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1. Small spaces, big impacts: contributions of micro-environmental variation to population persistence under climate change

   https://doi.org/10.1093/aobpla/plaa005  

   Denney, Derek A; Jameel, M Inam; Bemmels, Jordan B; Rochford, Mia E; Anderson, Jill T (April 2020, AoB PLANTS)

   Abdelaziz, Mohamed (Ed.)

   Abstract Individuals within natural populations can experience very different abiotic and biotic conditions across small spatial scales owing to microtopography and other micro-environmental gradients. Ecological and evolutionary studies often ignore the effects of micro-environment on plant population and community dynamics. Here, we explore the extent to which fine-grained variation in abiotic and biotic conditions contributes to within-population variation in trait expression and genetic diversity in natural plant populations. Furthermore, we consider whether benign microhabitats could buffer local populations of some plant species from abiotic stresses imposed by rapid anthropogenic climate change. If microrefugia sustain local populations and communities in the short term, other eco-evolutionary processes, such as gene flow and adaptation, could enhance population stability in the longer term. We caution, however, that local populations may still decline in size as they contract into rare microhabitats and microrefugia. We encourage future research that explicitly examines the role of the micro-environment in maintaining genetic variation within local populations, favouring the evolution of phenotypic plasticity at local scales and enhancing population persistence under global change. 

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2. Variation in the seasonal germination niche across an elevational gradient: the role of germination cueing in current and future climates

   https://doi.org/10.1002/ajb2.1425  

   Gremer, Jennifer_R; Chiono, Alec; Suglia, Elena; Bontrager, Megan; Okafor, Lauren; Schmitt, Johanna (February 2020, American Journal of Botany)

   PremiseThe timing of germination has profound impacts on fitness, population dynamics, and species ranges. Many plants have evolved responses to seasonal environmental cues to time germination with favorable conditions; these responses interact with temporal variation in local climate to drive the seasonal climate niche and may reflect local adaptation. Here, we examined germination responses to temperature cues inStreptanthus tortuosuspopulations across an elevational gradient. MethodsUsing common garden experiments, we evaluated differences among populations in response to cold stratification (chilling) and germination temperature and related them to observed germination phenology in the field. We then explored how these responses relate to past climate at each site and the implications of those patterns under future climate change. ResultsPopulations from high elevations had stronger stratification requirements for germination and narrower temperature ranges for germination without stratification. Differences in germination responses corresponded with elevation and variability in seasonal temperature and precipitation across populations. Further, they corresponded with germination phenology in the field; low‐elevation populations germinated in the fall without chilling, whereas high‐elevation populations germinated after winter chilling and snowmelt in spring and summer. Climate‐change forecasts indicate increasing temperatures and decreasing snowpack, which will likely alter germination cues and timing, particularly for high‐elevation populations. ConclusionsThe seasonal germination niche forS. tortuosusis highly influenced by temperature and varies across the elevational gradient. Climate change will likely affect germination timing, which may cascade to influence trait expression, fitness, and population persistence. 

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3. Genomic architecture controls multivariate adaptation to climate change

   https://doi.org/10.1111/gcb.17179  

   Terasaki Hart, Drew_E; Wang, Ian_J (February 2024, Global Change Biology)

   Abstract As climate change advances, environmental gradients may decouple, generating novel multivariate environments that stress wild populations. A commonly invoked mechanism of evolutionary rescue is adaptive gene flow tracking climate shifts, but gene flow from populations inhabiting similar conditions on one environmental axis could cause maladaptive introgression when populations are adapted to different environmental variables that do not shift together. Genomic architecture can play an important role in determining the effectiveness and relative magnitudes of adaptive gene flow and in situ adaptation. This may have direct consequences for how species respond to climate change but is often overlooked. Here, we simulated microevolutionary responses to environmental change under scenarios defined by variation in the polygenicity, linkage, and genetic redundancy of two independent traits, one of which is adapted to a gradient that shifts under climate change. We used these simulations to examine how genomic architecture influences evolutionary outcomes under climate change. We found that climate‐tracking (up‐gradient) gene flow, though present in all scenarios, was strongly constrained under scenarios of lower linkage and higher polygenicity and redundancy, suggesting in situ adaptation as the predominant mechanism of evolutionary rescue under these conditions. We also found that high polygenicity caused increased maladaptation and demographic decline, a concerning result given that many climate‐adapted traits may be polygenic. Finally, in scenarios with high redundancy, we observed increased adaptive capacity. This finding adds to the growing recognition of the importance of redundancy in mediating in situ adaptive capacity and suggests opportunities for better understanding the climatic vulnerability of real populations. 

