Ecotypic Variation Research Articles

Seed Source for Restoration: Little Bluestem (Schizachyrium scoparium (Michx.) Nash) and the Carolina Sandhills

Prairie and savanna ecosystems have declined dramatically worldwide. In the Southeastern United States, longleaf pine savannas have been reduced to less than 3% of their pre-European range. Restoring longleaf pine across the area has become a regional goal. Little bluestem (Schizachyrium scoparium (Michx.) Nash) is critical to carrying the ecologically important fire through this ecosystem in some longleaf pine savannas. Little bluestem has a range that spans most of north America and is thought to display ecotypic variation. As a part of a longleaf pine restoration project in Camden, SC, we investigated whether the seed source of little bluestem and the site preparation techniques impacted the survival and growth of broadcasted seeds. In the field and greenhouse, we compared locally and commercially sourced seeds and field site preparation techniques including discing, raking, or no treatment. At the end of the growing season, there were significantly more plants grown from seeds collected locally compared to plants from seeds available commercially. Plants grown from locally collected seeds also invested more heavily in roots than plants grown from commercial seeds. Site preparation techniques did not appear to significantly impact plant survival. Collecting seed locally will help to ensure long-term restoration success by establishing populations of plants that are adapted to the local environmental conditions.

The role of ecotypic variation for plant facilitation in a metal-polluted system: Stress-intolerant target ecotypes are the best beneficiaries and stress-tolerant nurse ecotypes the best benefactors

Disentangling competitive-response and -effect abilities has strongly improved our understanding of the role of competition for the diversity and composition of plant communities. Much less is known about the relative importance of facilitative-effect and -response abilities in harsh ecosystems. Here, we aim to fill this gap by simultaneously assessing the facilitative-response and -effect abilities of different species and ecotypes in former mining sites in the French Pyrenees, both in naturally occurring communities and in a common-garden designed on a slag heap. The response of two ecotypes of the target species Festuca rubra with contrasting metal-stress tolerances and the facilitative effects of two ecotypes with contrasting metal-stress tolerances of four different metallicolous nurse species were assessed. The results revealed that the response of the Festuca ecotype with lower metal-stress tolerance shifted from competitive (RII = −0.24) to facilitative (RII = 0.29) as pollution increased, consistently with the stress-gradient-hypothesis. The Festuca ecotype with high metal-stress tolerance did not show any facilitative response. Regarding facilitative effect ability assessed in the common-garden, nurse ecotypes from highly polluted habitats (RII = 0.04) had a significantly higher facilitative effects than ecotypes from less polluted habitats (RII = −0.05). Metal-intolerant target ecotypes of Festuca rubra were the most sensitive to the positive effects of neighbours, while metal-tolerant nurse ecotypes were the best benefactors. Facilitative-response ability appeared to be driven by a trade-off between stress-tolerance and facilitative response of target ecotypes. In contrast, facilitative-effect ability was positively correlated to the stress-tolerance of nurse plants. The results of this study show that the highest restoration success of highly metal-stressed systems should be found when highly stress-tolerant nurse ecotypes are associated with less stress-tolerant target ecotypes.

Seed size variation impacts local adaptation and life-history strategies in a perennial grass.

Seed mass is an ecologically important trait that often differs considerably among ecotypes. Yet, because few studies examine the impacts of seed mass on adult life-history traits, its role in local adaptation is unclear. In this study, using accessions of Panicum hallii that spanned the two major ecotypes, we examined whether covariation between seed mass, seedling and reproductive traits impacts ecotypic divergence and local adaptation. The perennial grass P. hallii has two distinct ecotypes-a large-seeded upland ecotype adapted to xeric environments and a small-seeded lowland ecotype adapted to mesic environments. In the greenhouse, seed mass varied greatly across P. hallii genotypes in a manner consistent with ecotypic divergence. Seed mass covaried significantly with several seedling and reproductive traits. At field sites representing the habitats of the two ecotypes, seed mass had different impacts on seedling and adult recruitment: selection favoured large seeds in upland habitat and small seeds in lowland habitat, which was consistent with local adaptation. By demonstrating the central role of seed mass in ecotypic differences in P. hallii and its importance to seedling and adult recruitment under field conditions, these studies show that early life-history traits can promote local adaptation and potentially explain ecotype formation.

