| 1. |
- Santangelo, James S., et al.
(author)
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Global urban environmental change drives adaptation in white clover
- 2022
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 375
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Journal article (peer-reviewed)abstract
- Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural dines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale.
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| 2. |
- Garcia, Yedra, et al.
(author)
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Floral scent divergence across an elevational hybrid zone with varying pollinators
- 2023
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In: Oecologia. - : Springer Nature. - 0029-8549 .- 1432-1939. ; 201:1, s. 45-57
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Journal article (peer-reviewed)abstract
- Divergence in floral traits attractive to different pollinators can promote reproductive isolation in related species. When isolation is incomplete, hybridization may occur, which offers the opportunity to explore mechanisms underlying reproductive isolation. Recent work suggests that divergence in floral scent may frequently contribute to reproductive barriers, although such divergence has seldom been examined in species with generalized pollination. Here, we used two closely related Penstemon species, P. newberryi and P. davidsonii, and their natural hybrids from an elevational gradient with pollinator communities that are predicted to vary in their reliance on floral scent (i.e., primarily hummingbirds at low elevation vs. bees at high elevation). The species vary in a suite of floral traits, but scent is uncharacterized. To address whether scent varies along elevation and potentially contributes to reproductive isolation, we genetically characterized individuals collected at field and identified whether they were parental species or hybrids. We then characterized scent amount and composition. Although the parental species had similar total emissions, some scent characteristics (i.e., scent composition, aromatic emission) diverged between them and may contribute to their isolation. However, the species emitted similar compound sets which could explain hybridization in the contact area. Hybrids were similar to the parents for most scent traits, suggesting that their floral scent would not provide a strong barrier to backcrossing. Our study suggests floral scent may be a trait contributing to species boundaries even in plants with generalized pollination, and reinforces the idea that evolutionary pollinator transitions may involve changes in multiple floral traits.
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| 3. |
- Burdon, Rosalie, 1988-, et al.
(author)
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Scented nectar and the challenge of measuring honest signals in pollination
- 2020
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In: Journal of Ecology. - : WILEY. - 0022-0477 .- 1365-2745. ; 108:5, s. 2132-2144
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Journal article (peer-reviewed)abstract
- Nectar scents are thought to function as honest signals of reward used by pollinators, but this hypothesis has rarely been tested. UsingPenstemon digitalis, we examined honest signalling of the nectar volatile (S)-(+)-linalool and pollinator responses to linalool in both field and laboratory settings. Because our previous work showed that linalool emission was associated with higher female fitness and that nectar is scented with linalool, we hypothesized that linalool was an honest signal of nectar reward. To assess honesty, we measured linalool-nectar associations including nectar volume, sugar amount, concentration and production rate for inflorescences and flowers in several populations. We also assessed whetherBombus impatiens, the main pollinator ofP. digitalisat our sites, can use linalool as a foraging signal. We supplemented real or artificial flowers in the field and laboratory with varying linalool-nectar combinations to measure pollinator behavioural responses. We found that an inflorescence's linalool emissions could be used to predict nectar rewards inP. digitalis, but this was driven by indirect associations with display size rather than directly advertising more profitable flowers. For flowers within inflorescences there was also no evidence for an association between signal and reward. Field tests of bumblebee behaviour were inconclusive. However, in laboratory assays, bumblebees generally used variation in linalool emissions to choose more profitable flowers, demonstrating they can detect differences in linalool emitted byP. digitalisand associate them with reward profitability. These results suggest experiments that decouple display size, scent and reward are necessary to assess whether (and when) bees prefer higher linalool emissions. Bees preferred nectars with lower linalool concentrations when linalool flavoured the nectar solution, suggesting the potential for conflicting pressures on scent emission in the field. Synthesis. Our results highlight the challenges of assessing function for traits important to fitness and suggest that the perception of floral signalling honesty may depend on whether pollinators use inflorescences or flowers within inflorescences when making foraging decisions. We conclude that future research on honest signalling in flowering plants, as well as its connection to phenotypic selection, should explicitly define honesty, in theoretical and experimental contexts.
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| 4. |
- Egan, Paul A., et al.
