Evolution of intraspecific floral variation in a generalist-specialist pollination system.

Intraspecific processes impact macroevolutionary patterns through individual variation, selection, and ecological specialisation. According to the niche variation hypothesis, the broader ecological niche of gen- eralist species results in an increased morphological variation among individuals, either because they are constituted of diversified specialised individuals each exploiting a fraction of the species' niche, or because they are constituted of true generalist individuals that experience relaxed selection. To test this hypoth- esis, we surveyed the individual floral morphology of species of Antillean Gesneriaceae, a group that has transitioned between specialisation for hummingbird pollination and generalisation multiple times throughout its evolutionary history. We characterised the profiles of corollas using geometric morpho- metrics and compared the intraspecific shape variance of specialists and generalists in a phylogenetic context. We used three approaches that differently accounted for the high dimensionality of morphologi- cal traits, the ancestral reconstruction of pollination syndromes over time, and the error associated with the estimation of the intraspecific variance. Our findings provide partial support for the niche variation hypothesis. If considering the whole shape in the analysis corroborated this idea, decomposing the shape into principal components indicated that not all aspects of the corolla exhibit the same pattern of vari- ation. Specifically, pollination generalists tend to display greater intraspecific variation than specialists in terms of tubularity, but not of curvature. Accounting for the error in the variance estimation also reduced the support for the hypothesis, suggesting that larger sample sizes may be required to reach stronger conclusions. This study emphasises the reciprocal influence between plants and their pollinators on floral morphology at different biodiversity scales, and suggests that ecological strategies of species can affect patterns of morphological variation at macroevolutionary scales.

Variation in flower size and shape of Impatiens capensis is correlated with urbanization in Montreal, Canada.

Urbanization is changing the conditions in which many species live, forcing them to adjust to these novel environments. Floral size and shape are critical traits for the reproduction of plants pollinated by animals as they are involved in the attraction of pollinators and in efficient pollination. Variation in size and shape could be affected by urbanization via its modification of the abiotic environment (habitat fragmentation, water availability, temperature, soil properties), or via its impact on the biotic environment of plants (pollination, herbivory). Although numerous studies have assessed the impact of urbanization on pollinator communities and many plant traits, few have investigated its impact on floral size and shape while quantifying the proportion of the total urbanization effect that is due to biotic interactions. In this study, we tested if urbanization and pollinator visitation rates affect the flower shape of the spotted jewelweed, Impatiens capensis. We quantified the size and shape of flowers in frontal and profile views using geometric morphometrics for 228 individuals from six populations from the region of Montreal, Canada. Pollinator visitation rates were estimated at each site and the main pollinators were found to be bumblebees, honeybees and hummingbirds. We found that floral size and shape are significantly correlated with urbanization as measured by the amount of vegetation in the surrounding environment of the plants (mean normalized vegetation index, NDVI) and by the visitation rates of bumblebees and honey bees. Partitioning of the total flower shape variation suggests that urbanization affects flower shape through abiotic factors and via its impact on pollinator visitation rates. While further studies from other cities are necessary to confirm the role of urbanization in shaping the floral shape of I. capensis, these results support the idea that urbanization could affect flower shapes.

Regional plant abundance explains patterns of host use by pollen-specialist bees in eastern North America.

Specialist insect herbivores make up a substantial fraction of Earth's biodiversity; however, they exploit a minority of plant lineages. For instance, in the eastern United States and Canada, ~25% of bee species are pollen specialists, but they are hosted by a small fraction of the native, animal-pollinated angiosperms in the region: Only 6% of plant genera and 3% of families support pollen-specialist bees. It is unclear why some plant lineages host specialist bees while others do not. We know that at least some specialist bees use plant taxa that are avoided by generalists, suggesting that specialist bees favor plants with low-quality pollen, potentially as a strategy to escape competition or obtain protection from natural enemies. There is also evidence that specialist bees prefer superabundant host plants. Here we investigate whether pollen quality and plant abundance predict patterns of host use by specialist bees in eastern North America. Through field observations, we find that plants hosting specialist bees are frequent sources of pollen for generalists, suggesting that their pollen is not generally avoided by bees due to poor pollen quality. In addition, our analysis of a large citizen-science data set shows that regional abundance strongly predicts which plant genera in the eastern United States host pollen-specialist bees. Our results show that bees specialize on regionally abundant-but not necessarily low-quality-plant lineages. These plant lineages may provide more opportunities for the evolution of specialists and lower likelihood of specialist extinction.

