Evolvability and trait function predict phenotypic divergence of plant populations.

Understanding the causes and limits of population divergence in phenotypic traits is a fundamental aim of evolutionary biology, with the potential to yield predictions of adaptation to environmental change. Reciprocal transplant experiments and the evaluation of optimality models suggest that local adaptation is common but not universal, and some studies suggest that trait divergence is highly constrained by genetic variances and covariances of complex phenotypes. We analyze a large database of population divergence in plants and evaluate whether evolutionary divergence scales positively with standing genetic variation within populations (evolvability), as expected if genetic constraints are evolutionarily important. We further evaluate differences in divergence and evolvability-divergence relationships between reproductive and vegetative traits and between selfing, mixed-mating, and outcrossing species, as these factors are expected to influence both patterns of selection and evolutionary potentials. Evolutionary divergence scaled positively with evolvability. Furthermore, trait divergence was greater for vegetative traits than for floral (reproductive) traits, but largely independent of the mating system. Jointly, these factors explained ~40% of the variance in evolutionary divergence. The consistency of the evolvability-divergence relationships across diverse species suggests substantial predictability of trait divergence. The results are also consistent with genetic constraints playing a role in evolutionary divergence.

Effects of experimental warming on floral scent, display, and rewards in two subalpine herbs.

BACKGROUND AND AIMS: Floral volatiles, visual traits, and rewards mediate attraction and defense in plant-pollinator and plant-herbivore interactions, but these floral traits may be altered by global warming through direct effects of temperature or longer term impacts on plant resources. We examined the effect of warming on floral and leaf volatile emissions, floral morphology, plant height, nectar production, and oviposition by seed predators. METHODS: We used open-top chambers that warmed plants in the field +2-3 °C on average (+6-11 °C increase in daily maxima) for 2-4 weeks across 1-3 years at 3 sites in Colorado, USA. Volatiles were sampled from two closely related species of subalpine Ipomopsis with different pollinators: I. aggregata ssp. aggregata, visited mainly by hummingbirds, and I. tenuituba ssp. tenuituba, often visited by hawkmoths. KEY RESULTS: While warming had no detected effects on leaf volatiles, the daytime floral volatiles of both I. aggregata and I. tenuituba responded in subtle ways to warming, with impacts that depended on the species, site, and year. In addition to the long-term effect of warming, temperature at the time of sampling independently affected the floral volatile emissions of I. aggregata during the day and I. tenuituba at night. Warming had little effect on floral morphology for either species, and no effect on nectar concentration, maximum inflorescence height, or flower redness in I. aggregata. However, warming increased nectar production in I. aggregata by 41%, a response that would attract more hummingbird visits, and reduced oviposition by fly seed predators by at least 72%. CONCLUSIONS: Our results suggest that floral traits can show different levels of plasticity to temperature changes in subalpine environments, with potential effects on animal behaviors that help or hinder plant reproduction. They also illustrate the need for more long-term field warming studies, as shown by responses of floral volatiles in different ways to weeks of warming versus temperature at the time of sampling.

Multiparametric ultrasound versus multiparametric MRI to diagnose prostate cancer (CADMUS): a prospective, multicentre, paired-cohort, confirmatory study.

