Biology subjects

Sexton, J. P.

Publications and source records attributed to Sexton, J. P..

6 recordsLinked to original sources

bioRxiv2026

Biotic niche expansion constrains the fundamental abiotic niche: Evidence from experimental evolution

In an ever-changing world, organisms are subject to selective pressures that shape their ecological niches. Niche theory predicts that environmental heterogeneity selects for niche expansion, yet niches are inherently multidimensional, and expansion in one dimension may impose severe constrains on others. In this study, we employed rigorous experimental evolution to investigate these cross-dimensional trade-offs in the wheat curl mite, Aceria tosichella. By adapting replicated lineages to either stable (single-host) or alternating (two-host) environments for hundreds of generations, we successfully expanded the mites fundamental biotic host niche, enabling lineages to exploit diverse host species, including those unencountered during their evolutionary history. Crucially, however, this biotic generalization incurred a significant cost in the abiotic niche dimension. Lineages adapted to alternating hosts exhibited significantly reduced thermal tolerance compared to host specialists, which maintained superior performance across a wider thermal range. This trade-off appears to be driven by a combination of genetically based metabolic constraints and behavioral dispersal strategies. Our results provide compelling experimental evidence for the "Jack-of-all-trades is master of none" hypothesis across niche dimensions. We demonstrate that physiological trade-offs between biotic versatility and abiotic resilience strictly constrain the evolution of the multidimensional niche, with critical implications for forecasting species distributions and invasion potential under climate change.

ecology↗

bioRxiv2026

Phenotypic plasticity evolved for climate variability constrains performance under climate warming

Phenotypic plasticity allows plants to rapidly respond to changing environments without the need for evolutionary change or migration. While selection can create variation in plasticity across natural populations, these responses are not adaptive in all environments. To predict whether plasticity will be adaptive requires evaluation of its fitness effects across a range of environments, including novel ones. Here, we test how traits and their plasticity vary for genotypes collected across a natural hybrid zone between two tree species with contrasting climatic niches. Fast-growing Populus trichocarpa inhabits maritime environments with relatively warm and stable temperatures, while P. balsamifera inhabits continental environments with cold winters and large temperature variance throughout the year. We planted 44 clonally replicated genotypes into thirteen common gardens and measured vegetative phenology, leaf morphology, stomata morphology and conductance, and photochemistry. Overall, genotypes from colder, more continental environments exhibited higher plasticity. P. balsamifera ancestry was associated with increased plasticity in timing of fall phenology, stomatal conductance, and leaf mass per unit area. We assessed the effects of trait plasticity on fitness estimated as yearly growth across common gardens and found that the plasticity-fitness relationship was often garden-specific, indicating that the planting environment did not consistently mediate plasticity-fitness relationships. When the effects of trait plasticity on growth varied by garden temperature, higher plasticity generally had neutral or negative associations with growth in warmer environments. These results suggest that elevated plasticity evolved in a P. balsamifera genomic background as part of a climate generalist strategy to seasonal temperature variability, but that there is a trade-off between plasticity and growth in warmer environments. Consequently, less-plastic but warm-adapted P. trichocarpa genotypes are likely to have a fitness advantage under warming climates. These results demonstrate that plasticity may sometimes be maladaptive and will not be universally beneficial in a warming world.

evolutionary biology↗

bioRxiv2026

Greater benefits of assisted gene flow in F2 vs F1 progeny at the cold edge of a species' range

Gene flow to marginal populations at a species range edge can facilitate rapid adaptation by increasing genetic diversity, reducing inbreeding depression, and introducing novel alleles. In highly inbred populations, hybrid vigor is often observed in the first generation (F1), but hybrid breakdown may diminish fitness in subsequent generations. Thus, benefits of gene flow may be overestimated when only F1 performance is assessed. We tested whether gene flow among populations of the annual plant Erythranthe laciniata (A. Gray) G.L. Nesom, from similar and contrasting environments, confers persistent fitness advantages across F1 and F2 generations at the high-elevation edge of its range in the California Sierra Nevada. Gene flow was experimentally introduced through pollen transfer between cold-edge populations, between cold edge and central populations, and within local cold edge populations, and compared to self-fertilized offspring, the predominant mating strategy of E. laciniata. For F1 progeny, we measured morphological, phenological, and fitness traits in a common garden located near the cold-climate range limit during 2008-2009, a relatively average year, and for F2 progeny in 2009-2010, a relatively wet year. Although F1 crosses showed no initial performance advantage measured in the previous year, F2 progeny from center-to-edge and edge-to-edge crosses significantly outperformed selfed and locally outcrossed lines in fruit mass, total pedicels, biomass, and height. Our findings demonstrate that gene flow can confer long-term fitness benefits, especially among populations adapted to similar selective pressures, and highlight the potential of assisted gene flow to bolster or rescue peripheral populations facing climate change. SIGNIFICANCE STATEMENTSpecies living at the edges of their geographic ranges often have small, isolated populations with limited genetic diversity, which can restrict their ability to adapt to environmental change. Gene flow from other populations may increase adaptive potential, but its long-term consequences remain uncertain because most studies evaluate only first-generation hybrids. Using experimental crosses in the mountain wildflower Erythranthe laciniata, we show that gene flow can produce stronger fitness benefits in second-generation hybrids than in the first generation at a high-elevation range edge. These results suggest that recombination among populations can generate advantageous genetic combinations that emerge over multiple generations. Our findings highlight the potential for assisted gene flow to enhance adaptation and persistence of range-edge populations under climate change.

