Floral Variation across Three Varieties of the Landscape-Dominant Tree Metrosideros polymorpha (Myrtaceae): Insights from a Hawaii Island Common Garden

2021 ◽  
Vol 182 (1) ◽  
pp. 46-58
Author(s):  
Elizabeth A. Stacy ◽  
Melissa A. Johnson
Keyword(s):  
Common Garden ◽  
Metrosideros Polymorpha ◽  
Floral Variation ◽  
Hawaii Island

scholarly journals Striking between-population floral divergences in a habitat specialized plant

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0253038
Author(s):  
Sumayya Abdul Rahim ◽  
Ullasa Kodandaramaiah ◽  
Aboli Kulkarni ◽  
Deepak Barua
Keyword(s):  
Common Garden ◽  
Habitat Specialization ◽  
Floral Traits ◽  
Sky Islands ◽  
Floral Variation ◽  
Floral Visitor ◽  
In The Wild ◽  
Specialist Species ◽  
Habitat Generalist ◽  
Common Garden Experiments

When the habitat occupied by a specialist species is patchily distributed, limited gene flow between the fragmented populations may allow population differentiation and eventual speciation. ‘Sky islands’—montane habitats that form terrestrial islands—have been shown to promote diversification in many taxa through this mechanism. We investigate floral variation in Impatiens lawii, a plant specialized on laterite rich rocky plateaus that form sky islands in the northern Western Ghats mountains of India. We focus on three plateaus separated from each other by ca. 7 to 17 km, and show that floral traits have diverged strongly between these populations. In contrast, floral traits have not diverged in the congeneric I. oppositifolia, which co-occurs with I. lawii in the plateaus, but is a habitat generalist that is also found in the intervening valleys. We conducted common garden experiments to test whether the differences in I. lawii are due to genetic differentiation or phenotypic plasticity. There were strong differences in floral morphology between experimental plants sourced from the three populations, and the relative divergences between population pairs mirrored that seen in the wild, indicating that the populations are genetically differentiated. Common garden experiments confirmed that there was no differentiation in I. oppositifolia. Field floral visitation surveys indicated that the observed differences in floral traits have consequences for I. lawii populations, by reducing the number of visitors and changing the relative abundance of different floral visitor groups. Our results highlight the role of habitat specialization in diversification, and corroborates the importance of sky islands as centres of diversification.

scholarly journals Recurrent modification of floral morphology in heterantherous Solanum reveals a parallel shift in reproductive strategy

2014 ◽  
Vol 369 (1649) ◽  
pp. 20130256 ◽  
Author(s):  
Mario Vallejo-Marín ◽  
Catriona Walker ◽  
Philip Friston-Reilly ◽  
Lislie Solís-Montero ◽  
Boris Igic
Keyword(s):  
Floral Morphology ◽  
Parallel Evolution ◽  
Common Garden ◽  
Spatial Separation ◽  
Spatial Arrangement ◽  
Evolutionary Transitions ◽  
Floral Variation ◽  
Morphometric Analyses ◽  
Self Fertilization ◽  
And Function

Floral morphology determines the pattern of pollen transfer within and between individuals. In hermaphroditic species, the spatial arrangement of sexual organs influences the rate of self-pollination as well as the placement of pollen in different areas of the pollinator's body. Studying the evolutionary modification of floral morphology in closely related species offers an opportunity to investigate the causes and consequences of floral variation. Here, we investigate the recurrent modification of flower morphology in three closely related pairs of taxa in Solanum section Androceras (Solanaceae), a group characterized by the presence of two morphologically distinct types of anthers in the same flower (heteranthery). We use morphometric analyses of plants grown in a common garden to characterize and compare the changes in floral morphology observed in parallel evolutionary transitions from relatively larger to smaller flowers. Our results indicate that the transition to smaller flowers is associated with a reduction in the spatial separation of anthers and stigma, changes in the allometric relationships among floral traits, shifts in pollen allocation to the two anther morphs and reduced pollen : ovule ratios. We suggest that floral modification in this group reflects parallel evolution towards increased self-fertilization and discuss potential selective scenarios that may favour this recurrent shift in floral morphology and function.

scholarly journals Divergent selection and primary gene flow shape incipient speciation of a riparian tree on Hawaii Island

2019 ◽  
Author(s):  
Jae Young Choi ◽  
Michael Purugganan ◽  
Elizabeth A. Stacy
Keyword(s):  
Gene Flow ◽  
Divergent Selection ◽  
Genomic Islands ◽  
Disruptive Selection ◽  
Metrosideros Polymorpha ◽  
Incipient Speciation ◽  
Island Endemic ◽  
Hawaii Island ◽  
Riparian Tree ◽  
Primary Gene