BACKGROUND: Multiparametric MRI of the prostate followed by targeted biopsy is recommended for patients at risk of prostate cancer. However, multiparametric ultrasound is more readily available than multiparametric MRI. Data from paired-cohort validation studies and randomised, controlled trials support the use of multiparametric MRI, whereas the evidence for individual ultrasound methods and multiparametric ultrasound is only derived from case series. We aimed to establish the overall agreement between multiparametric ultrasound and multiparametric MRI to diagnose clinically significant prostate cancer. METHODS: We conducted a prospective, multicentre, paired-cohort, confirmatory study in seven hospitals in the UK. Patients at risk of prostate cancer, aged 18 years or older, with an elevated prostate-specific antigen concentration or abnormal findings on digital rectal examination underwent both multiparametric ultrasound and multiparametric MRI. Multiparametric ultrasound consisted of B-mode, colour Doppler, real-time elastography, and contrast-enhanced ultrasound. Multiparametric MRI included high-resolution T2-weighted images, diffusion-weighted imaging (dedicated high B 1400 s/mm2 or 2000 s/mm2 and apparent diffusion coefficient map), and dynamic contrast-enhanced axial T1-weighted images. Patients with positive findings on multiparametric ultrasound or multiparametric MRI underwent targeted biopsies but were masked to their test results. If both tests yielded positive findings, the order of targeting at biopsy was randomly assigned (1:1) using stratified (according to centre only) block randomisation with randomly varying block sizes. The co-primary endpoints were the proportion of positive lesions on, and agreement between, multiparametric MRI and multiparametric ultrasound in identifying suspicious lesions (Likert score of ≥3), and detection of clinically significant cancer (defined as a Gleason score of ≥4 + 3 in any area or a maximum cancer core length of ≥6 mm of any grade [PROMIS definition 1]) in those patients who underwent a biopsy. Adverse events were defined according to Good Clinical Practice and trial regulatory guidelines. The trial is registered on ISRCTN, 38541912, and ClinicalTrials.gov, NCT02712684, with recruitment and follow-up completed. FINDINGS: Between March 15, 2016, and Nov 7, 2019, 370 eligible patients were enrolled; 306 patients completed both multiparametric ultrasound and multiparametric MRI and 257 underwent a prostate biopsy. Multiparametric ultrasound was positive in 272 (89% [95% CI 85-92]) of 306 patients and multiparametric MRI was positive in 238 patients (78% [73-82]; difference 11·1% [95% CI 5·1-17·1]). Positive test agreement was 73·2% (95% CI 67·9-78·1; κ=0·06 [95% CI -0·56 to 0·17]). Any cancer was detected in 133 (52% [95% CI 45·5-58]) of 257 patients, with 83 (32% [26-38]) of 257 being clinically significant by PROMIS definition 1. Each test alone would result in multiparametric ultrasound detecting PROMIS definition 1 cancer in 66 (26% [95% CI 21-32]) of 257 patients who had biopsies and multiparametric MRI detecting it in 77 (30% [24-36]; difference -4·3% [95% CI -8·3% to -0·3]). Combining both tests detected 83 (32% [95% CI 27-38]) of 257 clinically significant cancers as per PROMIS definition 1; of these 83 cancers, six (7% [95% CI 3-15]) were detected exclusively with multiparametric ultrasound, and 17 (20% [12-31]) were exclusively detected by multiparametric MRI (agreement 91·1% [95% CI 86·9-94·2]; κ=0·78 [95% CI 0·69-0·86]). No serious adverse events were related to trial activity. INTERPRETATION: Multiparametric ultrasound detected 4·3% fewer clinically significant prostate cancers than multiparametric MRI, but it would lead to 11·1% more patients being referred for a biopsy. Multiparametric ultrasound could be an alternative to multiparametric MRI as a first test for patients at risk of prostate cancer, particularly if multiparametric MRI cannot be carried out. Both imaging tests missed clinically significant cancers detected by the other, so the use of both would increase the detection of clinically significant prostate cancers compared with using each test alone. FUNDING: The Jon Moulton Charity Trust, Prostate Cancer UK, and UCLH Charity and Barts Charity.

Selection of Floral Traits by Pollinators and Seed Predators during Sequential Life History Stages.

AbstractOrganismal traits often influence fitness via interactions with multiple species. That selection is not necessarily predictable from pairwise interactions, such as when interactions occur during different life cycle stages. Theoretically, directional selection during two sequential episodes (e.g., pollination and seed survival) can generate quadratic or correlational selection for a set of traits that passes both selective filters. We compared strength of selection during pollination versus seed predation in the field and tested whether interactions with multiple species give rise to nonlinear selection on floral traits. We planted common gardens with seeds of two species of Ipomopsis and hybrids at sites where pollination was primarily by hummingbirds or also included hawk moths. We examined selection on six floral traits, including corolla width, sepal width, color, nectar, and two scent compounds. Female fitness (seeds) was broken down into fitness during (1) pollination (seeds initiated) and (2) seed predation (proportion of seeds escaping fly predation). All traits showed evidence of selection. Directional and quadratic selection were stronger during seed initiation than during seed predation. Correlational selection occurred mostly during seed initiation rather than arising from combining species interactions at two points in the life cycle. These results underscore how multispecies interactions can combine to exert selection on trait combinations.

Phenotypic plasticity and selection on leaf traits in response to snowmelt timing and summer precipitation.

