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1. Precipitation timing and soil substrate drive phenology and fitness of Arabidopsis thaliana in a Mediterranean environment

   https://doi.org/10.1111/1365-2435.14391  

   Martínez‐Berdeja, Alejandra ; Okada, Miki ; Cooper, Martha D. ; Runcie, Daniel E. ; Burghardt, Liana T. ; Schmitt, Johanna ( July 2023 , Functional Ecology)

   In Mediterranean climates, the timing of seasonal rains determines germination, flowering phenology and fitness. As climate change alters seasonal precipitation patterns, it is important to ask how these changes will affect the phenology and fitness of plant populations. We addressed this question experimentally with the annual plant speciesArabidopsis thaliana.

   In a first experiment, we manipulated the date of rainfall onset and recorded germination phenology on sand and soil substrates. In a second experiment, we manipulated germination date, growing season length and mid‐season drought to measure their effects on flowering time and fitness. Within each experiment, we manipulated seed dormancy and flowering time using multilocus near‐isogenic lines segregating strong and weak alleles of the seed dormancy geneDOG1and the flowering time geneFRI. We synthesized germination phenology data from the first experiment with fitness functions from the second experiment to project population fitness under different seasonal rainfall scenarios.

   Germination phenology tracked rainfall onset but was slower and more variable on sand than on soil. Many seeds dispersed on sand in spring and summer delayed germination until the cooler temperatures of autumn. The high‐dormancyDOG1allele also prevented immediate germination in spring and summer. Germination timing strongly affected plant fitness. Fecundity was highest in the October germination cohort and declined in spring germinants. The late floweringFRIallele had lower fecundity, especially in early fall and spring cohorts. Projections of population fitness revealed that: (1) Later onset of autumn rains will negatively affect population fitness. (2) Slow, variable germination on sand buffers populations against fitness impacts of variable spring and summer rainfall. (3) Seasonal selection favours high dormancy and early flowering genotypes in a Mediterranean climate with hot dry summers. The high‐dormancyDOG1allele delayed germination of spring‐dispersed fresh seeds until more favourable early fall conditions, resulting in higher projected population fitness.

   These findings suggest that Mediterranean annual plant populations are vulnerable to changes in seasonal precipitation, especially in California where rainfall onset is already occurring later. The fitness advantage of highly dormant, early flowering genotypes helps explain the prevalence of this strategy in Mediterranean populations.

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2. Independent and interactive effects of plant genotype and environment on plant traits and insect herbivore performance: A meta‐analysis with Salicaceae

   https://doi.org/10.1111/1365-2435.13249  

   Barker, Hilary L. ; Holeski, Liza M. ; Lindroth, Richard L. ; Koricheva, ed., Julia ( December 2018 , Functional Ecology)

   Ecological research has increasingly highlighted the importance of intraspecific variation in shaping the structure and function of communities and ecosystems. Indeed, the effects of intraspecific variation can match or exceed those of interspecific variation. Previous reviews of intraspecific variation in plant traits across heterogeneous environments have focused primarily onmeanphenotypic effects. We propose that a richer and fuller understanding of the ecological causes and consequences of intraspecific variation would be provided by partitioning traitvarianceinto its subcomponents (genetic, environment, genotype by environment interaction).

   We used a meta‐analysis of 352 sets of genetic, environment and genotype by environment (G×E) variation estimates from 72 studies of Salicaceae to compare these sources of variation across plant traits (growth, foliar nitrogen, defence compounds), insect herbivore performance metrics (e.g., survival, growth, fecundity) and environmental conditions (e.g., soil nutrients, water, defoliation).

   Our findings revealed that variation in levels of defence compounds (both condensed tannins and salicinoids) and insect herbivore performance were primarily genetically determined, while variation in plant growth and foliar nitrogen was more environmentally determined.

   Plasticity in plant growth, foliar nitrogen levels and insect herbivore performance varied substantially across different sites (year × location), and nutrient, water and carbon dioxide environments. Plasticity was lowest for chemical defence traits and all traits in contrasting ozone and defoliation environments.

   Our quantitative review also revealed several gaps in the literature, including a need for surveying more mature plants, a wider variety of insect herbivore species (e.g., leaf‐galling insects, specialist insects) and underrepresented environmental treatments (e.g., competition, defoliation, disease, light and water availability).

   Findings from this analysis highlight the importance of, and patterns within, intraspecific variation with respect to shaping the evolvability and plasticity of traits and governing the interactions of plants and insects.