AbstractA long-standing goal of evolutionary biology is to understand the mechanisms underlying the formation of species. Of particular interest is whether or not speciation can occur in the presence of gene flow and without a period of physical isolation. Here, we investigated this process within HawaiianMetrosideros, a hyper-variable and highly dispersible woody species complex that dominates the Hawaiian Islands in continuous stands. Specifically, we investigated the origin ofMetrosideros polymorphavar.newellii(newellii), a riparian ecotype endemic to Hawaii Island that is purportedly derived from the archipelago-wideM. polymorphavar.glaberrima(glaberrima). Disruptive selection across a sharp forest-riparian ecotone contributes to the isolation of these varieties and is a likely driver of newellii’s origin. We examined genome-wide variation of 42 trees from Hawaii Island and older islands. Results revealed a split between glaberrima and newellii within the past 0.3-1.2 million years. Admixture was extensive between lineages within Hawaii Island and between islands, but introgression from populations on older islands (i.e.secondary gene flow) did not appear to contribute to the emergence of newellii. In contrast, recurrent gene flow (i.e.primary gene flow) between glaberrima and newellii contributed to the formation of genomic islands of elevated absolute and relative divergence. These regions were enriched for genes with regulatory functions as well as for signals of positive selection, especially in newellii, consistent with divergent selection underlying their formation. In sum, our results support riparian newellii as a rare case of incipient ecological speciation with primary gene flow in trees.Author summaryA long-standing question in evolution is whether or not new species can arise in the presence of gene flow, which is expected to inhibit the formation of reproductive isolating barriers. We investigated the genomics underlying the origin of a Hawaii Island-endemic riparian tree and purported case of incipient sympatric speciation due to disruptive selection across a sharp forest-riparian ecotone. We find extensive evidence of ongoing gene flow between the riparian tree and its closest relative along with local genomic regions resistant to admixture that likely formed through selection on genes for ecological adaptation and/or reproductive isolation. These results strongly suggest that where disruptive selection is strong, incipient speciation with gene flow is possible even in long-lived, highly dispersible trees.

scholarly journals Divergent Selection and Primary Gene Flow Shape Incipient Speciation of a Riparian Tree on Hawaii Island

2019 ◽  
Vol 37 (3) ◽  
pp. 695-710 ◽  
Author(s):  
Jae Young Choi ◽  
Michael Purugganan ◽  
Elizabeth A Stacy
Keyword(s):  
Gene Flow ◽  
Evolutionary Biology ◽  
Woody Species ◽  
Divergent Selection ◽  
Genomic Islands ◽  
Disruptive Selection ◽  
Metrosideros Polymorpha ◽  
Hawaii Island ◽  
Riparian Tree ◽  
Primary Gene

Abstract A long-standing goal of evolutionary biology is to understand the mechanisms underlying the formation of species. Of particular interest is whether or not speciation can occur in the presence of gene flow and without a period of physical isolation. Here, we investigated this process within Hawaiian Metrosideros, a hypervariable and highly dispersible woody species complex that dominates the Hawaiian Islands in continuous stands. Specifically, we investigated the origin of Metrosideros polymorpha var. newellii (newellii), a riparian ecotype endemic to Hawaii Island that is purportedly derived from the archipelago-wide M. polymorpha var. glaberrima (glaberrima). Disruptive selection across a sharp forest-riparian ecotone contributes to the isolation of these varieties and is a likely driver of newellii’s origin. We examined genome-wide variation of 42 trees from Hawaii Island and older islands. Results revealed a split between glaberrima and newellii within the past 0.3–1.2 My. Admixture was extensive between lineages within Hawaii Island and between islands, but introgression from populations on older islands (i.e., secondary gene flow) did not appear to contribute to the emergence of newellii. In contrast, recurrent gene flow (i.e., primary gene flow) between glaberrima and newellii contributed to the formation of genomic islands of elevated absolute and relative divergence. These regions were enriched for genes with regulatory functions as well as for signals of positive selection, especially in newellii, consistent with divergent selection underlying their formation. In sum, our results support riparian newellii as a rare case of incipient ecological speciation with primary gene flow in trees.