Vegetative traits of plants can respond directly to changes in the environment, such as those occurring under climate change. That phenotypic plasticity could be adaptive, maladaptive, or neutral. We manipulated the timing of spring snowmelt and amount of summer precipitation in factorial combination and examined responses of specific leaf area (SLA), trichome density, leaf water content (LWC), photosynthetic rate, stomatal conductance and intrinsic water-use efficiency (iWUE) in the subalpine herb Ipomopsis aggregata. The experiment was repeated in three years differing in natural timing of snowmelt. To examine natural selection, we used survival, relative growth rate, and flowering as fitness indices. A 50% reduction in summer precipitation reduced stomatal conductance and increased iWUE, and doubled precipitation increased LWC. Combining natural and experimental variation, earlier snowmelt reduced soil moisture, photosynthetic rate and stomatal conductance, and increased trichome density and iWUE. Precipitation reduction reversed the mortality selection favoring high stomatal conductance under normal and doubled precipitation, and higher LWC improved growth. Earlier snowmelt is a strong signal of climate change and can change expression of leaf morphology and gas exchange traits, just as reduced precipitation can. Stomatal conductance and SLA showed adaptive plasticity under some conditions.

Earlier snow melt and reduced summer precipitation alter floral traits important to pollination.

Climate change can cause changes in expression of organismal traits that influence fitness. In flowering plants, floral traits can respond to drought, and that phenotypic plasticity has the potential to affect pollination and plant reproductive success. Global climate change is leading to earlier snow melt in snow-dominated ecosystems as well as affecting precipitation during the growing season, but the effects of snow melt timing on floral morphology and rewards remain unknown. We conducted crossed manipulations of spring snow melt timing (early vs. control) and summer monsoon precipitation (addition, control, and reduction) that mimicked recent natural variation, and examined plastic responses in floral traits of Ipomopsis aggregata over 3 years in the Rocky Mountains. We tested whether increased summer precipitation compensated for earlier snow melt, and if plasticity was associated with changes in soil moisture and/or leaf gas exchange. Lower summer precipitation decreased corolla length, style length, corolla width, sepal width, and nectar production, and increased nectar concentration. Earlier snow melt (taking into account natural and experimental variation) had the same effects on those traits and decreased inflorescence height. The effect of reduced summer precipitation was stronger in earlier snow melt years for corolla length and sepal width. Trait reductions were explained by drier soil during the flowering period, but this effect was only partially explained by how drier soils affected plant water stress, as measured by leaf gas exchange. We predicted the effects of plastic trait changes on pollinator visitation rates, pollination success, and seed production using prior studies on I. aggregata. The largest predicted effect of drier soil on relative fitness components via plasticity was a decrease in male fitness caused by reduced pollinator rewards (nectar production). Early snow melt and reduced precipitation are strong drivers of phenotypic plasticity, and both should be considered when predicting effects of climate change on plant traits in snow-dominated ecosystems.

Variation in floral volatiles across time, sexes, and populations of wind-pollinated Schiedea globosa.

PREMISE: Floral scent is a key aspect of plant reproduction, but its intraspecific variation at multiple scales is poorly understood. Sexual dimorphism and temporal regulation of scent can be shaped by evolution, and interpopulation variation may be a bridge to species differences. We tested whether intraspecific chemical diversity in a wind-pollinated species where selection from biotic pollination is absent is associated with genetic divergence across the Hawaiian archipelago. METHODS: Floral volatiles from females, males, and hermaphrodites of subdioecious Schiedea globosa grown in a common environment from 12 populations were sampled day and night and analyzed by gas chromatography-mass spectrometry. Variation among groups was analyzed by constrained ordination. We also examined the relationships of scent dissimilarity to geographic and genetic distance between populations. RESULTS: Flowers increased total emissions at night through higher emissions of several ketones, oximes, and phenylacetaldehyde. Females emitted less total scent per flower at night but more of some aliphatic compounds than males, and males emitted more ketones and aldoximes. Scent differed among populations during day and night. Divergence in scent produced at night increased with geographic distance within 70-100 km and increased with genetic distance for males during the day and night, but not for females. CONCLUSIONS: Schiedea globosa exhibits diel and sex-based variation in floral scent despite wind pollination and presumed loss of biotic pollination. In males, interpopulation scent differences are correlated with genetic differences, suggesting that scent evolved with dispersal within and across islands.

Genetic and spatial variation in vegetative and floral traits across a hybrid zone.

