, and critical determinant of plant fitness, plant phenology is an important frontier for the application of ML techniques for science and society. In the present article, we describe a generalized, modular ML workflow for extracting phenological data from images of herbarium specimens, and we discuss the advantages, limitations, and potential future improvements of this workflow. Strategic research and investment in specimen-based ML methods, along with the aggregation of herbarium specimen data, may give rise to a better understanding of life on Earth. [ABSTRACT FROM AUTHOR]

The evolution of seed size may be influenced by intrinsic attributes of populations, such as mating system and extrinsic factors, such as climate. Several hypotheses propose that the evolution of self‐fertilization from an outcrossing progenitor will be accompanied by a reduction in seed size, but this prediction has not been rigorously tested. Many studies report that the mean seed size of populations or taxa is associated with long‐term climate conditions. Here, we examined the effects on seed size of both mating system and climate within a single genus.In the California wildflower genus, Clarkia (Onagraceae), we sampled seeds from 58 populations representing three pairs of sister taxa; each pair included a predominantly outcrossing and a facultatively selfing taxon. We then examined the independent effects on population mean seed size of mating system, elevation, long‐term (30‐year) climate conditions, and climate anomalies (the deviation between conditions in the year of collection and the long‐term mean), focusing on maximum monthly temperature (Tmax), cumulative moisture deficit and cumulative precipitation (PPT) during Clarkia's growing season (fall, winter and spring).In each taxon pair, the selfing taxon had smaller seeds than the outcrosser. Local, long‐term (1921–1980 and 1981–2000) mean Tmax, PPT and elevation were independently and negatively associated with seed size. Long‐term means for Tmax and PPT explain geographical variation in seed size better than climate anomalies in the year of collection.Synthesis. We corroborated two key hypotheses concerning the drivers of geographical variation in mean seed size. Small seeds in Clarkia co‐evolve with selfing (although the mechanism remains elusive) and in response to chronically warm and wet conditions. The effect of long‐term mean precipitation on seed size differs qualitatively from the effect of precipitation anomalies; relatively large seeds are produced in populations experiencing wetter‐than‐normal years. Ongoing climate change may therefore generate conflicting selection on seed size in Clarkia: intensifying drought is likely to lead to an evolutionary increase in seed size due to its effects on seedling survivorship, while climate‐driven declines in pollinators or selection favouring more rapid reproduction may promote the evolution of self‐pollination, facilitating the evolution of smaller seeds. [ABSTRACT FROM AUTHOR]

Given that flower size and pigmentation can mediate plant–pollinator interactions, many studies have focused on pollinator-driven selection on these floral traits. However, abiotic factors such as precipitation, temperature, and solar radiation also contribute to geographic variation in floral color, pattern, and size within multiple species. Several studies have described an ecogeographic pattern within species in which high temperature, high ultraviolet (UV) radiation, low precipitation and/or low latitudes are associated with increased floral anthocyanin production, smaller flowers, and/or larger UV-absorbing floral patterns (nectar guides or bullseyes). However, latitude or elevation is often used as a proxy variable to study variation in floral traits associated with a wide range of climatic variables, making the proximate abiotic drivers of variation difficult to identify. In this study, we tested and corroborated several predictions for how the abiotic environment may directly or indirectly shape geographic patterns of floral color, pattern, and size in Clarkia unguiculata (Onagraceae). This study provides the first report of geographic variation in multispectral floral color and pattern in C. unguiculata , while also providing an experimental test of the putative protective role of UV absorption for pollen performance. We quantified geographic variation among greenhouse-raised populations in UV floral pattern size, mean UV petal reflectance, anthocyanin concentration, and petal area in C. unguiculata across its natural range in California and, using 30 year climate normals for each population, we identified climatic and topographic attributes that are correlated with our focal floral traits. In addition, we examined pollen performance under high and low UV light conditions to detect the protective function (if any) of UV floral patterns in this species. Contrary to our expectations, the nectar guide and the proportion of the petal occupied by the UV nectar guide were largest in low solar UV populations. Estimated floral anthocyanin concentration was highest in populations with high solar UV, which does support our predictions. The size of the UV nectar guide did not affect pollen performance in either of the light treatments used in this study. We conclude that, under the conditions examined here, UV-absorbing floral patterns do not serve a direct "pollen protection" function in C. unguiculata. Our results only partially align with expected ecogeographic patterns in these floral traits, highlighting the need for research in a wider range of taxa in order to detect and interpret broad scale patterns of floral color variation. [ABSTRACT FROM AUTHOR]

Premise: Herbarium specimens represent an outstanding source of material with which to study plant phenological changes in response to climate change. The fine‐scale phenological annotation of such specimens is nevertheless highly time consuming and requires substantial human investment and expertise, which are difficult to rapidly mobilize. Methods: We trained and evaluated new deep learning models to automate the detection, segmentation, and classification of four reproductive structures of Streptanthus tortuosus (flower buds, flowers, immature fruits, and mature fruits). We used a training data set of 21 digitized herbarium sheets for which the position and outlines of 1036 reproductive structures were annotated manually. We adjusted the hyperparameters of a mask R‐CNN (regional convolutional neural network) to this specific task and evaluated the resulting trained models for their ability to count reproductive structures and estimate their size. Results: The main outcome of our study is that the performance of detection and segmentation can vary significantly with: (i) the type of annotations used for training, (ii) the type of reproductive structures, and (iii) the size of the reproductive structures. In the case of Streptanthus tortuosus, the method can provide quite accurate estimates (77.9% of cases) of the number of reproductive structures, which is better estimated for flowers than for immature fruits and buds. The size estimation results are also encouraging, showing a difference of only a few millimeters between the predicted and actual sizes of buds and flowers. Discussion: This method has great potential for automating the analysis of reproductive structures in high‐resolution images of herbarium sheets. Deeper investigations regarding the taxonomic scalability of this approach and its potential improvement will be conducted in future work. [ABSTRACT FROM AUTHOR]

