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Abstract PremiseA key goal of evolutionary biologists is to understand how and why genetic variation is partitioned within species. In the yellow monkeyflower,Mimulus guttatus(syn.Erythranthe guttata), coastal perennial populations constitute a single genetically and morphologically differentiated ecotype compared to inlandM. guttatuspopulations. While the coastal ecotype's distinctiveness has now been well documented, there is also environmental variation across the ecotype's range that could drive more continuous differentiation among its component populations. MethodsBased on previous observations of a potential cline within this ecotype, we quantified plant height, among other traits, across coastal perennial accessions from 74 populations in a greenhouse common garden experiment. To evaluate potential drivers of the relationship between trait variation and latitude, we regressed height against multiple climatic factors, including temperature, precipitation, and coastal wind speeds. We also accounted for exposure to the open ocean in all analyses. ResultsMultiple traits were correlated with latitude of origin, but none more than plant height. Height was negatively correlated with latitude, and plants directly exposed to the open ocean were shorter than those protected from coastal winds. Further analyses revealed that height was correlated with climatic factors (precipitation, temperature, and wind speeds) that were autocorrelated with latitude. We hypothesize that one or more of these climatic factors drove the evolution of latitudinal clinal variation within the coastal ecotype. ConclusionsOverall, our study illustrates the complexity of how the distribution of environmental variation can simultaneously drive the evolution of both distinct ecotypesandcontinuous clines within those ecotypes. 

Abstract Despite multiple ecological and evolutionary hypotheses that predict patterns of phenotypic relationships between plant growth, reproduction and constitutive and/or induced resistance to herbivores, these hypotheses do not make any predictions about the underlying molecular genetic mechanisms that mediate these relationships.We investigated how divergent plant life‐history strategies in the yellow monkeyflower and a life‐history altering locus,DIV1, influence plasticity of phytochemical herbivory resistance traits in response to attack by two herbivore species with different diet breadth.Life‐history strategy (annual vs. perennial) and theDIV1locus significantly influenced levels of constitutive herbivory resistance, as well as resistance induction following both generalist and specialist herbivory. Perennial plants had higher total levels of univariate constitutive and induced defence than annuals, regardless of herbivore type. Annuals induced less in response to generalist herbivory than did perennials, while induction response was equivalent across the ecotypes for specialist herbivory.The effects of theDIV1locus on levels of constitutive and induced defence were dependent on genetic background, the annual versus perennial haplotype ofDIV1and herbivore identity. The patterns of univariate induction due toDIV1were non‐additive and did not always match expectations based on patterns of divergence for annual/perennial parents. For example, perennial plants had higher levels of constitutive and induced defence than did annuals, but when the annualDIV1was present in the perennial genetic background induction response to herbivory was higher than for the perennial parent lines.Patterns for multivariate defence arsenals generally echoed those of univariate, with annual and perennial monkeyflowers and those with alternative versions ofDIV1differing significantly in constitutive and induced resistance. Like univariate resistance, induced multivariate defence arsenals were affected by herbivore identity.Our results highlight the complexity of the genetic mechanisms underlying plastic response to herbivory. While a genetic locus underlying substantial phenotypic variation in life‐history strategy and constitutive defence also influences defence plasticity, the induction response also depends on genetic background. This result demonstrates the potential for some degree of evolutionary independence between constitutive and induced defence, or induced defence and life‐history strategy, in monkeyflowers. Read the freePlain Language Summaryfor this article on the Journal blog. 

Abstract In a rapidly changing environment, predicting changes in the growth and survival of local populations can inform conservation and management. Plastic responses vary as a result of genetic differentiation within and among species, so accurate rangewide predictions require characterization of genotype-specific reaction norms across the continuum of historic and future climate conditions comprising a species’ range. Natural hybrid zones can give rise to novel recombinant genotypes associated with high phenotypic variability, further increasing the variance of plastic responses within the ranges of the hybridizing species. Experiments that plant replicated genotypes across a range of environments can characterize genotype-specific reaction norms; identify genetic, geographic, and climatic factors affecting variation in climate responses; and make predictions of climate responses across complex genetic and geographic landscapes. The North American hybrid zone ofPopulus trichocarpaandP. balsamiferarepresents a natural system in which reaction norms are likely to vary with underlying genetic variation that has been shaped by climate, geography, and introgression. Here, we leverage a dataset containing 45 clonal genotypes of varying ancestry from this natural hybrid zone, planted across 17 replicated common garden experiments spanning a broad climatic range, including sites warmer than the natural species ranges. Growth and mortality were measured over two years, enabling us to model reaction norms for each genotype across these tested environments. Genomic variation associated with species ancestry and northern/southern regions significantly influenced growth across environments, with genotypic variation in reaction norms reflecting a trade-off between cold tolerance and growth. Using modeled reaction norms for each genotype, we predicted that genotypes with moreP. trichocarpaancestry may gain an advantage under warmer climates. Spatial shifts of the hybrid zone could facilitate the spread of beneficial alleles into novel climates. These results highlight that genotypic variation in responses to temperature will have landscape-level effects. 

