Biology subjects

Moeller, D. A.

Publications and source records attributed to Moeller, D. A..

10 recordsLinked to original sources

bioRxiv2026

Climate change effects on terpene expression differ among populations and have consequences for herbivory in an invasive plant

ABSTRACT 1. Plant secondary metabolites often moderate interactions with abiotic and biotic factors. For example, secondary metabolites often deter insect herbivores from and influence the extent of damage to plant tissues. However, little is known about how climate change may alter the expression of secondary metabolites and the nature of the resulting effects on plant-herbivore interactions. As climate change continues to shift environmental conditions away from historical norms, climate change effects on plant-herbivore interactions may have important consequences for the range expansion of invasive plants and the efficacy of biocontrol agents across the range. 2. In this study, we examined climate change effects on terpene expression in common tansy (Tanacetum vulgare) in four field transplant sites in Minnesota, U.S.A. that include experimental manipulation of precipitation and temperature. Each transplant site included genotypes from 10 natural populations that span climate variation across Minnesota. We quantified leaf terpene profiles in two years (2024 and 2025) using targeted gas chromatography-mass spectrometry. We surveyed insect herbivory to the same genotypes in experimental field sites to ask how terpene profiles and chemotypes contribute to the likelihood of herbivory. 3. We detected evidence that climate change manipulation altered terpene production and depended on source population. Similarly, the extent of temporal variation in terpene profiles depended upon source population. We also found variation in terpene profiles among sites, further emphasizing the role of the environment in shaping terpene production. These shifts in terpene profiles, in turn, influenced the likelihood of herbivory. Herbivory was higher at the southern compared to northern sites and susceptibility to herbivory was higher in the northern compared to southern populations, particularly at northern sites where average herbivory was lower. The likelihood of herbivory also varied among chemotypes and the frequency of chemotypes varied among source populations, suggesting a complex interplay between the historical and current environments, terpene production, and plant-herbivore interactions. 4. Synthesis. Together, our results suggest a combined role of the abiotic environment and population differentiation in moderating plant-herbivore interactions via shifts and variation in terpene profiles, which may influence invasive range dynamics and complicate the regional management strategies of common tansy.

ecology↗

bioRxiv2026

Expansion load reduces fitness at the range margin of an invasive plant

Genetic drift and natural selection jointly shape how populations evolve during range expansion, yet their joint influence on fitness at expanding range margins is rarely examined. Serial founder events during range expansion may amplify genetic drift and result in the accumulation (or greater expression) of deleterious mutations at range margins, termed expansion load. Conversely, natural selection should lead to local adaptation during expansion provided that populations harbor adequate genetic variation. We used a manipulative transplant experiment, genome-wide SNP data, and demographic surveys of the invasive plant, commontansy (Tanacetum vulgare), to evaluate evidence for expansion load and local adaptation during ca. 150 years of invasion in Minnesota, U.S.A. The common garden occurred near the southern range margin and included 16 populations that span (1) a chronosequence of invasion from northeastern MN (invasion core) to southern and western range margins and (2) environmental gradients in temperature and precipitation. We also manipulated temperature and precipitation to test whether environmental stress amplified the expression of expansion load or revealed population differentiation in climate adaptation. Population fitness declined strongly with distance from the invasion core, consistent with the accumulation of expansion load. This finding was corroborated by analyses of 173 populations that showed an increase in homozygosity (F) and a decrease in population size from the invasion core to range margins. We did not find any evidence of local adaptation; a strong positive relationship between population mean fitness and environmental distance was indicative of maladaptation. While the elevated temperature manipulation reduced fitness, it did not amplify the expression of expansion load. Taken together, our results are consistent with the hypothesis that serial population bottlenecks and strong genetic drift led to expansion load and reduced fitness at range margins. Teaser TextSpecies geographic ranges are dynamic over geologic time scales but may also shift rapidly in response to climate change and for invasive species. While range shifts are often viewed only through an ecological lens, the extent and pace of range expansion may be significantly modulated by evolutionary processes. We disentangled the influence of genetic drift and natural selection on population fitness across an invasion chronosequence (spanning ca. 150 years) for the herbaceous plant common tansy (Tanacetum vulgare). Our synthesis of analyses of a field transplant experiment, genome-wide SNP data, and demographic surveys provided evidence consistent with the accumulation of expansion load at leading range edges. While theory often predicts that local adaptation should occur readily in response to novel environments, our results were consistent with local maladaptation. Our findings emphasize the importance of stochastic processes in shaping the geographic distribution of species and their capacity to shift with changing environments.

evolutionary biology↗

bioRxiv2025

Two decades of satellite images reveal the spatial and temporal dynamics of leafy spurge invasion and improve species distribution models