The case for prioritizing ecology/behavior and hybridization over genomics/taxonomy and species' integrity in conservation under climate change

Climate change reinvigorates two debates: first, about relative roles of taxonomic, genetic and phenetic criteria in prioritizing entities for conservation and, second, on the role of hybrids in biodiversity assessments, as climate-change-induced range shifts create sympatry between formerly allopatric species/subspecies, thereby generating novel hybrids. We argue that rapid climate change necessitates a shift in the ethical balance sheet for conservation prioritization. Here we use the extensive ecotypic variation in a climate-sensitive butterfly, Euphydryas editha, to illustrate a case in which conservation biologists choosing extant populations as sources for reintroductions to extinct sites, translocations to novel sites, or genetic rescue of inbred populations should first select populations with appropriate phenotypes for climate adaptation and preferences for host and habitat and only then, within that group, rely on subspecies identity or genomic similarity between source and target populations. Preferences evolve rapidly, and we show that they differed sufficiently between an endangered subspecies and potential sources genomically close to it that restoration efforts would be doomed. Conversely, introductions from genomically more distant, ecologically similar populations would succeed and hybridize. Evolutionary biologists have argued that hybridizations, whether caused by climate change or genetic rescue projects, may be essential for retaining genetic diversity and adaptive potential at species/genus level. Conservation practitioners, in contrast, tend to oppose genetic change, arguing to preserve “purity” of existing groups. Our example of the role of climate change in conservation of a species with rapid evolution of critical traits and a mosaic pattern of local adaptation supports the evolutionary biologists' argument.

Edaphic ecotypic divergence in Senecio vulgaris and the evolutionary potential of predominantly self-fertilising species

ABSTRACT Background There is continued interest in ecotypic divergence because it is informative of local adaptation and can be an important step in speciation. Aim To investigate ecotypic divergence in a predominantly self-fertilising species, Senecio vulgaris, in response to variation in soil nitrogen (N) and phosphorus (P) concentrations. Methods Responses to increased N and P were compared among populations sampled from sand dune, bird sanctuary and garden habitats, containing soils of low, high and intermediate fertility, respectively. Responses were measured in terms of growth, with capitulum production and days to seed set recorded in some experiments. Results Population differences in response to increased N and P were detected and linked to differences in soil fertility among habitats. Thus, the sand dune population exhibited the lowest growth response to increased N and P concentrations, while a bird sanctuary population showed the greatest response to increased N supplied as either NaNO3, NH4NO3 or urea. Genetic variation in response to increased N was present in both of these populations. Conclusions The results indicate the presence of edaphic ecotypes in S. vulgaris, providing further evidence that questions the premise that self-fertilisation limits adaptation to environmental change and thus is an evolutionary dead-end.

Local adaptation of switchgrass drives trait relations to yield and differential responses to climate and soil environments

AbstractSwitchgrass, a potential biofuel crop, is a genetically diverse species with phenotypic plasticity enabling it to grow in a range of environments. Two primary divergent ecotypes, uplands and lowlands, exhibit trait combinations representative of acquisitive and conservative growth allocation strategies, respectively. Whether these ecotypes respond differently to various types of environmental drivers remains unclear but is crucial to understanding how switchgrass varieties will respond to climate change. We grew two upland, two lowland, and two intermediate/hybrid cultivars of switchgrass at three sites along a latitudinal gradient in the central United States. Over a 4‐year period, we measured plant functional traits and biomass yields and evaluated genotype‐by‐environment (G × E) interaction effects by analyzing switchgrass responses to soil and climate variables. We found substantial evidence of G × E interactions on biomass yield, primarily due to deviations in the response of the southern lowland cultivar Alamo, which produced more biomass in hotter and drier environments relative to other cultivars. While lowland cultivars had the highest potential for yield, their yields were more variable year‐to‐year compared to other cultivars, suggesting greater sensitivity to environmental perturbations. Models comparing soil and climate principal components as explanatory variables revealed soil properties, especially nutrients, to be most effective at predicting switchgrass biomass yield. Also, positive correlations between biomass yield and conservative plant traits, such as high stem mass and tiller height, became stronger at lower latitudes where the climate is hotter and drier, regardless of ecotype. Lowland cultivars, however, showed a greater predisposition to exhibit these conservative traits. These results suggest switchgrass trait allocation trade‐offs that prioritize aboveground biomass production are more tightly associated in hot, dry environments and that lowland cultivars may exhibit a more specialized strategy relative to other cultivars. Altogether, this research provides essential knowledge for improving the viability of switchgrass as a biofuel crop.

