Abstract
In tropical mountains, surviving temperature extremes demands finely tuned strategies. We investigated how populations of the bromeliad Pitcairnia flammea across a 2200 m elevational gradient balance genetic canalization and plasticity, and whether thermal strategies are coordinated between seeds and leaves. Seven populations (n ≥ 20 per site) were studied in the field and in a > 2-yr common-garden experiment. Leaf traits (mass per area, area, succulence, stomatal, and trichome densities) and thermal tolerance (T
for heat and cold) were measured, and germination assays (10-35°C) quantified seed thermal performances. Multivariate analyses linked leaf and seed traits to elevation and local thermal conditions. Heat tolerance and leaf traits were maintained in the common garden, indicating strong canalization, whereas cold tolerance was highly plastic, decreasing by up to 17.9°C. Seeds from high elevations germinated faster, with higher cardinal temperatures and c. 230 fewer growing degree days than lowland seeds. Thermal niche differentiation in P. flammea arises from canalized heat resistance and plastic cold responses, coordinated across leaves and seeds. Considering thermal traits across life stages improves predictions of population resilience under climate warming.