●Many angiosperms are hermaphroditic and produce bisexual flowers in which male (pollen export) and female (stigma receptivity) functions are separated temporally. This sequential hermaphroditism may be associated with variation in flower size, color, or pattern, all of which may influence pollinator attraction. In this study, we describe variation in these traits across discrete functional sex stages within and between 225 greenhouse‐grown individuals of Clarkia unguiculata (Onagraceae). In addition, to identify the effects of floral phenotype on pollinator attraction in this species, we examine the effects of these floral traits on pollen receipt in ~180 individuals in an experimental field array.●Petal area, ultraviolet (UV)‐absorbing nectar guide area, and blue and green mean petal reflectance differ significantly across the functional sex stages of C. unguiculata. Male‐ and female‐phase flowers display significantly different pollinator attraction traits. Petal and UV nectar guide area increase as flowers progress from male phase to female phase, while blue reflectance and green reflectance peak during anther maturation.●In field arrays of C. unguiculata, female‐phase flowers with large UV nectar guides receive more pollen than those with small nectar guides, and female‐phase flowers with high mean blue reflectance values are more likely to receive pollen than those with low blue reflectance. Female‐phase flowers with green mean reflectance values that differ most from background foliage also receive more pollen than those that are more similar to foliage. These findings indicate that components of flower color and pattern influence pollen receipt, independent of other plant attributes that may covary with floral traits. We discuss these results in the context of hypotheses that have been proposed to explain sex‐specific floral attraction traits, and we suggest future research that could improve our understanding of sexual dimorphism in sequentially hermaphroditic species and the evolution of features that promote outcrossing. [ABSTRACT FROM AUTHOR]

Aim: Climate affects the flowering time of many species. Little is known, however, about how climate influences the properties of regional floras, including the rate at which taxa flower sequentially throughout the flowering season. This study is the first to detect geographical variation in this rate across North America. In addition, we tested for the independent effects of intraspecific variation in flowering time and taxonomic composition on the rate of sequential flowering among regional floras distributed across a temperature gradient. Location: North America. Time period: This study examined >59,000 herbarium specimens that were collected in flower from 1901 to 2013. Major taxa studied: 2,803 angiosperm taxa. Methods: We identified 51 climatically homogeneous regions across the continental, mostly western states of the USA, in each of which ≥100 species were represented by herbarium specimens. We then examined the effects of mean annual temperature (MAT) on the rate of sequential flowering among species in each region. We also evaluated whether geographical variation in the rate of sequential flowering was attributable to intraspecific variation in the flowering time and/or the taxonomic composition of regional floras. Results: As MAT increased over space, the rate of sequential flowering (standardized by the absolute length of the flowering season in each region) increased among relatively early‐flowering taxa but decreased among the latest‐flowering taxa. Both intraspecific variation and shifts in taxonomic composition among floras contributed to this pattern. Main conclusions: Among floras throughout North America, the rate of sequential flowering among co‐occurring taxa changes with MAT. Intraspecific phenological variation primarily affects the rate of sequential flowering during the first half of the growing season, consistent with the inference that future warming will most strongly affect flowering synchrony among early‐flowering taxa. [ABSTRACT FROM AUTHOR]

Questions: All else being equal, populations of dioecious species with a 50:50 sex ratio have only half the effective reproductive population size of bisexual species of equal abundance. Consequently, there is a need to explain how dioecious and bisexual species coexist. Increased mean individual seed mass, fecundity, and population density have all been proposed as attributes of unisexual individuals or populations that may contribute to the persistence or resilience of dioecious species. To date, no studies have compared sympatric dioecious and cosexual species with respect to all three components of fitness. In this study, we sought evidence for these compensatory advantages (higher seed mass, greater seed production per unit basal area, and higher population density) in dioecious species. Location: Five 20–25 ha forest dynamic plots spanning a latitudinal gradient in China, including two temperate, two subtropical, and one tropical forest. Methods: We used a phylogenetically corrected generalized linear modelling approach to assess the phylogenetic dependence and joint evolution of sexual system, seed mass and production, and ecological abundances among 48–333 species and 32,568–136,237 individuals per forest. Results: Across all five forests, we detected no consistent advantage for dioecious relative to sympatric cosexual species with respect to mean individual seed mass, seed production or the density of stems in any size class. Conclusions: Our study suggests that seed traits may provide compensatory mechanisms in some forests, but most often the coexistence of sexual systems cannot be explained by advantages of dioecy related to seed quality and demographic parameters. Future investigations of the factors that promote coexistence may increase our understanding by expanding the search to include attributes such as lifespan and tolerance or resistance to herbivores. [ABSTRACT FROM AUTHOR]

Premise: Strong correlations between traits can obscure their independent effects on components of reproduction. Style length (SL) and petal area (PA) vary within species, for example, but their independent effects on the opportunity for selection among pollen genotypes are poorly understood. Previous work in Clarkia detected a positive effect of SL on pollen receipt, potentially intensifying selection. However, this apparent effect of SL may be influenced by a correlated trait, such as PA. Here, we examine the independent effects of these two traits on pollen receipt and performance. Methods: We collected petals and styles from wild populations of two insect‐pollinated Clarkia taxa and estimated the independent and combined effects of SL and PA on pollen receipt and performance. Results: In both taxa, SL and PA are positively correlated. In C. unguiculata, both traits positively and independently affect pollen receipt, but in C. xantiana ssp. xantiana, the two traits act only in combination to affect pollen receipt. In both taxa, pollen receipt positively affects the numbers of pollen tubes entering and penetrating the style, as well as pollen tube attrition. Conclusions: The effects of SL and PA on pollen receipt and performance are taxon specific. In C. unguiculata, both traits may be independent targets of selection due to their effects on pollen receipt. In C. xantiana ssp. xantiana, by contrast, the combined (but not independent) effects of SL and PA influence pollen receipt. Ecological differences between these taxa require exploration to understand the mechanisms by which these traits affect pollinator behavior. [ABSTRACT FROM AUTHOR]

