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.