Isolation of Metrosideros (`Ohi`a) taxa on O`ahu increases with elevation and extreme environments

Species radiations should be facilitated by short generation times and limited dispersal among discontinuous populations. Hawaii’s hyper-diverse, landscape-dominant tree,
Metrosideros, is unique among the islands’ radiations for its massive populations that occur continuously over space and time within islands, its exceptional capacity for gene flow by both pollen and seed, and its extended life span (ca. >650 years). Metrosideros shows the greatest phenotypic and microsatellite DNA diversity on O`ahu, where taxa occur in tight sympatry or parapatry in mesic and montane wet forest on two volcanoes. We document the nonrandom distributions of 12 taxa (including unnamed morphotypes) along elevation gradients, measure phenotypes of ~6-year-old common-garden plants of eight taxa to verify heritability of phenotypes, and examine genotypes of 476 wild adults at nine microsatellite loci to compare the strengths of isolation across taxa, volcanoes and distance. All eight taxa retained their ...