Biology subjects

Sheth, S. N.

Publications and source records attributed to Sheth, S. N..

10 recordsLinked to original sources

bioRxiv2026

Temporal stasis in three facets of biodiversity reveals mechanisms of community assembly across elevation gradients

Understanding spatial and temporal variation in community composition is central to protecting and monitoring biodiversity. Similarity in the composition of two communities decreases along spatial and temporal gradients, a relationship known as distance decay. Comparing distance-decay relationships across taxonomic, functional, and bioclimatic facets of diversity provides a means of interrogating niche-based versus neutral influences on community assembly. Furthermore, the context in which these facets yield overlapping or complementary information about global change impacts remains poorly understood. In this study, we examined spatiotemporal distance-decay relationships for taxonomic, functional, and bioclimatic facets of alpine plant diversity leveraging elevation gradients on five peaks in the White Mountains, California, USA, sampled at 3-4 time points between 2007 and 2024. Using multivariate Bayesian beta regression models, we estimated the slopes of elevation distance decay over multiple surveys and across taxonomic, functional and bioclimatic diversity to understand how spatial distance-decay relationships are changing through time and across different facets of diversity. We found strong spatial distance decay of taxonomic similarity across all peaks, with the highest elevation peak showing the strongest decay. Functional and bioclimatic similarities decayed more weakly than taxonomic similarity, suggesting environmental filtering shapes trait and niche distributions. Critically, spatial decay patterns showed no temporal signal across facets of diversity, indicating community stasis rather than biotic homogenization or differentiation. This study adds further evidence that xeric alpine plant communities are resisting climate change impacts through time.

ecology↗

bioRxiv2025

Two decades of resurrection studies: What have we learned about contemporary evolution of plant species?

Global change has profoundly altered the eco-evolutionary trajectories of plant species. Longitudinal studies often document phenotypic shifts in response to climate change, such as earlier flowering in the spring, but it remains challenging to disentangle the contributions of phenotypic plasticity and adaptive evolution to shifted phenotypic distributions. The resurrection approach has emerged as a powerful method to study genetic and plastic responses to novel selection imposed by global change by contrasting ancestral and descendant lineages from the same population under common conditions. Here, we compiled a database of 52 resurrection studies to examine key hypotheses about plant evolutionary responses to global change using a meta-analysis (40 of the studies) and quantitative review (all 52 studies). We found evidence for rapid, contemporary evolution, which often appeared adaptive, in over half of the cases, including some of the fastest cases of evolution in natural populations ever observed. Annual plants evolved earlier reproduction, and leaf economic traits associated with stress escape strategies. We also found evolution of increased plasticity for annual plants in phenology and physiology traits, and a reduction of plasticity in traits related to the leaf economic spectrum. We found less evidence for evolution in perennial species. Overall, our findings demonstrate the key role of drought escape in plant responses to a warming world. However, the lack of evolution in other traits and species indicates that constraints may dampen evolutionary responses in some scenarios. Our review also suggests promising avenues of future research for resurrection studies.

evolutionary biology↗

bioRxiv2025

Evolutionary responses to historic drought across the range of scarlet monkeyflower

Adaptive evolution is a key means for populations to persist under environmental change, yet whether populations across a species range can adapt quickly enough to keep pace with climate change remains unknown. The breeders equation predicts the evolutionary change in a trait from one generation to the next as the product of the selection differential and the narrow-sense heritability in that trait. Incorporating these aspects of the breeders equation, we performed a resurrection study with the scarlet monkeyflower (Mimulus cardinalis) to evaluate whether traits associated with drought adaptation have evolved in populations across a species range in response to extreme drought. We compared trait and fitness differences of pre-drought ancestors and post-drought descendants from six populations transplanted into three latitudinally-arrayed common gardens and quantified phenotypic selection and trait heritabilities. The strength, direction, and mode of selection varied among traits and gardens. Trait heritabilities were relatively low, and did not differ dramatically among populations or gardens. Overall, instances of evolutionary responses between ancestors and descendants were few and small in magnitude, but the magnitude of these evolutionary differences varied among gardens. Together, these results suggest that the expression of genetic variation, and thus traits, depend on the environment, and that environmental variability in field settings may mask the genetic variation that is often detected in greenhouse environments.

