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. \u3e650 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 2 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 8 taxa to verify heritability of phenotypes, and examine genotypes of 476 wild adults at 9 microsatellite loci to compare the strengths of isolation across taxa, volcanoes, and distance. All 8 taxa retained their diagnostic phenotypes in the common garden. Populations were isolated by taxon to a range of degrees (pairwise FST between taxa: 0.004–0.267), and there was no pattern of isolation by distance or by elevation; however, significant isolation between volcanoes was observed within monotypic species, suggesting limited gene flow between volcanoes. Among the infraspecific taxa of Metrosideros polymorpha, genetic diversity and isolation significantly decreased and increased, respectively, with elevation. Overall, 5 of the 6 most isolated taxa were associated with highest elevations or otherwise extreme environments. These findings suggest a principal role for selection in the origin and maintenance of the exceptional diversity that occurs within continuous Metrosideros stands on O`ahu

Data from: Phylogeography of the highly dispersible landscape-dominant woody species complex, Metrosideros, in Hawaii

Aim: Little is known about how diversification occurs within long-lived, highly dispersible and continuously distributed groups. We examined the distribution of genetic variation within the woody genus Metrosideros across the Hawaiian Islands for insights into how diversification occurs within this animal-pollinated, wind-dispersed group. Among Hawaiian plants, Metrosideros is unique in its formation of continuous stands within islands that span a remarkable range of environments and comprise numerous predominantly single-island taxa. Location: Hawaiian Islands Taxon: Metrosideros Methods: We performed population genetic analyses of variation at nine nuclear microsatellite loci from 1,486 adults of 23 Metrosideros morphotypes sampled from five main Hawaiian Islands plus additional Pacific Island populations. Results: American Samoa and Tahiti populations clustered most closely with the older islands. Results also revealed isolation by distance across the archipelago, clustering of populations predominantly by island, and evidence of multiple colonizations or back-colonizations of three islands. The number of genetic clusters peaked on islands of intermediate age, coincident with peak morphotype richness. All islands comprised a broad range of genetic distances among taxa with the greatest overall genetic distance observed on Oahu. The two taxa that are distributed broadly across the archipelago were weakly but significantly differentiated only on volcanically active Hawaii Island, where they partition early- and late-successional environments. One of these taxa was positioned centrally both within individual-island splitstree networks and across the archipelago-wide network. Main conclusions: Distance-dependent gene flow contributes to isolation of Metrosideros across islands, especially on terminal islands. Morphological diversity likely accumulates rapidly within this group, likely associated with differential adaptation across heterogeneous environments, but isolation of gene pools through speciation within continuous Metrosideros stands likely requires persistent disruptive selection where environments are stable for long periods. The generalist, wet-forest M. p. v. glaberrima may play a central role in the generation of the group's many, largely island-endemic, forms

SSR_data_from_each_of_7_islands

SSR (microsatellite) genotypes for 9 loci from Metrosideros populations/communities from each of 5 Hawaiian Islands, plus Tahiti and American Samoa. Taxon name, leaf type (glabrous vs. pubescent) and location (where available) of each sample are included

Hawaiian Cyrtandra genotypes

Genotypes based on SNPs for nine single-copy nuclear genes in Hawaiian Cyrtandra species and hybrids

Data from: Incipient radiation within the dominant Hawaiian tree Metrosideros polymorpha

Although trees comprise a primary component of terrestrial species richness, the drivers and temporal scale of divergence in trees remain poorly understood. We examined the landscape-dominant tree, Metrosideros polymorpha, for variation at nine microsatellite loci across 23 populations on young Hawai’i Island, sampling each of the island’s five varieties throughout its full geographic range. For four varieties, principal coordinate analysis revealed strong clustering of populations by variety across the 10 430 km island, indicating partitioning of the species into multiple evolutionarily significant units. The single island-endemic form, riparian var. newellii, showed especially strong differentiation from other varieties despite occurring in sympatry with other varieties and likely evolved from a bog form on the oldest volcano, Kohala, within the past 500 000 years. Along with comparable riparian forms on other Pacific Islands, var. newellii appears to represent parallel incipient ecological speciation within Metrosideros. Greater genetic distance among the more common varieties on the oldest volcano and an inverse relationship between allelic diversity and substrate age appear consistent with colonization of Hawai’i Island by older, partially diverged varieties followed by increased hybridization among varieties on younger volcanoes. This study demonstrates that broad population-level sampling is required to uncover patterns of diversification within a ubiquitous and long-lived tree species. Hawaiian Metrosideros appears to be a case of incipient radiation in trees and thus should be useful for studies of divergence and the evolution of reproductive isolating barriers at the early stages of speciation

