Data from: Genetic patterns of Magnolia in the Lesser Antilles: Stepwise colonisation leading to highly inbred island ‘populations’

Aim: Test for genetic signatures of island biogeographic patterns, using a
slowly evolving, recent colonist with a low dispersal capability in an
island chain without linear chronosequence; evaluate the multiple-endemic
status of the species; and quantify genetic diversity of extant island
populations. Location: The Lesser Antilles (Caribbean). Taxon: Magnolia
dodecapetala (Magnoliaceae). Methods: Genetic diversity was characterised
using Sanger sequencing of 21 individuals amplified for 11 DNA markers,
plus microsatellite data of 195 individuals genotyped with 19 simple
sequence repeat (SSR) markers. Sanger sequencing data were used to
construct a Bayesian phylogenetic hypothesis, while SSR markers were used
to run approximate Bayesian computation (ABC) demographic analyses and
calculate population statistics. Results: Both types of molecular data
support stepwise colonization, decoupled from known island ages. The ABC
analyses support a north to south migration while the Sanger sequencing
data indicates a mixture of island progression rule and stepping stone
dispersal. The SSR data show strong genetic structuring per island and
significant inbreeding in all populations except in Saint Lucia. The
lowest genetic diversity is found in the population from Saint Vincent. A
high amount of genetic linkage occurs in a subpopulation from Dominica.
Main conclusions: Biogeographic patterns for the complex geological
setting of the Lesser Antilles are uncovered using a slowly evolving study
species. All genetic data support treating each island as distinct
Management Units for conservation and call for a re-evaluation of the
species limits. Inbreeding threatens the survival of island populations
and the populations of Saint Vincent and Dominica represent conservation
priorities.