Environmental variation within a species’ range can create contrasting selective pressures, leading to divergent selection and novel adaptations. The conservation value of populations inhabiting ...environmentally marginal areas remains in debate and is closely related to the adaptive potential in changing environments. Strong selection caused by stressful conditions may generate novel adaptations, conferring these populations distinct evolutionary potential and high conservation value under climate change. On the other hand, environmentally marginal populations may be genetically depauperate, with little potential for new adaptations to emerge. Here, we explored the use of ecological niche models (ENMs) linked with common garden experiments to predict and test for genetically determined phenotypic differentiation related to contrasting environmental conditions. To do so, we built an ENM for the alpine plant Silene ciliata in central Spain and conducted common garden experiments, assessing flowering phenology changes and differences in leaf cell resistance to extreme temperatures. The suitability patterns and response curves of the ENM led to the predictions that: (1) the environmentally marginal populations experiencing less snowpack and higher minimum temperatures would have delayed flowering to avoid risks of late‐spring frosts and (2) those with higher minimum temperatures and greater potential evapotranspiration would show enhanced cell resistance to high temperatures to deal with physiological stress related to desiccation and heat. The common garden experiments revealed the expected genetically based phenotypic differentiation in flowering phenology. In contrast, they did not show the expected differentiation for cell resistance, but these latter experiments had high variance and hence lower statistical power. The results highlight ENMs as useful tools to identify contrasting putative selective pressures across species ranges. Linking ENMs with common garden experiments provides a theoretically justified and practical way to study adaptive processes, including insights regarding the conservation value of populations inhabiting environmentally marginal areas under ongoing climate change.
Environmental variation within a species’ range can create contrasting selective pressures, leading to divergent selection and novel adaptations. Here, we explored the use of ecological niche models (ENMs) linked with common garden experiments to predict and test for genetically determined phenotypic differentiation related to contrasting environmental conditions. The results highlight ENMs as useful tools to identify contrasting putative selective pressures across species ranges. ENMs in conjunction with laboratory and field experiments provide a theoretically justified and practical way to study adaptive processes, including the evolutionary capabilities of species confronted with climate change.
Aim
Understanding the historical and contemporaneous drivers of invasion success in island systems can decisively contribute to identifying sources and pathways that are more likely to give rise to ...new invaders. Based on a floristic‐driven approach, we aimed at determining the origins of the invasive alien flora of the Canary Islands and shedding light in the mechanisms shaping their distribution within the archipelago.
Location
Canary Islands.
Taxon
Vascular plants.
Methods
An updated checklist of the invasive alien flora of the Canary Islands was assembled along with complementary information related to the native biogeographical regions, stage of invasiveness and dates of naturalization. Statistical models were employed to describe differences in the number of species over space and time. We also used multivariate techniques to evaluate competing hypotheses related to the mechanisms driving invasive floristic composition within the archipelago.
Results
We provided a list of 149 alien plant species with a certain degree of invasiveness. The greatest number of invasive species originated from the Neotropics followed by the Cape Region, tropical Africa and the Mediterranean Basin. We observed a slow but steady increase in numbers of invasive species until the 1950s, followed by a stronger rise thereafter. In order to explain composition dissimilarity of the invasive flora among islands, a climatic matching hypothesis was fully supported, with geographic isolation and contemporary human‐mediated connectivity hypotheses receiving less and null support respectively.
Main Conclusions
We showed that the Neotropical region is the main source of plant invasions to the Canary Islands, outnumbering those from other regions with a Mediterranean‐type bioclimate. The assembly of the invasive flora within the archipelago appears to be driven primarily by climate, but with geographic distance also playing a role. This study calls for archipelago‐dependent assessments of the underlying mechanisms that contribute to plant invasion success within insular systems.
To what extent do parallel and unique local adaptation occur along elevational gradients? In a reciprocal transplant experiment, Bachmann and Van Buskirk found stronger evidence for parallel ...adaptation to elevation than for unique local adaptation in Rana temporaria populations of the Swiss Alps. This finding has important implications for understanding gene flow effects on adaptive patterns and provides a useful investigative framework for the study of adaptation.
