title: The founding of Mauritian endemic coffee trees by a synchronous long-distance dispersal event.
abstract: The stochastic process of long-distance dispersal is the exclusive means by which plants colonize oceanic islands. Baker's rule posits that self-incompatible plant lineages are unlikely to successfully colonize oceanic islands because they must achieve a coordinated long-distance dispersal of sufficiently numerous individuals to establish an outcrossing founder population. Here, we show for the first time that Mauritian Coffea species are self-incompatible and thus represent an exception to Baker's rule. The genus Coffea (Rubiaceae) is composed of approximately 124 species with a paleotropical distribution. Phylogenetic evidence strongly supports a single colonization of the oceanic island of Mauritius from either Madagascar or Africa. We employ Bayesian divergence time analyses to show that the colonization of Mauritius was not a recent event. We genotype S-RNase alleles from Mauritian endemic Coffea, and using S-allele gene genealogies, we show that the Mauritian allelic diversity is confined to just seven deeply divergent Coffea S-RNase allelic lineages. Based on these data, we developed an individual-based model and performed a simulation study to estimate the most likely number of founding individuals involved in the colonization of Mauritius. Our simulations show that to explain the observed S-RNase allelic diversity, the founding population was likely composed of fewer than 31 seeds that were likely synchronously dispersed from an ancestral mainland species.
authors.affiliation: National Centre for Biosystematics, Natural History Museum, University of Oslo, Oslo, Norway.
authors.forename: M D
authors.initials: MD
authors.lastname: Nowak
authors.forename: B C
authors.initials: BC
authors.lastname: Haller
authors.forename: A D
authors.initials: AD
authors.lastname: Yoder
mesh_terms: D001499:Bayes Theorem; D040503:Coffea / Q000502:physiology*; D017343:Genes, Plant; D005838:Genotype; D008436:Mauritius; D008957:Models, Genetic; D010802:Phylogeny; D011157:Population Dynamics; D058614:Seed Dispersal; D017422:Sequence Analysis, DNA
keywords: gametophytic self-incompatibility; genetic bottleneck; long-distance dispersal; negative frequency-dependent selection; trans-specific polymorphism