Studying flowers in 3D using photogrammetry.

Flowers are intricate and integrated three-dimensional (3D) structures predominantly studied in 2D due to the difficulty in quantitatively characterising their morphology in 3D. Given the recent development of analytical methods for high-dimensional data, the reconstruction of flower models in three dimensions represents the limiting factor to studying flowers in 3D. We developed a floral photogrammetry protocol to reconstruct 3D models of flowers based on images taken with a digital single-lens reflex camera, a turntable and a portable lightbox. We demonstrate that photogrammetry allows a rapid and accurate reconstruction of 3D models of flowers from 2D images. It can reconstruct all visible parts of flowers and has the advantage of keeping colour information. We illustrated its use by studying the shape and colour of 18 Gesneriaceae species. Photogrammetry is an affordable alternative to micro-computed tomography (micro-CT) that requires minimal investment and equipment, allowing it to be used directly in the field. It has the potential to stimulate research on the evolution and ecology of flowers by providing a simple way to access 3D morphological data from a variety of flower types.

Chromosome size matters: genome evolution in the cyperid clade.

BACKGROUND AND AIMS: While variation in genome size and chromosome numbers and their consequences are often investigated in plants, the biological relevance of variation in chromosome size remains poorly known. Here, we examine genome and mean chromosome size in the cyperid clade (families Cyperaceae, Juncaceae and Thurniaceae), which is the largest vascular plant lineage with predominantly holocentric chromosomes. METHODS: We measured genome size in 436 species of cyperids using flow cytometry, and augment these data with previously published datasets. We then separately compared genome and mean chromosome sizes (2C/2n) amongst the major lineages of cyperids and analysed how these two genomic traits are associated with various environmental factors using phylogenetically informed methods. KEY RESULTS: We show that cyperids have the smallest mean chromosome sizes recorded in seed plants, with a large divergence between the smallest and largest values. We found that cyperid species with smaller chromosomes have larger geographical distributions and that there is a strong inverse association between mean chromosome size and number across this lineage. CONCLUSIONS: The distinct patterns in genome size and mean chromosome size across the cyperids might be explained by holokinetic drive. The numerous small chromosomes might function to increase genetic diversity in this lineage where crossovers are limited during meiosis.

Testing candidate genes linked to corolla shape variation of a pollinator shift in Rhytidophyllum (Gesneriaceae).

Floral adaptations to specific pollinators like corolla shape variation often result in reproductive isolation and thus speciation. But despite their ecological importance, the genetic bases of corolla shape transitions are still poorly understood, especially outside model species. Hence, our goal was to identify candidate genes potentially involved in corolla shape variation between two closely related species of the Rhytidophyllum genus (Gesneriaceae family) from the Antilles with contrasting pollination strategies. Rhytidophyllum rupincola has a tubular corolla and is strictly pollinated by hummingbirds, whereas R. auriculatum has more open flowers and is pollinated by hummingbirds, bats, and insects. We surveyed the literature and used a comparative transcriptome sequence analysis of synonymous and non-synonymous nucleotide substitutions to obtain a list of genes that could explain floral variation between R. auriculatum and R. rupincola. We then tested their association with corolla shape variation using QTL mapping in a F2 hybrid population. Out of 28 genes tested, three were found to be good candidates because of a strong association with corolla shape: RADIALIS, GLOBOSA, and JAGGED. Although the role of these genes in Rhytidophyllum corolla shape variation remains to be confirmed, these findings are a first step towards identifying the genes that have been under selection by pollinators and thus involved in reproductive isolation and speciation in this genus.

Red and yellow pigments in autumn leaves are associated with higher nitrogen resorption: A comment on Peña-Novas and Marchetti 2021 (https://doi.org/10.1111/jeb.13903).