In the present framework of global warming, it is unclear whether evolutionary adaptation can happen quick enough to preserve the persistence of many species. Specifically, we lack knowledge about ...the adaptive potential of the different populations in relation to the various constraints that may hamper particular adaptations. There is evidence indicating that early flowering often provides an adaptive advantage to plants in temperate zones in response to global warming. Thus, the objective of this study was to assess the adaptive potential for advancing flowering onset in Lupinus angustifolius L. (Fabaceae). Seeds from four populations from two contrasting latitudes in Spain were collected and sown in a common garden environment. Selecting the 25% of the individuals that flowered earlier in the first generation, over three generations, three different early flowering selection lines were established, involving both self‐crosses and outcrosses. All artificial selection lines advanced their flowering significantly with respect to the control line in the northernmost populations, but not in the southern ones. Selection lines obtained from outcrossing had a greater advancement in flowering than those from self‐crossing. No differences were found in the number or weight of the seeds produced between control and artificial selection lines, probably because plants in the common garden were drip irrigated. These results suggest that northern populations may have a greater adaptive potential and that southern populations may be more vulnerable in the context of climate warming. However, earlier flowering was also associated with changes in other traits (height, biomass, shoot growth, specific leaflet area, and leaflet dry matter content), and the effects of these changes varied greatly depending on the latitude of the population and selection line. Assessments of the ability of populations to cope with climate change through this and other approaches are essential to manage species and populations in a more efficient way.
The evolutionary potential of populations inhabiting marginal areas has been extensively debated and directly affects their conservation value. Gene flow is one of the main factors influencing ...selection, adaptive potential and thus, local adaptation processes in marginal areas. The effects of differential gene flow provenance are still not well understood, since studies on gene flow between marginal populations have been underrepresented in the literature. This kind of gene flow can be especially beneficial because it can provide both adaptive allelic combinations originated under similar environmental conditions and genetic variation on which selection can act.
We conducted a study on the effects of different gene flow provenance on marginal populations of Mediterranean alpine Silene ciliata Pourret (Caryophyllaceae) replicated in three mountain ranges of Central Spain. The delineation of optimal and marginal areas of the species distribution was based on environmental differentiation and relied on the ecological definition of centrality and marginality. We experimentally tested the effect of three different types of pollen‐mediated gene flow on germination rate, seedling size and survival rate in marginal populations and assessed their effects by establishing in situ common gardens. To further assess the evolutionary potential of marginal populations, we performed a reciprocal sowing experiment and measured the same fitness components to determine the extent of local adaptation.
We found that gene flow between marginal populations improved germination rate and seedling survival with regard to gene flow from optimal to marginal populations and within marginal populations. In reciprocal sowing experiments, seedling survival rate was higher when the seed source was from marginal areas than when it was from optimal areas in both marginal and optimal sowing sites.
Synthesis. Our results suggest that gene flow between marginal populations from similar environmental conditions increases the fitness of the recipient population by increasing genetic diversity and simultaneously providing adaptive alleles generated under similar selective pressures. Results also highlight the adaptive potential of marginal populations as genetic diversity from marginal areas may provide a fitness advantage to the populations in optimal areas. In this context, the adaptive value of marginal populations increases their relevance and potential use in conservation management.
Resumen
El potencial evolutivo de las poblaciones que habitan en áreas marginales ha sido ampliamente debatido y afecta directamente a su valor de conservación. El flujo genético es uno de los principales factores que influyen sobre la selección, el potencial adaptativo y, por tanto, sobre los procesos de adaptación local en áreas marginales. Los efectos diferenciales del flujo genético según su procedencia aún no se comprenden bien ya que los estudios sobre el flujo genético entre poblaciones marginales son muy escasos en la literatura. Este tipo de flujo genético puede ser especialmente beneficioso porque puede proporcionar combinaciones alélicas adaptativas originadas en condiciones ambientales similares y aportar variación genética en las poblaciones, sobre la cual puede actuar la selección.
Realizamos un estudio sobre los efectos de diferentes procedencias de flujo genético en poblaciones marginales de Silene ciliata Pourret (Caryophyllaceae), una especie alpina del Mediterráneo, en tres cadenas montañosas del centro de España. Las áreas óptimas y marginales se delimitaron basándose en la diferenciación ambiental entre ellas y en la definición ecológica de centralidad‐marginalidad Estudiamos experimentalmente el efecto de tres tipos diferentes de flujo genético mediados por polen sobre la tasa de germinación, el tamaño de las plántulas y la tasa de supervivencia en poblaciones marginales y evaluamos sus efectos realizando jardines comunes in situ. Para evaluar de manera directa el potencial evolutivo de las poblaciones marginales, realizamos un experimento de siembra recíproca y tomamos medidas de las mismas variables utilizadas en el experimento anterior para determinar el alcance de la adaptación local.
