Biology subjects

Worthy, S. J.

Publications and source records attributed to Worthy, S. J..

7 recordsLinked to original sources

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↗

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↗

bioRxiv2023

Decomposing intraspecific phenotypic variation: implications for species and functional diversity

Researchers have a history of seeking explanation for and understanding of diversity patterns. High-dimensional trait-based trade-offs have been hypothesized as important for maintaining species and functional diversity. These relationships have primarily been investigated at the community-level, despite the importance of intraspecific variation to diversity maintenance. The goal of this research is to determine if alternative phenotypes are present within species and the impacts of this on diversity in a tropical seedling community in China. We ask 1) do trait combinations found across species, at the community-level, also exist within species?; 2) how consistent are alternative phenotypes and their contributions to growth across species?; and 3) how do findings align with species co-occurrence patterns? We model species-specific growth with individual-level trait measurements, environmental data, and their interactions, allowing for identification of intraspecific alternative phenotypes and quantification of the contribution of variables to growth. We find that two of three species have intraspecific alternative phenotypes. Specifically, individuals within these species share a trait combination, but how they combine the traits differs depending on the type and level of soil nutrients. Furthermore, we find that similarity among species in alternative phenotypes and variables that contribute most to growth may lead to negative spatial co-occurrence of species. Overall, we find that multiple traits or interactions between traits and the environment drive species-specific strategies for growth. These results highlight how individuals are highly variable, with phenotypically different individuals having similar growth performance, and suggest how high species and functional diversity can be maintained in communities.

ecology↗

bioRxiv2022

Leaf gene expression trajectories during the growing season are consistent between sites and years in American beech.

Transcriptomics provides a versatile tool for ecological monitoring. Here, through genome-guided profiling of transcripts mapping to 33,042 gene models, expression differences can be discerned among multi-year and seasonal leaf samples collected from American beech trees at two latitudinally separated sites. Despite a bottleneck due to post-Columbian deforestation, the SNP-based population genetic background analysis has yielded sufficient variation to account for differences between populations and among individuals. Our expression analyses during spring-summer and summer-fall transitions for two consecutive years involved 4197 differentially expressed protein coding genes. Using Populus orthologs we reconstructed a protein-protein interactome representing leaf physiological states of trees during the seasonal transitions. Gene set enrichment analysis revealed GO terms that highlight molecular functions and biological processes possibly influenced by abiotic forcings such as recovery from drought and response to excess precipitation. Further, based on 324 co-regulated transcripts, we focused on a subset of GO terms that could be putatively attributed to late spring phenological shifts. Our conservative results indicate that extended transcriptome-based monitoring of forests can capture diverse ranges of responses including air quality, chronic disease, as well as herbivore outbreaks that require activation and/or downregulation of genes collectively tuning reaction norms maintaining the survival of long living trees such as the American beech (Fagus grandifolia).

ecology↗

bioRxiv2021

Comparative Transcriptomics of Tropical Woody Plants Supports Fast and Furious Strategy along the Leaf Economics Spectrum in Lianas.

Lianas, climbing woody plants, influence the structure and function of tropical forests. Climbing traits have evolved multiple times, including ancestral groups such as gymnosperms and pteridophytes, but the genetic basis of the liana strategy is largely unknown. Here, we use a comparative transcriptomic approach for 47 tropical plant species, including ten lianas of diverse taxonomic origins, to identify genes that are consistently expressed or downregulated only in lianas. Our comparative analysis of full-length transcripts enabled the identification of a core interactomic network common to lianas. Sets of transcripts identified from our analysis reveal features related to functional traits pertinent to leaf economics spectrum in lianas, include upregulation of genes controlling epidermal cuticular properties, cell wall remodeling, carbon concentrating mechanism, cell cycle progression, DNA repair and a large suit of downregulated transcription factors and enzymes involved in ABA-mediated stress response as well as lignin and suberin synthesis. All together, these genes are known to be significant in shaping plant morphologies through responses such as gravitropism, phyllotaxy and shade avoidance.

plant biology↗