Premise of the Study: Wild plant species that require the services of pollen‐feeding insects for reliable pollination may evolve features that attract and reward their mutualistic partners. Heterantherous species have been proposed to exhibit a "division of labor" whereby "feeding anthers" (which produce pollen that may be consumed by an insect) are distinguished from "reproductive anthers" (which produce pollen more likely to contribute to reproduction). In some heterantherous species, including Clarkia unguiculata (Onagraceae), these two anther types differ with respect to stamen length, anther size, pollen production, and pollen color. Methods: The primary goal of this study was to test one component of the "division of labor" hypothesis by comparing the performance of the pollen produced by each type of anther in C. unguiculata. To achieve this goal, under greenhouse conditions, we hand pollinated and assessed pollen performance (using epifluorescence microscopy) within ~228 flowers. Key Results: The pollen produced by the two anther types differed significantly with respect to both stigma and style penetration. The inner series of anthers produce pollen with higher performance than the outer series of longer, dark red anthers. Conclusions: These findings contradict previous descriptions of the genus, reporting that the inner diminutive series of anthers in Clarkia produce "abortive and nonfunctional" pollen. We outline the future research required to demonstrate the ecological function of heteranthery in this iconic wildflower group. [ABSTRACT FROM AUTHOR]

Background: The absence of pollinators may prevent sexual reproduction and affect the distribution and persistence of individual plant populations, but the role of pollinators in shaping the patterns of distributions of plant species or populations has not been well studied. Aims: Here, we tested the hypothesis that failure of sexual reproduction due to the absence of pollinators may contribute to the disjunct distribution of Iris ensata. Methods: We assessed floral traits and pollinator visitation frequencies in three native and two ex situ populations. We also conducted controlled pollination experiments and examined progeny performance to estimate pollen limitation (PL) and inbreeding depression. Results: Hand-pollinations indicated that I. ensata was a partially self-compatible outcrosser. Sexual reproduction in our study region depended on Bombus trifasciatus. We observed inbreeding depression for seed set and germination, but not for seedling survival. Native populations had higher frequencies of pollinator visitation and lower pollen-limitation of seed set than ex situ populations. Among populations, the magnitude of PL was negatively related to pollinator visitation rate (P = 0.04). Conclusions: Pollinator limitation and inbreeding depression may both restrict the southern distribution of I. ensata, preventing its northward expansion, thus explaining the disjunct distribution of I. ensata in East Asia. [ABSTRACT FROM AUTHOR]

Determining the manner in which plant species shift their flowering times in response to climatic conditions is essential to understanding and forecasting the impacts of climate change on the world's flora. The limited taxonomic diversity and duration of most phenological datasets, however, have impeded a comprehensive, systematic determination of the best predictors of flowering phenology. Additionally, many studies of the relationship between climate conditions and plant phenology have included only a limited set of climate parameters that are often chosen a priori and may therefore overlook those parameters to which plants are most phenologically sensitive. This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a large number (25) of climate parameters on the flowering time of a very large number (2,468) of angiosperm taxa throughout North America. In addition, we compare the predictive capacity of phenological models constructed from the collection dates of herbarium specimens vs. repeated in situ observations of individual plants using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. When herbarium‐derived data and in situ phenological observations were used to predict flowering onset, the multivariate models based on each of these data sources had similar predictive capacity (R2 = 0.27). Further, apart from mean maximum temperature (TMAX), the two best predictors of flowering time have not commonly been included in phenological models: the number of frost‐free days (NFFD) and the quantity of precipitation as snow (PAS) in the seasons preceding flowering. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling. This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a 25 of climate parameters on the flowering time of 2,468 of angiosperm taxa throughout North using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. Multivariate models based on herbarium‐derived data and in situ phenological observations had similar predictive capacity. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling. [ABSTRACT FROM AUTHOR]

Background and Aims The evolution of selfing from outcrossing may be the most common transition in plant reproductive systems and is associated with a variety of ecological circumstances and life history strategies. The most widely discussed explanation for these associations is the reproductive assurance hypothesis - the proposition that selfing is favoured because it increases female fitness when outcross pollen receipt is limited. Here an alternative explanation, the time limitation hypothesis, is addressed, one scenario of which proposes that selfing may evolve as a correlated response to selection for a faster life cycle in seasonally deteriorating environments. Methods Artificial selection for faster maturation (early flowering) or for low herkogamy was performed on Clarkia unguiculata (Onagraceae), a largely outcrossing species whose closest relative, C. exilis, has evolved higher levels of autogamous selfing. Direct responses to selection and correlated evolutionary changes in these traits were measured under greenhouse conditions. Direct responses to selection on early flowering and correlated evolutionary changes in the node of the first flower, herkogamy, dichogamy, gas exchange rates and water use efficiency (WUE) were measured under field conditions. Key Results Lines selected for early flowering and for low herkogamy showed consistent, statistically significant responses to direct selection. However, there was little or no evidence of correlated evolutionary changes in flowering date, floral traits, gas exchange rates or WUE. Conclusions These results suggest that the maturation rate and mating system have evolved independently in Clarkia and that the time limitation hypothesis does not explain the repeated evolution of selfing in this genus, at least through its indirect selection scenario. They also suggest that the life history and physiological components of drought escape are not genetically correlated in Clarkia, and that differences in gas exchange physiology between C. unguiculata and C. exilis have evolved independently of differences in mating system and life history. [ABSTRACT FROM AUTHOR]

