Biology subjects

Rymer, P. D.

Publications and source records attributed to Rymer, P. D..

10 recordsLinked to original sources

bioRxiv2026

Intermediate, rather than Isohydric or Anisohydric, Species were More Resilient to an Extreme Heatwave in a Common Garden in Sydney

Urban forests are increasingly exposed to climate extremes, yet selecting resilient urban species remains difficult as it is unclear why some species fail and others succeed. We monitored growth and survival of 48 urban tree and shrub species, respectively, for about five years after planting, plus we quantified species' crown dieback after a natural extreme heatwave (three days with temperatures exceeding 40 degrees C) in a common garden in Sydney, Australia. For 30 species we measured 15 plant functional traits, including both hydraulic and morphological traits. Native species had less crown dieback and higher absolute growth but lower survival than exotic species. Plant functional traits linked to heat and drought tolerance explained 20-30% of the variation in observed crown dieback across species. Extensive dieback exceeding 40% after the extreme heatwave was found for seven species with large leaf size (and leaf width), high leaf relative water content, and low wood density. Nonlinear relationships between crown dieback and leaf water potential traits identified that both isohydric and anisohydric species were vulnerable, indicating that vulnerability did not align neatly with a single hydraulic strategy. Hydraulic failure likely occurred for some, but not all, vulnerable isohydric and anisohydric species, suggesting vulnerability of certain species was directly caused by cumulative thermal stress. Importantly, survival was not related to any single functional trait, indicating that crown dieback was a more sensitive and earlier indicator of cumulative thermal stress than mortality. These findings support a shift from climate of origin-based to trait-based species selection in urban forestry.

physiology↗

bioRxiv2026

Topographic complexity shapes adaptive genomic variation in co-occurring plant species

Co-occurring species often face similar selective environments, although adaptive responses to these environments are generally assumed to be species-specific, particularly in complex landscapes where selective pressures are likely to be multi-dimensional. We test this assumption by contrasting genotype-environment associations (GEAs) among a range of co-occurring but unrelated plants with different life histories from an isolated, mountainous national park in south-eastern Australia. Analyses were performed using single nucleotide polymorphism (SNP) loci derived from reduced genome representation sequencing to investigate genomic associations with spatial and environmental drivers across unrelated plant species within the same heterogeneous landscape. Several species showed GEAs that aligned with similar environmental gradients, particularly edaphic features, suggesting that similar selective pressures can shape genomic responses across taxa. Other species exhibited distinct spatial and environmental associations, highlighting idiosyncratic outcomes. Notably, GEAs were detected at fine spatial scales despite generally low levels of genome-wide divergence, suggesting adaptive variants can persist in the face of gene flow under strong selective pressure. This study highlights how community-level genomic diversity is shaped by common environmental processes, with implications for biodiversity management in rapidly changing environments, where diverse ecosystem-level responses to selection may underpin resilience.

evolutionary biology↗

bioRxiv2026

Water beneath the pavement: assessing the benefits of passive irrigation for urban Lophostemon confertus trees in western Sydney

Urban environments typically experience higher temperatures than surrounding natural landscapes, making urban vegetation crucial for cooling local areas and improving the health of city residents. Impervious urban surfaces limit the absorption and retention of precipitation, potentially limiting tree water access and threatening long-term survival. Here, we measured tree physiology and growth of Lophostemon confertus (Queensland brush box) trees to investigate how a passive irrigation system that stores stormwater affected the performance of young, establishing trees in a hot and dry suburb of western Sydney, Australia. During the 2024-2025 austral summer, three years after planting, the local climate was periodically hot and dry, with a total of 16 days above 35 C. Irrigated L. confertus trees had higher water availability (i.e., higher predawn leaf water potential, {Psi}pre), lower water stress (i.e., higher midday leaf water potential, {Psi}mid, more frequently above turgor loss point), greater stomatal conductance (gs) on hot and dry summer days, and reduced leaf temperatures (Tleaf), compared to control trees. No significant differences in growth rates were observed between irrigated and control trees during the first three establishment years, but irrigated trees had greater crown survival during the hot, dry summer. Our results suggest passive irrigation may mitigate periods of short-term heat and drought stress in urban trees by increasing water access to support transpiration that prevents leaves from overheating, improving tree health. Higher tree transpiration may lead to greater ecosystem services by increasing cooling benefits, contributing to mitigation of urban heat island effects.