(author)
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Pollinators and herbivores interactively shape selection on strawberry defence and attraction
- 2021
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In: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 5:6, s. 636-643
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Journal article (other academic/artistic)abstract
- Tripartite interactions between plants, herbivores, and pollinators hold fitness consequences for most angiosperms. However, little is known on how plants evolve in response-and in particular what the net selective outcomes are for traits of shared relevance to pollinators and herbivores. In this study, we manipulated herbivory ("presence" and "absence" treatments) and pollination ("open" and "hand pollination" treatments) in a full factorial common-garden experiment with woodland strawberry (Fragaria vesca L.). This design allowed us to quantify the relative importance and interactive effects of herbivore- and pollinator-mediated selection on nine traits related to plant defence and attraction. Our results showed that pollinators imposed stronger selection than herbivores on traits related to both direct and indirect (i.e., tritrophic) defence. However, conflicting selection was imposed on inflorescence density: a trait that appears to be shared by herbivores and pollinators as a host plant signal. However, in all cases, selection imposed by one agent depended largely on the presence or ecological effect of the other, suggesting that dynamic patterns of selection could be a common outcome of these interactions in natural populations. As a whole, our findings highlight the significance of plant-herbivore-pollinator interactions as potential drivers of evolutionary change, and reveal that pollinators likely play an underappreciated role as selective agents on direct and in direct plant defence.
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| 5. |
- Garcia, Yedra, et al.
(author)
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Spatial variation in scent emission within flowers
- 2021
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In: Nordic Journal of Botany. - : John Wiley & Sons. - 0107-055X .- 1756-1051. ; 39:7
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Journal article (peer-reviewed)abstract
- Floral scent is considered an important long-distance signal that attracts pollinators, but also has been suggested to function at shorter distances such as within-flower nectar guides or as a defense against antagonists. Indeed, in some species floral scent production and emission show spatial patterns of variation within flowers, as certain compounds are exclusively emitted from specific floral tissues. In other species, the different volatile organic compounds that constitute the floral bouquet are emitted evenly from the entire flower. Here, we summarize the current evidence on floral scent variation within flowers by combining a literature review of published data on tissue-level floral scent variation (41 species) with floral scent dissections (17 species). For each species, we recorded the total number of volatile compounds separately and grouped in major chemical classes. To facilitate comparisons across diverse species, we compared volatiles emitted by 1) the whole flower, 2) the visual floral tissues (i.e. petals and colored structures), 3) non-visual floral tissues (i.e. green parts and reproductive structures), as well as 4) the compounds emitted by both visual and non-visual tissues. Results show that floral scent variation is frequent, but by no means ubiquitous, occurring in species from distantly related groups. We discuss the two main functional hypotheses promoting floral scent variation within flowers, i.e. as a pollinator attractant at short-distances or a defensive function against antagonists, together with non-functional hypotheses (e.g. pleiotropic effects, ecological costs). We point out further directions on this topic and suggest experimental approaches testing the attractiveness of compounds emitted by different floral parts alone and in combination with other floral signals. Our synthesis provides a foundation for future studies on the functional ecology of floral scent and reinforces the idea of high complexity in floral chemical signals.
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| 6. |
- García, Yedra, et al.
(author)
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Water deficit changes patterns of selection on floral signals and nectar rewards in the common morning glory
- 2023
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In: AoB Plants. - 2041-2851. ; 15:5
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Journal article (peer-reviewed)abstract
- Understanding whether and how resource limitation alters phenotypic selection on floral traits is key to predict the evolution of plant-pollinator interactions under climate change. Two important resources predicted to decline with our changing climate are pollinators and water in the form of increased droughts. Most work, however, has studied these selective agents separately and in the case of water deficit, studies are rare. Here, we use the common morning glory (Ipomoea purpurea) to investigate the effects of experimental reduction in pollinator access and water availability on floral signals and nectar rewards and their effects on phenotypic selection on these traits. We conducted a manipulative experiment in a common garden, where we grew plants in three treatments: (1) pollinator restriction, (2) water reduction and (3) unmanipulated control. Plants in pollinator restriction and control treatments were well-watered compared to water deficit. We found that in contrast to pollinator restriction, water deficit had strong effects altering floral signals and nectar rewards but also differed in the direction and strength of selection on these traits compared to control plants. Water deficit increased the opportunity for selection, and selection in this treatment favoured lower nectar volumes and larger floral sizes, which might further alter pollinator visitation. In addition, well-watered plants, both in control and pollinator deficit, showed similar patterns of selection to increase nectar volume suggesting non-pollinator-mediated selection on nectar. Our study shows that floral traits may evolve in response to reduction in water access faster than to declines in pollinators and reinforces that abiotic factors can be important agents of selection for floral traits. Although only few experimental selection studies have manipulated access to biotic and abiotic resources, our results suggest that this approach is key for understanding how pollination systems may evolve under climate change.
