Morphological differentiation among populations of Quercus elliptica Neé (Fagaceae) along an environmental gradient in Mexico and Central America

Abstract

Background: Variation in leaf morphology is an important indicator of how plants respond to different environmental conditions. Leaf trait variation is associated with physiological responses of plants to gradients of humidity and temperature. 
 Objective: We analyzed the variation in the leaf morphological and functional traits of Quercus elliptica and its relationships with environmental and geographic variables across the distribution of this species to evaluate population differentiation using ecological niche models.
 Study species: Quercus elliptica Neé (Fagaceae).
 Study sites and dates: Plants were collected in diverse forest types between 350 and 2,400 m in elevation in Mexico and Central America during 2016 and 2017.
 Methods: We measured and analyzed the differentiation in morphological and functional traits of 4,017 leaves from 402 trees from 41 populations using univariate and multivariate analyses.
 Results: The leaf length and thickness and specific leaf area (SLA) of Q. elliptica were significantly correlated with the seasonality of temperature, precipitation, elevation and aridity. We identified two divergent morphological groups: (1) populations distributed along the Pacific coast with broad and thin elliptical leaves with high SLA values and inhabited humid forests at more than 1,200 m elevation, and (2) populations located along the Gulf of Mexico coast, and in southern Mexico and Central America with thicker, narrower leaves and lower SLA values and inhabited seasonal tropical forests in less than 1,200 m in elevation. 
 Conclusions: Climate and geographic barriers and the ecological niche models supported the population differentiation of Q. elliptica .