Species with red and yellow leaves in the fall have a greater resorption of their nitrogen before leaf fall than species with green leaves. This supports the photoprotection hypothesis that proposes that red and yellow pigments protect the leaves from photooxidative stress under cool temperatures and intense light that occur in the fall with the breakdown of chlorophyl, allowing a better recycling of nutrients.

Judge it by its shape: a pollinator-blind approach reveals convergence in petal shape and infers pollination modes in the genus Erythrina.

PREMISE: Pollinators are thought to exert selective pressures on plants, mediating the evolution of convergent floral shape often recognized as pollination syndromes. However, little is known about the accuracy of using petal shape for inferring convergence in pollination mode without a priori pollination information. Here we studied the genus Erythrina L. as a test case to assess whether ornithophyllous pollination modes (hummingbirds, passerines, sunbirds, or mixed pollination) can be inferred based on the evolutionary analysis of petal shape. METHODS: We characterized the two-dimensional dissected shape of standard, keel, and wing petals from 106 Erythrina species using geometric morphometrics and reconstructed a phylogenetic tree of 83 Erythrina species based on plastid trnL-F and nuclear ribosomal ITS sequences. We then used two phylogenetic comparative methods based on Ornstein-Uhlenbeck models, SURFACE and l1OU, to infer distinct morphological groups using petal shape and identify instances of convergent evolution. The effectiveness of these methods was evaluated by comparing the groups inferred to known pollinators. RESULTS: We found significant petal shape differences between hummingbird- and passerine-pollinated Erythrina species. Our analyses also revealed that petal combinations generally provided better inferences of pollinator types than individual petals and that the method and optimization criterion can affect the results. CONCLUSIONS: We show that model-based approaches using petal shape can detect convergent evolution of floral shape and relatively accurately infer pollination modes in Erythrina. The inference power of the keel petals argues for a deeper investigation of their role in the pollination biology of Erythrina and other bird-pollinated legumes.

Repeated evolution of a reproductive polyphenism in plants is strongly associated with bilateral flower symmetry.

Polyphenisms are a special type of phenotypic plasticity in which the products of development are not continuous but instead are separate and distinct phenotypes produced in the same genetic background. One of the most widespread polyphenisms in the flowering plants is cleistogamy, in which the same individual plant produces both open, cross-pollinated flowers as well as highly reduced and closed, self-pollinated (cleistogamous) flowers.1-5 Cleistogamy is not a rare evolutionary phenomenon. It has evolved independently at least 41 times.1 But what favors the evolution of cleistogamy is still largely unknown.1 Darwin6 proposed a hypothesis that has never been properly tested. He observed that cleistogamy is more common in taxa with bilaterally symmetric (zygomorphic) flowers than in those with radially symmetric (actinomorphic) flowers. Moreover, Darwin suggested that cleistogamous flowers help to ensure pollination, which he postulated is less certain in zygomorphic taxa that rely on more specialized groups of pollinators. Here, we combined the largest datasets on floral symmetry and cleistogamy and used phylogenetic approaches to show that cleistogamy is indeed disproportionately associated with zygomorphic flowers and that zygomorphic species are more likely to evolve cleistogamy than actinomorphic species. We also show that zygomorphic species are less capable of autonomous open-flower self-pollination (lower autofertility), suggesting that selection of cleistogamy via reproductive assurance in zygomorphic taxa could help account for Darwin's observation. Our results provide support for the hypothesis that polyphenisms are favored when organisms encounter contrasting environments.

Temperate Forests Dominated by Arbuscular or Ectomycorrhizal Fungi Are Characterized by Strong Shifts from Saprotrophic to Mycorrhizal Fungi with Increasing Soil Depth.

