Limited phylogenetic patterns in physiologically plastic traits
Our study included species belonging to families that differ widely in their earliest occurrence in evolutionary history, and therefore in climate regimes they have experienced throughout their existence. For example, Fabaceae have existed in the Neotropics for at least 58 million years (Wing et al . 2009) and their relative abundance did not decrease during the Paleocene-Eocene Thermal Maximum (~56 Ma) when temperatures in the tropics rapidly rose by 3 to 5°C (Jaramillo et al . 2010). We found no evidence, however, that Fabaceae or other relatively old families have greater heat tolerance and are therefore better equipped for end-of-century conditions than taxa that emerged more recently. Knight & Ackerly (2003) found that congeneric species of Californian coastal and desert ecosystems had very similar T50 when grown in a common environment, despite maximum temperatures being 10°C greater in the desert than in the coastal region. The lack of convergent adaptation of heat tolerance suggested high plasticity in heat tolerance instead (Knight & Ackerly 2003). Across the phylogenetic tree there were some distinct clusters, indicating similarity in heat tolerance among sister species; overall the phylogenetic signal in heat tolerance was weak, however, in accordance with other recent studies (Lancaster & Humphries 2020; Perez & Feeley 2020b). The predominance of plasticity over evolutionary legacies is consistent with the plasticity in the temperature relations of other aspects of metabolism in trees from the aseasonal lowland tropics, such as the convergence of the optimum temperature for photosynthesis on local mean temperatures in diverse forest communities (Slot & Winter 2017a), and acclimation of photosynthesis (Slot & Winter 2017b) and leaf respiration (Cheesman & Winter 2013; Slot et al . 2014) to experimental warming.