Genomic variation across Chinook salmon populations reveals effects of a duplication on migration alleles and supports fine scale structure.

The distribution of ecotypic variation in natural populations is influenced by neutral and adaptive evolutionary forces that are challenging to disentangle. This study provides a high-resolution portrait of genomic variation in Chinook salmon (Oncorhynchus tshawytscha) with emphasis on a region of major effect for ecotypic variation in migration timing. With a filtered data set of ~13million single nucleotide polymorphisms (SNPs) from low-coverage whole genome resequencing of 53 populations (3566 barcoded individuals), we contrasted patterns of genomic structure within and among major lineages and examined the extent of a selective sweep at a major effect region underlying migration timing (GREB1L/ROCK1). Neutral variation provided support for fine-scale structure of populations, while allele frequency variation in GREB1L/ROCK1 was highly correlated with mean return timing for early and late migrating populations within each of the lineages (r2 = .58-.95; p< .001). However, the extent of selection within the genomic region controlling migration timing was much narrower in one lineage (interior stream-type) compared to the other two major lineages, which corresponded to the breadth of phenotypic variation in migration timing observed among lineages. Evidence of a duplicated block within GREB1L/ROCK1 may be responsible for reduced recombination in this portion of the genome and contributes to phenotypic variation within and across lineages. Lastly, SNP positions across GREB1L/ROCK1 were assessed for their utility in discriminating migration timing among lineages, and we recommend multiple markers nearest the duplication to provide highest accuracy in conservation applications such as those that aim to protect early migrating Chinook salmon. These results highlight the need to investigate variation throughout the genome and the effects of structural variants on ecologically relevant phenotypic variation in natural species.

Range‐edge populations of seaweeds show niche unfilling and poor adaptation to increased temperatures

AbstractAimGlobal warming is affecting the distribution of species worldwide, but the level of adaptation of edge populations to warmer temperatures remains an open question. Here, we assess the thermal tolerance of populations of two habitat‐forming seaweeds along their latitudinal range, using thermal niche unfilling to assess their resilience to global warming.LocationEuropean Atlantic coastline.TaxonAscophyllum nodosum (Linnaeus) Le Jolis (Phaeophyceae) and Chondrus crispus Stackhouse (Rhodophyta).MethodsWe studied the ecotypic variation in upper survival temperatures (USTs) by measuring survival and growth of adults representing populations under a gradient of seawater temperature (12–30°C). Comparing the USTs with maximum seawater temperatures obtained from satellites, we investigated safety margins and niche unfilling states, both in recent history and under future climate scenarios.ResultsUSTs (≈24°C) did not differ significantly between populations, except for higher values (27.9°C) for the northernmost populations (cold edge) of A. nodosum. Populations of both species had thermal safety margins over the last few decades (from 1982 to 2021). However, projections based on USTs showed that in several years these margins have been eliminated and will completely disappear in the Bay of Biscay under RCP4.5 and RCP6.0 2090–2100 IPCC scenarios for C. crispus and under RCP8.5 for both species, threatening the populations there.Main ConclusionsSouthern marginal populations were not better adapted to global warming than populations elsewhere. Both seaweed species tolerated higher temperatures than the ambient maxima, suggesting a thermal niche unfilling state with thermal safety margins in their recent history. However, those are being depleted by ongoing climate change and this trend is predicted to increase. Marine heat waves are important threats to these habitat‐forming species, transiently reducing or even eliminating safety margins in the hottest parts of the European Atlantic coastline, contributing to explaining the distributional gap there.

Variation in Leaf Reflectance Spectra Across the California Flora Partitioned by Evolutionary History, Geographic Origin, and Deep Time

AbstractEvolutionary relatedness underlies patterns of functional diversity in the natural world. Hyperspectral remote sensing has the potential to detect these patterns in plants through inherited patterns of leaf reflectance spectra. We collected leaf reflectance data across the California flora from plants grown in a common garden. Regions of the reflectance spectra vary in the depth and strength of phylogenetic signal. We also show that these differences are much greater than variation due to the geographic origin of the plant. At the phylogenetic extent of the California flora, spectral variation explained by the combination of ecotypic variation (divergent evolution) and convergent evolution of disparate lineages was minimal (3%–7%) but statistically significant. Interestingly, at the extent of a single genus (Arctostaphylos) no unique variation could be attributed to geographic origin. However, up to 18% of the spectral variation among Arctostaphylos individuals was shared between phylogeny and intraspecific variation stemming from ecotypic differences (i.e., geographic origin). Future studies could conduct more structured experiments (e.g., transplants or observations along environmental gradients) to disentangle these sources of variation and include other intraspecific variation (e.g., plasticity). We constrain broad‐scale spectral variability due to ecotypic sources, providing further support for the idea that phylogenetic clusters of species might be detectable through remote sensing. Phylogenetic clusters could represent a valuable dimension of biodiversity monitoring and detection.