PREMISE: Genetic variation influences the potential for evolution to rescue populations from impacts of environmental change. Most studies of genetic variation in fitness-related traits focus on either vegetative or floral traits, with few on floral scent. How vegetative and floral traits compare in potential for adaptive evolution is poorly understood. METHODS: We measured variation across source populations, planting sites, and genetic families for vegetative and floral traits in a hybrid zone. Seeds from families of Ipomopsis aggregata, I. tenuituba, and F1 and F2 hybrids of the two species were planted into three common gardens. Measured traits included specific leaf area (SLA), trichomes, water-use efficiency (WUE), floral morphology, petal color, nectar, and floral volatiles. RESULTS: Vegetative traits SLA and WUE varied greatly among planting sites, while showing weak or no genetic variation among source populations. Specific leaf area and trichomes responded plastically to snowmelt date, and SLA exhibited within-population genetic variation. All aspects of floral morphology varied genetically among source populations, and corolla length, corolla width, and sepal width varied genetically within populations. Heritability was not detected for volatiles due to high environmental variation, although one terpene had high evolvability, and high emission of two terpenes, a class of compounds emitted more strongly from the calyx than the corolla, correlated genetically with sepal width. Environmental variation across sites was weak for floral morphology and stronger for volatiles and vegetative traits. The inheritance of three of four volatiles departed from additive. CONCLUSIONS: Results indicate stronger genetic potential for evolutionary responses to selection in floral morphology compared with scent and vegetative traits and suggest potentially adaptive plasticity in some vegetative traits.

Genetic potential for changes in breeding systems: Predicted and observed trait changes during artificial selection for male and female allocation in a gynodioecious species.

PREMISE: Evolution of separate sexes from hermaphroditism often proceeds through gynodioecy, but genetic constraints on this process are poorly understood. Genetic (co-)variances and between-sex genetic correlations were used to predict evolutionary responses of multiple reproductive traits in a sexually dimorphic gynodioecious species, and predictions were compared with observed responses to artificial selection. METHODS: Schiedea (Caryophyllaceae) is an endemic Hawaiian lineage with hermaphroditic, gynodioecious, subdioecious, and dioecious species. We measured genetic parameters of Schiedea salicaria and used them to predict evolutionary responses of 18 traits in hermaphrodites and females in response to artificial selection for increased male (stamen) biomass in hermaphrodites or increased female (carpel, capsule) biomass in females. Observed responses over two generations were compared with predictions in replicate lines of treatments and controls. RESULTS: In only two generations, both stamen biomass in hermaphrodites and female biomass in females responded markedly to direct selection, supporting a key assumption of models for evolution of dioecy. Other biomass traits, pollen and ovule numbers, and inflorescence characters important in wind pollination evolved indirectly in response to selection on sex allocation. Responses generally followed predictions from multivariate selection models, with some responses unexpectedly large due to increased genetic correlations as selection proceeded. CONCLUSIONS: Results illustrate the power of artificial selection and utility of multivariate selection models incorporating sex differences. They further indicate that pollen and ovule numbers and inflorescence architecture could evolve in response to selection on biomass allocation to male versus female function, producing complex changes in plant phenotype as separate sexes evolve.

Early snowmelt projected to cause population decline in a subalpine plant.

How climate change influences the dynamics of plant populations is not well understood, as few plant studies have measured responses of vital rates to climatic variables and modeled the impact on population growth. The present study used 25 y of demographic data to analyze how survival, growth, and fecundity respond to date of spring snowmelt for a subalpine plant. Fecundity was estimated by seed production (over 15 y) and also divided into flower number, fruit set, seeds per fruit, and escape from seed predation. Despite no apparent effects on flower number, plants produced more seeds in years with later snowmelt. Survival and probability of flowering were reduced by early snowmelt in the previous year. Based on demographic models, earlier snowmelt with warming is expected to lead to negative population growth, driven especially by changes in seedling establishment and seed production. These results provide a rare example of how climate change is expected to influence the dynamics of a plant population. They furthermore illustrate the potential for strong population impacts even in the absence of more commonly reported visual signs, such as earlier blooming or reduced floral display in early melting years.

Oncology clinic nurses' attitudes and perceptions regarding implementation of routine fall assessment and fall risk screening: A survey study.