In temperate and boreal forests, competition for soil resources between free-living saprotrophs and ectomycorrhizal (EcM) fungi has been suggested to restrict saprotrophic fungal dominance to the most superficial organic soil horizons in forests dominated by EcM trees. By contrast, lower niche overlap with arbuscular mycorrhizal (AM) fungi could allow fungal saprotrophs to maintain this dominance into deeper soil horizons in AM-dominated forests. Here we used a natural gradient of adjacent forest patches that were dominated by either AM or EcM trees, or a mixture of both to determine how fungal communities characterized with high-throughput amplicon sequencing change across organic and mineral soil horizons. We found a general shift from saprotrophic to mycorrhizal fungal dominance with increasing soil depth in all forest mycorrhizal types, especially in organic horizons. Vertical changes in soil chemistry, including pH, organic matter, exchangeable cations, and extractable phosphorus, coincided with shifts in fungal community composition. Although fungal communities and soil chemistry differed among adjacent forest mycorrhizal types, variations were stronger within a given soil profile, pointing to the importance of considering horizons when characterizing soil fungal communities. Our results also suggest that in temperate forests, vertical shifts from saprotrophic to mycorrhizal fungi within organic and mineral horizons occur similarly in both ectomycorrhizal and arbuscular mycorrhizal forests.

Reversing extinction trends: new uses of (old) herbarium specimens to accelerate conservation action on threatened species.

Although often not collected specifically for the purposes of conservation, herbarium specimens offer sufficient information to reconstruct parameters that are needed to designate a species as 'at-risk' of extinction. While such designations should prompt quick and efficient legal action towards species recovery, such action often lags far behind and is mired in bureaucratic procedure. The increase in online digitization of natural history collections has now led to a surge in the number new studies on the uses of machine learning. These repositories of species occurrences are now equipped with advances that allow for the identification of rare species. The increase in attention devoted to estimating the scope and severity of the threats that lead to the decline of such species will increase our ability to mitigate these threats and reverse the declines, overcoming a current barrier to the recovery of many threatened plant species. Thus far, collected specimens have been used to fill gaps in systematics, range extent, and past genetic diversity. We find that they also offer material with which it is possible to foster species recovery, ecosystem restoration, and de-extinction, and these elements should be used in conjunction with machine learning and citizen science initiatives to mobilize as large a force as possible to counter current extinction trends.

Development and experimental demonstration of negative first-order quasi-phase matching in a periodically poled Rb-doped KTiOPO4 crystal.

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped KTiOPO4 biaxial crystal. This new approach naturally extends to other periodically poled uniaxial crystals such as periodically poled LiNbO3.

A four-year phytoremediation trial to decontaminate soil polluted by wood preservatives: phytoextraction of arsenic, chromium, copper, dioxins and furans.

Widely used as wood preservatives for the last century, Pentachlorophenol (PCP) and chromated copper arsenate (CCA) have been shown to leach from treated surfaces and contaminate soil of wood storage sites. We performed a four-year field phytoremediation trial in southern Quebec (Canada) on a site contaminated with PCP and CCA with the following objectives: (1) assess the potential of willow, fescue, alfalfa and Indian mustard to tolerate and translocate CCA and PCP residues in their aerial tissues, (2) investigate the possibility of phytoextraction of dioxins and furans, and (3) test the effect of nitrogen fertilizer on phytoremediation performance. We showed that while nitrogen fertilization increased the chlorophyll content of plants, it did not result in a significantly greater plant biomass. We also showed that plants grown in the presence of PCP/CCA residues were able to translocate and concentrate trace elements in their aerial tissues, but also dioxins and furans (PCDD/F). This suggests that plants grown on sites polluted by PCP might contain dioxins and furans and should be treated as contaminated by these toxic chemicals. Finally, the reduction of soil contaminants at the end of the trial suggests that phytoremediation is a promising approach for decontaminating such sites.

An evaluation of alternative explanations for widespread cytonuclear discordance in annual sunflowers (Helianthus).

Cytonuclear discordance is commonly observed in phylogenetic studies, yet few studies have tested whether these patterns reflect incomplete lineage sorting or organellar introgression. Here, we used whole-chloroplast sequence data in combination with over 1000 nuclear single-nucleotide polymorphisms to clarify the extent of cytonuclear discordance in wild annual sunflowers (Helianthus), and to test alternative explanations for such discordance. Our phylogenetic analyses indicate that cytonuclear discordance is widespread within this group, both in terms of the relationships among species and among individuals within species. Simulations of chloroplast evolution show that incomplete lineage sorting cannot explain these patterns in most cases. Instead, most of the observed discordance is better explained by cytoplasmic introgression. Molecular tests of evolution further indicate that selection may have played a role in driving patterns of plastid variation - although additional experimental work is needed to fully evaluate the importance of selection on organellar variants in different parts of the geographic range. Overall, this study represents one of the most comprehensive tests of the drivers of cytonuclear discordance and highlights the potential for gene flow to lead to extensive organellar introgression in hybridizing taxa.