Quantitative genetic-by-soil microbiome interactions in a perennial grass affect functional traits.

Plants interact with diverse microbiomes that can impact plant growth and performance. Recent studies highlight the potential beneficial aspects of plant microbiomes, including the possibility that microbes facilitate the process of local adaptation in their host plants. Microbially mediated local adaptation in plants occurs when local host genotypes have higher fitness than foreign genotypes because of their affiliation with locally beneficial microbes. Here, plant adaptation results from genetic interactions of the host with locally beneficial microbes (e.g. host genotype-by-microbiome interactions). We used a recombinant inbred line (RIL) mapping population derived from upland and lowland ecotypes of the diploid C4 perennial bunch grass Panicum hallii to explore quantitative genetic responses to soil microbiomes focusing on functional root and shoot traits involved in ecotypic divergence. We show that the growth and development of ecotypes and their trait divergence depends on soil microbiomes. Moreover, we find that the genetic architecture is modified by soil microbiomes, revealing important plant genotype-by-microbiome interactions for quantitative traits. We detected a number of quantitative trait loci (QTL) that interact with the soil microbiome. Our results highlight the importance of microbial interactions in ecotypic divergence and trait genetic architecture in C4 perennial grasses.

Genotypic variation, phylogeography, unified species concept, and the ‘grey zone’ of taxonomic uncertainty in kānuka: recognition of Kunzea ericoides (A.Rich.) Joy Thomps. sens. lat. (Myrtaceae)

ABSTRACT In vascular plant systematics there are sometimes conflicts between phenotypic and ecotypic variation and genetic differentiation that challenge species concepts, introduce taxonomic confusion, and create nomenclatural uncertainty. Until a 2014 taxonomic revision that segregated Kunzea ericoides into 10 species, it and K. sinclairii were the only species recognised in New Zealand. A recent DNA microsatellite study failed to support any of the new species, instead revealing biogeographic variation. Here we present the results of a genotyping by sequencing study with 1,361 single nucleotide polymorphisms (SNPs), sampling 48 populations representing four Kunzea species from South Island and southern North Island. The SNP study confirms the microsatellite findings: the two widespread species, K. robusta and K. serotina, are indistinguishable and share northern and southern genotypes with other species; a single metapopulation lineage reflects a national north-to-south clinal pattern; and population differentiation is low and net migration high. A significant isolation by distance pattern was revealed with SNPs. The 2014 revision was explicitly based on the unified species concept, but the primary criterion, that each species represents a separate metapopulation lineage, was not demonstrated. Species recognition was based on morphological and ecological criteria that have proved difficult to apply. Applying the unified species concept and the primary criterion of a single metapopulation genetic lineage, we now recognise just a single New Zealand species, K. ericoides, with other species constituting taxonomic synonyms. In doing so, we distinguish a grey zone of taxonomic uncertainty that reflects incomplete lineage sorting, gene flow coupled with a lack of reproductive isolation, and only partial ecotypic and phenotypic differentiation. As demonstrated in the Kunzea revision, there is considerable phenotypic and ecotypic variation in regional populations that is likely to be of ecological and conservation importance. We suggest informal ecotypes are a better way to recognise this level of variation.

Comparison and Phylogenetic Analysis of Mitochondrial Genomes of Talpidae Animals.