Encontramos que el flujo de genes entre poblaciones marginales mejoró la tasa de germinación y la supervivencia de las plántulas con respecto al flujo de genes de poblaciones óptimas a marginales y dentro de poblaciones marginales. En los experimentos de siembra recíproca, la tasa de supervivencia de las plántulas fue mayor, tanto en áreas de siembra marginales como óptimas, cuando las semillas provenían de áreas marginales que cuando provenían de áreas óptimas.
Síntesis. Nuestros resultados sugieren que el flujo de genes entre poblaciones marginales que experimentan condiciones ambientales similares mejora la eficacia biológica de la población receptora al aumentar la diversidad genética y, simultáneamente, proporcionar alelos adaptativos generados bajo presiones selectivas similares. Los resultados también destacan el potencial adaptativo de las poblaciones marginales, ya que la diversidad genética de las áreas marginales puede proporcionar una mejora en la eficacia biológica de las poblaciones en las áreas óptimas. En este contexto, el valor adaptativo de las poblaciones marginales aumenta su relevancia y uso potencial en el manejo de la conservación.
Our results suggest that gene flow between marginal populations from similar environmental conditions increases the fitness of the recipient population by increasing genetic diversity and simultaneously providing adaptive alleles generated under similar selective pressures. Results also highlight the adaptive potential of marginal populations as genetic diversity from marginal areas may provide a fitness advantage to the populations in optimal areas. In this context, the adaptive value of marginal populations increases their relevance and potential use in conservation management.
Agricultural fields are commonly characterized by high nutrient and water availabilities, which are favourable for plant growth. Such conditions might promote the evolution of resource‐acquisitive ...strategies. We asked whether crop plants show root traits typical of resource‐acquisitive strategies and whether this strategy is primarily a result of their evolution under domestication or of the early selection of successful candidates for domestication.
We studied a set of 30 crop species and their wild progenitors. We set up a greenhouse experiment to measure five root traits: root thickness, root tissue density, specific root length (SRL), root mass fraction (RMF) and root length ratio. In addition, we compiled data from other wild herbaceous species, growth in similar conditions to this experiment, to place the root traits of our crops in the context of wider botanical variation.
Wild progenitors had thicker and less dense roots, with higher RMF and lower SRL, than other wild herbs. Thicker and less dense roots are indicative of fertile soils, which suggest that wild progenitors could have been adapted for success in agricultural conditions. Additionally, we found that domestication generally increased total plant dry mass, but none of the root traits evolved consistently towards a more resource‐acquisitive strategy after domestication across all species. Root trait values differed between progenitors and crop species for most pairs surveyed, but this occurred in diverse directions depending on crop species. Such differences were independent of phylogeny, functional group or variability in the domestication processes, such as timing of the domestication event or organ under focal artificial selection.
Our comparative study revealed that the root phenotype exhibited by wild progenitors (thick roots with low density and SRL), when compared with other wild herbs, was in accordance with plants typical of fertile habitats. However, none of the root traits reacted to domestication in accordance with evolution towards faster growth strategies. Thus, the adaptation of crop root phenotypes to the fertile conditions of agricultural fields might be largely determined by early choices of wild species, rather than by further evolution under domestication.
A plain language summary is available for this article.
Plain Language Summary
Phenology is often identified as one of the main structural driving forces of plant - flower visitor networks. Nevertheless, we do not yet have a full understanding of the effects of phenology in ...basic network build up mechanisms such as ecological modularity. In this study, we aimed to identify the effect of within-season temporal variation of plant and flower visitor activity on the network structural conformation. Thus, we analysed the temporal dynamics of a plant - flower visitor network in two Mediterranean alpine communities during one complete flowering season. In our approach, we built quantitative interaction networks and studied the dynamics through temporal beta diversity of species, interaction changes and modularity analysis. Within-season dissimilarity in the identity of interactions was mainly caused by species replacement through time (species turnover). Temporal replacement of species and interactions clearly impacted modularity, to the extent that species phenology emerged as a strong determinant of modularity in our networks. From an applied perspective, our results highlight the importance of considering the temporal variation of species interactions throughout the flowering season and the requirement of making comprehensive temporal sampling when aiming to build functionally consistent interaction networks.
