Occurrence of Polyploidy
Part 1. Mutation Events Part 2. In Species and Genera Part 3. Plant Evolutionary History • Autopolyploid mutations:
~1/500 plants in diploid pops are neopolyploid (triploids and tetraploids most common)
• Allopolyploid mutations:
Interspecific hybridization is rate limiting step
Neopolyploids common when plants cultivated and experimentally crossed • Variation Among Plant Genera:
~35% of species are polyploid relative to the base chromosome number of their genus
Small variation in occurrence explained by high level classification (Family, Order, etc.)
Complication of deciding what a species is…
• Incidence in Evolutionary History:
Incidence tracked by genomic analysis of gene families (sudden increases = polyploidy)
Many extant plants are diploidized
Base ploidy level among extant angiosperms is (at least) paleo-hexaploid
Polyploidy in Grasses: Major Examples
Part 1. Autopolyploidy Part 2. Allopolyploidy Big Bluestem (Andropogon gerardii) • Autopolyploid complex with ecological races
• 2n = 2x, 4x, 6x, 8x, 10x
• Hexaploids and octoploids common in Great Plains
• Variable within pops
• Kathleen Keeler (UNL) Loretta Johnson (KSU) Big Bluestem (Andropogon gerardii) Big Bluestem (Andropogon gerardii) Big Bluestem (Andropogon gerardii) Orchardgrass (Dactylis glomerata) • Autopolyploid complex with multiple subspecies
• 2n = 2x and 4x
• Native to Europe, Africa (introduced worldwide)
• Ecological differences (only tetraploids invasive)
• Rosalyn Lumaret (FR) Orchardgrass (Dactylis glomerata) Orchardgrass (Dactylis glomerata) Common Reed (Phragmites australis) • Autopolyploid complex with ecological races
• 2n = 4x, 6x, 8x, 10x, 12x (4x and 8x most common)
• Native to USA but rapid expansion since 1900s (subsp. americanus?)
• Ploidy effects but unclear if relevant to invasion Common Reed (Phragmites australis) Common Reed (Phragmites australis) Common Reed (Phragmites australis) Common Reed (Phragmites australis) Common Cordgrass (Spartina anglica)
• Allopolyploid species 2n = 12x
• Formed ~1860 in UK S. alternifolia (e. USA, 6x) S. maritima (Europe, 6x)
• Planted (erosion control), now highly invasive
• Malika Ainouche (FR) Common Cordgrass (Spartina anglica) Common Cordgrass (Spartina anglica)