Talpidae is a model group for evolutionary studies due to their highly specialized morphologies and diverse lifestyles. Mitochondrial genomes are molecular markers commonly used in species evolution and phylogenetic studies. In this study, the complete mitochondrial genome sequence of Scaptochirus moschatus was obtained by Illumina NovaSeq sequencing. The complete mitochondrial genomes of 14 Talpidae species (including Scaptochirus moschatus obtained in the present study) and the cytochrome b (Cyt b) gene sequences of 48 Talpidae species were downloaded from the NCBI database for comparison and phylogenetic studies to analyze the phylogenetic relationships and to find the possible reasons of the niche differentiation and ecotype specialization of Talpidae animals. The results showed that the mitochondrial genome sequences of 14 species belonging to the family Talpidae were 16,528 to 16,962 bp, all containing 13 protein-coding genes, 22 tRNA, two rRNA, and a non-coding region (control region). The difference in the number of repetitive repeats in the control region is responsible for the difference in the length of Talpidae mitochondrial genome sequences. Combining the divergence time of Talpidae animals with the geological history, it is found that the niche differentiation and ecotype divergence of Talpidae is closely related to historically global climate changes. Semi-aquatic groups diverged in the early Oligocene (about 31.22 MYA), probably in response to the global climate transition from warm to cool. During the early Miocene (about 19.54 MYA), some species of Talpidae moved to underground habitats and formed fossorial groups that were adept at digging due to the effects of the glaciation. In the middle Miocene (about 16.23 MYA), some Talpidae animals returned to the ground and formed semi-fossorial shrew moles as global climate warming again.

Selection for high growth displaces costs of digestion from SDA to SMR in divergent ecotypes of rainbow trout

AbstractTo understand the drivers of variation in digestive performance and their effects on growth, we examined relationships among food consumption, digestive metabolism, food processing efficiency, and growth rate in juveniles of fast‐growing piscivore versus slow‐growing insectivore ecotypes of rainbow trout reared at satiation rations on the same diet (i.e., commercial food pellets). Relative to slow‐growing insectivores with lower basal metabolism, and despite a much larger maximum food ration, faster‐growing piscivores presented an unexpected pattern of higher digestive efficiency through a reduction in the absolute costs of postprandial metabolism coupled with shorter or similar gut residence time and higher assimilation efficiency. These results suggest that the increase in digestive metabolism following the ingestion of larger meals can be mitigated by displacing the costs of digestion from SDA to SMR. Reducing total digestion costs (SDA + SMR) while maintaining higher assimilation efficiency may be possible through potential adaptations including (1) increased intestinal absorption capacity; (2) economies of scale that shorten gut transit time with increasing ration level; or (3) a permanently larger digestive tract that increases maintenance costs but reduces the need for cyclic upregulation and associated overhead costs.

The ecology and quantitative genetics of seed and seedling traits in upland and lowland ecotypes of a perennial grass.

Plants have evolved diverse reproductive allocation strategies and seed traits to aid in dispersal, persistence in the seed bank, and establishment. In particular, seed size, dormancy, and early seedling vigor are thought to be key functional traits with important recruitment and fitness consequences across abiotic stress gradients. Selection for favored seed-trait combinations, or against maladaptive combinations, is likely an important driver shaping recruitment strategies. Here, we test for seed-trait plasticity and patterns of recruitment using two genotypes representative of contrasting upland and lowland ecotypes of Panicum hallii with field experiments in native versus foreign habitats. Furthermore, we test whether seed traits have been under directional selection in P. hallii using the v-test based on trait variance in a genetic cross. Finally, we evaluate the genetic architecture of ecotypic divergence for these traits with quantitative trait locus (QTL) mapping. Field experiments reveal little plasticity but support a hypothesis of adaptation divergence among ecotypes based on recruitment. Patterns of segregation within recombinant hybrids provides strong support for directional selection driving ecotypic divergence in seed traits. Genetic mapping revealed a polygenic architecture with evidence of genetic correlation between seed mass, dormancy, and seedling vigor. Our results suggest that the evolution of these traits may involve constraints that affect the direction of adaptive divergence. For example, seed size and germination percentage shared two colocalized QTL with antagonistic additive effects. This supports the hypothesis of a functional genetic relationship between these traits, resulting in either large seed/strong dormancy or small seed/weak dormancy trait combinations. Overall, our study provides insights into the factors facilitating and potentially constraining ecotypic differentiation in seed traits.

Machine learning assisted dynamic phenotypes and genomic variants help understand the ecotype divergence in rapeseed.