Tree growth and age in an ancient Hawaiian wet forest: vegetation dynamics at two spatial scales

2009 ◽  
Vol 26 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Patrick J. Hart
Keyword(s):  
Spatial Scales ◽  
Age Groups ◽  
Metrosideros Polymorpha ◽  
Island Growth ◽  
Class Model ◽  
Hawaii Island ◽  
Gap Phase ◽  
Old Trees ◽  
Succession Model ◽  
Age Estimates

Abstract:In this study I document the growth rate and age of trees in an old-growth montane Hawaiian wet forest and use these results to evaluate the cyclic succession model for forest dynamics. I used two methods to estimate the age of trees – the crown-class model and radiocarbon dating. Over 6000 trees belonging to eight species were tagged and measured over 7 y on Hawaii Island. Growth rates for the dominant tree (Metrosideros polymorpha) were relatively low (mean = 1.3 mm y−1) and varied with tree size and crown class. 14C-based age estimates for 27 M. polymorpha trees loosely corroborated estimates based on the crown-class method. The oldest tree dated by 14C had a median age of 647 y BP, placing it among the oldest documented angiosperm trees in the northern hemisphere. 14C dating revealed that the upper canopy may be comprised of three distinct age groups of M. polymorpha trees of similar size, with the median age of each group separated by 200–250 y. The high density of large, very old trees in multiple groups is unusual for a tropical forest and indicates that forest development may occur through gap-phase regeneration at a fine scale and stand-level mortality at a coarser scale.

scholarly journals Isolation of Metrosideros (ʻOhiʻa) Taxa on Oʻahu Increases with Elevation and Extreme Environments

2019 ◽  
Vol 111 (1) ◽  
pp. 103-118 ◽  
Author(s):  
Elizabeth A Stacy ◽  
Tomoko Sakishima ◽  
Heaven Tharp ◽  
Neil Snow
Keyword(s):  
Gene Flow ◽  
Isolation By Distance ◽  
Extreme Environments ◽  
Common Garden ◽  
Metrosideros Polymorpha ◽  
Elevation Gradients ◽  
Principal Role ◽  
Generation Times ◽  
Limited Dispersal ◽  
Limited Gene Flow

Abstract 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 Oʻahu, 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 Oʻahu.

scholarly journals Large-scale tree mortality from Rapid Ohia Death negatively influences avifauna in lower Puna, Hawaii Island, USA

The Condor ◽  
2019 ◽  
Vol 121 (2) ◽  
Author(s):  
Richard J Camp ◽  
Dennis A LaPointe ◽  
Patrick J Hart ◽  
Daniel E Sedgwick ◽  
Lisa K Canale
Keyword(s):  
Large Scale ◽  
Tree Mortality ◽  
Bird Community ◽  
Abundant Species ◽  
Metrosideros Polymorpha ◽  
Vascular Wilt ◽  
Point Counts ◽  
Canker Pathogen ◽  
Hawaii Island ◽  
The Impact

Abstract ‘Ōhi’a lehua (Metrosideros polymorpha) is the principle tree species in forests across the Hawaiian Islands and provides critical foraging and nesting habitat for native passerines. Rapid Ohia Death (ROD), caused by the vascular wilt fungus Ceratocystis lukuohia and the canker pathogen C. huliohia, was first detected in the Puna District of Hawaii Island in 2010. It affects all life stages of ‘ōhi’a and as of July 2018 had spread to an estimated 40,469 ha across Hawaii Island. To determine the impact of ROD on the forest bird community we conducted point counts in lowland ‘ōhi’a forest in 2016 and compared them to counts from 2003 to 2004, before the appearance of ROD. We found an increase in species diversity and a significant decrease in the densities of a native Hawaiian honeycreeper, the Hawaii Amakihi (Chlorodrepanus virens), and the nonnative Japanese White-eye (Zosterops japonicus). Yellow-fronted Canary (Crithagra mozambica) and Saffron Finch (Sicalis flaveola), 2 nonnative passerines associated with the shrub layer and more open habitats, were only detected in 2016. Proportion of survey points occupied were comparable between survey periods, but relative abundances were generally lower. Hawaii Amakihi densities declined by 79% and Japanese White-eye densities declined by 33%. Our findings suggest that the loss of ‘ōhi’a canopy due primarily to ROD has adversely affected populations of native Hawaii Amakihi and nonnative Japanese White-eye, 2 of the most abundant species of lowland Hawaiian forests.

Radionuclide hybrid imaging in common garden slugs (Arionidae)

2020 ◽  
Author(s):  
N Beindorff ◽  
D Messroghli ◽  
JF Eary ◽  
W Brenner
Keyword(s):  
Hybrid Imaging ◽  
Common Garden
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