Developing accurate and cost-effective methods to detect and predict the spread of invasive species remains an ongoing challenge. Species distribution models (SDMs) are used to predict invasion under current and future climates. However, occurrence datasets are often spatially and temporally biased because they are collected in an unstructured and opportunistic manner. Remote sensing individual species over broad spatial and temporal scales has become increasingly feasible with the accumulation of satellite images and the development of convolutional neural networks. In this study, we used a 21-year archival Landsat satellite imagery (2000-2020) to train a temporal convolutional neural network model to predict the probability of occurrence of the invasive species, leafy spurge (Euphorbia virgata), across Minnesota. We validated our predictions with an independent dataset. First, we show that that leafy spurge has expanded from 1,067 km{superscript 2} occupied in 2000-2002 to 7,156 km{superscript 2} in 2018-2020, a 570% increase. Surprisingly, drought severity modulated the predicted area invaded and was associated with fluctuations over the study period. Second, we tracked changes in probability over time for individual pixels and showed that invasion has been concentrated in two largely disjunct regions of Minnesota. Third, our remotely-sensed occurrence dataset and community science dataset were biased to roadsides, although the latter was more severely biased. Last, we showed that SDMs built using remotely-sensed occurrences had higher discrimination, were less overfit, and had higher performance outside of urban areas. Overall, twenty one years of archival satellite imagery provided valuable insight into the spatial and temporal population dynamics of leafy spurge invasion and improved forecasts of future invasion by reducing spatial bias.

ecology↗

bioRxiv2023

Mating system and environment predict the direction and extent of introgression between incipient Clarkia species

Introgression is pervasive across the tree of life, varying across taxa, geography, and genomes. However, we are only beginning to understand the factors that modulate this variation and how they may be affected by global change. Here, we used 200 genomes and a 15-year site-specific environmental dataset to investigate the effect of mating system divergence and environmental variation on the magnitude of introgression between two recently diverged annual plants. Two subspecies of Clarkia xantiana diverged ca. 65k years ago and subsequently came into secondary sympatry where they form replicated contact zones. We found that introgression is asymmetric between taxa, with substantially more introgression from the self-fertilizing taxon to the outcrossing taxon. This asymmetry is caused by a bias in the direction of initial F1 hybrid formation and subsequent backcrossing. We also found extensive variation in the outcrossers admixture proportion among contact zones, which is predicted nearly entirely by interannual variance in spring precipitation. Greater fluctuations in spring precipitation result in higher admixture proportions, likely mediated by the effects of spring precipitation on the expression of traits that determine premating reproductive isolation. Climate-driven hybridization dynamics may be particularly affected by global change, potentially reshaping species boundaries and adaptation to novel environments.

evolutionary biology↗

bioRxiv2023

Chronosequence of invasion reveals minimal losses of population genomic diversity, niche expansion, and trait divergence in the polyploid, leafy spurge.

Rapid evolution may play an important role in the range expansion of invasive species and modify forecasts of invasion, which are the backbone of land management strategies. However, losses of genetic variation associated with colonization bottlenecks may constrain trait and niche divergence at leading range edges, thereby impacting management decisions that anticipate future range expansion. The spatial and temporal scales over which adaptation contributes to invasion dynamics remains unresolved. We leveraged detailed records of the [~]130 year invasion history of the invasive polyploid plant, leafy spurge (Euphorbia virgata), across [~]500km in Minnesota, U.S.A. We examined the consequences of range expansion for population genomic diversity, niche breadth, and the evolution of germination behavior. Using genotyping-by-sequencing, we found some population structure in the range core, where introduction occurred, but panmixia among all other populations. Range expansion was accompanied by only modest losses in sequence diversity, with small, isolated populations at the leading edge harboring similar levels of diversity to those in the range core. The climatic niche expanded during most of range expansion, and the niche of the range core was largely non-overlapping with the invasion front. Ecological niche models indicated that mean temperature of the warmest quarter was the strongest determinant of habitat suitability and that populations at the leading edge had the lowest habitat suitability. Guided by these findings, we tested for rapid evolution in germination behavior over the time course of range expansion using a common garden experiment and temperature manipulations. Germination behavior diverged from early to late phases of the invasion, with populations from later phases having higher dormancy at lower temperatures. Our results suggest that trait evolution may have contributed to niche expansion during invasion and that distribution models, which inform future management planning, may underestimate invasion potential without accounting for evolution.

evolutionary biology↗

bioRxiv2022

Bet hedging is not sufficient to explain intraspecific variation in germination patterns of a winter annual plant