Abstract: Animal taxa that differ in the intensity of sperm competition often differ in sperm production or swimming speed, arguably due to sexual selection on postcopulatory male traits affecting siring success. In plants, closely related self‐ and cross‐pollinated taxa similarly differ in the opportunity for sexual selection among male gametophytes after pollination, so traits such as the proportion of pollen on the stigma that rapidly enters the style and mean pollen tube growth rate (PTGR) are predicted to diverge between them. To date, no studies have tested this prediction in multiple plant populations under uniform conditions. We tested for differences in pollen performance in greenhouse‐raised populations of two Clarkia sister species: the predominantly outcrossing C. unguiculata and the facultatively self‐pollinating C. exilis. Within populations of each taxon, groups of individuals were reciprocally pollinated (n = 1153 pollinations) and their styles examined four hours later. We tested for the effects of species, population, pollen type (self vs. outcross), the number of competing pollen grains, and temperature on pollen performance. Clarkia unguiculata exhibited higher mean PTGR than C. exilis; pollen type had no effect on performance in either taxon. The difference between these species in PTGR is consistent with predictions of sexual selection theory. [ABSTRACT FROM AUTHOR]

The timing of the seasonal activity of organisms is a tractable indicator of climate change. Many studies in North America have investigated the role of temperature on the onset date of phenological transitions in temperate deciduous trees and found that the onset of leafing and flowering in numerous species has occurred earlier in recent years, apparently in response to higher temperatures in winter and spring., Few studies have examined the climatic and biogeographic drivers of phenological responses in water-limited ecosystems or explored interspecific variation in responses of phenological metrics other than the timing of onset, such as the periodicity or duration of phenological activity., This study used phenological observations of four species of Quercus contributed to the USA National Phenology Network database from 2009 to 2014 to investigate how responses to climate (temperature and precipitation) and geographic location (latitude, longitude and elevation) varied among two western North American species ( Q. agrifolia and Q. lobata) and two eastern and central North American species ( Q. alba and Q. rubra)., Within years, in species in the western, water-limited ecosystems, the phenological phases observed here (bud break, flowers or flower buds) tend to occur intermittently throughout the growing season, and each event is of longer duration than the same phenophases of the temperate-zone species, rendering a single onset date an incomplete metric with which to track responsiveness or to compare species. By contrast, the eastern/central U.S. species were phenologically more responsive than the western species to spatial and temporal variation in winter, spring, and fall precipitation and maximum temperature., Synthesis. Within and between regions these congeners exhibited a diversity of responses to seasonal temperature and precipitation. This indicates that for predictive model development it is critical to understand how each underlying driver influences species that are adapted to different climatic regimes. These results underscore the value of studying a range of phenological metrics and species from a variety of ecosystems to better predict phenological responses to short-term variation and to long-term change in climate. [ABSTRACT FROM AUTHOR]

In terrestrial ecosystems, atmospheric nitrogen (N) deposition has greatly increased N availability relative to other elements, particularly phosphorus (P). Alterations in the availability of N relative to P can affect plant growth rate and functional traits, as well as resource allocation to above- versus belowground biomass ( MA and MB). Biomass allocation among individual plants is broadly size-dependent, and this can often be described as an allometric relationship between MA and MB, as represented by the equation [ABSTRACT FROM AUTHOR]

Pollen viability is an important component of reproductive success, with inviable pollen causing failure of reproduction. Pollen grains have evolved mechanisms to avoid negative impacts of adverse environmental conditions on viability, including the ability to sustain ionizing radiation and repair DNA. We assessed the viability of 109,000 pollen grains representing 675 pollen samples from 111 species of plants in Chernobyl across radiation gradients that spanned three orders of magnitude. We found a statistically significant but small and negative main effect of radiation on pollen viability rates across species (Pearson's r = 0.20). Ploidy level and the number of nucleate cells (two vs. three) were the only variables that influenced the strength of the effect of radiation on pollen viability, as reflected by significant interactions between these two variables and background radiation, while there were no significant effects of genome size, pollen aperture type, life cycle duration, or pollination agent on the strength of the effect of radiation on pollen viability. Keywords: adaptation, Alexander stain, Chernobyl, indicator species, interspecific differences, pollen viability, radiation. [ABSTRACT FROM AUTHOR]

Background and Aims Mating systems of plants are diverse and evolutionarily labile. Abiotic environmental factors, such as seasonal drought, may impose selection on physiological traits that could lead to transitions in mating system if physiological traits are genetically correlated with traits that influence mating system. Within Clarkia, self-fertilizing taxa have higher photosynthetic rates, earlier flowering phenology, faster individual floral development and more compressed flowering periods than their outcrossing sister taxa, potentially reducing the selfing taxa’s exposure to drought. In theory, this contrast in trait combinations between sister taxa could have arisen via correlated evolution due to pleiotropy or genetic linkage. Alternatively, each trait may evolve independently as part of a life history that is adaptive in seasonally dry environments. Methods To evaluate these hypotheses, we examined relationships between photosynthetic rates (adjusted for plant height and leaf node position) and outcrossing rates (estimated by allozyme variation in progeny arrays) during two consecutive years in multiple wild populations of two mixed-mating Clarkia taxa, each of which is sister to a derived selfing taxon. If the negative association between photosynthetic rate and outcrossing previously observed between sister taxa reflects correlated evolution due to a strong negative genetic correlation between these traits, then a similarly negative relationship would be observed within populations of each taxon. By contrast, if the combination of elevated photosynthetic rates and reduced outcrossing evolved independently within taxa, we predicted no consistent relationship between photosynthetic rate and outcrossing rate. Key Results We found no significant difference in outcrossing rates within populations between groups of plants with high versus low photosynthetic rates. Conclusions Overall, these results provide support for the hypothesis that the joint divergence in photosynthetic rate and mating system observed between Clarkia sister taxa is the result of independent evolutionary transitions. [ABSTRACT FROM AUTHOR]

