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 identified for SNPs associated with temperature seasonality and mean precipitation of the warmest quarter, suggesting that both temperature and precipitation are important factors in adaptation. SNPs with similar gene functions, had analogous allelic turnover along climate gradients, while SNPs among temperature and precipitation variables had uncorrelated patterns of adaptation. These contrasting patterns provide evidence that there may be standing genomic variation adapted to current climate gradients, providing the basis for adaptive management strategies to bolster forest resilience in the future. The second experimental chapter (Chapter 3) explored seed germination response to temperature in jarrah and marri populations from wide-ranging climate origins, to estimate the thermal optima and constraints. Seeds from across the entire geographic distribution were collected from independent populations of each species. Patterns of germination observed differences between species on a thermal gradient plate (5-40°C) and provided a temperature range for explicit germination tests. Germination tests were carried out at five constant temperatures between 9 and 33°C. We discuss how the germination niche (1) differs between species, (2) varies among populations, and (3) relates to climatic origin. Temperature response of germination differed among species, specifically the optimum temperature for germination (jarrah – 23.4°C; marri - 31°C). Temperature response of germination also differed among populations within species and was related to the climate-origin only for marri. Lastly, for the third experimental chapter (Chapter 4), a reciprocal transplant common garden experiment was used to investigate variation in marri`s functional traits using hyperspectral data. Hyperspectral remote sensing has the potential to assess plant functional status rapidly and non-destructively across climatic gradients to support conservation and management strategies, such as assisted migration, for forests under climate change. This study explored the variability of functional traits in marri to estimate patterns of local adaptation. Trees from natural populations spanning marri’s geographic distribution were grown in two common garden plantation sites with different climate settings. High-resolution field-based spectral measurements were collected from leaves of adult plants at both sites in two seasons (summer and autumn). Partial least squares regression analyses of full reflectance spectra highlighted differences among populations, sites, and seasons in spectral regions associated with photosynthetic pigments and water content, among other spectral traits, related to leaf condition and stress responses. Variation in these traits was further explored with analyses of spectral indices tailored to pigment and water absorptions. Analyses of spectral indices variation identified significant differences between populations, suggesting there is heritable variation in climatic tolerances, but stronger effects of season and site

Biogeographical variation of herbivore response and competitive ability of Centaurea species

FILIPE, João Carlos Melanda - Biogeographical variation of herbivore response and competitive ability of Centaurea species. Coimbra : [s.n.], 2016. Dissertação de Mestrado.Plant invasions have an important impact in the environment and the economy. Once introduced in their non-native range, exotic plants can experience rapid evolutionary processes which can be crucial for invasive success. Assessing trait-shifts between native and non-native ranges is an important step for understanding evolutionary changes occurring in the non-native ranges and, ultimately, for the development of management plans. Centaurea solstitialis and Centaurea sulphurea are annual herbs native to the Mediterranean Basin region that were introduced into California (USA) two centuries ago. While C. sulphurea has only naturalized into three known populations in California, C. solstitialis has become a noxious and widespread weed invasive. C. solstitialis has also been introduced into Chile, Argentina and Australia with different invasive success. The main objective of this thesis was to assess trait-shifts between native and non-native ranges of the two congeneric Centaurea species. Two main comparative approaches were developed in greenhouse studies: competitive ability of individuals from native and non-native ranges of C. sulphurea, and herbivory responses from a generalist herbivore species fed with leaves of both Centaurea species. For the assessment of competitive ability, we assessed total biomass of plants from both ranges, as well as inter-regional hybrids either growing alone in a control group, or in competition with the common competitor grass Bromus hordeaceus. Individuals from California were found to be larger and better competitors than individuals from Spain, whereas inter-regional hybrids from both regions showed competitive responses more similar to that of individuals from California. To assess for biogeographic differences on the response of herbivore, we fed a generalist and widespread herbivore (common snail Helix aspersa), with plant leaves from both ranges in order to assess the snail’s final weight. Snails fed with leaves from Spanish native populations of non-invasive C. sulphurea grew significantly less compared to snails fed with leaves from non-native California. For snails fed with the invasive C. solstitialis, significant differences were also found among regions, but the response was more complex, depending on population, with snails fed with Turkish and Australian plants presenting higher growth rates than the rest of the regions. Overall, these results deliver solid evidence for rapid differentiation between ranges, illustrated by phenotypic changes which might contribute for the invasive potential of exotic species, as exemplified by the observed differences in invasive success between the two studied congeneric species.As invasões por plantas desempenham um papel fulcral para o ambiente e economia globais. Uma vez introduzidas em áreas não-nativas, as plantas exóticas podem sofrer rápidos processos evolucionários que por sua vez são decisivos para o sucesso dos invasores. Conhecer as mudanças nas características destas plantas entre as áreas nativas e não-nativas é um importante passo para perceber as alterações evolutivas que ocorrem na área colonizada e, em última instância, para o desenvolvimento de plano de gestão e controlo. Centaurea solstitialis e Centaurea sulphurea são plantas anuais nativas da Bacia Mediterrânea e introduzidas na Califórnia (EUA) há cerca de dois séculos. Enquanto C. sulphurea está naturalizada sem comportamento invasor e apresenta apenas três populações conhecidas na Califórnia, C. solstitialis é atualmente uma invasora agressiva e bastante disseminada. C. solstitialis está também introduzida no Chile, Argentina e Austrália com diferentes graus de sucesso invasor. O principal objetivo deste projeto foi explorar as possíveis alterações em características específicas de plantas entre a zona nativa e a zona não-nativa das mesmas. Dois estudos comparativos em ambiente controlado de estufa foram realizados, avaliando nomeadamente a habilidade competitiva entre indivíduos das áreas nativa e não-nativa de C. sulphurea e a resposta herbívora por parte de um herbívoro generalista alimentado com folhas de ambas as espécies de Centaurea em estudo. Para o estudo de habilidade competitiva foi registada a biomassa total das plantas de ambas as áreas, assim como de híbridos inter-regionais, a crescer sozinhas ou em competição com uma herbácea abundante – Bromus hordeaceus. As plantas da Califórnia provaram ser maiores e melhores competidores que os seus conspecíficos oriundos de Espanha, enquanto os híbridos inter-regionais de ambas as regiões apresentaram respostas competitivas semelhantes a indivíduos da Califórnia. Para o estudo de herbívora, um herbívoro generalista de elevada dispersão – caracol de jardim Helix aspersa – foi alimentado com folhas de ambas as áreas e o peso final destes indivíduos registado a fim de explorar possíveis diferenças significativas. Os caracóis alimentados com folhas de populações nativas de Espanha da não-invasora C. sulphurea cresceram significativamente menos quando comparados com caracóis alimentados com folhas das populações não-nativas da Califórnia. Para os caracóis alimentados com a invasora C. solstitialis, foram também registadas diferenças significativas, no entanto as respostas foram mais complexas, dependendo da população em causa, com caracóis alimentados por populações da Turquia e Austrália a registarem taxas de crescimento mais elevadas. Estes resultados introduzem evidências para a rápida diferenciação entre zonas, ilustrada pelas alterações fenotípicas aqui registadas e que por sua vez poderão contribuir para o potencial invasor de espécies exóticas, como exemplificados pelas diferenças previamente conhecidas no sucesso invasor das duas espécies congêneres em estudo