Genetic variation and resilience to climate change in Mediterranean-type trees

Climate models predict that temperature means will continuously increase globally, and that heatwaves and drought periods will become more frequent and intense, particularly in Mediterranean-type climates. The Southwest Western Australia (SWWA) Biodiversity Hotspot has extensive forest environments that have been subject to heatwaves and drought-induced forest mortality in recent years, impacting forest carbon sequestration and local ecological structure. Although, species may persist through enhanced physiological tolerance, phenotypic plasticity and/or genetic adaptation. Genetic variation is critical for ecological adaptive capacity - the potential and ability to adjust to, and persist through, external factors - and consequently, the evolutionary potential of the species. Evolution to a specific environment through natural selection results in patterns of local adaptation (when a local population experiences higher fitness compared to non-local counterparts). Local adaptation can be identified by either genome wide surveys that link genetic variants to climate variables or measuring plant traits indicative of plant performance and survival through reciprocal transplants in common environments. Exploring genetic adaptation patterns associated with physiological tolerance to climate can guide forest management approaches to enhance forests’ resilience to climate change, such as assisted gene migration. The genetic survey (Chapter 2) sampled natural jarrah populations and obtained 13,534 independent single nucleotide polymorphic (SNP) markers across the genome. Three genotype-association analyses were used to identify putatively adapted SNPs associated with independent climate variables. While overall levels of population differentiation were low (FST=0.04), environmental association analyses found a total of 2,336 unique SNPs associated with temperature and precipitation variables, with 1,440 SNPs annotated to genic regions. Considerable allelic turnover was ident