Adaptive variation for growth and resistance to a novel pathogen along climatic gradients in a foundation tree

Abstract

Natural ecosystems are under pressure from increasing abiotic and biotic stressors, including climate change and novel pathogens, which are putting species at risk of local extinction, and altering community structure, composition and function. Here, we aim to assess adaptive variation in growth and fungal disease resistance within a foundation tree, Corymbia calophylla to determine local adaptation, trait heritability and genetic constraints in adapting to future environments. Two experimental planting sites were established in regions of contrasting rainfall with seed families from 18 populations capturing a wide range of climate origins (~4,000 individuals at each site). Every individual was measured in 2015 and 2016 for growth (height, basal diameter) and disease resistance to a recently introduced leaf blight pathogen (Quambalaria pitereka). Narrow‐sense heritability was estimated along with trait covariation. Trait variation was regressed against climate‐of‐origin, and multivariate models were used to develop predictive maps of growth and disease resistance. Growth and blight resistance traits differed significantly among populations, and these differences were consistent between experimental sites and sampling years. Growth and blight resistance were heritable, and comparisons between trait differentiation (QST) and genetic differentiation (FST) revealed that population differences in height and blight resistance traits are due to divergent natural selection. Traits were significantly correlated with climate‐of‐origin, with cool and wet populations showing the highest levels of growth and blight resistance. These results provide evidence that plants have adaptive growth strategies and pathogen defence strategies. Indeed, the presence of standing genetic variation and trait heritability of growth and blight resistance provide capacity to respond to novel, external pressures. The integration of genetic variation into adaptive management strategies, such as assisted gene migration and seed sourcing, may be used to provide greater resilience for natural ecosystems to both biotic and abiotic stressors.

Plant functional traits differ in adaptability and are predicted to be differentially affected by climate change

“…We found evidence to support adaptation of functional traits in C. calophylla across populations in southwest Western Australia. These patterns of adaptation are consistent with previous studies of genetics, growth, and physiology of C. calophylla (Ahrens, Byrne, et al, ; Ahrens, Mazanec, et al, ; Aspinwall et al, ; Blackman et al, ). This study builds upon previous research by focusing on the genetic determination of functional traits, elucidating the relationship between functional traits, determining the relationship between functional traits and climate, and predicting genetically determined trait distributions under current and future climates.…”

Standing genomic variation within coding and regulatory regions contributes to the adaptive capacity to climate in a foundation tree species

“…Thus, we used maximum temperature of the warmest month ( T MAX ), mean annual precipitation ( P MA ) and aridity index (AI) as our climatic predictors when searching for signatures of selection. Of all the temperature and precipitation variables (e.g., bioclim 1–19), T MAX and P MA were found to be the most correlated to physiology in another study (Ahrens et al, ), and AI was included due to its importance in adaptive studies on physiology of C. calophylla (Aspinwall et al, ; Blackman et al, ). T MAX (Bio5) and P MA (Bio12) climatic layers were downloaded from worldclim v2 (Fick & Hijmans, ).…”

“…This was evident during the 2010/2011 drought and heat wave conditions, which resulted in large scale forest collapse in the northern part of its range (Matusick, Ruthrof, Brouwers, Dell, & Hardy, ). Recent studies on C. calophylla have shown that the temperature‐of‐origin was a more important determinant than precipitation and aridity for growth characteristics, hydraulic traits and physiological performance (Ahrens et al, ; Aspinwall et al, ; Blackman, Aspinwall, Tissue, & Rymer, ). Specifically, photosynthesis and dark respiration elicit plastic and adaptive responses to different temperature conditions among provenances (Aspinwall et al, ).…”

“…In addition, leaf hydraulic conductance shows regional patterns of adaptation to temperature, where cool‐climate provenances have greater leaf hydraulic vulnerability (Blackman et al, ). Investigation of growth was found to be moderately heritable, such that slow‐growth strategies evolved in provenances from warm regions and fast‐growth strategies evolved in cooler regions (Ahrens et al, ). These traits are likely genetically determined and their differences are the product of adaptation to local climate.…”

“…We aimed to develop our understanding of the underlying genomic variation associated with along climatic gradients. We tested hypotheses developed from previous experiments documenting phenotypic adaptations (Blackman et al, ; Aspinwall et al, ; Ahrens et al, ): (a) genomic variation is associated with climate, and (b) genomic variation is more likely to be associated with temperature than precipitation or aridity. To support or refute these hypotheses, we employed a reduced‐representation genomic sequencing approach to search for adaptive variation across the climatically heterogeneous distribution of C. calophylla .…”