Three ecotypes of rapeseed, winter, spring, and semi-winter, have been formed to enable the plant to adapt to different geographic areas. Although several major loci had been found to contribute to the flowering divergence, the genomic footprints and associated dynamic plant architecture in the vegetative growth stage underlying the ecotype divergence remain largely unknown in rapeseed. Here, a set of 41 dynamic i-traits and 30 growth-related traits were obtained by high-throughput phenotyping of 171 diverse rapeseed accessions. Large phenotypic variation and high broad-sense heritability were observed for these i-traits across all developmental stages. Of these, 19 i-traits were identified to contribute to the divergence of three ecotypes using random forest model of machine learning approach, and could serve as biomarkers to predict the ecotype. Furthermore, we analyzed genomic variations of the population, QTL information of all dynamic i-traits, and genomic basis of the ecotype differentiation. It was found that 213, 237, and 184 QTLs responsible for the differentiated i-traits overlapped with the signals of ecotype divergence between winter and spring, winter and semi-winter, and spring and semi-winter, respectively. Of which, there were four common divergent regions between winter and spring/semi-winter and the strongest divergent regions between spring and semi-winter were found to overlap with the dynamic QTLs responsible for the differentiated i-traits at multiple growth stages. Our study provides important insights into the divergence of plant architecture in the vegetative growth stage among the three ecotypes, which was contributed to by the genetic differentiation, and might contribute to environmental adaption and yield improvement.

Maximizing genetic gain through unlocking genetic variation in different ecotypes of kalmegh (Andrographis paniculata (Burm. f.) Nee).

Andrographis paniculata, commonly known as kalmegh is among the most popular medicinal herbs in Southeast Asia. It is widely cultivated for medicinal purposes. The bioactive molecule, Andrographolide accumulated in herb leaves has immense therapeutic and economic potential. However, comprehensive information regarding genetic diversity is very limited in this species. The present study assessed genetic diversity between and within the six populations (ecotypes) of twenty-four kalmegh accessions using multiple datasets (agro-morphological traits, phytochemical traits, and genic markers). This is the established report where EST-SSR (Expressed sequence tags-Simple Sequence Repeat) markers have been used to unlock genetic variation in kalmegh. Here, we identified and developed ninety-one metabolic pathway-specific EST-SSR markers. Finally, 32 random EST-SSR primer pairs were selected for genetic diversity assessment. Multivariate analysis to unveil the agro-morphological, phytochemical and genotypic variability was helpful in discriminating various germplasms studied in the present study. Among all the morphological discriptors used in present study, days to fifty percent flowering and dry herb yield were found as potential selection index for AP genetic improvement. Hierarchical cluster analysis built with agro-morphological data identified three major groups. However, corresponding analysis with phytochemical and molecular data generated two clear-cut groups among the studied individuals. Moreover, the grouping of individuals into different clusters using multiple datasets was geographically independent, and also showed inconsistency in grouping among agromorphological, phytochemical and molecular dataset based clusters. However, joint analysis using agro-morphological, phytochemical and genotypic information generated two genetic groups, which could be a valuable resource for identifying complementary crossing panels in the kalmegh breeding program. The accessions AP7, AP13, AP5, AP3 belong to cluster I and accessions AP17, AP18 belong to cluster II could be utilized as potential donors for high dry herb yield and andrographolide content, respectively in different selective breeding programs of AP. Thus, our results provided useful information about the overall genetic diversity and variation in economic traits useful for initiating selective breeding programs for contrasting traits of interest and maximizing genetic gain in kalmegh.

A Pleiotropic Flowering Time QTL Exhibits Gene-by-Environment Interaction for Fitness in a Perennial Grass.

Appropriate flowering time is a crucial adaptation impacting fitness in natural plant populations. Although the genetic basis of flowering variation has been extensively studied, its mechanisms in nonmodel organisms and its adaptive value in the field are still poorly understood. Here, we report new insights into the genetic basis of flowering time and its effect on fitness in Panicum hallii, a native perennial grass. Genetic mapping in populations derived from inland and coastal ecotypes identified flowering time quantitative trait loci (QTL) and many exhibited extensive QTL-by-environment interactions. Patterns of segregation within recombinant hybrids provide strong support for directional selection driving ecotypic divergence in flowering time. A major QTL on chromosome 5 (q-FT5) was detected in all experiments. Fine-mapping and expression studies identified a gene with orthology to a rice FLOWERING LOCUS T-like 9 (PhFTL9) as the candidate underlying q-FT5. We used a reciprocal transplant experiment to test for local adaptation and the specific impact of q-FT5 on performance. We did not observe local adaptation in terms of fitness tradeoffs when contrasting ecotypes in home versus away habitats. However, we observed that the coastal allele of q-FT5 conferred a fitness advantage only in its local habitat but not at the inland site. Sequence analyses identified an excess of low-frequency polymorphisms at the PhFTL9 promoter in the inland lineage, suggesting a role for either selection or population expansion on promoter evolution. Together, our findings demonstrate the genetic basis of flowering variation in a perennial grass and provide evidence for conditional neutrality underlying flowering time divergence.

