Plant-Plant Interaction in Early- Vs. Late-Successional Varieties of the Hawaiian Landscape-Dominant Tree, \u3cem\u3eMetrosideros polymorpha\u3c/em\u3e

Plant-plant interactions play an important role in assembling plant communities. Interactions between neighboring plants can vary as a result of the genetic relatedness of neighbors, impacting rates of growth and patterns of resource allocation. When growing alongside close relatives, some species decrease their growth in a form of cooperation, while others grow faster through facilitation. A complication of plant interaction studies arises because decreased growth in the presence of close relatives can also be due to competition for resources, which increases with phenotypic similarity. Further complicating matters, mycorrhizal fungi, through their connections with plant roots, may strongly influence plant interactions. My research compares the nature of plant-plant interactions within and between early- and late-successional varieties of Hawaiian trees, Metrosideros polymorpha var. incana (hereafter incana) and var. glaberrima (hereafter glaberrima), that differ in population density and the prevalence of mycorrhizal fungi in their native environments. I predicted that seedlings would respond (grow) differentially in the presence of genetically different neighbors and that the pattern of response would differ between the varieties in the presence/absence of mycorrhizae. Germinants of the two varieties were planted in pairs in experimental pots such that each pot contained a target seedling and a single neighbor, with the genetic relatedness of neighboring seedlings varying among treatments. One-half of the pots were supplemented with mycorrhizal fungi, and all were kept under ambient greenhouse conditions. After ~15 months, growth rates of the target seedlings were measured under the three treatments (sib = sibling neighbor, pop = neighbor derives from a different population of the same variety, and var = neighbor is from the opposite variety) as well as from control seedlings grown alone, both with and without mycorrhizal fungi. Additionally, hyphal growth was quantified in each pot with mycorrhizae to assess the relative roles of cooperation versus competition; cooperating seedlings were expected to increase the flow of photosynthates (i.e., carbohydrates) to their mycorrhizal symbionts, thus increasing hyphal growth. Based on the results, an increase in nutrient uptake with mycorrhizal fungi seems to be common in both the early- and late-successional varieties, but the seedling behaviors especially towards siblings seem to be different between incana and glaberrima. The overall growth of both varieties of M. polymorpha was increased, and allocation to root length relative to shoot length was reduced in the presence of mycorrhizae compared to the absence of mycorrhizae, suggesting an increase in nutrient uptake with mycorrhizal fungi. Differences among treatments were completely restricted to the sibling treatment versus the pop and var treatments. In the presence of sibling neighbors, target seedlings of incana and glaberrima had lower and higher root:shoot length ratios, respectively, than those grown with more genetically distant neighbors. Interestingly, root:shoot mass ratios did not vary among treatments for either variety. These results imply that seedlings of glaberrima grown with sibling neighbors prioritized vertical root growth over horizontal root growth to obtain nutrients. Also in the sibling treatment, but in the absence of mycorrhizal fungi, higher specific leaf area (SLA) of target seedlings was observed in both incana and glaberrima, but statistically supported only in glaberrima. In glaberrima, both the greater SLA of target seedlings grown with sibling neighbors and the constant shoot length among treatments suggest the ability of seedlings of this variety to increase light capture without shading sibling neighbors. Further, with a single exception, the sizes of target and neighboring seedlings were negatively correlated as expected, due to competition; the exception was the sibling treatment for which there was a significant positive relationship for glaberrima alone, not incana. Finally, the greatest mycorrhizal hyphal length was observed in both varieties in the sibling treatment, suggesting cooperative behavior, yet this increase was statistically significant only in glaberrima. These four lines of evidence suggest that seedlings of late-successional glaberrima may be adapted to recognize and/or respond to genetically different neighbors, while such evidence was minimal or absent in seedlings of early-successional incana. Given that the differential response of seedlings to genetically different neighbors occurred even in the absence of mycorrhizal fungi, mycorrhizal symbionts do not appear to facilitate kin recognition or response in Metrosideros. Beyond their responses to neighbor genetic relatedness, incana and glaberrima seemingly have different strategies for resource allocation affecting growth of both seedlings and their mycorrhizal symbionts that is consistent with their differential adaptation to early- and late-successional environments. Higher overall growth rates (i.e., final sizes) were observed in seedlings of incana relative to glaberrima regardless of neighbor treatment or the presence or absence of mycorrhizal symbionts. Rapid seedling growth in incana may reflect adaptation of this variety to the harsh conditions of early-successional environments where seedling establishment is likely restricted to occasional, brief periods of favorable conditions. In addition, mycorrhizal hyphal density was higher in incana-target pots relative to glaberrima-target pots. Despite a lack of correlation between total dry mass and hyphal density for incana or glaberrima separately or combined, the relatively higher growth rates of both target seedlings and mycorrhizal fungi in the incana pots may suggest a mutually positive relationship between incana and mycorrhizal fungi. Such a relationship may be expected in incana given the mycorrhizae-limiting nature and low population density characteristic of early-successional environments in Hawaii, where rapid seedling growth may be favored and can occur without intensifying competition among well-spaced neighbors. In contrast, growth of seedlings of glaberrima and their mycorrhizal symbionts may be restricted to minimize competition for resources in the high population densities of late-successional forests. Results of this research provide novel insights into the poorly known world of neighboring interactions in trees affected by genetic relatedness and successional stage, with implications for forest restoration

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

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

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