plant biology↗

bioRxiv2021

Closely-related tree species with overlapping ranges exhibit divergent adaptation to climate

With global climate change shifting and altering temperature and precipitation regimes, the ability of natural forest stands to persist in their local environments are being challenged. For many taxa, particularly among long lived tree species, the potential to respond is underpinned by genetic and trait diversity and may be limited. We sampled 326 and 366 individuals of two widely distributed and closely-related red gum Eucalyptus species (E. blakelyi and E. tereticornis) from across their entire Australian range. We identified putatively adaptive variants associated within genes of key biological processes for both species. We mapped the change of allele frequencies of two hierarchical gene ontology groups shared by both species across geography and climate and predict genomically vulnerable regions under a projected 2070 climate scenario. Regions of potential vulnerability to decline under future climate differed between species and may be applied to guide conservation and restoration strategies. Our study indicated that some populations may contain the adaptive genomic variation necessary for these species to persist through climate change, while others may benefit from the adaptive variation of those populations to enhance resilience.

evolutionary biology↗

bioRxiv2021

Genomic constraints to drought adaptation

Global shifts in climate and precipitation patterns are altering the diversity and structure of forests. The ability for species to adapt is especially difficult for long lived foundation species with unknown genetic and trait diversity. We harnessed genomic, physiological, and climate data to determine adaptation constraints. We used denovo assembly and 6.5 million genomic variants with drought related traits from 432 individuals sourced from across the complete range of the foundation tree species Corymbia calophylla. We found genomic variants determining traits predominantly in gene regulatory regions. The ability for populations to adapt was limited by within population genetic diversity associated with traits, and epistatic interactions within traits and pleiotropic interactions among traits. Nevertheless, we could accurately predict adaptive traits using genomic and climate data to guide reforestation. Our study indicated that some populations may contain variation sufficient for the species to adapt to the effects of drought, while other populations will need increased variability from those sources.

evolutionary biology↗

bioRxiv2021

Climate-change risk analysis for global urban forests

Urban forests (i.e. all vegetation present in urban areas), provide environmental and socioeconomic benefits1 to more than half of the global population2. Projected climate change threatens these benefits to society3-5. Here, we assess vulnerability to climate change of 16,006 plant species present in the urban forests of 1,010 cities within 93 countries, using three vulnerability metrics: exposure, safety margin and risk. Exposure expresses the magnitude of projected changes in climate in a given area, safety margin measures species sensitivity to climate change, and risk is the difference between exposure and safety margin6. We identified 9,676 (60.5%) and 8,344 (52.1%) species exceeding their current climatic tolerance (i.e. safety margin) for mean annual temperature (MAT) and annual precipitation (AP), respectively. By 2050, 13,479 (84.2%) and 9,960 (62.2%) species are predicted to be at risk from projected changes in MAT and AP, respectively, with risk increasing in cities at lower latitudes. Our results can aid evaluation of the impacts of climate change on urban forests and identify the species most at risk. Considering future climates when selecting species for urban plantings will enhance the long-term societal benefits provided by urban forests, including their contribution to mitigating the magnitude and impacts of climate change.

ecology↗

bioRxiv2020

Drought tolerance of Hakea species (Proteaceae) from a range of biomes and life-histories predicted by climatic niche.

Extreme drought conditions across the globe are impacting biodiversity with serious implications for the persistence of native species. However, quantitative data on drought tolerance is not available for diverse flora to inform conservation management. We quantified physiological drought tolerance in the diverse Hakea genus (Proteaceae) to test predictions based on climatic-origin, life history and functional traits. We sampled terminal branches of replicate plants of 16 species in a common garden. Xylem cavitation was induced in branches under varying water potential (tension) in a centrifuge and the tension generating 50% loss of conductivity (stem P50) was characterized as a metric for drought tolerance. The same branches were used to estimate plant functional traits, including wood density, specific leaf area, and Huber value (sap flow area to leaf area ratio). There was significant variation in stem P50 among species, which was negatively associated with the species climate-origin (rainfall and aridity). Drought tolerance did not differ among life histories; however, a drought avoidance strategy with terete leaf form and greater Huber value may be important for species to colonize and persist in the arid biome. Our findings will contribute to future prediction of species vulnerability to drought and adaptive management under climate change.