Validation of the angular quasi-phase-matching theory for the biaxial optical class using PPRKTP.

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO4 (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Soil contamination alters the willow root and rhizosphere metatranscriptome and the root-rhizosphere interactome.

Phytoremediation using willows is thought to be a sustainable alternative to traditional remediation techniques involving excavation, transport, and landfilling. However, the complexity of the interaction between the willow and its associated highly diverse microbial communities makes the optimization of phytoremediation very difficult. Here, we have sequenced the rhizosphere metatranscriptome of four willow species and the plant root metatranscriptome for two willow species growing in petroleum hydrocarbon-contaminated and non-contaminated soils on a former petroleum refinery site. Significant differences in the abundance of transcripts related to different bacterial and fungal taxa were observed between willow species, mostly in contaminated soils. When comparing transcript abundance in contaminated vs. non-contaminated soil for each willow species individually, transcripts for many microbial taxa and functions were significantly more abundant in contaminated rhizosphere soil for Salix eriocephala, S. miyabeana and S. purpurea, in contrast to what was observed in the rhizosphere of S. caprea. This agrees with the previously reported sensitivity of S. caprea to contamination, and the superior tolerance of S. miyabeana and S. purpurea to soil contamination at that site. The root metatranscriptomes of two species were compared and revealed that plants transcripts are mainly influenced by willow species, while microbial transcripts mainly responded to contamination. A comparison of the rhizosphere and root metatranscriptomes in the S. purpurea species revealed a complete reorganization of the linkages between root and rhizosphere pathways when comparing willows growing in contaminated and non-contaminated soils, mainly because of large shifts in the rhizosphere metatranscriptome.

Greater pollination generalization is not associated with reduced constraints on corolla shape in Antillean plants.

Flowers show important structural variation as reproductive organs but the evolutionary forces underlying this diversity are still poorly understood. In animal-pollinated species, flower shape is strongly fashioned by selection imposed by pollinators, which is expected to vary according to guilds of effective pollinators. Using the Antillean subtribe Gesneriinae (Gesneriaceae), we tested the hypothesis that pollination specialists pollinated by one functional type of pollinator have maintained more similar corolla shapes through time due to more constant and stronger selection constraints compared to species with more generalist pollination strategies. Using geometric morphometrics and evolutionary models, we showed that the corolla of hummingbird specialists, bat specialists, and species with a mixed-pollination strategy (pollinated by hummingbirds and bats; thus a more generalist strategy) have distinct shapes and that these shapes have evolved under evolutionary constraints. However, we did not find support for greater disparity in corolla shape of more generalist species. This could be because the corolla shape of more generalist species in subtribe Gesneriinae, which has evolved multiple times, is finely adapted to be effectively pollinated by both bats and hummingbirds. These results suggest that ecological generalization is not necessarily associated with relaxed selection constraints.

Transcriptomic Response of Purple Willow (Salix purpurea) to Arsenic Stress.