In habitats where resource availability declines during the growing season , selection may favor early-flowering individuals. Under such ephemerally favorable conditions, late-blooming species (and individuals) may be particularly vulnerable to resource limitation of seed production. In California, a region prone to seasonal drought, members of the annual genus Clarkia are among the last to flower in the spring. We compared pollen limitation ( PL) of seed set and outcrossing rates between early- and late-flowering individuals in two mixed-mating Clarkia taxa to detect whether flowering time is associated with changes in seed set due to resource depletion, PL, or increased selfing. In 2008-2010, we hand-pollinated one flower on a total of 1855 individual plants either Early (near the onset of flowering) or Late (near the end of flowering) in the flowering season and compared seed set to adjacent, open-pollinated flowers on the same stem. To assess the contribution of pollen quality to reproduction, we first (2008) used allozymes to estimate outcrossing rates of seeds produced by Early and Late open-pollinated flowers. Second (2009), we conducted an anther-removal experiment to estimate self-pollen deposition. Seed set in Clarkia unguiculata was not pollen-limited. Clarkia xantiana ssp . xantiana was pollen-limited in 2008 and 2010, but not 2009. PL did not differ between Early and Late treatments. In both taxa, seed set of Early flowers was greater than Late flowers, but not due to PL in the latter. Reproduction was generally pollinator-dependent. Most pollen deposition was xenogamous, and outcrossing rates were >0.7 - and similar between Early and Late periods. These results suggest that pollen receipt and pollen quality remain seasonally consistent. By contrast, the resources necessary to provision seeds decline, reducing the fitness benefits associated with resource allocation to ovules. [ABSTRACT FROM AUTHOR]

For most species, a precise understanding of how climatic parameters determine the timing of seasonal life cycle stages is constrained by limited long-term data. Further, most long-term studies of plant phenology that have examined relationships between phenological timing and climate have been local in scale or have focused on single climatic parameters. Herbarium specimens, however, can expand the temporal and spatial coverage of phenological datasets., Using Trillium ovatum specimens collected over > 100 yr across its native range, we analyzed how seasonal climatic conditions (mean minimum temperature ( Tmin), mean maximum temperature and total precipitation ( PPT)) affect flowering phenology. We then examined long-term changes in climatic conditions and in the timing of flowering across T. ovatum's range., Warmer Tmin advanced flowering, whereas higher PPT delayed flowering. However, Tmin and PPT were shown to interact: the advancing effect of warmer Tmin was strongest where PPT was highest, and the delaying effect of higher PPT was strongest where Tmin was coldest. The direction of temporal change in climatic parameters and in the timing of flowering was dependent on geographic location. Tmin, for example, decreased across the observation period in coastal regions, but increased in inland areas., Our results highlight the complex effects of climate and geographic location on phenology. [ABSTRACT FROM AUTHOR]

Phenology is an integrative science that comprises the study of recurring biological activities or events. In an era of rapidly changing climate, the relationship between the timing of those events and environmental cues such as temperature, snowmelt, water availability, or day length are of particular interest. This article provides an overview of the observer-based plant phenology sampling conducted by the U.S. National Ecological Observatory Network ( NEON), the resulting data, and the rationale behind the design. Trained technicians will conduct regular in situ observations of plant phenology at all terrestrial NEON sites for the 30-yr life of the observatory. Standardized and coordinated data across the network of sites can be used to quantify the direction and magnitude of the relationships between phenology and environmental forcings, as well as the degree to which these relationships vary among sites, among species, among phenophases, and through time. Vegetation at NEON sites will also be monitored with tower-based cameras, satellite remote sensing, and annual high-resolution airborne remote sensing. Ground-based measurements can be used to calibrate and improve satellite-derived phenometrics. NEON's phenology monitoring design is complementary to existing phenology research efforts and citizen science initiatives throughout the world and will produce interoperable data. By collocating plant phenology observations with a suite of additional meteorological, biophysical, and ecological measurements (e.g., climate, carbon flux, plant productivity, population dynamics of consumers) at 47 terrestrial sites, the NEON design will enable continental-scale inference about the status, trends, causes, and ecological consequences of phenological change. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: One proposed function of long styles is to intensify selection among male gametophytes relative to short styles. If so, given sufficient competition, longer styles will have higher rates of pollen tube attritin (failure to reach the style base) with in the style than shorter ones. Alternatively, style length may influence pollen receipt, which itself may affect attrition rates. METHODS: We tested these predictions by collecting senescing styles from wild populations of two insect-pollinated Clarkia species. We examined the number of pollen grains adhering to the stigma, length of styles, and rates of attrition from the stigma surface to the stigma-style junction (SSJ), from the SSJ to the style base, and from the stigma surface to the style base. Multivariate analyses estimated the independent effects of pollen grains per stigma, the number of pollen tubes at the SSJ, and style length on attrition. KEY RESULTS: Style length was generally positively correlated w ith pollen receipt, and the number of pollen grains per stigma was positively correlated with all three attrition rates. In neither species was any attrition rate affected by style length independent of the number of pollen grains per stigma. CONCLUSIONS: Pollen attrition was mediated by style length, but the function of style length was primarily to increase the number of germinating pollen grains, which affected attrition rates either through stigma clogging or pollen-pollen interactions. Style length may have a direct effect on pollen receipt due to the stigma's position relative to pollinator body parts, but traits correlated with style length may also directly affect pollen receipt. [ABSTRACT FROM AUTHOR]