evolutionary biology↗

bioRxiv2025

Range-wide responses to an extreme heat event in Mimulus cardinalis

PremiseExtreme events are an understudied aspect of ongoing anthropogenic climate change that could play a disproportionate role in the threat that rapid environmental shifts pose to natural populations. MethodsWe used a short-term heatwave treatment in controlled growth chamber environments to study evolutionary responses in Mimulus cardinalis populations to a recent repeated extreme heat event. Individuals from before (ancestors) and after (descendants) this extreme heat event were resurrected from seeds harvested from six populations across the range of M. cardinalis, and their physiological, performance, and functional responses (stomatal conductance, leaf temperature difference, photosystem II efficiency, relative growth rate, specific leaf area, and leaf dry matter content) to the heatwave treatment were assessed. Key ResultsOur results allow for two main conclusions: 1) plants responded favorably to the heatwave treatment in terms of their overall performance and the magnitude of response was generally greatest among trailing-edge populations, and 2) despite some evidence of divergent evolutionary responses among regions to the recent natural extreme heat event, we did not find adaptive evolution that affected how M. cardinalis populations responded to the heatwave treatment. ConclusionsThese results demonstrate that many M. cardinalis populations may be residing in natural environments that are below their optimum average temperature, indicating that M. cardinalis populations could exhibit resiliency to future warming. However, limited evolutionary responses in M. cardinalis to the recent extreme heatwave could still indicate that there is potential for future vulnerability to extreme climate events of increased intensity, frequency, and duration in the future.

evolutionary biology↗

bioRxiv2024

Evolutionary rescue during extreme drought

Populations declining due to climate change may need to evolve to persist. While evolutionary rescue has been demonstrated in theory and the lab, its relevance to natural populations facing climate change remains unknown. Here we link rapid evolution and population dynamics in scarlet monkeyflower, Mimulus cardinalis, during an exceptional drought. We leverage whole-genome sequencing across 55 populations to identify climate-associated loci. Simultaneously we track demography and allele frequency change throughout the drought. We establish range-wide population decline during the drought, geographically variable rapid evolution, and variable population recovery that is predictable by standing genetic variation in and rapid evolution at climate-associated loci. These findings demonstrate evolutionary rescue in the wild, showing that genetic variation at adaptive, but not neutral loci, predicts population recovery.

evolutionary biology↗

bioRxiv2020

The evolution of thermal performance in native and invasive populations of Mimulus guttatus

1. The rise of globalization has spread organisms beyond their natural range, allowing further opportunity for species to adapt to novel environments and potentially become invaders. Yet, the role of climatic niche evolution in promoting the success of invasive species remains poorly understood. Here, we use thermal performance curves (TPCs) to test hypotheses about thermal adaptation during the invasion process. First, if novel temperature regimes impose strong selection in the introduced range, invasive populations may evolve distinct TPCs relative to native populations. Second, invasive species may not exhibit specialist-generalist tradeoffs and instead may be "masters-of-all" with high maximum performance and broad TPCs. Third, with sufficient time, standing genetic variation, and temperature-mediated selection, TPCs of native and invasive populations may show parallel evolution in response to thermal gradients. 2. To test these hypotheses, we built TPCs for 18 native (United States) and 13 invasive (United Kingdom) populations of the yellow monkeyflower, Mimulus guttatus. We grew clones of multiple genotypes per population across six temperature regimes in growth chambers. 3. Invasive populations have not evolved different thermal optima or performance breadths, providing evidence for evolutionary stasis of thermal performance between the native and invasive ranges after over 200 years post-introduction. Further, both native and invasive populations experienced similar specialist-generalist tradeoffs whereby broad TPCS come at the cost of lower peak performance. Inconsistent with the idea that the degree of thermal specialization varies across spatial or temperature gradients, native and invasive populations did not exhibit adaptive clines in thermal performance breadth with latitude or temperature seasonality. However, thermal optimum increased with mean annual temperature in the native range, indicating some adaptive differentiation among native populations 4. Synthesis: These findings suggest that thermal niches were static during the invasion process, and that general-purpose genotypes, rather than rapid evolution in the introduced range, may promote invasion.

evolutionary biology↗

bioRxiv2020

A resurrection study reveals limited evolution of thermal performance in response to recent climate change across the geographic range of the scarlet monkeyflower

Evolutionary rescue can prevent populations from declining under climate change, and should be more likely at high-latitude, "leading" edges of species ranges due to greater temperature anomalies and gene flow from warm-adapted populations. Using a resurrection study with seeds collected before and after a seven-year period of record warming, we tested for thermal adaptation in the scarlet monkeyflower Mimulus cardinalis. We grew ancestors and descendants from northern-edge, central, and southern-edge populations across eight temperatures. Despite recent climate anomalies, populations showed limited evolution of thermal performance curves. However, one southern population evolved a narrower thermal performance breadth by 1.25 {degrees}C, which matches the direction and magnitude of the average decrease in seasonality experienced. Consistent with the climate variability hypothesis, thermal performance breadth increased with temperature seasonality across the species geographic range. Inconsistent with performance trade-offs between low and high temperatures across populations, we did not detect a positive relationship between thermal optimum and mean temperature. These findings fail to support the hypothesis that evolutionary response to climate change is greatest at the leading edge, and suggest that the evolution of thermal performance is unlikely to rescue most populations from the detrimental effects of rapidly changing climate.