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| 7. |
- Kuppler, Jonas, et al.
(author)
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Global gradients in intraspecific variation in vegetative and floral traits are partially associated with climate and species richness
- 2020
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In: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 29:6, s. 992-1007
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Journal article (peer-reviewed)abstract
- AimIntraspecific trait variation (ITV) within natural plant communities can be large, influencing local ecological processes and dynamics. Here, we shed light on how ITV in vegetative and floral traits responds to large‐scale abiotic and biotic gradients (i.e., climate and species richness). Specifically, we tested whether associations of ITV with temperature, precipitation and species richness were consistent with any of four hypotheses relating to stress tolerance and competition. Furthermore, we estimated the degree of correlation between ITV in vegetative and floral traits and how they vary along the gradients.LocationGlobal.Time period1975–2016.Major taxa studiedHerbaceous and woody plants.MethodsWe compiled a dataset of 18,401 measurements of the absolute extent of ITV (measured as the coefficient of variation) in nine vegetative and seven floral traits from 2,822 herbaceous and woody species at 2,372 locations.ResultsLarge‐scale associations between ITV and climate were trait specific and more prominent for vegetative traits, especially leaf morphology, than for floral traits. The ITV showed pronounced associations with climate, with lower ITV values in colder areas and higher values in drier areas. The associations of ITV with species richness were inconsistent across traits. Species‐specific associations across gradients were often idiosyncratic, and covariation in ITV was weaker between vegetative and floral traits than within the two trait groups.Main conclusionsOur results show that, depending on the traits considered, ITV either increased or decreased with climate stress and species richness, suggesting that both factors can constrain or enhance ITV, which might foster plant‐population persistence in stressful conditions. Given the species‐specific responses and covariation in ITV, associations can be hard to predict for traits and species not yet studied. We conclude that consideration of ITV can improve our understanding of how plants cope with stressful conditions and environmental change across spatial and biological scales.
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| 8. |
- Palmqvist, Björn, et al.
(author)
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Differences in Floral Scent and Petal Reflectance Between Diploid and Tetraploid Chamerion angustifolium
- 2021
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In: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 9
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Journal article (peer-reviewed)abstract
- Genome duplication in plants is thought to be a route to speciation due to cytotype incompatibility. However, to reduce cross-pollination between cytotypes in animal-pollinated species, distinctive floral phenotypes, which would allow pollinator-mediated assortative mating between flowers, are also expected. Chamerion angustifolium is a Holarctic species that forms a hybrid zone between diploid and tetraploid populations in the North American Rocky Mountains. Extensive research has shown that these cytotypes differ in many ways, including some floral traits, and that pollinators can discriminate between cytotypes, leading to assortative mating. However, two signals commonly used by insect pollinators have not been measured for this species, namely petal colour and floral scent. Using greenhouse-grown diploids and tetraploids of C. angustifolium from the ploidy hybrid-zone in the North American Rocky Mountains, we show that both floral scent signals and petal reflectance differ between cytotypes. These differences, along with differences in flower size shown previously, could help explain pollinator-mediated assortative mating observed in previous studies. However, these differences in floral phenotypes may vary in importance to pollinators. While the differences in scent included common floral volatiles readily detected by bumblebees, the differences in petal reflectance may not be perceived by bees based on their visual sensitivity across the spectra. Thus, our results suggest that differences in floral volatile emissions are more likely to contribute to pollinator discrimination between cytotypes and highlight the importance of understanding the sensory systems of pollinators when examining floral signals.
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