Ecologists and evolutionary biologists have been interested in the functional biology of pollen since the discovery in the 1800s that pollen grains encompass tiny plants (male gametophytes) that develop and produce sperm cells. After the discovery of double fertilization in flowering plants, botanists in the early 1900s were quick to explore the effects of temperature and maternal nutrients on pollen performance, while evolutionary biologists began studying the nature of haploid selection and pollen competition. A series of technical and theoretic developments have subsequently, but usually separately, expanded our knowledge of the nature of pollen performance and how it evolves. Today, there is a tremendous diversity of interests that touch on pollen performance, ranging from the ecological setting on the stigma, structural and physiological aspects of pollen germination and tube growth, the form of pollen competition and its role in sexual selection in plants, virus transmission, mating system evolution, and inbreeding depression. Given the explosion of technical knowledge of pollen cell biology, computer modeling, and new methods to deal with diversity in a phylogenetic context, we are now more than ever poised for a new era of research that includes complex functional traits that limit or enhance the evolution of these deceptively simple organisms. [ABSTRACT FROM AUTHOR]

Premise of research. Gynodioecy, a dimorphic sexual system where individual plants are either female or hermaphroditic, has been documented in≪1% of plant species. This rarity suggests that gynodioecy can evolve and persist only under a restrictive set of conditions. One approach to determining these conditions is to identify the phenotypic traits and ecological factors that are associated with gynodioecy, as such traits or factors may facilitate the evolution and persistence of the sexual system. Methodology. We assembled an angiosperm-wide database of gynodioecious species and used this database to test whether gynodioecy was associated with two phenotypic traits/ecological factors: an herbaceous growth form and a temperate geographic distribution. Species-level analyses were used to confirm that gynodioecious species are predominately herbaceous and temperate. Family-level analyses were then used to test whether the presence of herbaceous and temperate species in a lineage was associated with the presence of gynodioecious species. Pivotal results. An herbaceous growth form and a temperate geographic distribution were significantly overrepresented in gynodioecious species relative to their frequency in all plant species. Families that contained species with an herbaceous growth form and a temperate geographic distribution were significantly more likely to also contain gynodioecious species. Conclusions. Gynodioecy was associated with an herbaceous growth form and a temperate distribution, suggesting that herbaceousness and temperateness can facilitate the evolution and/or persistence of gynodioecy. In addition, our results suggest that gynodioecy is associated with different phenotypic traits/ecological factors than dioecy, a closely related sexual system. Consequently, whether gynodioecy is a transitional state in the evolution of dioecy may depend on the growth form and geographic distribution of the lineage in which it evolves. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Project Baseline is a seed bank that offers an unprecedented opportunity to examine spatial and temporal dimensions of micro-evolution during an era of rapid environmental change. Over the upcoming 50 years, biologists will withdraw genetically representative samples of past populations from this time capsule of seeds and grow them contemporaneously with modern samples to detect any phenotypic and molecular evolution that has occurred during the intervening time. METHODS: We carefully developed this living genome bank using protocols to enhance its experimental value by collecting from multiple populations and species across a broad geographical range in sites that are likely to be preserved into the future. Seeds are accessioned with site and population data and are stored by maternal line under conditions that maximize seed longevity. This open-access resource will be available to researchers at regular intervals to evaluate contemporary evolution. KEY RESULTS: To date, the Project Baseline collection includes 100-200 maternal lines of each of 61 species collected from over 831 populations on sites that are likely to be preserved into the future across the United States (∼78,000 maternal lines). Our strategically designed collection circumvents some problems that can cloud the results of "resurrection" studies involving naturally preserved or existing seed collections that are available fortuitously. CONCLUSIONS: The resurrection approach can be coupled with long-established and newer techniques over the next five decades to elucidate genetic change and thereby vastly improve our understanding of temporal and spatial changes in phenotype and the evolutionary processes underlying it. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Climate change models for California predict a warmer, drier future, potentially resulting in shorter growing seasons. If phenotypic differences between closely related species currently distributed across a moisture and temperature gradient represent adaptations to their abiotic environment, then as conditions become warmer and drier, populations presently adapted to cooler and wetter conditions may evolve to become more similar to those adapted to warmer and drier conditions. Two sister species, Clarkia unguiculata and C exilis, are distributed across a moisture and temperature gradient in the southern Sierra Nevada, providing an opportunity to predict how this process may occur. METHODS: In a greenhouse experiment using wild-collected seeds from 11 populations in the southern Sierra Nevada, we examined relationships among elevation, climatic conditions, and population means for each trait, then evaluated bivariate relationships among maternal family means, using raw values and controlling for population and seed mass effects on phenotype. KEY RESULTS: Clarkia exilis occupied warmer, drier conditions, typically at lower elevations, than C. unguiculata did and flowered earlier and faster, producing smaller flowers with lower herkogamy. In C. unguiculata, petal area, herkogamy, and the rate of flower production were positively correlated with days tofirst flower. CONCLUSIONS: If selection favors earlier flowering, smaller petals, or faster flower production in C unguiculata, then the genetic correlations among these traits should reinforce their joint evolution. Moreover, the correlations between these traits and herkogamy may promote the evolution of self-fertilization as an indirect response to selection, a previously unrecognized potential outcome of climate change. [ABSTRACT FROM AUTHOR]

