Genetic analysis of an ephemeral intraspecific hybrid zone in the hypervariable tree, Metrosideros polymorpha, on Hawai‘i Island

Stacy, Elizabeth A.; Johansen, Jennifer; Sakishima, Tomoko; Price, Daniel O.

doi:10.1038/hdy.2016.40

Cited by 31 publications

(53 citation statements)

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“…polymorpha var. incana genes through hybridization on intermediate‐aged lava flows (Stacy et al, ), may offer a versatile ancestral phenotype (i.e. flexible stem West‐Eberhard, ; Wund, Baker, Clancy, Golub, & Foster, ) not offered by the more constrained pioneering M .…”

Section: Discussionmentioning

confidence: 99%

“…Common environment studies of seedlings from three islands (Cordell, Goldstein, Melcher, & Meinzer, 2000;Cordell, Goldstein, Mueller-Dombois, Webb, & Vitousek, 1998;Corn & Hiesey, 1973;Kitayama, Pattison, Cordell, Webb, & Mueller-Dombois, 1997;Stemmermann, 1983;Stacy et al, unpub. data) and parent-offspring analysis of variety-diagnostic traits (Stacy, Johansen, Sakishima, & Price, 2016) reveal a heritable basis for vegetative traits and eliminate plasticity as an explanation for differences among taxa. In spite of this striking variation, speciation within the group has been limited (Simon, 1987); only five species of Metrosideros are recognized in Hawaii, including eight varieties of the widespread M. polymorpha and four additional species with more restricted distributions (Dawson & Stemmermann, 1990).…”

Section: Introductionmentioning

confidence: 99%

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Phylogeography of the highly dispersible landscape‐dominant woody species complex,Metrosideros, in Hawaii

Stacy

Sakishima

2019

Journal of Biogeography

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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. polymorpha var. glaberrima may play a central role in the generation of the group's many, largely island‐endemic, taxa.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phylogeography of the highly dispersible landscape‐dominant woody species complex,Metrosideros, in Hawaii

Stacy

Sakishima

2019

Journal of Biogeography

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“…glaberrima , is consistent with the genetic and ecological differentiation between the two varieties (DeBoer & Stacy ; Morrison & Stacy ; Stacy et al . ).…”

Section: Discussionmentioning

confidence: 97%

“…glaberrima (Stacy et al . ). Trees with different leaf morphology show different functional properties such as efficiency of light use, stomatal traits and leaf composition (Martin et al .…”

Section: Introductionmentioning

confidence: 97%

“…In spite of the prediction that the continuous change in phenotypes could be due to frequent hybridization between varieties (DeBoer & Stacy ; Stacy et al . , ), a definition of variety and its admixture has not been supported by clustering of genotypes. The admixture proportions of the genetic clusters did not differ between individuals, populations or varieties; thus, rather homogeneous spatial genetic structures across populations or varieties were detected (Harbaugh et al .…”

Section: Introductionmentioning

confidence: 99%

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The population genomic signature of environmental association and gene flow in an ecologically divergent tree speciesMetrosideros polymorpha(Myrtaceae)

et al. 2017

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Genomewide markers enable us to study genetic differentiation within a species and the factors underlying it at a much higher resolution than before, which advances our understanding of adaptation in organisms. We investigated genomic divergence in Metrosideros polymorpha, a woody species that occupies a wide range of ecological habitats across the Hawaiian Islands and shows remarkable phenotypic variation. Using 1659 single nucleotide polymorphism (SNP) markers annotated with the genome assembly, we examined the population genetic structure and demographic history of nine populations across five elevations and two ages of substrates on Mauna Loa, the island of Hawaii. The nine populations were differentiated into two genetic clusters distributed on the lower and higher elevations and were largely admixed on the middle elevation. Demographic modelling revealed that the two genetic clusters have been maintained in the face of gene flow, and the effective population size of the high-altitude cluster was much smaller. A F -based outlier search among the 1659 SNPs revealed that 34 SNPs (2.05%) were likely to be under divergent selection and the allele frequencies of 21 of them were associated with environmental changes along elevations, such as temperature and precipitation. This study shows a genomic mosaic of M. polymorpha, in which contrasting divergence patterns were found. While most genomic polymorphisms were shared among populations, a small fraction of the genome was significantly differentiated between populations in diverse environments and could be responsible for the dramatic adaptation to a wide range of environments.

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Varieties of the highly dispersible and hypervariable tree, Metrosideros polymorpha, differ in response to mechanical stress and light across a sharp ecotone

Ekar

Price

Johnson

et al. 2019

American J of Botany

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Premise The drivers of isolation between sympatric populations of long-lived and highly dispersible conspecific plants are not well understood. In the Hawaiian Islands, the landscape-dominant tree, Metrosideros polymorpha, displays extraordinary phenotypic differences among sympatric varieties despite high dispersibility of its pollen and seeds, thereby presenting a unique opportunity to investigate how disruptive selection alone can maintain incipient forms. Stenophyllous M. polymorpha var. newellii is a recently evolved tree endemic to the waterways of eastern Hawai'i Island that shows striking neutral genetic differentiation from its ancestor, wet-forest M. polymorpha var. glaberrima, despite sympatry of these forms. We looked for evidence for, and drivers of, differential local adaptation of these varieties across the range of M. polymorpha var. newellii. 1,2,✉ 2,3 4 2,3 1 2 3 4 7/8/2019 e.Proofing https://wileyproofs.sps.co.in/eproofing_wiley_v2/printpage.php?token=7JMrMjTTqfJvX-UJ14w7DpRmdO3Dnwzi 2/19Methods For paired populations of these varieties, we compared seedling performance under contrasting light conditions and a strong water current characteristic of the riparian zone. In a reciprocal transplant experiment, adult leaf anatomy of the two varieties was contrasted. ResultsResults suggest that the riparian zone is harsh and that selection involving the mechanical stress of rushing water, and secondarily, light, led to significant reciprocal immigrant inviability in adjacent forest and riparian environments. The strongest adaptive divergence between varieties was seen in leaves and seedlings from the site with the sharpest ecotone, coincident with the strongest genetic isolation of M. polymorpha var. newellii observed previously.Conclusions These findings suggest that disruptive selection across a sharp ecotone contributes to the maintenance of an incipient riparian ecotype from within a continuous population of a long-lived and highly dispersible tree species.

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Genetic analysis of an ephemeral intraspecific hybrid zone in the hypervariable tree, Metrosideros polymorpha, on Hawai‘i Island

Cited by 31 publications

References 58 publications

Phylogeography of the highly dispersible landscape‐dominant woody species complex,Metrosideros, in Hawaii

Phylogeography of the highly dispersible landscape‐dominant woody species complex,Metrosideros, in Hawaii

The population genomic signature of environmental association and gene flow in an ecologically divergent tree speciesMetrosideros polymorpha(Myrtaceae)

Varieties of the highly dispersible and hypervariable tree, Metrosideros polymorpha, differ in response to mechanical stress and light across a sharp ecotone

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