The value of long-term ecological research for evolutionary insights.

Scientists must have an integrative understanding of ecology and evolution across spatial and temporal scales to predict how species will respond to global change. Although comprehensively investigating these processes in nature is challenging, the infrastructure and data from long-term ecological research networks can support cross-disciplinary investigations. We propose using these networks to advance our understanding of fundamental evolutionary processes and responses to global change.

Lineage diversification and rampant hybridization among subspecies explain taxonomic confusion in the endemic Hawaiian fern Polypodium pellucidum.

Premise: Polypodium pellucidum, a fern endemic to the Hawaiian Islands, encompasses five ecologically and morphologically variable subspecies, suggesting a complex history involving both rapid divergence and rampant hybridization.

Methods: We employed a large target-capture data set to investigate the evolution of genetic, morphological, and ecological variation in P. pellucidum.

Does urbanisation lead to parallel demographic shifts across the world in a cosmopolitan plant?

Urbanisation is occurring globally, leading to dramatic environmental changes that are altering the ecology and evolution of species. In particular, the expansion of human infrastructure and the loss and fragmentation of natural habitats in cities is predicted to increase genetic drift and reduce gene flow by reducing the size and connectivity of populations. Alternatively, the 'urban facilitation model' suggests that some species will have greater gene flow into and within cities leading to higher diversity and lower differentiation in urban populations.

Demographic consequences of an extreme heat wave are mitigated by spatial heterogeneity in an annual monkeyflower.

Heat waves are becoming more frequent and intense with climate change, but the demographic and evolutionary consequences of heat waves are rarely investigated in herbaceous plant species. We examine the consequences of a short but extreme heat wave in Oregon populations of the common yellow monkeyflower () by leveraging a common garden experiment planted with range-wide populations and observational studies of 11 local populations. In the common garden, 89% of seedlings died during the heat wave including >96% of seedlings from geographically local populations.

Haplotype-Resolved, Chromosome-Level Assembly of White Clover (Trifolium repens L., Fabaceae).

White clover (Trifolium repens L.; Fabaceae) is an important forage and cover crop in agricultural pastures around the world and is increasingly used in evolutionary ecology and genetics to understand the genetic basis of adaptation. Historically, improvements in white clover breeding practices and assessments of genetic variation in nature have been hampered by a lack of high-quality genomic resources for this species, owing in part to its high heterozygosity and allotetraploid hybrid origin.

Unique drought resistance strategies occur among monkeyflower populations spanning an aridity gradient.

Premise: Annual plants often exhibit drought-escape and avoidance strategies to cope with limited water availability. Determining the extent of variation and factors underlying the evolution of divergent strategies is necessary for determining population responses to more frequent and severe droughts.

Methods: We leveraged five Mimulus guttatus populations collected across an aridity gradient within manipulative drought and quantitative genetics experiments to examine constitutive and terminal-drought induced responses in drought resistance traits.

Life history and chemical defense interact to drive patterns of adaptation in an annual monkeyflower.

Although chemical defenses and herbivore pressure are widely established as key targets and agents of selection, their roles in local adaptation and determining potential evolutionary responses to changing climates are often neglected. Here, we explore fitness differences between 11 rangewide M. guttatus populations in a field common garden experiment and assess the agents and targets of selection driving relative fitness patterns.

Evolution in response to climate in the native and introduced ranges of a globally distributed plant.

The extent to which species can adapt to spatiotemporal climatic variation in their native and introduced ranges remains unresolved. To address this, we examined how clines in cyanogenesis (hydrogen cyanide [HCN] production-an antiherbivore defense associated with decreased tolerance to freezing) have shifted in response to climatic variation in space and time over a 60-year period in both the native and introduced ranges of Trifolium repens. HCN production is a polymorphic trait controlled by variation at two Mendelian loci (Ac and Li).

Adaptive and nonadaptive causes of heterogeneity in genetic differentiation across the Mimulus guttatus genome.