Bet hedging consists of life history strategies that buffer against environmental variability by trading off immediate and long-term fitness. Delayed germination in annual plants is a classic example of bet hedging, and is often invoked to explain low germination fractions. We examined whether bet hedging explains low and variable germination fractions among 20 populations of the winter annual plant Clarkia xantiana ssp. xantiana that experience substantial variation in reproductive success among years. Leveraging 15 years of demographic monitoring and 3 years of field germination experiments, we assessed the fitness consequences of seed banks and compared optimal germination fractions from a density-independent bet-hedging model to observed germination fractions. We did not find consistent evidence of bet hedging or the expected trade-off between arithmetic and geometric mean fitness, though delayed germination increased long-term fitness in 7 of 20 populations. Optimal germination fractions were 2 to 5 times higher than observed germination fractions, and among-population variation in germination fractions was not correlated with risks across the life cycle. Our comprehensive test suggests that bet hedging is insufficient to explain the observed germination patterns. Understanding variation in germination strategies will likely require integrating bet hedging with complementary forces shaping the evolution of delayed germination.

ecology↗

bioRxiv2022

Rapid evolution in response to climate-change-induced drought and its demographic and genetic controls

Populations often vary in their evolutionary responses to a shared environmental perturbation. A key hurdle in building more predictive models of rapid evolution is understanding this variation - why do some populations and traits evolve while others do not? We combined long-term demographic and environmental data, estimates of quantitative genetic variance components, a resurrection experiment, and individual-based evolutionary simulations to gain mechanistic insights into contrasting evolutionary responses to a severe multiyear drought. We examined five traits in two populations of a native California plant, Clarkia xantiana, at three timepoints over 7 years. Earlier flowering phenology evolved in only one of the two populations, though both populations experienced similar drought severity and demographic declines and were estimated to have considerable additive genetic variance for flowering phenology. Pairing demographic and experimental data with evolutionary simulations suggested that while seed banks in both populations likely constrained evolutionary responses, a stronger seed bank in the non-evolving population resulted in evolutionary stasis. Gene flow through time via germ banks may be an important, underappreciated control on rapid evolution in response to extreme environmental perturbations.

evolutionary biology↗

bioRxiv2021

Genetic load may increase or decrease with selfing depending upon the recombination environment

The ability of natural selection to remove deleterious mutations from a population is a function of the effective population size. Increases in selfing rate, and concomitant increases in population-level homozygosity, can increase or decrease the efficacy of selection, depending on the dominance and selection coefficients of the deleterious mutations. Most theory has focused on how (partial) selfing affects the efficacy of selection for mutations of a given dominance and fitness effect in isolation. It remains unclear how selfing affects the purging of deleterious mutations in a genome-wide context where mutations with different selection and dominance coefficients co-segregate. Here, we use computer simulations to investigate how mutation, selection and recombination interact with selfing rate to shape genome-wide patterns of genetic load. We recover various mechanisms previously described for how (partial) selfing affects the efficacy of selection against mutations of a given dominance class. However, we find that the interaction of purifying selection against mutations of different dominance classes changes with selfing rate. In particular, as outcrossing populations transition from purifying selection to pseudo-overdominance they experience a dramatic increase in the genetic load caused by additive, mildly deleterious mutations. We describe the threshold selfing rate that prevents pseudo-overdominance and decreases genetic load.

genetics↗

bioRxiv2018

Seed predation increases from the Arctic to the Equator and from high to low elevations

Species interactions have long been predicted to increase in intensity towards the tropics and low elevations, due to gradients in climate, productivity, or biodiversity. Despite their importance for understanding global ecological and evolutionary processes, plant-animal interaction gradients are particularly difficult to test systematically across large geographic gradients, and evidence from smaller, disparate studies is inconclusive. By systematically measuring post-dispersal seed predation using 6980 standardized seed depots along 18 mountains in the Pacific cordillera, we found that seed predation increases 18% from the Arctic to Equator and 16% from 4000 masl to sea level. Clines in total predation, likely driven by invertebrates, were consistent across tree-line ecotones and in continuous forest, and were better explained by climate seasonality than by productivity, biodiversity, or latitude. These results suggest that species interactions play predictably greater ecological and evolutionary roles in tropical, lowland, and other less seasonal ecosystems.\n\nOne Sentence SummaryPost-dispersal seed predation increases from the Arctic to the Equator and from high elevations to sea level.

ecology↗

bioRxiv2018

Biotic interactions limit the geographic range of an annual plant: herbivory and phenology mediate fitness beyond a range margin

Species range limits offer powerful opportunities to study environmental factors regulating distributions and probe the limits of adaptation. However, we rarely know what aspects of the environment are actually constraining range expansion, much less which traits are mediating the organisms response to these environmental gradients. Though most studies focus on climatic limits to species distributions, biotic interactions may be just as important. We used field experiments and simulations to estimate contributions of mammal herbivory to a range boundary in the annual plant Clarkia xantiana ssp. xantiana. A steep gradient of increasing probability of herbivory occurs across the boundary, and herbivory drives several-fold declines in lifetime fitness at and beyond the boundary. By including in our analyses data from a sister taxon with more rapid phenology, we show that delayed phenology drives C. xantiana ssp. xantianas susceptibility to herbivory and low fitness beyond its border.

ecology↗