ecology↗

bioRxiv2020

Adaptive plasticity in plant traits increases time to hydraulic failure under drought in a foundation tree

O_LIThe viability of forest trees, in response to climate change-associated drought, will depend on their capacity to survive through genetic adaptation and phenotypic plasticity in drought tolerance traits. Genotypes with enhanced plasticity for drought tolerance (adaptive plasticity) will have a greater ability to persist and delay the onset of hydraulic failure. C_LIO_LICorymbia calophylla populations from two contrasting climate-origins (warm-dry and cool-wet) were grown under well-watered and chronic soil water deficit treatments in large containers. Hydraulic and allometric traits were measured and then trees were dried-down to critical levels of drought stress. C_LIO_LISignificant plasticity was detected in the warm-dry population in response to water-deficit, with adjustments in drought tolerance traits that resulted in longer dry-down times from stomatal closure to 88% loss of stem hydraulic conductance (time to hydraulic failure, THF). Plasticity was limited in the cool-wet population, indicating a significant genotype-by-environment interaction in THF. C_LIO_LIOur findings contribute information on intraspecific variation in key drought tolerance traits and THF. It highlights the need to quantify adaptive capacity in populations of forest trees facing climate change-type drought to improve predictions of forest die-back. Corymbia calophylla may benefit from assisted gene migration by introducing adaptive warm-dry populations into vulnerable cool-wet population regions. C_LI

physiology↗

bioRxiv2020

Clonality and inbreeding amplifies genetic isolation and mate limitation in a rare montane woody plant (Persoonia hindii; Proteaceae)

Small populations have genetic attributes that make them prone to extinction, including low effective population size (Ne), increased levels of inbreeding, and negative impacts from genetic drift. Some small populations are also clonal with low levels of genetic diversity, restricted seed dispersal, and high levels of genetic structure. Together, these attributes make species with small, isolated, clonal populations unlikely to persist under environmental change. We investigated an endangered woody plant species (Persoonia hindii) in eastern Australia to answer key questions about genetic differentiation, migration rates, population sizes, size of clones, mating system and Ne. We identified 587 single nucleotide polymorphisms. Of the 88 individual stems collected from 15 sites across the entire distribution of P. hindii, we identified 30 multi-locus genotypes (MLG). Additional fine-scale genotyping of two sites (49 and 47 stems) detected a dominant genet within each site occupying a minimum area of 20 m2. Global population differentiation was high (FST 0.22) with very low migration rates (0.048 - 0.064). We identified some population structure with variable site pairwise differentiation (0.015 - 0.32) with no detectable spatial autocorrelation. Species wide inbreeding coefficient was 0.42 (FIT), supporting the direct estimate of 82% selfing. Estimated Ne was extremely small (15), indicating that genetic drift may be reducing genetic diversity and increasing genetic load through fixation of deleterious alleles. Clonality and inbreeding combined with negligible gene flow suggests limited adaptive capacity to respond to climate challenges. Genetic rescue, through assisted gene migration and experimental translocations, would enhance the persistence of natural populations.

evolutionary biology↗

bioRxiv2019

Spatial, climate, and ploidy factors drive genomic diversity and resilience in the widespread grass Themeda triandra

O_LIFragmented grassland ecosystems, and the species that shape them, are under immense pressure. Restoration and management strategies should include genetic diversity and adaptive capacity to improve success but these data are generally unavailable. Therefore, we use the foundational grass, Themeda triandra, to test how spatial, environmental, and ploidy factors shape patterns of genetic variation. C_LIO_LIWe used reduced-representation genome sequencing on 487 samples from 52 locations to answer fundamental questions about how the distribution of genomic diversity and ploidy polymorphism supports adaptation to harsher climates. We explicitly quantified isolation-by-distance (IBD), isolation-by-environment (IBE), and predicted population genomic vulnerability in 2070. C_LIO_LIWe found that a majority (54%) of the genomic variation could be attributed to IBD, while 22% of the genomic variation could be explained by four climate variables showing IBE. Results indicate that heterogeneous patterns of vulnerability across populations are due to genetic variation, multiple climate factors, and ploidy polymorphism, which lessened genomic vulnerability in the most susceptible populations. C_LIO_LIThese results indicate that restoration and management of T. triandra should incorporate knowledge of genomic diversity and ploidy polymorphisms to increase the likelihood of population persistence and restoration success in areas that will become hotter and more arid. C_LI

genomics↗