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4. Genomic time‐series data show that gene flow maintains high genetic diversity despite substantial genetic drift in a butterfly species

   https://doi.org/10.1111/mec.16111  

   Gompert, Zachariah; Springer, Amy; Brady, Megan; Chaturvedi, Samridhi; Lucas, Lauren K. (August 2021, Molecular Ecology)

   Abstract Effective population size affects the efficacy of selection, rate of evolution by drift and neutral diversity levels. When species are subdivided into multiple populations connected by gene flow, evolutionary processes can depend on global or local effective population sizes. Theory predicts that high levels of diversity might be maintained by gene flow, even very low levels of gene flow, consistent with species long‐term effective population size, but tests of this idea are mostly lacking. Here, we show thatLycaeidesbutterfly populations maintain low contemporary (variance) effective population sizes (e.g. ~200 individuals) and thus evolve rapidly by genetic drift. However, populations harboured high levels of genetic diversity consistent with an effective population size several orders of magnitude larger. We hypothesized that the differences in the magnitude and variability of contemporary versus long‐term effective population sizes were caused by gene flow of sufficient magnitude to maintain diversity but only subtly affect evolution on generational timescales. Consistent with this hypothesis, we detected low but nontrivial gene flow among populations. Furthermore, using short‐term population‐genomic time‐series data, we documented patterns consistent with predictions from this hypothesis, including a weak but detectable excess of evolutionary change in the direction of the mean (migrant gene pool) allele frequencies across populations and consistency in the direction of allele frequency change over time. The documented decoupling of diversity levels and short‐term change by drift inLycaeideshas implications for our understanding of contemporary evolution and the maintenance of genetic variation in the wild. 

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5. Reproductive losses due to climate change‐induced earlier flowering are not the primary threat to plant population viability in a perennial herb

   https://doi.org/10.1111/1365-2745.13146  

   Iler, Amy M.; Compagnoni, Aldo; Inouye, David W.; Williams, Jennifer L.; CaraDonna, Paul J.; Anderson, Aaron; Miller, Tom E. X.; Catford, ed., Jane (March 2019, Journal of Ecology)

   Abstract Despite a global footprint of shifts in flowering phenology in response to climate change, the reproductive consequences of these shifts are poorly understood. Furthermore, it is unknown whether altered flowering times affect plant population viability.We examine whether climate change‐induced earlier flowering has consequences for population persistence by incorporating reproductive losses from frost damage (a risk of early flowering) into population models of a subalpine sunflower (Helianthella quinquenervis). Using long‐term demographic data for three populations that span the species’ elevation range (8–15 years, depending on the population), we first examine how snowmelt date affects plant vital rates. To verify vital rate responses to snowmelt date experimentally, we manipulate snowmelt date with a snow removal experiment at one population. Finally, we construct stochastic population projection models and Life Table Response Experiments for each population.We find that populations decline (λ_s < 1) as snowmelt dates become earlier. Frost damage to flower buds, a consequence of climate change‐induced earlier flowering, does not contribute strongly to population declines. Instead, we find evidence that negative effects on survival, likely due to increased drought risk during longer growing seasons, drive projected population declines under earlier snowmelt dates.Synthesis.Shifts in flowering phenology are a conspicuous and important aspect of biological responses to climate change, but here we show that the phenology of reproductive events can be unreliable measures of threats to population persistence, even when earlier flowering is associated with substantial reproductive losses. Evidence for shifts in reproductive phenology, along with scarcer evidence that these shifts actually influence reproductive success, are valuable but can paint an incomplete and even misleading picture of plant population responses to climate change. 

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