Falls in older adults with cancer are often under-recognized and under-reported. The objective of this study was to explore oncology clinic nurses' willingness and perceived barriers to implement routine falls assessment and falls screening in their practice. Nurses working in outpatient oncology clinics were invited to complete an online survey. Data were analyzed using descriptive statistics and sorted into thematic categories. The majority of respondents indicated willingness to routinely ask older patients about falls (85.7%) and screen for fall risks (73.5%). The main reasons for unwillingness included: belief that patients report falls on their own, lack of time, and lack of support staff. Findings from this study show many oncology nurses believe in the importance of routine fall assessment and screening and are willing to implement them routinely, although falls are not routinely asked about or assessed. Future work should explore strategies to address barriers nurses face given the implications of falls amongst this vulnerable population.

Noninvasive Detection of Clinically Significant Prostate Cancer Using Circulating Tumor Cells.

PURPOSE: Prostate specific antigen testing results in unnecessary biopsy and over diagnosis with consequent overtreatment. Tissue biopsy is an invasive procedure associated with significant morbidity. More accurate noninvasive or minimally invasive diagnostic approaches should be developed to avoid unnecessary prostate biopsy and over diagnosis. We investigated the potential of using circulating tumor cell analysis in cancer diagnosis, particularly to predict clinically significant prostate cancer in prebiopsy cases. MATERIALS AND METHODS: We enrolled 155 treatment naïve patients with prostate cancer and 98 before biopsy for circulating tumor cell enumeration. RNA was extracted from circulating tumor cells of 184 patients for gene expression analysis. The Kruskal-Wallis and Spearman rank tests, multivariate logistic regression and the random forest method were applied to assess the association of circulating tumor cells with aggressive prostate cancer. RESULTS: Of patients with localized prostate cancer 54% were scored as having positive circulating tumor cells, which was associated with a higher Gleason score (p=0.0003), risk group (p <0.0001) and clinically significant prostate cancer (p <0.0001). In the prebiopsy group a positive circulating tumor cell score combined with prostate specific antigen predicted clinically significant prostate cancer (AUC 0.869). A 12-gene panel prognostic for clinically significant prostate cancer was also identified. When combining the prostate specific antigen level, the circulating tumor cell score and the 12-gene panel, the AUC of clinically significant prostate cancer prediction was 0.927. Adding those data to cases with available multiparametric magnetic resonance imaging data significantly increased prediction accuracy (AUC 0.936 vs 0.629). CONCLUSIONS: Circulating tumor cell analysis has the potential to significantly improve patient stratification by prostate specific antigen and/or multiparametric magnetic resonance imaging for biopsy and treatment.

Pollinator visitation rate and effectiveness vary with flowering phenology.

PREMISE: Flowering time may influence pollination success and seed set through a variety of mechanisms, including seasonal changes in total pollinator visitation or the composition and effectiveness of pollinator visitors. METHODS: We investigated mechanisms by which changes in flowering phenology influence pollination and reproductive success of Mertensia ciliata (Boraginaceae). We manipulated flowering onset of potted plants and assessed the frequency and composition of pollinator visitors, as well as seed set. We tested whether floral visitors differed in their effectiveness as pollinators by measuring pollen receipt and seed set resulting from single visits to virgin flowers. RESULTS: Despite a five-fold decrease in pollinator visitation over four weeks, we detected no significant difference in seed set among plants blooming at different times. On a per-visit basis, each bumblebee transferred more conspecific pollen than did a solitary bee or a fly. The proportion of visits by bumblebees increased over the season, countering the decrease in visitation rate so that flowering time had little net effect on seed set. CONCLUSIONS: This work illustrates the need to consider pollinator effectiveness, along with changes in pollinator visitation and species composition to understand the mechanisms by which phenology affects levels of pollination.

Phenotypic plasticity of floral volatiles in response to increasing drought stress.

