Population-Level Differentiation in Growth Rates and Leaf Traits in Seedlings of the Neotropical Live Oak Quercus oleoides Grown under Natural and Manipulated Precipitation Regimes

Abstract

Widely distributed species are normally subjected to spatial heterogeneity in environmental conditions. In sessile organisms like plants, adaptive evolution and phenotypic plasticity of key functional traits are the main mechanisms through which species can respond to environmental heterogeneity and climate change. While extended research has been carried out in temperate species in this regard, there is still limited knowledge as to how species from seasonally-dry tropical climates respond to spatial and temporal variation in environmental conditions. In fact, studies of intraspecific genetically-based differences in functional traits are still largely unknown and studies in these ecosystems have largely focused on in situ comparisons where environmental and genetic effects cannot be differentiated. In this study, we tested for ecotypic differentiation and phenotypic plasticity in leaf economics spectrum (LES) traits, water use efficiency and growth rates under natural and manipulated precipitation regimes in a common garden experiment where seedlings of eight populations of the neotropical live oak Quercus oleoides were established. We also examined the extent to which intraspecific trait variation was associated with plant performance under different water availability. Similar to interspecific patterns among seasonally-dry tropical tree species, live oak populations with long and severe dry seasons had higher leaf nitrogen content and growth rates than mesic populations, which is consistent with a “fast” resource-acquisition strategy aimed to maximize carbon uptake during the wet season. Specific leaf area (SLA) was the best predictor of plant performance, but contrary to expectations, it was negatively associated with relative and absolute growth rates. This observation was partially explained by the negative association between SLA and area-based photosynthetic rates, which is contrary to LES expectations but similar to other recent intraspecific studies on evergreen oaks. Overall, our study shows strong intraspecific differences in functional traits in a tropical oak, Quercus oleoides, and suggests that precipitation regime has played an important role in driving adaptive divergence in this widespread species.

Sympatric parallel diversification of major oak clades in the Americas and the origins of Mexican species diversity

“…S10), suggesting that deciduousness evolved as a strategy to avoid drought and freezing. Moisture regime has been shown in previous studies to exert selection on leaf abscission and drought tolerance (Ramírez‐Valiente & Cavender‐Bares, ) as well as leaf growth rate and nitrogen content (Ramirez‐Valiente et al ., ) in a Neotropical Virentes oak, and severity of cold season has similarly been shown to shape convergent transitions in leaf morphology in Viburnum (Schmerler et al ., ).…”

Natural selection and neutral evolutionary processes contribute to genetic divergence in leaf traits across a precipitation gradient in the tropical oak Quercus oleoides

“…A thorough phenotypic characterization was carried out in seedlings of Q. oleoides growing in two common garden experiments under natural and controlled conditions. These gardens were part of a network of experiments established over a decade within the native range of the species in several countries of Central America complemented by greenhouse experiments at the University of Minnesota to test for local adaptation and population‐level variation in this tropical oak (see Cavender‐Bares & Ramírez‐Valiente ; Cavender‐Bares , ; Center ; Center et al., ; Deacon & Cavender‐Bares, ; Koehler, Center, & Cavender‐Bares, , Ramírez‐Valiente, Koehler et al., ; Ramírez‐Valiente et al., ). In this study, we used the most complete common garden experiments of the series, which included populations from across the entire species distribution and climatic range and had well‐replicated family structure.…”

“…The same process was repeated in April–May 2014 (dry season). Aboveground growth metrics were used to estimate total biomass and absolute growth rate (AGR) using allometric equations (following Ramírez‐Valiente et al., ).…”

“…First, this species is widely distributed across a high variety of precipitation regimes in seasonally dry tropical forests of Central America (Cavender‐Bares et al., ). Second, intraspecific differences have been previously reported in traits such as germination, growth, photoprotective pigments, morphology, physiology and survival (Cavender‐Bares, Sack, & Savage, , Cavender‐Bares, Gonzalez‐Rodríguez, Pahlich, Koehler, & Deacon, ; Center, Etterson, Deacon, & Cavender‐Bares, ; Deacon & Cavender‐Bares, ; Ramírez‐Valiente, Koehler, & Cavender‐Bares, ; Ramírez‐Valiente, Valladares, Delgado, Nicotra, & Aranda, ; Ramírez‐Valiente & Cavender‐Bares, ; Ramírez‐Valiente et al., ). Third, the species exhibits a complex evolutionary history with a clear genetic disjunction in neutral molecular markers between southern populations and population from the rest of the distribution range (Cavender‐Bares et al., , ).…”

Diversification, adaptation, and community assembly of the American oaks (Quercus), a model clade for integrating ecology and evolution

“…As such, the oaks can provide critical insights linking the biogeographic past and current assembly processes that impact ecosystem functions and services that contribute to human well‐being (Cavender‐Bares, ; Cavender‐Bares et al ., , ; Cannon et al ., ). Finally, there is a large and increasing number of studies focused on population level processes within the oaks (Sork et al ., ; Cavender‐Bares, ; Ramírez‐Valiente et al ., , , , ; Koehler et al ., ; Hampe et al ., ; Homolka et al ., ; Platt et al ., ; Firmat et al ., ; Ramírez‐Valiente & Cavender‐Bares, ). These studies reveal that oaks are an important system for understanding the roles of gene flow, adaptation, and plasticity in the persistence of populations of long‐lived organisms, which tend to face more variable environments and fluctuating selection over their lifespan than short‐lived organisms do.…”