Occurrence of Polyploidy

Part 1. Mutation Events Part 2. In Species and Genera Part 3. Evolutionary History • Autopolyploid mutations:

~1/500 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 ( glomerata) • Autopolyploid complex with multiple subspecies

• 2n = 2x and 4x

• Native to , (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 ( 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)