Premise of research. Invasive plants usually have growth and reproductive abilities that allow them to cope with new habitats and environments. The small balsam, Impatiens parviflora, is one of the most widespread annual invasive species in Europe. As no precise physiological assessment for this species has been performed, we compared physiological traits linked to growth performance in contrasting environments. Methodology. Plants were cultivated in growth chambers under four different treatments varying by light and water conditions. We assessed the impact of water stress and low light levels on traits related to plant growth, leaf physiology, photosynthesis, and water status. Pivotal results. Tolerance of low light level was reflected by several morphological and physiological characteristics. The number of leaves initiated was not affected by light condition, whereas specific leaf area increased for plants grown under low light. In addition, the chlorophyll fluorescence parameters revealed that low light did not affect the light-dependent reactions of photosynthesis. Although the net rate of photosynthesis was reduced, plant growth was not markedly affected. Our results thus suggest that I. parviflora generally copes well with shady conditions. The traits involved in efficiency of water use and water conservation indicated that I. parviflora is also highly tolerant to water stress. Although a reduction in plant growth and abscission of old leaves were observed after 4 wk of stress, I. parviflora demonstrated several mechanisms to maintain the light-dependent reactions of photosynthesis under water-stress conditions. Water use efficiency strongly increased in response to water stress, and plants adjusted their water potential to maintain their water supply. Conclusions. Impatiens parviflora shows physiological traits that allow plant growth under contrasting and stressful environments. These physiological traits may contribute to its invasive ability. [ABSTRACT FROM AUTHOR]

Premise of research. The Wisconsin Fast Plants lines of Brassica rapa (RCBr) have been a useful model system for plant ecology, evolution, physiology, and development. However, inheritance of flowering time in the B. rapa Fast Plants has not been explored. Methodology. I used quantitative genetics to explore additive, dominant, and epistatic genetic components of between-line variance in flowering time and for genotype × photoperiod interaction effects in crosses between RCBr and naturalized Californian populations. Pivotal results. Strong directional dominance for rapid flowering was evident in the F1 and F2 generations. Evidence was equivocal for epistatic genetic variance between the RCBr and California parental types. The expression of additive genetic variance for flowering time in the naturalized California populations was not masked when combined with the RCBr genetic background. A strong genotype × photoperiod interaction was found; whereas flowering time for RCBr was unaffected by day length, flowering time was halved for California plants under a 24-h photoperiod compared with that under their natural photoperiod regime. Importantly, rapid cycling was completely dominant under constant light but partially dominant under shorter photoperiods. Conclusions. Early flowering in the commonly used laboratory-derived lines of B. rapa compared with wild populations involves directional dominance that is intensified under long photoperiods. The dominance of accelerated flowering in this case contrasts with the different inheritance patterns seen in independently derived rapid cycling B. rapa lines. Generally, the apparent multiplicity of pathways available for flowering time evolution may contribute to the high incidence of local adaptation in this trait. [ABSTRACT FROM AUTHOR]

* Premise of the study: One explanation for the evolution of selfing, the drought escape hypothesis, proposes that self-fertilization may evolve under conditions of intensifying seasonal drought as part of a suite of traits that enable plants to accelerate the completion of their life cycle, thereby escaping late-season drought. Here, we test two fundamental assumptions of this hypothesis in Clarkia xantiana: (1) that a seasonal decline in precipitation causes an increase in drought stress and (2) that this results in changes in physiological performance, reflecting these deteriorating conditions. * Methods: We examined seasonal and interannual variation in abiotic environmental conditions (estimated by ambient temperature, relative humidity, predawn leaf water potentials, and carbon isotope ratios) and physiological traits (photosynthesis, conductance, transpiration, instantaneous water-use efficiency, ascorbate peroxidase and glutathione reductase activities, quantum yield of photosystem II, PSII potential efficiency) in field populations of C. xantiana in 2009 and 2010. * Key results: In both years, plants experienced intensifying drought across the growing season. Gas exchange rates decreased over the growing season and were lower in 2009 (a relatively dry year) than in 2010, suggesting that the temporal changes from early to late spring were directly linked to the deteriorating environmental conditions. * Conclusions: Seasonal declines in transpiration rate may have increased survival by protecting plants from desiccation. Concomitant declines in photosynthetic rate likely reduced the availability of resources for seed production late in the season. Thus, the physiological patterns observed are consistent with the conditions required for the drought escape hypothesis. [ABSTRACT FROM AUTHOR]

Plant-pollinator mutualisms can be disrupted in fragmented and isolated populations. Isolated populations attract fewer and less diverse pollinators, but it is not generally known whether this is due to reductions in the abundance and/or diversity of flowers at a site or to the biogeography of pollinators (or both). Islands represent one system potentially suitable to analyze the effects of spatial isolation. Here, we examine the contribution that differences in visitor composition make to increased selfing and seed production by examining the major visitors to Plectritis congesta in populations on the Gulf Islands and Vancouver Island. We find that (1) connectivity is more strongly associated with visitor assemblages and seed production than components of the floral community and (2) taking phylogeny into account suggests that increased visitation by solitary bees as opposed to other functional groups increases female fitness in P. congesta. [ABSTRACT FROM AUTHOR]

Premise of research. Genetic variation for ecologically important traits is necessary for populations to adapt to environmental change. Many authors have called for a greater emphasis on directly measuring quantitative genetic variation in rare species, which are expected to have reduced amounts of genetic variation due to genetic drift in small populations. The extent of among-population differentiation for quantitative traits may also help to evaluate the likelihood that genetic rescue/translocation will be a successful conservation strategy. Despite these merits, relatively few studies measure quantitative genetic variation for ecologically important traits as a function of population size. Methodology. Sixteen populations of the endangered plant Hypericum cumulicola were sampled, capitalizing on previous work that has estimated relative effective population sizes and demonstrated minimal migration between populations. This context allows more direct inference about the role of drift in small populations on quantitative genetic variation, the focus of this study. Using controlled pollinations and a greenhouse common garden, quantitative genetic variation within populations and differentiation among populations were estimated for six putatively ecologically important traits. Pivotal results. There were few significant estimates of genetic variation for most traits irrespective of population size. There was a positive correlation between population size and genetic variation for anther-stigma distance, a floral trait expected to influence the degree of self-fertilization. There was also limited differentiation among populations for all traits. Conclusions. Limited genetic variation for ecologically important traits in these populations could slow or limit adaptive responses to future environmental change, possibly increasing extinction risk. The smallest populations will be particularly sensitive to environmental/habitat changes that result in reduced pollinator visitation. Limited phenotypic differentiation, combined with previous evidence of strong heterosis in crosses between small populations, suggests little risk of outbreeding depression if genetic rescue efforts become necessary to preserve this species. [ABSTRACT FROM AUTHOR]

