Phenotypic plasticity and local adaptation favor range expansion of a Neotropical palm

Abstract

One of the most intriguing questions in plant ecology is which evolutionary strategy allows widely distributed species to increase their ecological range and grow in changing environmental conditions. Phenotypic plasticity and local adaptations are major processes governing species range margins, but little is known about their relative contribution for tree species distribution in tropical forest regions. We investigated the relative role of phenotypic plasticity and local adaptation in the ecological distribution of the widespread palm Euterpe edulis in the Brazilian Atlantic Forest. Genetic sampling and experiments were performed in old-growth remnants of two forest types with higher (Seasonal Semideciduous Forests vs. Submontane Rainforest) and lower biogeographic association and environmental similarities (Submontane Rainforest vs. Restinga Forest). We first assessed the molecular genetic differentiation among populations, focusing on the group of loci potentially under selection in each forest, using single-nucleotide polymorphism (SNPs) outliers. Further, we looked for potential adaptive divergence among populations in a common garden experiment and in reciprocal transplants for two plant development phases: seedling establishment and sapling growth. Analysis with outlier loci indicated that all individuals from the Semideciduous Forest formed a single group, while another group was formed by overlapping individuals from Submontane Rainforest and Restinga Forest. Molecular differentiation was corroborated by reciprocal transplants, which yielded strong evidence of local adaptations for seedling establishment in the biogeographically divergent Rainforest and Semideciduous Forest, but not for Restinga Forest and Submontane Rainforest. Phenotypic plasticity for palm seedling establishment favors range expansion to biogeographically related or recently colonized forest types, while persistence in the newly colonized ecosystem may be favored by local adaptations if climatic conditions diverge over time, reducing gene flow between populations. SNPs obtained by next-generation sequencing can help exploring adaptive genetic variation in tropical trees, which impose several challenges to the use of reciprocal transplants.

Keywords: Atlantic Forest; Euterpe edulis; SNP genotyping; common garden; ecological ranges; ecotypes; evolutionary ecology; next‐generation sequencing; reciprocal transplants.

Figure 1

Genetic structuring using 501 neutral and 84 outlier SNPs of Euterpe edulis populations from different forest types of the Brazilian Atlantic Forest: scatter plot of clusters of individuals and density plots of individuals using neutral loci (a and b, respectively) and outlier loci (c and d, respectively)

Figure 2

Venn diagram indicating the common outlier loci of Euterpe edulis among forest types of the Brazilian Atlantic Forest

Figure 3

Paired comparisons of the influence of seed provenance (RnF: Rainforest; SdF: Semideciduous Forest) on adaptive traits in reciprocal transplants established with Euterpe edulis within these forest types in the Brazilian Atlantic Forest. Mann–Whitney test was used for counting data and t test for the log‐transformed data. *p < 0.05; **p < 0.01; ***p < 0.0001

Figure 4

Paired comparisons of the influence of seed provenance (RnF: Rainforest; RtF: Restinga Forest) on adaptive traits in reciprocal transplants established with Euterpe edulis within these forest types in the Brazilian Atlantic Forest. Mann–Whitney test was used for counting data and t‐test for the log‐transformed data. *p < 0.05; **p < 0.01; ***p < 0.0001