plant biology↗

bioRxiv2026

Resurrected in the field: benefits of rapid adaptation to historic drought seen mainly at the leading edge of a plant' species range

Montane plant populations are experiencing novel conditions due to climate change. Furthermore, climate change is causing increased climate perturbations, such as the 2012-2016 drought in the western US, remarkable in its aridity, longevity, and warmer temperatures. This drought provided an opportunity to understand how montane populations respond to extreme perturbations, including at range limits. We resurrected seeds of the endemic annual plant Erythranthe laciniata, collected in 2008 or earlier (before the drought) and in 2014 (the height of the drought), in a common garden experiment to understand how drought influenced evolution in contemporary field conditions. The study included nine populations across the species range, including range edges. Over 2,100 replicates were sown in three common gardens at natural populations at low, central, and high elevations. We recorded phenology and flower production to estimate lifetime fitness. This experiment took place in 2021, a year with low precipitation and high temperatures. We found higher fitness in the drought generation at the high garden, while both generations showed similar fitness at the central and low gardens. We detected climate adaptation at the low and high gardens, and rapidly evolved faster phenology at the high garden. Lifetime fitness was substantially lower at lower gardens overall, even for low-elevation populations. Low-elevation populations outperformed central populations at the central garden, suggesting adaptive mismatch. Together, these results indicate rapid contemporary adaptation that is beneficial at the leading edge of the species range. Nevertheless, low fitness at lower elevations may foreshadow range contraction under continued climate change.

evolutionary biology↗

bioRxiv2025

Variation in responses to temperature across admixed genotypes of Populus trichocarpa x P. balsamifera predict geographic shifts in regions where hybrids are favored

O_LIPlastic responses of plants to their environment vary as a result of genetic differentiation within and among species. To accurately predict rangewide responses to climate change, it is necessary to characterize genotype-specific reaction norms across the continuum of historic and future climate conditions comprising a species range. C_LIO_LIThe North American hybrid zone of Populus trichocarpa and P. balsamifera represents a natural system that has been shaped by climate, geography, and introgression. We leverage a dataset containing 45 clonal genotypes from this natural hybrid zone, planted across 17 replicated common garden experiments spanning a broad climatic range. Growth and mortality were measured over two years, enabling us to model reaction norms for each genotype across these tested environments. C_LIO_LISpecies ancestry and intraspecific genomic variation significantly influenced growth across environments, with genotypic variation in reaction norms reflecting a trade-off between cold tolerance and growth. Using modeled reaction norms for each genotype, we predicted that genotypes with more P. trichocarpa ancestry may gain an advantage under warmer climates. C_LIO_LISpatial shifts of the hybrid zone could facilitate the spread of beneficial alleles into novel climates. These results highlight that genotypic variation in responses to temperature will have landscape-level effects. C_LI

evolutionary biology↗

bioRxiv2024

Climatic determinants of plant phenology in vernal pool habitats

Vernal pool plants are small, colorful, and specialized to both desiccated and inundated conditions that distinguish the ephemeral wetlands in which they grow. These species germinate rapidly in response to the first rain and grow quickly to take advantage of available water supplies. The floral phenology of vernal pool plant species is little understood despite being a crucial developmental stage for producing seeds and determining population growth rates. The current study focuses on two vernal pool plants, Limnanthes douglasii ssp. rosea (meadowfoam), a vernal pool specialist, and Trifolium variegatum (whitetip clover), a generalist vernal pool associate, and characterizes their phenology in response to interannual climate variation. We recorded phenology and climate data over seven years during a period of highly variable precipitation and temperature patterns, which serve as a robust dataset for quantifying the relationship of floral phenology with various climatic factors. We found that warmer and drier environmental conditions occurring during early growth periods were strongly associated with advanced floral phenology later in the life cycle for both species. Over the seven-year dataset, which was increasingly warm and dry, phenology advanced by 4.7 days per year for meadowfoam and 5.6 days per year for whitetip clover, respectively. The floral duration of the habitat specialist was influenced by microtopographic features of vernal pools, whereas no such patterns were observed for the habitat generalist. Finally, warmer and drier conditions were associated with reduced occupancy rates of both focal species within vernal pools. To our knowledge, this is the first study quantifying the relationship between vernal pool floral phenology and climate, offering insights into how phenology may shift in response to modern climate change.

plant biology↗