Abstract

Adaptive evolution is a major driver of organism diversification, but the links between phenotypic traits and environmental niche remain little documented in tropical trees. Moreover, trait‐niche relationships are complex because a correlation between the traits and environmental niches displayed by a sample of species may result from (a) convergent evolution if different environmental conditions have selected different sets of traits, and/or (b) phylogenetic inertia if niche and morphological differences between species are simply function of their phylogenetic divergence, in which case the trait‐niche correlation does not imply any direct causal link. Here, we aim to assess the respective roles of phylogenetic inertia and convergent evolution in shaping the differences of botanical traits and environmental niches among congeneric African tree species that evolved in different biomes.This issue was addressed with the tree genus Guibourtia Benn. (Leguminosae and Detarioideae), which contains 13 African species occupying various forest habitat types, from rain forest to dry woodlands, with different climate and soil conditions. To this end, we combined morphological data with ecological niche modelling and used a highly resolved plastid phylogeny of the 13 African Guibourtia species.First, we demonstrated phylogenetic signals in both morphological traits (Mantel test between phylogenetic and morphological distances between species: r = .24, p = .031) and environmental niches (Mantel test between phylogenetic and niche distances between species: r = .23, p = .025). Second, we found a significant correlation between morphology and niche, at least between some of their respective dimensions (Mantel's r = .32, p = .013), even after accounting for phylogenetic inertia (Phylogenetic Independent Contrast: r = .69, p = .018). This correlation occurred between some leaflet and flower traits and solar radiation, relative humidity, precipitations, and temperature range.Our results demonstrate the convergent evolution of some morphological traits in response to climatic factors in congeneric tree species and highlight the action of selective forces, along with neutral ones, in shaping the divergence between congeneric tropical plants.

Highlights

  • Historical and environmental factors contribute both to variation in traits across species (Freckleton & Jetz, 2008)

  • This issue was addressed with the tree genus Guibourtia Benn. (Leguminosae and Detarioideae), which contains 13 African species occupying various forest habitat types, from rain forest to dry woodlands, with different climate and soil conditions

  • It is crucial to distinguish the similarity between traits of related species and niche that can be attributable to common ancestry from similar‐ ity to convergent evolutionary change

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Summary

| INTRODUCTION

Historical and environmental factors contribute both to variation in traits across species (Freckleton & Jetz, 2008). To study the relationships between traits and environmental drivers following an ecomorpho‐ logical approach (Motta & Kotrschal, 1991; Wiens & Graham, 2005), Broennimann et al (2012) proposed multivariate techniques to quantitatively compare the environmental niches between pairs of species (e.g., indices of niche overlap, niche equivalency and niche similarity) These new niche modelling tools combined with phylo‐ genetic information (a) help to assess how the realized niches (see Soberón, 2007) of closely related species have evolved over time (e.g., Guisan & Thuiller, 2005; Ortiz‐Medrano et al, 2016), and (b) allow to explain the observed biogeographical patterns and to test ecological hypotheses (Rato et al, 2015). This genus represents a good model for our questions because (a) its species occur over a wide range of habitat types (rainforests, dry forests/ savannas), and (b) a well‐resolved phylogeny of this genus is available (Tosso et al, 2018) and shows three clades, each including species occupying contrasting environments

| METHODS
Findings
CONFLICT OF INTEREST
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