Biology subjects

Gremer, J. R.

Publications and source records attributed to Gremer, J. R..

8 recordsLinked to original sources

bioRxiv2025

Adaptational lag at high elevations depends on life stage in a California wildflower.

O_LIHigh elevation populations are expected to receive reduced snowpack, warmer temperatures, and more variable precipitation patterns, potentially putting them at risk if rates of adaptation do not keep pace with climate change. Populations from climates more closely aligned with the changing high elevation conditions may prove better suited to current climate than the current local populations. Thus, it is essential to assess 1) whether high elevation populations are locally adapted to current climate, and 2) whether fitness of lower elevation populations from warmer climates is higher than for local populations in high elevation conditions. C_LIO_LIWe conducted a common garden study with Streptanthus tortuosus at a high elevation site. Twenty-three populations from across the species range were measured weekly for mortality, and reproductive output was measured at the end of the growing season. We examined the effects of climatic distance from the site of origin on plant performance. The effects of weekly weather on mortality were also assessed. C_LIO_LIWe observed adaptational lag for high elevation populations, including the native population, but only for some life stages. Low elevation populations had higher survival through the first year and over winter. Additionally, the probability of reproducing was highest for populations from the warmest climates. Warmer ambient temperatures at the high elevation garden were also associated with higher weekly mortality across populations. However, survival to reproduction in the second year was higher in populations from climates closer to the garden, i.e. high elevation populations. Thus, adaptational lag differed among life stages. C_LIO_LISynthesis: This study highlights the importance of considering variation in life history and seasonal conditions when evaluating how species that occur across an elevational gradient may respond to climate change. This adds to a growing body of evidence that reveals warming temperatures as a threat to high elevation populations. However, unlike previous studies, this threat was not consistent across life stages. These results suggest that strategic assisted gene flow that combines the benefits of warm-adapted low elevation populations with the benefits of snow-adapted life history from high elevation populations may be beneficial in this species, and similar systems. C_LI

ecology↗

bioRxiv2025

Spectral network analysis illuminates coordinated trait adaptation across plant populations

O_LIUnderstanding how plant populations respond to environmental variation through functional leaf traits remains challenging due to limitations of traditional phenotyping approaches. Hyperspectral reflectance offers a rapid, non-destructive and high-throughput method to capture functional trait variation and detect signatures of local adaptation across populations. C_LIO_LIWe combined hyperspectral data, inverse modeling, and network analysis to investigate population-level variation in Streptanthus tortuosus. Using a common garden experiment with four geographically distinct populations, we applied partial least square discriminant analysis (PLS-DA) and ridge regression for population discrimination, inverse PROSPECT modeling to estimate leaf biochemical traits, and canonical correlation analysis to examine trait-climate relationships across historical (1900-1994) and recent (1995-2024) periods. We developed a spectral network approach treating wavelength correlations as biologically meaningful trait networks. C_LIO_LIPopulations showed distinct, heritable spectral signatures with high classification accuracy. Significant population differences emerged in anthocyanins, carotenoids, chlorophyll, and water content. Trait-climate correlations shifted between time periods, consistent with historical climate adaptation. Network analysis revealed population-specific integration patterns, with more variable environments displaying greater spectral modularity. C_LIO_LIHyperspectral signatures provide a high-throughput tool for detecting population-level adaptation and trait coordination. Our findings provide a framework to investigate how plant populations respond to climate change through evolved shifts in trait networks rather than isolated traits alone. C_LI

plant biology↗

bioRxiv2025

Herbarium specimens reveal a constrained seasonal climate niche despite diverged annual climates across a wildflower clade