Adaptive strategies of Scots pine under shade: Increase in lignin synthesis and ecotypic variation in defense-related gene expression.

Shade is a stressful condition for plants characterized by low Red:Far-Red (R:FR) ratio. The northern latitudes in Sweden daily receive more hours of FR-enriched light (twilight) or shade-like conditions compared to southern forests during the growing season. Scots pine (Pinus sylvestris L.) is a shade-intolerant species. Yet, it is well adapted to this latitudinal variation in light, which is evident by a northward increase in FR requirement to maintain growth. Shade adversely affects plant growth; it makes the plant weak and, therefore, susceptible to pathogen attack. Lignin is involved in plant protection against pathogen invasion mainly by forming a physical barrier. We studied lignin synthesis and expression of defense-related genes (growth-defense trade-offs) under a low R:FR (shade) ratio in Scots pine. A higher number of immunity/defense-related genes were up-regulated in response to shade in northern populations compared to southern ones, which can be viewed as a local adaptation to light quality for optimal growth and survival. Light quality regulates lignin metabolism; light stimulates lignin synthesis, while shade causes a decrease in lignin synthesis in most angiosperms. In contrast, Scots pine shows an increase in lignin synthesis supported by the higher expression of a few key genes in the lignin biosynthetic pathway, a novel finding reported by our study. These findings can be applied to future breeding strategies in forestry to produce disease-resilient trees.

Late frost as a driver of ecotypic differentiation in sugar maple: Implications for assisted migration

Global warming advances bud break, mismatches plant phenology from the local climate, and exposes the developing leaves to higher risks of frost damage. Bud break of sugar maple [Acer saccharum (Marsh.)], a species included in recent programs of assisted migration, is sensitive to nighttime spring temperatures. This suggests a link between frost events and leaf development. In this study, we raise the hypothesis that late frost is an evolutionary driver of growth reactivation in sugar maple provenances. We investigated the ecotypic variation of bud phenology in 30 provenances planted in two common gardens within and at the northern limit of the species range, in the Province of Quebec, Canada. Eight phases of bud break were assessed twice a week during 2020 on 252 and 272 seedlings in southern and northern sites, respectively. In the southern site, bud break occurred in May, starting on average 12 days earlier and ending 3 days earlier compared to the northern site. Logistic regression was used to estimate the probability of late frost and the results showed that regions located in the north, at higher elevations, and along the northeastern coast of the native maple range showed the latest occurrences of frost events in spring. This pattern mirrored the timing of bud break. When planted in the same common garden, provenances originating from sites with later spring frosts leafed out earlier. Such differences were maintained across the eight bud phenological phases and between the two common gardens, which indicates a similar response of the provenances to changing growing conditions. To avoid frost damage to sugar maple plantations, assisted migration should account for phenotypic traits in bud phenology, ensuring that the frost regime at the origin of the provenances is compatible with that of plantations.

Enhanced lignin synthesis and ecotypic variation in defense-related gene expression in response to shade in Norway spruce.

During the growth season, northern forests in Sweden daily receive more hours of far-red (FR)-enriched light or twilight (shade) as compared to southern forests. Norway spruce (shade-tolerant) are adapted to latitudinal variation in twilight characterized by a northward increase in FR requirement to maintain growth. Shade is a stressful condition that affects plant growth and increases plant's susceptibility to pathogen attack. Lignin plays a central role in plant defense and its metabolism is regulated by light wavelength composition (light quality). In the current work, we studied regulation of lignin synthesis and defense-related genes (growth-defense trade-offs) in response to shade in Norway spruce. In most angiosperms, light promotes lignin synthesis, whereas shade decreases lignin production leading to weaker stem, which may make plants more disease susceptible. In contrast, enhanced lignin synthesis was detected in response to shade in Norway spruce. We detected a higher number of immunity/defense-related genes up-regulated in northern populations as compared to south ones in response to shade. Enhanced lignin synthesis coupled with higher defense-related gene expression can be interpreted as an adaptive strategy for better survival in northern populations. Findings will contribute to ensuring deployment of well-adapted genetic material and identifying tree families with enhanced disease resistance.