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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 (Erythranthe guttata) and conducted phenotypic selection analyses in low- and high-elevation common gardens in Oregon to examine relative fitness and the traits mediating relative fitness. Californian low-elevation populations have the highest relative fitness at the low-elevation site, and Californian high-elevation populations have the highest relative fitness at the high-elevation site. Relative fitness differences are mediated by selection for properly timed transitions to flowering, with selection favoring more rapid growth rates at the low-elevation site and greater vegetative biomass prior to flowering at the high-elevation site. Fitness advantages for Californian plants occur despite incurring higher herbivory at both sites than the native Oregonian plants. Our findings suggest that a lag in adaptation causes maladaptation in extreme years that may be more prevalent in future climates, but local populations still have high growth rates and thus are not yet threatened.

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. We explore how competition has impacted niche differentiation in two monkeyflowers, Mimulus alsinoides and M. guttatus, which often co-occur. Through field observations, common gardens, and competition experiments, we demonstrate that M. alsinoides is restricted to marginal habitats in sympatry and that the impacts of character displacement on niche differentiation are complex. Competition with M. guttatus alters selection gradients and has favored taller M. alsinoides with earlier seasonal flowering at low elevation and floral shape divergence at high elevation. However, no trait exhibits the pattern typically associated with character displacement, higher divergence between species in sympatry than allopatry. Thus, although character displacement was unlikely the process driving initial divergence along niche axes necessary for coexistence, we conclude that competition in sympatry has likely driven trait evolution along additional niche axes.

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. With a broad sampling across five Hawaiian Islands, we deciphered the evolutionary history of P. pellucidum, identified nonhybrid lineages and intraspecific hybrids, and inferred the relative influence of geography and ecology on their distributions. Results: Polypodium pellucidum is monophyletic, dispersing to the Hawaiian archipelago 11.53–7.77 Ma and diversifying into extant clades between 5.66 and 4.73 Ma. We identified four nonhybrid clades with unique morphologies, ecological niches, and distributions. Additionally, we elucidated several intraspecific hybrid combinations and evidence for undiscovered or extinct "ghost" lineages contributing to extant hybrid populations. Conclusions: We provide a foundation for revising the taxonomy of P. pellucidum to account for cryptic lineages and intraspecific hybrids. Geologic succession of the Hawaiian Islands through cycles of volcanism, vegetative succession, and erosion has determined the available habitats and distribution of ecologically specific, divergent clades within P. pellucidum. Intraspecific hybrids have likely arisen due to ecological and or geological transitions, often persisting after the local extinction of their progenitors. This research contributes to our understanding of the evolution of Hawai'i's diverse fern flora and illuminated cryptic taxa to allow better‐informed conservation efforts. [ABSTRACT FROM AUTHOR]

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. We use piecewise structural equation models to disentangle associations between chemical defenses, (phenylpropanoid glycosides; PPGs), and life history traits with herbivory and fitness. While the historical environment of populations is not predictive of fitness differences between populations, >90% of variation in fitness can be predicted by the flowering time and foliar PPG defense arsenal of a population. Piecewise structural equation models indicate that life history traits, particularly earlier flowering time, are strongly and directly linked to fitness. However, herbivory, particularly fruit predation, is also an important agent of selection that creates indirect links between fitness and both chemical defenses and life history traits. Our results emphasize the multivariate nature of the agents and targets of selections in producing adaptation and suggest that future responses to selection must navigate a complex fitness landscape. [ABSTRACT FROM AUTHOR]

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. We also assessed variation in the critical photoperiod for flowering and surveyed neutral genetic markers to control for demography when analyzing clinal patterns., Many drought escape (e.g. flowering time) and drought avoidance (e.g. specific leaf area, succulence) traits exhibited geographic or climatic clines, which often remained significant after accounting for population structure. Critical photoperiod and flowering time in glasshouse conditions followed distinct clinal patterns, indicating different aspects of seasonal phenology confer adaptation to unique agents of selection. Although escape and avoidance traits were negatively correlated range-wide, populations from sites with short growing seasons produced both early flowering and dehydration avoidance phenotypes., Our results highlight how abundant genetic variation in the component traits that build multivariate adaptations to drought stress provides flexibility for intraspecific adaptation to diverse climates. [ABSTRACT FROM AUTHOR]

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. Both cyanogenic and acyanogenic plants occur in this species, and the ecological forces that maintain this chemical defence polymorphism have been studied for several decades. Using a sample of 65 plants, we investigated the molecular evolution of sequences flanking the two underlying cyanogenesis genes: Ac/ac (controlling the presence/absence of cyanogenic glucosides) and Li/li (controlling the presence/absence of their hydrolysing enzyme, linamarase). A combination of genome walking, PCR assays, DNA sequence analysis and Southern blotting was used to test whether these adaptive P/A polymorphisms show evidence of long-term balancing selection, or whether gene-absence alleles have evolved repeatedly through independent deletion events. For both loci, we detect no signatures of balancing selection in the closest flanking genomic sequences. Instead, we find evidence for variation in the size of the deletions characterizing gene-absence alleles. These observations strongly suggest that both of these polymorphisms have been evolving through recurrent gene deletions over time. We discuss the genetic mechanisms that could account for this surprising pattern and the implications of these findings for mechanisms of rapid adaptive evolution in white clover. [ABSTRACT FROM AUTHOR]

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). One or both cyanogenic components were detected in seven species, all within section Trifoliastrum; polymorphisms for the presence/absence (PA) of components were detected in six species. In a pattern that parallels our previous findings for white clover, all observed biochemical polymorphisms correspond to gene PA polymorphisms at CYP79D15 and Li. Relationships of DNA sequence haplotypes at the cyanogenesis loci and flanking genomic regions suggest independent evolution of gene deletions within species. This study thus provides evidence for the parallel evolution of adaptive biochemical polymorphisms through recurrent gene deletions in multiple species., (© 2014 The Author(s) Published by the Royal Society. All rights reserved.)