Quantifying species niches across a clade reveals how environmental tolerances evolve, and offers insights into present and future distributions. We use herbarium specimens to explore climate niche evolution across 14 annual species of the Streptanthus (s.l.) clade (Brassicaceae), which originated in deserts and diversified into cooler, moister areas. To understand how climate niches evolved, we used historical climate records to estimate each species 1) classic annual climate niche, averaged over specimen collection sites; 2) growing season niche, from estimated specimen germination date to collection date, averaged across specimens (specimen-specific niche); and 3) standardized seasonal niche based on average growing seasons of all species (clade-seasonal niche). In addition to estimating how phenological variation maps onto climate niche evolution, we explored how spatial refugia shape the climate experienced by species by 1) analyzing how field soil texture changes relative to the climate space that species occupy and 2) comparing soil water holding capacity from each specimen locality to that of surrounding areas. Specimen-specific niches exhibited less clade-wide variation in climatic water deficit than did annual or clade-seasonal niches, and specimen-specific temperature niches showed no phylogenetic signal, in contrast to annual and clade-seasonal temperature niches. Species occupying cooler regions tracked hotter and drier climates by growing later into the summer, and by inhabiting refugia on drought-prone soils. These results underscore how phenological shifts, spatial refugia, and germination timing shape "lived" climate. Despite occupying a large range of annual climates, we found these species are constrained in the conditions under which they thrive. Significance statementHere, we show that closely related species that appear to have diverged in their climate niches based on highly differentiated annual conditions are actually tracking very similar seasonal climate conditions. This climate similarity, estimated from collection locations and associated weather data of nearly 2000 herbarium specimens, is achieved through the evolution of germination timing and plant flowering phenology, as well as establishment in spatial refugia with suitable microclimates. Our results highlight how occupation of a subset of seasonal conditions can be conserved across diverse species, resulting in less climate niche evolution than expected. Restricted climate niches imply that species may be less adaptable than we expect based on annual climates, and have implications for conservation, management and persistence under hotter climates.

ecology↗

bioRxiv2025

Specimen-tailored "lived" climate reveals precipitation onset and amount best predict specimen phenology, but only weakly predict specimen reproductive success across a clade

Herbarium specimens are broadly distributed in space and time, enabling investigation of climate impacts on phenology and fitness. We reconstructed specimen "lived" climate from knowledge of germination cues and collection dates for 14 annual species in the Streptanthus (s.l.) clade (Brassicaceae) to ask: Which climate attributes, including the timing of precipitation onset, best explain specimen phenological stage and estimated reproduction? We also asked whether climate effects on phenology and reproduction were evolutionarily conserved. Precipitation amount and onset date, more than temperature, best predicted specimen phenology, but only weakly predicted reproduction. Earlier rainfall onset was associated with more phenologically advanced specimens, a relationship that showed phylogenetic signal. Few climate predictors explained variation in specimen reproduction. The lack of association between specimen reproduction and climate may arise from phenological shifts that buffer impacts of climate, interactions with other species, or challenges in estimating total reproduction from specimens. Our results highlight the value of specimen-tailored growing season conditions for reconstructing climate, incorporating evolutionary relationships in assessing responses to climate, and the complexities of estimating fitness from specimens. For the latter, we propose supplemental herbarium collections and community science protocols to increase the utility of these data for understanding climate impacts on populations.

ecology↗

bioRxiv2024

Accelerated phenology fails to buffer fitness loss from delayed rain onset in a clade of wildflowers

The timing of early life cycle events has cascading effects on phenology and fitness. These effects may be critical for climate resilience of plant populations, especially in Mediterranean environments, where delayed rainfall onset causes delayed germination. To examine impacts of germination timing on ten species of the Streptanthus/Caulanthus clade, we induced germination across a range of dates in ambient seasonal conditions and recorded phenological and fitness traits. Later germination cohorts accelerated flowering, partially stabilizing flowering date, but the degree of this compensatory plasticity differed across species. Fitness declined with later germination; the magnitude of this decline depended on the balance between direct negative effects of later germination and compensatory positive effects of accelerated flowering. The resulting species differences in fitness responses suggest differential vulnerability to climate change. Species from wetter, cooler, less variable habitats accelerated flowering more and declined less in seed set with later germination, suggesting climate adaptation. However, other fitness responses to germination timing, like first year fitness, were evolutionarily labile across the clade and unrelated to climate. Although compensatory phenological plasticity may buffer the impacts of delayed germination, it cannot prevent long term declines in population fitness as fall rains come later with climate change.

