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The ecology, evolution, and genetics of the Hawaiian Silversword Alliance : The ecology, evolution, and genetics of the Hawaiian Silversword Alliance Kurt Hartman
Silversword researchers : Silversword researchers Gerald Carr Robert Robichaux Bruce Baldwin
Silversword researchers : Donald W. Kyhos Bruce Bohm Bill Crins Leslie Bohm Silversword researchers
Adaptive Radiation on Hawaii : Adaptive Radiation on Hawaii Bidens menziesii Geranium cuneatum Delissea undulata Campanulaceae
Adaptive Radiation on Hawaii : Adaptive Radiation on Hawaii Drosophilidae honeycreeper
What is the Silversword Alliance? : What is the Silversword Alliance? 28 species endemic to Hawaii
3 genera
Argyroxiphium
(5 spp.)
Dubautia (21 spp.)
Wilkesia (2 spp.)
Genus #1 - Argyroxiphium = the “silverswords” & “greenswords” : Genus #1 - Argyroxiphium = the “silverswords” & “greenswords” Most recognized genus of silversword alliance
Capitulum with ray flowers (contrast with Wilkesia & Dubautia which only have disk flowers)
Hybrid between Argyroxiphium, Wilkesia, and Dubautia species
Found on Maui and Hawaii
Silversword species (3) : Silversword species (3) A. caliginis Bog silversword A. kauense A. sandwicense
2 subspecies of A. sandwicence : 2 subspecies of A. sandwicence ssp. sandwicense ssp. macrocephalum
Argyroxiphium : Argyroxiphium
Argyroxiphium sandwicense habitat : Argyroxiphium sandwicense habitat Habitat on cinder cone
7000 to 10000 feet – intense sunlight
Hot in summer day & below freezing in winter night
Snowfall, zero humidity, low ppt = alpine desert
Silversword trichomes : Silversword trichomes
Slide13 : (Melcher et. al 1994)
Unusual features : Unusual features Pectic warts
Secondary growth
Greenswords (2) : Greenswords (2) Argyroxiphium grayanum Argyroxiphium virescens hybrid
Changes in soil characteristics below Argyroxiphium : Changes in soil characteristics below Argyroxiphium Soil below silversword increased in water and nutrient retention, lower temperature (18C), greater nutrient concentration for up to 7-9 yrs post mortum.
Therefore good for current survival and future offspring who may be close in proximity to parent.
(Perez 2001)
Genus #2 - Wilkesia : Genus #2 - Wilkesia W. gymnoxiphium
grows on pockets in eastern Kaua’i (oldest high island) and may prefer certain soil types
Dry, shrubby forest
2 species: Wilkesia gymnoxiphium & Wilkesia hobdyi
Wilkesia gymnoxiphium : Wilkesia gymnoxiphium
Slide19 : Wilkesia gymnoxiphium Wilkesia gymnoxiphium Inflorescence with whorls of heads, all discoid flowers
Wilkesia hobdyi : Wilkesia hobdyi Freely branching, decumbent to erect, endangered, grows only on Kaua’i, restricted to very dry ridges (75 - 100cm ppt / yr, elevation 275 - 400m)
Wilkesia hobdyi : Wilkesia hobdyi
Genus #3 - Dubautia : Genus #3 - Dubautia Most “recent” genus
21 species with differential spatial and habitat distribution
Found on Kaua’i, O’ahu, Moloka’i, Lana’i, Maui, Hawai’i
2 other mainland islands have no Dubautia
17 out of 21 species of Dubautia are single- island endemics
Slide23 : D. ciliolata D. plantaginea D. scabra D. latifolia
Movie Part IDubautia species : Movie Part I Dubautia species
Slide25 : D. latifolia (vine) – “reticulate vein pattern with polygonal areoles containing numerous free-terminating veins” D. microcephala (left)
D. linearis (right) W. gymnoxiphium (Carlquist 1959) Veination patterns in Dubautia and Wilkesia
Dubatia herbstobatae : Dubatia herbstobatae
Dubatia arborea : Dubatia arborea
Dubautia menziesii - kupaoa : Dubautia menziesii - kupaoa
Dubautia waialealae : Dubautia waialealae
Dubatia latifolia (vine) : Dubatia latifolia (vine)
D. laevigata : D. laevigata Dubautia laevigata
Dubautia pauciflorula : Dubautia pauciflorula
2 studies in conservationFriar et. al 2000A. sandwicense in bad shape Friar et. al 2001A. kauense in good shape : 2 studies in conservation Friar et. al 2000 A. sandwicense in bad shape Friar et. al 2001 A. kauense in good shape
Habitat divergence : Habitat divergence Elevation from 75 to 3750m
Habitats of dry shrublands, dry forests, subalpine shrublands, subalpine forests, alpine deserts, mesic forests, wet forests, bogs, young lava flows (Carr 1985)
Physiological and morphological divergences : Physiological and morphological divergences Different tissue and elastic properties to maintain turgor at low water potentials (Robichaux 1985)
Different cell structures - especially Dubautia,
Wet environments – Thin cuticle, thin leaves, loose mesophyll
Dry environments – Thick cuticle, thick leaves, compact mesophyll, extracellular mesophyll, and white hairs (Carlquist 1958)
Veination –Dubautia latifolia – highly reticulate; Wilkesia – monocot-like veination with few crosscutting veinlets; Others – subparallel or longitudinally directed veins (Givnish & Sytsma 1997)
Who are the ancestors of silversword alliance? : Who are the ancestors of silversword alliance? Tarweeds found in California “floristic province” = CA and Mex.