Genetic diversity becomes structured among populations over time due to genetic drift and divergent selection. Although population structure is often treated as a uniform underlying factor, recent resequencing studies of wild populations have demonstrated that diversity in many regions of the genome may be structured quite dissimilar to the genome-wide pattern. Here, we explored the adaptive and nonadaptive causes of such genomic heterogeneity using population-level, whole genome resequencing data obtained from annual Mimulus guttatus individuals collected across a rugged environment landscape.

Evolutionary history and ecology shape the diversity and abundance of phytochemical arsenals across monkeyflowers.

We examine the extent to which phylogenetic effects and ecology are associated with macroevolutionary patterns of phytochemical defence production across the Mimulus phylogeny. We grew plants from 21 species representing the five major sections of the Mimulus phylogeny in a common garden to assess how the arsenals (NMDS groupings) and abundances (concentrations) of a phytochemical defence, phenylpropanoid glycosides (PPGs), vary across the phylogeny. Very few PPGs are widespread across the genus, but many are common to multiple sections of the genus.

Population responses to a historic drought across the range of the common monkeyflower (Mimulus guttatus).

Premise: Due to climate change, more frequent and intense periodic droughts are predicted to increasingly pose major challenges to the persistence of plant populations. When a severe drought occurs over a broad geographical region, independent responses by individual populations provide replicated natural experiments for examining the evolution of drought resistance and the potential for evolutionary rescue.

Methods: We used a resurrection approach to examine trait evolution in populations of the common monkeyflower, Mimulus guttatus, exposed to a record drought in California from 2011 to 2017.

The Genetic Architecture of Plant Defense Trade-offs in a Common Monkeyflower.

Determining how adaptive combinations of traits arose requires understanding the prevalence and scope of genetic constraints. Frequently observed phenotypic correlations between plant growth, defenses, and/or reproductive timing have led researchers to suggest that pleiotropy or strong genetic linkage between variants affecting independent traits is pervasive. Alternatively, these correlations could arise via independent mutations in different genes for each trait and extensive correlational selection.

Lagging Adaptation to Climate Supersedes Local Adaptation to Herbivory in an Annual Monkeyflower.

While native populations are often adapted to historical biotic and abiotic conditions at their home site, populations from other locations in the range may be better adapted to current conditions due to changing climates or extreme conditions in a single year. We examine whether local populations of a widespread species maintain a relative advantage over distant populations that have evolved at sites better matching the current climate. Specifically, we grew lines derived from low- and high-elevation annual populations in California and Oregon of the common monkeyflower () and conducted phenotypic selection analyses in low- and high-elevation common gardens in Oregon to examine relative fitness and the traits mediating relative fitness.

Are drought resistance strategies associated with life history strategy? A commentary on: 'Arabidopsis species deploy distinct strategies to cope with drought stress'.

This article comments on: . species deploy distinct strategies to cope with drought stress. Annals of Botany : 27–40.

Freeze-induced cyanide toxicity does not maintain the cyanogenesis polymorphism in white clover (Trifolium repens).

Premise Of The Study: The maintenance of adaptive polymorphisms within species requires fitness trade-offs reflecting selection for each morph. Cyanogenesis, the ability to produce hydrogen cyanide (HCN) after tissue damage, occurs in >3000 plant species and exists as a discrete polymorphism in white clover. This polymorphism is spatially distributed in recurrent clines, with higher frequencies of cyanogenic plants in warmer climates.

Competition drives trait evolution and character displacement between Mimulus species along an environmental gradient.

Closely related species may evolve to coexist stably in sympatry through niche differentiation driven by in situ competition, a process termed character displacement. Alternatively, past evolution in allopatry may have already sufficiently reduced niche overlap to permit establishment in sympatry, a process called ecological sorting. The relative importance of each process to niche differentiation is contentious even though they are not mutually exclusive and are both mediated via multivariate trait evolution.

Optimal defense theory explains deviations from latitudinal herbivory defense hypothesis.