Premise of research. Sex allocation, the relative energy devoted to producing pollen, ovules, and floral displays, can significantly affect reproductive output and population dynamics. In this study, we investigated floral morphology and gamete production in bisexual, distylous plants from a self-incompatible hybrid complex (Piriqueta cistoides ssp. caroliniana Walter [Arbo]; Turneraceae). Sampling focused on two parent types (C, V) and their stable hybrid derivative (H). Since H morphotypes are heterotic for growth and fruit production, we hypothesized that they would produce larger flowers with more gametes. We also anticipated that plants with long styles (long morphs) would produce less pollen than short morphs, since long-morph pollen is larger. Methodology. Over two consecutive summers, flowers were collected from 1465 individual plants in 28 field populations. Floral parameters were measured digitally, and each flower's pollen number, ovule number, and stigma-anther separation was quantified under a dissecting microscope. Gamete production (n = 332) and stigma-anther separation (n = 119) were also quantified for plants from a greenhouse accession. Pivotal results. Floral display differed among morphotypes, with H plants producing the largest flowers and C plants displaying the least petal separation. Hybrid morphotypes produced significantly more pollen than parental morphotypes, and pollen quantity was significantly greater for long morphs. Ovule production, however, was greatest for V flowers. Stigma-anther separation differed between years and style morphs (greater for short morphs) but not among morphotypes or within a single season. Conclusions. Differences in pollen production between morphs were not consistent with trade-offs in pollen size and number or selection for increased male function in short morphs. Greater stigma-anther separation in short morphs supported the hypothesis of selection to reduce pollen interference. Enhanced floral display and pollen production followed other heterotic traits observed in H morphotypes. The superior ability of H morphotypes to attract pollinators and sire seeds might partially explain this hybrid zone's continuing expansion. [ABSTRACT FROM AUTHOR]

Phenological events - defined points in the life cycle of a plant or animal - have been regarded as highly plastic traits, reflecting flexible responses to various environmental cues., The ability of a species to track, via shifts in phenological events, the abiotic environment through time might dictate its vulnerability to future climate change. Understanding the predictors and drivers of phenological change is therefore critical., Here, we evaluated evidence for phylogenetic conservatism - the tendency for closely related species to share similar ecological and biological attributes - in phenological traits across flowering plants. We aggregated published and unpublished data on timing of first flower and first leaf, encompassing ˜4000 species at 23 sites across the Northern Hemisphere. We reconstructed the phylogeny for the set of included species, first, using the software program Phylomatic, and second, from DNA data. We then quantified phylogenetic conservatism in plant phenology within and across sites., We show that more closely related species tend to flower and leaf at similar times. By contrasting mean flowering times within and across sites, however, we illustrate that it is not the time of year that is conserved, but rather the phenological responses to a common set of abiotic cues., Our findings suggest that species cannot be treated as statistically independent when modelling phenological responses., Synthesis. Closely related species tend to resemble each other in the timing of their life-history events, a likely product of evolutionarily conserved responses to environmental cues. The search for the underlying drivers of phenology must therefore account for species' shared evolutionary histories. [ABSTRACT FROM AUTHOR]

Premise of the study: Numerous long-term studies in seasonal habitats have tracked interannual variation in first flowering date (FFD) in relation to climate, documenting the effect of warming on the FFD of many species. Despite these efforts, long-term phenological observations are still lacking for many species. If we could forecast responses based on taxonomic affinity, however, then we could leverage existing data to predict the climate-related phenological shifts of many taxa not yet studied. Methods: We examined phenological time series of 1226 species occurrences (1031 unique species in 119 families) across seven sites in North America and England to determine whether family membership (or family mean FFD) predicts the sensitivity of FFD to standardized interannual changes in temperature and precipitation during seasonal periods before flowering and whether families differ significantly in the direction of their phenological shifts. Key results: Patterns observed among species within and across sites are mirrored among family means across sites; early-flowering families advance their FFD in response to warming more than late-flowering families. By contrast, we found no consistent relationships among taxa between mean FFD and sensitivity to precipitation as measured here. Conclusions: Family membership can be used to identify taxa of high and low sensitivity to temperature within the seasonal, temperate zone plant communities analyzed here. The high sensitivity of early-flowering families (and the absence of early-flowering families not sensitive to temperature) may reflect plasticity in flowering time, which may be adaptive in environments where early-season conditions are highly variable among years. [ABSTRACT FROM AUTHOR]

The use of local seed sources for revegetation is accepted practice to reduce the potential that propagules will be poorly adapted to site conditions. However, data are often lacking to determine the distance within which seed sources represent local genotypes. Short-term reciprocal transplant studies represent a class of tools to detect local adaptation of target species. We conducted a reciprocal transplant of Nassella pulchra between two central California locations to test for adaptation to local environmental conditions over a 3-year period. Experimental plots at one location were split between grazed and ungrazed sites to evaluate the potential influence of livestock grazing on the detection or magnitude of local adaptation. During each year of the study, evidence of a home-site advantage depended on the location, traits studied, and population. At the end of the 3-year study period, however, we detected consistent evidence of a home-site advantage for seedling biomass among grazed sites at one location and ungrazed plots at the other location. In effect, local adaptation was only apparent in the final year of the study. Short-term reciprocal transplant studies are an effective tool to guide the selection of seed sources most likely to germinate and to become established at a restoration site, but such studies cannot rule out local adaptation, which may not be immediately detectable. [ABSTRACT FROM AUTHOR]