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3. Assortative mating by flowering time and its effect on correlated traits in variable environments

   https://doi.org/10.1002/ece3.4765  

   Rubin, Matthew J. ; Schmid, Kelly M. ; Friedman, Jannice ( December 2018 , Ecology and Evolution)

   Reproductive timing is a key life‐history trait that impacts the pool of available mates, the environment experienced during flowering, and the expression of other traits through genetic covariation. Selection on phenology, and its consequences on other life‐history traits, has considerable implications in the context of ongoing climate change and shifting growing seasons. To test this, we grew field‐collected seed from the wildflowerMimulus guttatusin a greenhouse to assess the standing genetic variation for flowering time and covariation with other traits. We then created full‐sib families through phenological assortative mating and grew offspring in three photoperiod treatments representing seasonal variation in daylength. We find substantial quantitative genetic variation for the onset of flowering time, which covaried with vegetative traits. The assortatively‐mated offspring varied in their critical photoperiod by over two hours, so that families differed in their probability of flowering across treatments Allocation to flowering and vegetative growth changed across the daylength treatments, with consistent direction and magnitude of covariation among flowering time and other traits. Our results suggest that future studies of flowering time evolution should consider the joint evolution of correlated traits and shifting seasonal selection to understand how environmental variation influences life histories.

    

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4. Chilling consequences: Herbarium records reveal earlier reproductive phenology of winter annual gladecress in a wetter, cooler climate

   https://doi.org/10.1002/ppp3.10095  

   Banaszak, Caitlin ; Grinath, Joshua B. ; Herlihy, Christopher R. ( January 2020 , PLANTS, PEOPLE, PLANET)

   Networks of digitized herbarium records are rich resources for understanding plant responses to climate change. While the climate is warming globally, some localities are experiencing climate cooling, the effects of which are poorly understood. Our herbarium‐based study of a geographically restricted species shows that the timing of reproduction can shift earlier as the climate becomes cooler and wetter. Local variation in climate change may be a key factor driving the high variability of changes observed in plant reproduction and climate cooling should be considered along with other global change drivers. This will help enable accurate predictions for the successful management of climate change effects.

   Summary

   Plant phenological responses to global warming are well studied. However, while many locations are experiencing increased temperatures, some locations are experiencing climate cooling. Little work has been conducted to understand plant phenological responses to cooling trends, much less the combined effects of cooling and other factors, such as changing precipitation. Furthermore, studies based on herbarium specimens have been instrumental in demonstrating plant responses to global warming; but to our knowledge, herbarium records have not been used to investigate responses to cooling.

   We collected data from 98 years of herbarium records to evaluate whether the reproductive phenology (flowering/fruiting) of an annual mustard, cedar gladecress (Leavenworthia stylosa), has changed as the climate has become cooler and wetter in central Tennessee, USA. Additionally, we conducted two field experiments to assess reproductive consequences of different flowering times.

   Over the last century, gladecress reproductive phenology has shifted 2.1 days earlier per decade, concurrent with wetter conditions during germination and cooler conditions during reproduction. Field experiments showed that plants with extremely early and moderately early flowering had equivalent reproduction, but these plants had greater reproduction than intermediate‐ and late‐flowering plants.

   Counter to expectations from global warming studies, our work demonstrates that climate cooling and greater rainfall can result in earlier plant reproductive phenology, potentially due to asymmetric selection for early flowering. Future studies may need to consider climate cooling along with other global change factors to fully explain changes in plant phenology. Our understanding of plant responses to climate cooling can be enhanced through additional herbarium‐based research.

    

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5. Spatial and ontogenetic variance in local densities modify selection on demographic traits

   https://doi.org/10.1111/1365-2435.14335  

   Mutz, Jessie ; Inouye, Brian D. ( April 2023 , Functional Ecology)

   Local density can affect individual performance by altering the strength of species interactions. Within many populations, local densities vary spatially (individuals are patchily distributed) or change across life stages, which should influence the selection and eco‐evolutionary feedback because local density variance affects mean fitness and is affected by traits of individuals. However, most studies on the evolutionary consequences of density‐dependent interactions focus on populations where local densities are relatively constant through time and space.

   We investigated the influence of spatial and ontogenetic variance in local densities within an insect population by comparing a model integrating both types of local density variance with models including only spatial variance, only ontogenetic variance, or no variance. We parameterized the models with experimental data, then used elasticity and invasion analyses to characterize selection on traits that affect either the local density an individual experiences (mean clutch size) or individuals' sensitivity to density (effect of larval crowding on pupal mass).

   Spatial and ontogenetic variance reduced population elasticity to effects of local density by 76% and 34% on average, respectively.

   Spatial variance modified selection and adaptive dynamics by altering the tradeoff between density‐dependent and density‐independent vital rates. In models including spatial variance, strategies that maximized density‐dependent survival were favoured over fecundity‐maximizing strategies even at low population density, counter to predictions of density‐dependent selection theory. Furthermore, only models that included spatial variance, thus linking the scales of oviposition and density‐dependent larval survival, had an evolutionarily stable clutch size.

   Ontogenetic variance weakened selection on mean clutch size and sensitivity to larval crowding by disrupting the relationship between trait values and performance during critical life stages.

   We demonstrate that local density variance can strongly modify selection at empirically observed interaction strengths and identify mechanisms for the effects of spatial and ontogenetic variance. Our findings reveal the potential for local density variance to mediate eco‐evolutionary feedback by shaping selection on demographically important traits.

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