Shrubby, sprawling plants
Similar in floral morphology and anatomy to silverswords
Sticky substance on flowers and fruits
Arrived in Hawaii on bird feathers (most likely) roughly 5 mya (Baldwin & Robichaux 1995)
What’s in a name? – “Tarweeds” : What’s in a name? – “Tarweeds” Tarweed A. sandwicense Raillardiopsis muirrii
The original silversword was a polyploid… what kind of polyploid? : The original silversword was a polyploid… what kind of polyploid?
Hypothesis for polypolidy (n = 14) : Hypothesis for polypolidy (n = 14)
Hypothesis for polypolidy (n = 14) : Hypothesis for polypolidy (n = 14) Best explanation
In what way did the silverswords move around Hawaii in terms of biogeography and habitats? : In what way did the silverswords move around Hawaii in terms of biogeography and habitats?
Biogeography & phylogeny : Biogeography & phylogeny Minimum inter-island dispersal and large ecological divergence
Generally westward to eastward movement
Kaua’i, Oahu, Maui Nui – once contiguous islands facilitated this movement
How do we investigate these evolutionary relationships? : How do we investigate these evolutionary relationships?
Laboratory methods of investigation : Laboratory methods of investigation Cytogenetic & hybridization analysis
Nuclear DNA (nDNA)
Chloroplast DNA (cpDNA)
Mitochondrial DNA (mDNA)
Ribosomal DNA (rDNA)
Isozymic analysis
Q: How do silverswords evolve so fast? : Q: How do silverswords evolve so fast? Problem: rates of morphological evolution are generally not correlated with rates of molecular evolution… how is this possible?
ASAP3/TM6 – controls petal and stamen development
ASAP 1 – controls floral primordia and sepal and petal identity
Rapid regulatory gene mutations relative to the number of mutations of structural genes.
(Baldwin & Sanderson 1998)
Q: How fast do silverswords evolve relative to continental groups? : Q: How fast do silverswords evolve relative to continental groups? Kure 29 mya = oldest island
Actually Compositae is more recent (mid-oligocene ca. 25 mya)
Shift about 15 mya from wet summer to dry summer
Tarweeds begin to diverge
Used ITS (internal transcribed spacer) region of nuclear DNA
Excluded annuals in analysis b/c higher rate of evolution
(Baldwin & Sanderson 1998)
Slide55 : Found silverswords are “well nested” in tarweeds because left N. America after tarweeds diverged
Today tarweeds ca. 114 species in 17 genera
Estimated age of arrival in Hawaii to be 5.2 ± 0.8 mya which is age of Kaua’I (5.1 ± 0.2 mya; is the oldest high island)
Slide56 : Other species are older on Hawaii
Drosophila > 10 mya
Lobelioids 15 mya
Honeycreepers 7-8 or 15-20 mya
Older ancestor is possible from N. Am, but only one lineage survived at 5.2 mya
Slide57 : Divergence rate is 0.56 ± 0.17 species / million yrs
Angiosperm families (0.12 species / million yrs)
Rodent families (0.22 to 0.35 species / million yrs)
African large mammals (0.0 to 0.39 species / million yrs)
However early Neocene horses show 0.5 to 1.4 species / million yrs) which indicates fast radiation then slow. Similar to above rate for silverswords.
Likely that early radiation is very fast then slows
Hybrids : Hybrids Today’s silverswords are polyploid
Most silverswords are n=14 with few n=13 in Dubautia subgroup
Was original ancestor a hybrid derived from allopolyploid or autopolyploid individual?
Movie Part IIHybrids : Movie Part II Hybrids
Hybridization : Hybridization
Trigeneric hybrid : Trigeneric hybrid
Study Carraway et. al 2001 : Study Carraway et. al 2001 D. ciliolata – 1855 lava flow
D. scabra – 1935 lava flow
Hybrids and introgression of only D. ciliolata.
D. ciliolata genes in hybrid swarm able to colonize 1935 lava flow.
I.e. occupy new habitat with hybridization and genetic restructuring.
Why is silversword alliance a “textbook” example of adaptive radiation? (Raven et. al 1992) : Why is silversword alliance a “textbook” example of adaptive radiation? (Raven et. al 1992) Includes ecology – long distance and local dispersal; morphology; physiology and adaptation
Includes evolution – phylogeny; hybridization; rates of evolution
Includes genetics – cpDNA; nrDNA; rDNA; isozyme; congruencies and incongruencies
Conservation – population dynamics; extinction; positive and negative human influences
Summary : Summary Single colonist (allopolyploid) – 3 genera today
Biogeographical movement west to east (mostly)
Most are single-island endemics
Radiate to different habitats on islands
Morphological and physiological adaptation
Systematics are well studied
Needs protection from humans and grazing
The End : The End
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