BACKGROUND AND AIMS: Flowers emit a wide range of volatile compounds which can be critically important to interactions with pollinators or herbivores. Yet most studies of how the environment influences plant volatiles focus on leaf emissions, with little known about abiotic sources of variation in floral volatiles. Understanding phenotypic plasticity in floral volatile emissions has become increasingly important with globally increasing temperatures and changes in drought frequency and severity. Here quantitative relationships of floral volatile emissions to soil water content were analysed. METHODS: Plants of the sub-alpine herb Ipomopsis aggregata and hybrids with its closest congener were subjected to a progressive dry down, mimicking the range of soil moistures experienced in the field. Floral volatiles and leaf gas exchange were measured at four time points during the drought. KEY RESULTS: As the soil dried, floral volatile emissions increased overall and changed in composition, from more 1,3-octadiene and benzyl alcohol to higher representation of some terpenes. Emissions of individual compounds were not linearly related to volumetric water content in the soil. The dominant compound, the monoterpene α-pinene, made up the highest percentage of the scent mixture when soil moisture was intermediate. In contrast, emission of the sesquiterpene (E,E)-α-farnesene accelerated as the drought became more intense. Changes in floral volatiles did not track the time course of changes in photosynthetic rate or stomatal conductance. CONCLUSIONS: This study shows responses of specific floral volatile organic compounds to soil moisture. The non-linear responses furthermore suggest that extreme droughts may have impacts that are not predictable from milder droughts. Floral volatiles are likely to change seasonally with early summer droughts in the Rocky Mountains, as well as over years as snowmelt becomes progressively earlier. Changes in water availability may have impacts on plant-animal interactions that are mediated through non-linear changes in floral volatiles.

Water influences how seed production responds to conspecific and heterospecific pollen.

PREMISE: Outcrossing species depend on pollen from conspecific individuals that may not be exposed to the same abiotic conditions as maternal plants. Additionally, many flowers receive heterospecific pollen, which can also influence seed production. Studies aimed to understand how abiotic conditions influence seed production tend to focus on maternal conditions and leave unexplored the effect of abiotic conditions experienced by pollen donors. We tested how water availability to pollen donors, both conspecific and heterospecific, influenced the seed production of recipient plants exposed to different water availability regimes. METHODS: In a greenhouse setting we manipulated the water availability (low- or high-water treatment) to potted recipient plants (Phacelia parryi), to conspecific pollen donors, and to heterospecific pollen donors (Brassica nigra). We hand pollinated recipient plants with different pollen mixes that represented all combinations of conspecific pollen mixed with heterospecific pollen. From these hand pollinations we determined the amount of pollen that was transferred, pollen volume, pollen shape, and seed production. RESULTS: Higher water availability to conspecific pollen donors led to higher seed production. Under low water availability to heterospecific pollen donors, seed production was unaffected by recipient or conspecific pollen donor treatment. Under high water availability to heterospecific pollen donors, seed production was highest when conspecific pollen donors and pollen recipients also received the high-water treatment. CONCLUSIONS: Environmental conditions of pollen donors can influence the seed production of maternal plants. These results illustrate potential impacts of environmental heterogeneity on post-pollination events that lead to seed production and thus impact a pollinator's contribution to plant fitness.

Clines in traits compared over two decades in a plant hybrid zone.

Background and Aims: Clines in traits across hybrid zones reflect a balance between natural selection and gene flow. Changes over time in average values for traits, and especially the shapes of their clines, are rarely investigated in plants, but could result from evolution in an unstable hybrid zone. Differences in clines between floral and vegetative traits could indicate different strengths of divergent selection. Methods: Five floral and two vegetative traits were measured in 12 populations along an elevational gradient spanning a natural hybrid zone between Ipomopsis aggregata and Ipomopsis tenuituba. We compared clines in the floral traits with those measured 25 years ago. Observed changes in mean trait values were compared with predictions based on prior estimates of natural selection. We also compared the steepness and position of clines between the floral and vegetative traits. Key Results: Corolla length has increased over five generations to an extent that matches predictions from measurements of phenotypic selection and heritability. The shape of its cline, and that of other traits, has not changed detectably. Clines varied across traits, but not all floral traits showed steeper clines than did vegetative traits. Both suites of morphological traits had steeper clines than did neutral molecular markers. Conclusions: The increase in corolla length provides a rare example of a match between predicted and observed evolution of a plant trait in natural populations. The clinal properties are consistent with the hypothesis that habitat-mediated divergent selection on vegetative traits and pollinator-mediated selection on floral traits both maintain species differences across the hybrid zone.

Is Plant Fitness Proportional to Seed Set? An Experiment and a Spatial Model.