Abstract PremiseIncreased aridity and drought associated with climate change are exerting unprecedented selection pressures on plant populations. Whether populations can rapidly adapt, and which life history traits might confer increased fitness under drought, remain outstanding questions. MethodsWe utilized a resurrection ecology approach, leveraging dormant seeds from herbarium collections to assess whether populations ofPlantago patagonicafrom the semi‐arid Colorado Plateau have rapidly evolved in response to approximately ten years of intense drought in the region. We quantified multiple traits associated with drought escape and drought resistance and assessed the survival of ancestors and descendants under simulated drought. ResultsDescendant populations displayed a significant shift in resource allocation, in which they invested less in reproductive tissues and relatively more in both above‐ and below‐ground vegetative tissues. Plants with greater leaf biomass survived longer under terminal drought; moreover, even after accounting for the effect of increased leaf biomass, descendant seedlings survived drought longer than their ancestors. ConclusionsOur results document rapid adaptive evolution in response to climate change in a selfing annual and suggest that shifts in tissue allocation strategies may underlie adaptive responses to drought in arid or semi‐arid environments. This work also illustrates a novel approach, documenting that under specific circumstances, seeds from herbarium specimens may provide an untapped source of dormant propagules for future resurrection experiments. 

Leaf fungal microbiomes can be fundamental drivers of host plant success, as they contain pathogens that devastate crop plants and taxa that enhance nutrient uptake, discourage herbivory, and antagonize pathogens. We measured leaf fungal diversity with amplicon sequencing across an entire growing season in a diversity panel of switchgrass ( Panicum virgatum ). We also sampled a replicated subset of genotypes across 3 additional sites to compare the importance of time, space, ecology, and genetics. We found a strong successional pattern in the microbiome shaped both by host genetics and environmental factors. Further, we used genome-wide association (GWA) mapping and RNA sequencing to show that 3 cysteine-rich receptor-like kinases (crRLKs) were linked to a genetic locus associated with microbiome structure. We confirmed GWAS results in an independent set of genotypes for both the internal transcribed spacer (ITS) and large subunit (LSU) ribosomal DNA markers. Fungal pathogens were central to microbial covariance networks, and genotypes susceptible to pathogens differed in their expression of the 3 crRLKs, suggesting that host immune genes are a principal means of controlling the entire leaf microbiome. 

Abstract Ionomics measures elemental concentrations in biological organisms and provides a snapshot of physiology under different conditions. In this study, we evaluate genetic variation of the ionome in outbred, perennial switchgrass in three environments across the species’ native range, and explore patterns of genotype-by-environment interactions. We grew 725 clonally replicated genotypes of a large full sib family from a four-way linkage mapping population, created from deeply diverged upland and lowland switchgrass ecotypes, at three common gardens. Concentrations of 18 mineral elements were determined in whole post-anthesis tillers using ion coupled plasma mass spectrometry (ICP-MS). These measurements were used to identify quantitative trait loci (QTL) with and without QTL-by-environment interactions (QTLxE) using a multi-environment QTL mapping approach. We found that element concentrations varied significantly both within and between switchgrass ecotypes, and GxE was present at both the trait and QTL level. Concentrations of 14 of the 18 elements were under some genetic control, and 77 QTL were detected for these elements. Seventy-four percent of QTL colocalized multiple elements, half of QTL exhibited significant QTLxE, and roughly equal numbers of QTL had significant differences in magnitude and sign of their effects across environments. The switchgrass ionome is under moderate genetic control and by loci with highly variable effects across environments.