evolutionary biology↗

bioRxiv2024

A chromosome-level genome assembly of the varied leaved jewelflower, Streptanthus diversifolius, reveals a recent whole genome duplication

The Streptanthoid complex, a clade of primarily Streptanthus and Caulanthus genera in the Thelypodieae tribe (Brassicaceae) is an emerging model system for ecological and evolutionary studies. This Complex spans the full range of the California Floristic Province including desert, foothill, and mountain environments. The ability of these related species to radiate into dramatically different environments makes them a desirable study subject for exploring how plant species expand their ranges and adapt to new environments over time. Ecological and evolutionary studies for this complex have revealed fascinating variation in serpentine soil adaptation, defense compounds, germination, flowering, and life history strategies. Until now a lack of available genomic resources has hindered the ability to relate these phenotypic observations to their underlying genetic and molecular mechanisms. To help remedy this situation we present here a chromosome-level genome assembly of Streptanthus diversifolius, a member of the Streptanthoid Complex, developed using Illumina, Hi-C, and HiFi sequencing technologies. Construction of this assembly also provides further evidence to support the previously reported recent whole genome duplication unique to the Thelypodieae tribe. This whole genome duplication may have provided individuals in the Streptanthoid Complex the genetic arsenal to rapidly radiate throughout the California Floristic Province and to occupy commonly inhospitable environments including serpentine soils.

genomics↗

bioRxiv2023

Germination responses to experimental rainfall timing identify potential vulnerability to climate change across a clade of California wildflowers

The timing of germination, driven by seasonal cues, is critical for the life cycle of plants. Variation among species in germination responses can reflect evolutionary processes and adaptation to local climate and can affect vulnerability to changing conditions. Indeed, climate change is altering the timing of precipitation and associated temperatures, which may interact with germination cueing to affect the timing, quantity, and speed of germination. Germination responses to change can then have consequences for individual fitness, population dynamics, and species distributions. Here, we assessed responses to the timing of germination-triggering rains and corresponding temperatures for 11 species spanning the Streptanthus (s.l.) clade (Brassicaceae). To do so, we experimentally manipulated the onset date of rainfall events, measured effects on germination fraction and rate, and evaluated whether responses were constrained by evolutionary relationships across the phylogeny. We then explored the possible consequences of these responses to contemporary shifts in precipitation timing. Later onset rains and cooler temperatures significantly reduced germination rates for all species. Germination fractions decreased with later rains and cooler temperatures for all but three Caulanthus species. Species germination responses to the timing of rainfall and seasonal temperatures were phylogenetically constrained, with Caulanthus species appearing less sensitive. Further, six species are likely already experiencing significant decreases in germination fractions or rates (or both) with observed climate change, which has shifted the timing of rainfall towards the cooler, winter months in California. Overall, our findings highlight the importance of the germination responses to seasonal timing, how they have evolved across the clade, and their implications under climate change.

plant biology↗

bioRxiv2022

Extinction Risk of Sonoran Desert Annuals Following Potential Changes in Precipitation Regimes

Rapid environmental change can affect both the mean and variability in environmental conditions. Natural selection tends to favour those organisms that best respond to such changes. Here, we consider delayed germination as bet hedging strategies for 10 Sonoran Desert annuals. We use a germination model parameterized with long-term demographic and climate data to explore potential effects of changes in the mean and variance in precipitation on the evolution of germination strategies, as well as the risk of extinction. We then explored the potential for evolutionary rescue in response to these changes. As expected, results indicate that as rainfall declines, or uncertainty in rainfall increases, all species have higher extinction risk (the former being more detrimental). These shifts also increased the benefit of delayed germination. Results also indicate that evolutionary rescue can often occur for small shifts, especially for more variable rainfall regimes, but would not likely save populations experiencing larger environmental changes. Finally, we identified life history traits and functional responses to precipitation that were most strongly correlated to the ability to cope with changes in rainfall and with potential for evolutionary rescue: dormant seed survivorship and, to a smaller degree, chance of reproduction and seed yield sensitivity to precipitation.

ecology↗