Switching plant species visited by pollinators (partner flexibility) has been proposed as a behavioural mechanism able to attenuate the negative impacts of shifts in plant communities on pollination. ...However, it is unclear whether the magnitude of such response is generalizable or depends on the environmental context. Moreover, the ability of pollinators to exploit plants with dissimilar traits (trait flexibility) has been overlooked, even though it can affect the spectrum of new partners available.
To shed some light on this problem, we quantified partner and trait flexibility in five communities from four different environments, from Alpine to semi‐arid. We evaluated whether the rate at which pollinators incorporated new plant species throughout the flowering season was similar across communities or context dependent. Then, we assessed whether pollinators changed the type of flowers visited and if such trait flexibility was related to their capacity to visit new plant species. Finally, we developed an agent‐based model to explore whether diet flexibility can protect pollination when the plant community changes. To this end, we used scenarios of phenological decoupling.
In general, pollinators switched interaction partners to cope with the temporal replacement of plant species. Yet, the magnitude of such behaviour varied across communities, probably in response to differences in the number of floral resources available. Also, pollinators were able to visit plant species with dissimilar traits, though both components of diet flexibility (partner identity and traits) did not necessarily covary. Thus, to have a full picture of pollinators' diet flexibility, we need to consider the floral traits of partners. Finally, our theoretical model shows that diet flexibility can protect pollination after shifts in plant communities, but that such positive effects are limited by trait‐matching between co‐occurring species.
Synthesis. Overall, our study highlights the importance of incorporating plant traits when evaluating the ability of pollinators to find new interaction partners. Besides, our simulation results suggest that diet flexibility may not unequivocally protect pollination against changes in plant communities, especially if they entail shifts in the characteristics of the floral assemblage, and hence, the ability of pollinators to find new interaction partners can be compromised.
Overall, our study highlights the importance of incorporating plant traits when evaluating the ability of pollinators to find new interaction partners. Besides, our simulation results suggest that diet flexibility may not unequivocally protect pollination against changes in plant communities, especially if they entail shifts in the characteristics of the floral assemblage, and hence, the ability of pollinators to find new interaction partners can be compromised.
Summary
Mutualistic interactions structure ecological communities and they are strongly influenced by the combined effect of different drivers of global change. Land‐use changes and global warming ...have elicited rapid shrub encroachment in alpine grasslands in recent decades, which may have detrimental outcomes for native alpine forbs. In spite of the importance of this process, we lack knowledge about how shrub encroachment modifies community‐wide patterns of plant–pollinator mutualistic interactions.
Based on the functional biodiversity hypothesis (FBH), which predicts higher pollinator biodiversity in species‐rich plant communities, we asked whether the increase in nutritional resources available for pollinators due to shrub expansion modifies pollinator niche breadth and species richness, and whether these changes affect plant–plant interactions.
For this purpose, we compared quantitative plant–flower visitor interaction network assemblages at replicated plots in two habitat types in dry cryophilic grasslands of Sierra de Guadarrama (Spain): (i) encroached pastures (EP) and (ii) pastures dominated by forb species where shrub species are absent (PA).
As predicted by FBH, flower visitor richness increased in EP, but their niche breadth did not vary. Furthermore, shrubs had more interactions with flower visitors and received more visits per plant than forbs in EP in agreement with their significantly higher linkage and strength.
Overall, results revealed that moderate levels of shrub encroachment affected the flower visitation patterns of forb species in alpine grasslands as flower visitor diversity increased and plant–plant competition for shared flower visitors became greater. These findings highlight the need to use an integrative approach to study the cascading effects of global change drivers on species interactions and their impact on the structure and functioning of threatened ecological communities.
Lay Summary
Although the ecological network approach has substantially contributed to the study of plant-pollinator interactions, current understanding of their functional structure is biased towards diurnal ...pollinators. Nocturnal pollinators have been systematically ignored despite the publication of several studies that have tried to alleviate this diurnal bias. Here, we explored whether adding this neglected group of pollinators had a relevant effect on the overall architecture of three high mountain plant-pollinator networks. Including nocturnal moth pollinators modified network properties by decreasing total connectivity, connectance, nestedness and robustness to plant extinction; and increasing web asymmetry and modularity. Nocturnal moths were not preferentially connected to the most linked plants of the networks, and they were grouped into a specific "night" module in only one of the three networks. Our results indicate that ignoring the nocturnal component of plant-pollinator networks may cause changes in network properties different from those expected from random undersampling of diurnal pollinators. Consequently, the neglect of nocturnal interactions may provide a distorted view of the structure of plant-pollinator networks with relevant implications for conservation assessments.
PDF
