Résumé
Aim The diversity and composition of species pools within oceanic
archipelagos is determined by a combination of colonization, abiotic
tolerance, in situ diversification, biotic interactions, and extinction.
The signature of biogeographic events and evolutionary processes, however,
may be masked by recent coalescence and hybridization between closely
related species. We used the species-rich plant genus Cyrtandra
(Gesneriaceae) to investigate the roles of colonization and hybridization
in shaping community assemblages on the geologically young Hawaii Island.
Location Hawaiian Islands. Taxon Cyrtandra (Gesneriaceae). Methods We
sampled 29 Cyrtandra taxa and putative hybrids across the main Hawaiian
Islands and generated single nucleotide polymorphisms (SNPs) from nine
single-copy nuclear genes. Maximum likelihood and Bayesian inference were
used to reconstruct phylogenetic relationships, divergence times were
estimated using secondary calibrations and island ages, and ancestral area
estimation was done using likelihood models. Lastly, we used a Bayesian
population assignment test and principal components analysis to infer
population genetic structure. Results Cyrtandra colonization of the main
Hawaiian Islands appears to have followed the progression rule, whereby
the oldest high Hawaiian Islands (Kauai and Oahu) were colonized first,
followed by colonization of the younger islands as habitat became
available. Hawaii Island was colonized four times, with two dispersal
events from Oahu and two from Maui Nui. The different colonization events
gave rise to significantly uneven numbers of species, and hybridization
among the incipient lineages was detected in the form of intermediate
genotypes. Main Conclusions Our investigation into community assembly in a
species-rich plant genus on a geologically young oceanic island revealed a
history of multiple colonizations and hybridization among colonizing
lineages. The rapid diversification (3.5 species/My) of one of four
Cyrtandra lineages on Hawaii Island may be the result of hybridization
between genetically diverse lineages that stem from independent
colonization events. Multiple colonization events followed by a merging of
lineages may be particularly common during early-stage community assembly
on islands and, through the generation of genetic variation, may be
especially important for species diversification.