Primers for Low-Copy Nuclear Genes in <i>Metrosideros</i> and Cross-Amplification in Myrtaceae

Premise of the study: Primers were developed to amplify low-copy nuclear genes in Hawaiian Metrosideros (Myrtaceae). Methods and Results: Data from a pooled 454 Titanium run of the partial transcriptomes of four Metrosideros taxa were used to identify the loci of interest. Ten exon-primed intron-crossing (EPIC) markers were amplified and sequenced directly with success in Metrosideros, as well as in a representative selection of Myrtaceae, including Syzygium, Psidium, and Melaleuca for most of the markers. The loci amplified ranged between 500 and 1100 bp, and up to 117 polymorphic sites were observed within an individual gene alignment. Two introns contained microsatellites in some of the species. Conclusions: These novel primer pairs should be useful for phylogenetic analysis and population genetics of a broad range of Myrtaceae, particularly the diverse fleshy-fruited tribes Syzygieae and Myrteae

Primers for Low-Copy Nuclear Genes in the Hawaiian Endemic <i>Clermontia</i> (Campanulaceae) and Cross-Amplification in Lobelioideae

Premise of the study: Primers were developed to amplify 12 intron-less, low-copy nuclear genes in the Hawaiian genus <i>Clermontia</i> (Campanulaceae), a suspected tetraploid. Methods and Results: Data from a pooled 454 titanium run of the partial transcriptomes of seven <i>Clermontia</i> species were used to identify the loci of interest. Most loci were amplified and sequenced directly with success in a representative selection of lobeliads even though several of these loci turned out to be duplicated. Levels of variation were comparable to those observed in commonly used plastid and ribosomal markers. Conclusions: We found evidence of a genome duplication that likely predates the diversification of the Hawaiian lobeliads. Some genes nevertheless appear to be single-copy and should be useful for phylogenetic studies of <i>Clermontia</i> or the entire Lobelioideae subfamily

Stacyetal_HeredityMay2016_IndividualSeedlingPhenotypes

Stacyetal_HeredityMay2016_IndividualSeedlingPhenotype

An Expanded <I>Metrosideros</I> (Myrtaceae) to Include <I>Carpolepis</I> and <I>Tepualia</I> Based on Nuclear Genes

International audienceThe genus Metrosideros (Myrtaceae) comprises 50-60 species found largely across the Pacific Islands. The relationships within this genus, including the circumscriptions of the subgenera Mearnsia and Metrosideros and their relationships with the other members of the tribe Metrosidereae (namely the New Caledonian endemic genus Carpolepis and the South American Tepualia), are poorly understood. Phylogenetic analyses were carried out using previously published ITS sequences, covering most species of the tribe, and new sequences of five single-copy nuclear genes with a reduced taxon sampling. The independent and combined analyses of the five nuclear genes using a range of approaches, including Bayesian single-gene, concatenated (MrBayes), concordance (BUCKy) and coalescent (*BEAST) analyses, yielded different topologies, indicating important conflicts among phylogenies based on individual genes. The deep relationships within the tribe Metrosidereae remain poorly resolved, but our results indicate that the species of Carpolepis and Tepualia are likely nested in the genus Metrosideros. A broad circumscription of the genus Metrosideros is therefore adopted, and the new combinations Metrosideros laurifolia var. demonstrans, Metrosideros tardiflora and Metrosideros vitiensis are here published