Arsenic (As) is a toxic element for plants and one of the most common anthropogenic pollutants found at contaminated sites. Despite its severe effects on plant metabolism, several species can accumulate substantial amounts of arsenic and endure the associated stress. However, the genetic mechanisms involved in arsenic tolerance remains obscure in many model plant species used for land decontamination (phytoremediation), including willows. The present study assesses the potential of Salix purpurea cv. 'Fish Creek' for arsenic phytoextraction and reveals the genetic responses behind arsenic tolerance, phytoextraction and metabolism. Four weeks of hydroponic exposure to 0, 5, 30 and 100 mg/L revealed that plants were able to tolerate up to 5 mg/L arsenic. Concentrations of 0 and 5 mg/L of arsenic treatment were then used to compare alterations in gene expression of roots, stems and leaves using RNA sequencing. Differential gene expression revealed transcripts encoding proteins putatively involved in entry of arsenic into the roots, storage in vacuoles and potential transport through the plant as well as primary and secondary (indirect) toxicity tolerance mechanisms. A major role for tannin as a compound used to relieve cellular toxicity is implicated as well as unexpected expression of the cadmium transporter CAX2, providing a potential means for internal arsenic mobility. These insights into the underpinning genetics of a successful phytoremediating species present novel opportunities for selection of dedicated arsenic tolerant crops as well as the potential to integrate such tolerances into a wider Salix ideotype alongside traits including biomass yield, biomass quality, low agricultural inputs and phytochemical production.

Bioclimatic niches are conserved and unrelated to pollination syndromes in Antillean Gesneriaceae.

The study of the evolution of abiotic niches can be informative regarding the speciation drivers in a given group. Yet, two factors that could potentially affect niche evolution have seldom been addressed concomitantly, which are biotic interactions and geographical isolation. In this study, we used as a model group the Antillean plant genera Gesneria and Rhytidophyllum (Gesneriaceae) to evaluate the effect of pollinators and geographical isolation on the bioclimatic niche. These genera possess species characterized by interspecific geographical isolation in different islands and are pollinated by different pollinators. Some species are pollinated by hummingbirds, other by bats, while some are more generalists and are pollinated by pollinators from both functional groups. After describing the bioclimatic niches of plant species, we measured niche overlap for species pairs and we fitted Brownian motion and Ornstein-Uhlenbeck (OU) evolution models with multiple evolutionary regimes to test for an effect of pollination strategy or geographical isolation on bioclimatic niche evolution of these plants. The analysis of niche overlap between plant species, which could not be corrected for phylogenetic relationships, showed that it was significantly influenced by pollination mode and island distribution. By contrast, the best fitting evolutionary model on niche optima and tolerance was always an OU model with a unique selective regime, suggesting that neither pollination strategy nor island isolation had an important effect on bioclimatic niches at a macroevolutionary scale. Instead, we conclude that bioclimatic niches of Antillean Gesneriaceae evolved under phylogenetic conservatism and hypothesize that this macroevolutionary pattern could result from adaptation to temporally variable climates in the Antilles.

Comparative Transcriptomic Approaches Exploring Contamination Stress Tolerance in Salix sp. Reveal the Importance for a Metaorganismal de Novo Assembly Approach for Nonmodel Plants.

Metatranscriptomic study of nonmodel organisms requires strategies that retain the highly resolved genetic information generated from model organisms while allowing for identification of the unexpected. A real-world biological application of phytoremediation, the field growth of 10 Salix cultivars on polluted soils, was used as an exemplar nonmodel and multifaceted crop response well-disposed to the study of gene expression. Sequence reads were assembled de novo to create 10 independent transcriptomes, a global transcriptome, and were mapped against the Salix purpurea 94006 reference genome. Annotation of assembled contigs was performed without a priori assumption of the originating organism. Global transcriptome construction from 3.03 billion paired-end reads revealed 606,880 unique contigs annotated from 1588 species, often common in all 10 cultivars. Comparisons between transcriptomic and metatranscriptomic methodologies provide clear evidence that nonnative RNA can mistakenly map to reference genomes, especially to conserved regions of common housekeeping genes, such as actin, α/ß-tubulin, and elongation factor 1-α. In Salix, Rubisco activase transcripts were down-regulated in contaminated trees across all 10 cultivars, whereas thiamine thizole synthase and CP12, a Calvin Cycle master regulator, were uniformly up-regulated. De novo assembly approaches, with unconstrained annotation, can improve data quality; care should be taken when exploring such plant genetics to reduce de facto data exclusion by mapping to a single reference genome alone. Salix gene expression patterns strongly suggest cultivar-wide alteration of specific photosynthetic apparatus and protection of the antenna complexes from oxidation damage in contaminated trees, providing an insight into common stress tolerance strategies in a real-world phytoremediation system.