and directional evolution Greg and Ray and Tim Proteaceae are the - - PowerPoint PPT Presentation

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Sep 03, 2023 353 likes •631 views

Cell size, genome size, plant strategies and directional evolution Greg and Ray and Tim Proteaceae are the best organisms in the world a short stroll through leaf anatomy Palisade Leaf (lamina) Vein thickness Vessels Epidermis see

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Cell size, genome size, plant strategies and directional evolution…

Greg and Ray and Tim

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Proteaceae are the best organisms in the world

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a short stroll through leaf anatomy

Palisade Vein Vessels Epidermis see detail… Leaf (lamina) thickness

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Detail of an epidermis

Epidermal cells stomate

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Epidermis in surface view

small epidermal cells small stomates high stomatal density big epidermal cells big stomates low stomatal density

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paradermal section showing vein density

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a short stroll through leaf anatomy

Palisade cells Vein Vessels Epidermis with stomata Leaf (lamina) thickness

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unified changes in leaf cell size (across 80 million years!)

stomatal size epidermal cell size vessel diameter leaf thickness palisade cell size phenotypic phylogenetic significant correlations

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Do we expect directional evolution

* Systematic changes over the Cenozoic (last 65 million years)

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Stomatal size affects photosynthetis

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packing density and stomata

10 20 30 40 50 60 70 80 90 200 400 600

stomatal length (μm) abaxial stomatal density (mm-2)

hypostomatic species amphistomatic species

stomatal length ~ 1/√stomatal density

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small stomata are more efficient

per stomate conductance scales linearly with

size

number of stomates scales 1/quadratically

with size

small stomates lead to high conductance

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matching water supply (veins) and demand (stomata)

functional links

1/stomatal size vein density stomatal density 1/vessel size packing constraints

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Expected directional evolution

1 CO2 model

– low CO2 = a need for greater conductance – small stomata are more efficient – guard cell size should have decreased

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genetic link

genome size
other genetic factors

10 100 0.9 9 90 guard cell length (microns) genome size pg

Grevilleoideae Persoonioideae + Bellendena Proteoideae + Symphynematoideae

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Do we expect directional evolution

1 CO2 model

– low CO2 = a need for greater conductance – small stomata are more efficient – guard cell size should have decreased

2 genome size model

– genome size drifts up (one-way path to obesity) – Guard cell should have increased

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strong evolutionary association with open

vegetation (versus rainforest)

leaf thickness
stomata on both leaf surfaces

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Do we expect directional evolution

1 CO2 model

– low CO2 = a need for greater conductance – small stomata are more efficient – guard cell size should have decreased

2 genome size model

– genome size drifts up (one-way path to obesity) – Guard cell should have increased

3 ecological model

– follows changes in habitat – mostly increase - as woodland replaced rainforest

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So, what has happened to stomatal size through time?

ancestral state analyses
fossils

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ancestral state reconstruction

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scatter plot of reconstruction versus age for each node

10 100 25 50 75

guard cell length (μm) - log scale Time (millions of years ago)

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but fossils say

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guard cell length (μm) - log scale Time (millions of years ago)

ancestral states fossils

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and it happens within clades

5 10 15 20 25 30 35 40 20 40 60 80

guard cell l length (μm) Time (millions of years ago

Banksieae

fossil ancestral states

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directional evolution

driver either

– habitat shift with global climate change – systematic trend in genome size

invalidates the ancestral state reconstructions