Adaptação local entre populações costeiras e interioranas de Epidendrum fulgens Brongn. (Orchidaceae: Epidendroideae)

Author(s)

Thales Moreira de Lima

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2023-02-14

Examining board members

Fábio Pinheiro; Gustavo Habermann; Cleber Juliano Neves Chaves

• Advisor: Rafael Vasconcelos Ribeiro; Fábio Pinheiro

Abstract

Local adaptation occurs when divergent natural selection surpasses gene flow. Local adaptation has been extensively studied, but unraveling the selective pressures that lead to the evolution of local adaptation is still an open field of research. This work analyzes the local adaptation between coastal and inland populations of Epidendrum fulgens Brongn., an orchid species endemic to southern and southeastern Brazil. While coastal populations occur on sandy coastal plains (i.e., restingas), inland populations occur on rocky outcrops. The main hypothesis tested is that coastal plants would be more resistant to salt in the form of salt spray. To test this hypothesis, we first carried out a pilot salt spray resistance experiment (Chapter 1). Using 10 potted plants, including individuals from both the coast and the interior, we applied 4 levels of spray treatment, corresponding to different concentrations of salt spray (0 (control), 200, 400 and 800 mM Na). We sprayed each plant every day for 10 days. We evaluated plant performance by measuring maximum PSII yield (Fv/Fm), osmotic potential (??), relative water content (RWC), leaf chlorophyll index and Na, K, Ca and Mg leaf concentrations. Our results showed that E. fulgens is highly resistant to salt stress, its main resistance mechanisms being the prevention of salt entry through the epidermis and active osmotic adjustment. With these results in hand, we moved on to the main experiment to test local adaptation to salt spray (Chapter 2). We carried out an experiment exposing 96 plants – two coastal populations and two inland ones – to seawater spray (400 mM) for 60 days and evaluated their performance by measuring the maximum PSII yield (Fv/Fm), leaf expansion rate, osmotic potential (??), relative water content (RWC), leaf chlorophyll index, Na, K, Ca and Mg leaf concentrations and relative growth rate (RGR). The only parameters that responded significantly to salt were RGR and leaf expansion rate, but they responded similarly between groups. Overall, both groups are considerably resistant to salt, contradicting the hypothesis of local adaptation to salt spray. Finally, we also carried out analyzes of the realized climatic niche overlap, analyzes of correlation between the neutral genetic structure (Fst) and the climatic differentiation and analyzes of phenotypic differentiation in four phenotypic attributes (specific leaf area, saturated water content, stomatal density, and height) (Chapter 3). Niche overlap was null, as expected if local adaptation were present. We also detected a positive correlation between Fst and climatic differentiation, indicating isolation by environment and a possible process of local adaptation. On the other hand, the phenotypic variation between the groups is basically due to phenotypic plasticity, with no sign of local adaptation in the phenotype. When we combine all the evidence collected in this work, we conclude that the most likely hypothesis is that local adaptation between coastal and inland populations is nonexistent (AU)

• FAPESP's process: 20/12723-0 - Functional traits and local adaptation in Epidendrum fulgens Brongn (Orchidaceae) ecotypes
• Grantee: Thales Moreira de Lima
• Support Opportunities: Scholarships in Brazil - Master