evolutionary biology↗

bioRxiv2019

Community turnover by composition and climate affinity across scales in an alpine system

Premise of the studyExamining community turnover across climate gradients at multiple scales is vital to understanding biogeographic response to climate change. This approach is especially important for alpine plants in which the relative roles of topographic complexity and non-climatic or stochastic factors vary across spatial scales.\n\nMethodsWe examined the structure of alpine plant communities across elevation gradients in the White Mountains, California. Using community climatic niche means (CCNMs) and measures of community dissimilarity, we explored the relationship between community composition and elevation gradients at three scales: the mountain range, individual peaks, and within elevation contours.\n\nKey ResultsAt the mountain range scale, community turnover and CCNMs showed strongly significant relationships with elevation, with an increase in the abundance of cooler and wetter-adapted species at higher elevations. At the scale of a single peaks, we found weak and inconsistent relationships between CCNMs and elevation, but variation in community composition explained by elevation increased. Within the elevation contours, the range of CCNMs was weakly positively correlated with turnover in species identity, likely driven by microclimate and other site-specific factors.\n\nConclusionsOur results suggest that there is strong environmental sorting of alpine plant communities at broad scales, but microclimatic and site-specific, non-climatic factors together shape community turnover at finer scales. In the context of climate change, our results imply that community-climate relationships are scale-dependent, and predictions of local alpine plant range shifts are limited by a lack of topoclimatic and habitat information.

ecology↗

bioRxiv2019

Additive genetic variance for lifetime fitness and the capacity for adaptation in the wild

The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, VA(W). Mean absolute fitness, [Formula], is predicted to change at the rate [Formula], according to Fishers Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of VA(W) and the capacity for ongoing adaptation is exceedingly rare. We estimated VA(W) and [Formula] in three pedigreed populations of annual Chamaecrista fasciculata, over three years in the wild. Contrasting with common expectations, we found significant VA(W) in all populations and years, predicting increased mean fitness in subsequent generations (0.83 to 6.12 seeds per individual). Further, we detected two cases predicting \"evolutionary rescue\", where selection on standing VA(W) was expected to increase fitness of declining populations ([Formula] < 1.0) to levels consistent with population sustainability and growth. Within populations, interannual differences in genetic expression of fitness were striking. Significant genotype-by-year interactions reflected modest correlations between breeding values across years (all r < 0.490), indicating temporally variable selection at the genotypic level; that could contribute to maintaining VA(W). By directly estimating VA(W) and total lifetime [Formula], our study presents an experimental approach for studies of adaptive capacity in the wild.

evolutionary biology↗

bioRxiv2017

Demographic compensation does not rescue populations at a trailing range edge

As climate change shifts species' climatic envelopes across the landscape, equilibrium between geographic ranges and niches is likely diminishing due to time lags in demography and dispersal. If a species' range and niche are out of equilibrium, then population performance should decrease from cool, \"leading\" range edges, where populations are expanding into recently ameliorated habitats, to warm, \"trailing\" range edges, where populations are contracting from newly unsuitable areas. Population contraction signals that compensatory changes in vital rates are insufficient to buffer population growth from deteriorating environments. Life history theory predicts tradeoffs between fast development, high reproduction, and short longevity at low latitudes and slow development, less frequent but multiple bouts of reproduction, and long lifespan at high latitudes. If demographic compensation is driven by life history evolution, compensatory negative correlations in vital rates may be associated with this fast-slow continuum. An outstanding question is whether range limits and range contractions reflect inadequate compensatory life history shifts along environmental gradients, causing population growth rates to fall below replacement levels at range edges. We surveyed demography of 32 populations of the scarlet monkeyflower (Erythranthe cardinalis) spanning 11{degrees} latitude in western North America and used integral projection models to infer population dynamics and assess demographic compensation. Population growth rates decreased from north to south, consistent with leading-trailing dynamics. Southern populations are declining due to reduced survival, growth, and recruitment, despite compensatory increases in reproduction and faster life history characteristics, suggesting that demographic compensation will not rescue populations at the trailing range edge.\n\nSIGNIFICANCE STATEMENTWhile climate change is causing poleward shifts in many species' geographic distributions, some species' ranges have remained stable, particularly at low-latitude limits. One explanation for why some species' ranges have not shifted is demographic compensation, whereby declines in some demographic processes are offset by increases in others, potentially buffering populations from extinction. However, we have limited understanding of whether demographic compensation can prevent collapse of populations facing climate change. We examined the demography of natural populations of a perennial herb spanning a broad latitudinal gradient. Despite increases in reproduction, low-latitude populations declined due to diminished survival, growth, and recruitment. Thus, demographic compensation may not be sufficient to rescue low-latitude, warm-edge populations from extinction.

ecology↗