Individual differences in fecundity often serve as proxies for differences in overall fitness, especially when it is difficult to track the fate of an individual's offspring to reproductive maturity. Using fecundity may be biased, however, if density-dependent interactions between siblings affect survival and reproduction of offspring from high- and low-fecundity parents differently. To test for such density-dependent effects in plants, we sowed seeds of the wildflower Ipomopsis aggregata (scarlet gilia) to mimic partially overlapping seed shadows of pairs of plants, one of which produced twice as many seeds. We tested for differences in offspring success using a genetic marker to track offspring to flowering multiple years later. Without density dependence, the high-fecundity parent should produce twice as many surviving offspring. We also developed a model that considered the geometry of seed shadows and assumed limited survivors so that the number of juvenile recruits is proportional to the area. Rather than a ratio of 2∶1 offspring success from high- versus low-fecundity parents, our model predicted a ratio of 1.42∶1, which would translate into weaker selection. Empirical ratios of juvenile offspring and of flowers produced conformed well to the model's prediction. Extending the model shows how spatial relationships of parents and seed dispersal patterns modify inferences about relative fitness based solely on fecundity.

Shifts in water availability mediate plant-pollinator interactions.

Altered precipitation patterns associated with anthropogenic climate change are expected to have many effects on plants and insect pollinators, but it is unknown if effects on pollination are mediated by changes in water availability. We tested the hypothesis that impacts of climate on plant-pollinator interactions operate through changes in water availability, and specifically that such effects occur through alteration of floral attractants. We manipulated water availability in two naturally occurring Mertensia ciliata (Boraginaceae) populations using water addition, water reduction and control plots and measured effects on vegetative and floral traits, pollinator visitation and seed set. While most floral trait values, including corolla size and nectar, increased linearly with increasing water availability, in this bumblebee-pollinated species, pollinator visitation peaked at intermediate water levels. Visitation also peaked at an intermediate corolla length, while its relationship to corolla width varied across sites. Seed set, however, increased linearly with water. These results demonstrate the potential for changes in water availability to impact plant-pollinator interactions through pollinator responses to differences in floral attractants, and that the effects of water on pollinator visitation can be nonlinear. Plant responses to changes in resource availability may be an important mechanism by which climate change will affect species interactions.

An enigmatic Hawaiian moth is a missing link in the adaptive radiation of Schiedea.

Shifts in pollination may drive adaptive diversification of reproductive systems within plant lineages. The monophyletic genus Schiedea is a Hawaiian lineage of 32 extant species, with spectacular diversity in reproductive systems. Biotic pollination is the presumed ancestral condition, but this key element of the life history and its role in shaping reproductive systems has remained undocumented. We observed floral visitors to two species of Schiedea and conducted field experiments to test pollinator effectiveness. We used choice tests to compare attraction of pollinators to species hypothesized to be biotically vs wind-pollinated. Pseudoschrankia brevipalpis (Erebidae), a recently described moth species known only from O'ahu, visited hermaphroditic Schiedea kaalae and S. hookeri and removed nectar from their unique tubular nectary extensions. Pseudoschrankia brevipalpis effectively pollinates S. kaalae; single visits to emasculated flowers resulted in pollen transfer. In choice tests, P. brevipalpis strongly preferred these hermaphroditic species over two subdioecious species capable of wind pollination. A shift from biotic to abiotic pollination is clearly implicated in the diversification of reproductive systems within Schiedea. Abundant pollination by a previously unknown native moth in experimental and restored populations suggests the potential for restoration to re-establish native plant-pollinator interactions critical for production of outcrossed individuals with high fitness.

Reproductive isolation between Zaluzianskya species: the influence of volatiles and flower orientation on hawkmoth foraging choices.

Floral trait differences between related species may play a key role in reproductive isolation imposed by pollinators. Volatile emissions can influence pollinator choice, but how they act in combination with traits such as flower orientation is rarely studied. We compared flower-opening patterns, morphology, colour, orientation and volatile emissions for two closely related species of Zaluzianskya and their natural hybrids. Hawkmoth pollinators were tested for preference between flowers of the two species, and between flowers with manipulations of volatiles or orientation. Flowers of Z. natalensis and Z. microsiphon open at night and day, respectively, but they overlap during early evening, when hawkmoths showed a strong preference for Z. natalensis. The species have similar flower size and colour, but Z. natalensis emits more floral volatiles in the evening and presents flowers vertically face-up as opposed to horizontally in Z. microsiphon, whereas natural hybrids are intermediate. Adding methyl benzoate and linalool to flowers of Z. microsiphon did not increase hawkmoth attraction, but re-orientation of flowers to face vertically increased attraction when scent cues were present, whereas re-orientation of Z. natalensis flowers to face horizontally decreased attraction. This study highlights the importance of flower orientation in imposing reproductive isolation.