Résumé
Oceanic islands are commonly considered as natural laboratories for
studies on evolution and speciation. The evolutionary specificities of
islands associated with species biology provide unique scenarios to study
the role of geography and climate in driving population divergence.
However, few studies have addressed this subject in small oceanic islands
with heterogeneous climates. Being widely distributed in Reunion Island
forest, Coffea mauritiana represents an interesting model case for
investigating patterns of within-island differentiation at small spatial
scale. In this study, we examined the genetic diversity and population
divergences of C. mauritiana using SNP markers obtained from 323
individuals across 34 locations in Reunion Island. Using redundancy
analysis, we further evaluated the contribution of geographic and climatic
factors to shaping genetic divergence among populations. Genetic diversity
analyses revealed that accessions clustered according to the source
population, with further grouping in regional clusters. Genetic
relationships among the regional clusters underlined a recent process of
expansion in the form of step-by-step colonization on both sides of the
island. Divergence among source populations was mostly driven by the joint
effect of geographic distance and climatic heterogeneity. The pattern of
isolation-by-geography was in accordance with the dispersal
characteristics of the species, while isolation-by-environment was mostly
explained by the heterogeneous rainfall patterns, probably associated with
an asynchronous flowering among populations. These findings advance our
knowledge on the patterns of genetic diversity and factors of population
differentiation of species native to Reunion Island, and will also
usefully guide forest management for conservation.