The latitudinal herbivory defense hypothesis (LHDH) postulates that the prevalence of species interactions, including herbivory, is greater at lower latitudes, leading to selection for increased levels of plant defense. While latitudinal defense clines may be caused by spatial variation in herbivore pressure, optimal defense theory predicts that clines could also be caused by ecogeographic variation in the cost of defense. For instance, allocation of resources to defense may not increase plant fitness when growing seasons are short and plants must reproduce quickly.

The evolution of drought escape and avoidance in natural herbaceous populations.

While the functional genetics and physiological mechanisms controlling drought resistance in crop plants have been intensely studied, less research has examined the genetic basis of adaptation to drought stress in natural populations. Drought resistance adaptations in nature reflect natural rather than human-mediated selection and may identify novel mechanisms for stress tolerance. Adaptations conferring drought resistance have historically been divided into alternative strategies including drought escape (rapid development to complete a life cycle before drought) and drought avoidance (reducing water loss to prevent dehydration).

Replicate altitudinal clines reveal that evolutionary flexibility underlies adaptation to drought stress in annual Mimulus guttatus.

Examining how morphology, life history and physiology vary along environmental clines can reveal functional insight into adaptations to climate and thus inform predictions about evolutionary responses to global change. Widespread species occurring over latitudinal and altitudinal gradients in seasonal water availability are excellent systems for investigating multivariate adaptation to drought stress. Under common garden conditions, we characterized variation in 27 traits for 52 annual populations of Mimulus guttatus sampled from 10 altitudinal transects.

Adaptive gains through repeated gene loss: parallel evolution of cyanogenesis polymorphisms in the genus Trifolium (Fabaceae).

Variation in cyanogenesis (hydrogen cyanide release following tissue damage) was first noted in populations of white clover more than a century ago, and subsequent decades of research have established this system as a classic example of an adaptive chemical defence polymorphism. Here, we document polymorphisms for cyanogenic components in several relatives of white clover, and we determine the molecular basis of this trans-specific adaptive variation. One hundred and thirty-nine plants, representing 13 of the 14 species within Trifolium section Trifoliastrum, plus additional species across the genus, were assayed for cyanogenic components (cyanogenic glucosides and their hydrolysing enzyme, linamarase) and for the presence of underlying cyanogenesis genes (CYP79D15 and Li, respectively).

Aridity shapes cyanogenesis cline evolution in white clover (Trifolium repens L.).

Adaptive differentiation between populations is often proposed to be the product of multiple interacting selective pressures, although empirical support for this is scarce. In white clover, populations show adaptive differentiation in frequencies of cyanogenesis, the ability to produce hydrogen cyanide after tissue damage. This polymorphism arises through independently segregating polymorphisms for the presence/absence of two required cyanogenic components, cyanogenic glucosides and their hydrolysing enzyme.

Recurrent gene deletions and the evolution of adaptive cyanogenesis polymorphisms in white clover (Trifolium repens L.).

Understanding the molecular evolution of genes that underlie intraspecific polymorphisms can provide insights into the process of adaptive evolution. For adaptive polymorphisms characterized by gene presence/absence (P/A) variation, underlying loci commonly show signatures of long-term balancing selection, with gene-presence and gene-absence alleles maintained as two divergent lineages. We examined the molecular evolution of two unlinked P/A polymorphisms that underlie a well-documented adaptive polymorphism for cyanogenesis (hydrogen cyanide release with tissue damage) in white clover.

Rapid evolution of an adaptive cyanogenesis cline in introduced North American white clover (Trifolium repens L.).

White clover is polymorphic for cyanogenesis (HCN production after tissue damage), and this herbivore defence polymorphism has served as a classic model for studying adaptive variation. The cyanogenic phenotype requires two interacting biochemical components; the presence/absence of each component is controlled by a simple Mendelian gene (Ac/ac and Li/li). Climate-associated cyanogenesis clines occur in both native (Eurasian) and introduced populations worldwide, with cyanogenic plants predominating in warmer locations.