Adaptation of Mimulus guttatus Phrymaceae to serpentine soil

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Adaptation of Mimulus guttatus (Phrymaceae) to
serpentine soil Kristy U. BradyDepartment of
Biology University of Washington
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Many Thanks! Toby Bradshaw Meade Krosby Liz
Van Volkenburgh Suzie Graham Josh
Tewksbury Christina Pince Sarah
Reichard David Haak Art
Kruckeberg Margaret Hendrick Dick Walker Joe
Callizo, Paul Aigner Cathy Koehler Doug Ewing,
Jeanette Milne, Paul Beeman Judy Farrow,
Patti Owens, Dave King Biology Staff
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Adaptive Evolution
Adaptation to novel environments leads to
speciation.
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• Serpentine Systems are Great for Studying
  Adaptive Evolution
• Extensive literature available
• Strong selection imposed by factors amenable to
  manipulative experiments in the field,
  greenhouse, and lab
• Differential adaptation demonstrated by
  reciprocal transplants
• Physiological differences between serpentine and
  non-serpentine races and sister taxa permit
  investigation of speciation mechanisms and
  evolutionary trajectories

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• Serpentine Soil
• Originates in the Earths mantle
• Adverse chemical conditions including
• Low CaMg
• Low levels of nutrients (e.g., P, K)
• High levels of heavy metals (e.g., Ni, Cr, Fe)
• Rocky and often steep with sparse vegetative
  cover
• Plant morphological responses include
• Reduced stature
• Xeromorphic foliage
• Highly developed root systems
• High rates of plant endemism

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Insight Into Mineral Nutrition Physiology
Magnesium deposits at White Seep, McLaughlin
Natural Reserve, California, USA
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Insight Into Endemism

• In California, USA, serpentine soil comprises
  1.5 of landscape, but hosts 13 of endemic
  plant species.
• 11 of CA plant taxa listed as threatened or
  endangered are serpentine endemics.
• (Safford, Viers, Harrison, 2005, Madroño.)

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Serpentinized Rock in Architecture
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Kruckeberg (1985) Two Strategies for Serpentine
Tolerance

• Endemic species
• Restricted to serpentine soil
• Bodenvag or indifferent species
• Widely distributed species with populations or
  races occurring on serpentine soil.

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• Mimulus guttatus
• (Common Monkeyflower, Yellow Monkeyflower, Seep
  Monkeyflower)
• Wide-ranging distribution.
• Found in seeps, riparian areas.
• A bodenvag species populations on and off
  serpentine soil.
• Thrives in a greenhouse environment.

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Mimulus as a study system

• Long history of study
• Phylogeny
• Genetic genomic tools

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Location
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Survival After 6 Weeks on Serpentine Soil (n11)
Photos taken 6 days after transplanting onto
treatment soil.
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Segregating Population
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Segregating Population
NP
F2
SP
F2
F2
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First Transplant
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Transplant Details

• Serpentine soil collected from McLaughlin Natural
  Reserve, CA.
• Plants germinated on greenhouse soil.
• Transplanted onto treatment soil 2 weeks after
  germination.
• Growth, flowering, and red phenotype data
  collected every other day for 4-5 weeks after
  transplanting.

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Flowering as a Fitness Indicator

• Proportion of Individuals that Flowered

Mode of inheritance F1s suggest dominance
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Red Phenotype as a Fitness Indicator

• Mean red score for last 11 days of transplant

Number of effective factors (Lande 1981)
6.5Maximum magnitude of leading factor 39
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Second Transplant
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Soil Elemental Differences Examined
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Two Sets of Hypotheses Tested

• Mechanistic hypotheses
• Adaptive differences between serpentine plants
  (SP) and non-serpentine plants (NP) that enable
  SP to survive on serpentine soil.
• Ca-limiting hypotheses
• Testing whether supplementing serpentine soil
  with Ca enables NP to survive.

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Hypotheses
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg High Mg requirement Mg
toxicity avoidance Heavy metal toxicity avoidance
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg Mg toxicity susceptibility Heavy metal
toxicity susceptibility
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Transplant Details

• Serpentine soil collected from McLaughlin Natural
  Reserve, CA.
• Plants germinated on greenhouse soil.
• Transplanted onto treatment soil approx. 2 weeks
  after germination.
• Plants watered with dH2O or a 4mM Ca(NO3)2
  solution.
• 10 days after transplanting onto treatment soil,
  leaf tissue collected for ICP-MS.

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Hypothesis 1 CaMg

• Mechanistic Loew May (1901) low CaMg of
  serpentine soil problematic for non-serpentine
  plants.
• SP tolerate the low CaMg ratio in serpentine
  soil better than NP.
• Prediction SP preserve a higher CaMg in
  their leaf tissue than NP when grown on
  serpentine soil.

• Ca-limiting Kruckeberg (1954) addition of Ca
  (CaSO4) to serpentine soil permitted
  non-serpentine strains of Phacelia californica to
  survive on serpentine soil.
• Supplementing Ca to serpentine soil ameliorates
  the serpentine effect by increasing Ca
  availability.
• Prediction NP have a higher CaMg in their
  leaf tissue when grown on serpentine soil
  supplemented with Ca.

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Hypothesis 1 CaMg
n11, one-tailed t-test, experiment-wise P
0.05, Bonferroni corrected
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Conclusions for M. guttatus
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg
?
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg
?
? hypothesis not supported by data ?
hypothesis supported by data
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Hypothesis 2 Mg requirement

• Mechanistic Madhok Walker (1969) The
  serpentine sunflower Helianthus bolanderi ssp.
  exilis requires high external levels of Mg for
  optimal growth.
• For optimal growth, SP require higher levels of
  Mg externally than NP.
• Prediction Without high levels of Mg
  externally, SP will experience a reduced growth
  rate.

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Hypothesis 2 Mg requirement
n11, one-tailed t-test, experiment-wise P
0.05, Bonferroni corrected
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Conclusions for M. guttatus
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg High Mg requirement
? ?
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg
?
? hypothesis not supported by data ?
hypothesis supported by data
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Hypothesis 3 Mg toxicity

• Mechanistic Proctor (1970 1971)
  non-serpentine plants are susceptible to Mg
  toxicity on serpentine soil.
• SP avoid Mg toxicity whereas NP are susceptible
  to Mg toxicity on serpentine soil.
• Prediction SP maintain lower levels of Mg in
  their leaf tissue than NP when grown on
  serpentine soil.

• Ca-limiting Proctor (1971) addition of Ca
  (CaSO4 or CaCO3) to serpentine soil ameliorated
  Mg toxicity in oats (Avena sativa var.
  Victory).
• Supplementing Ca to serpentine soil decreases
  amount of Mg taken up by NP.
• Prediction NP contain lower levels of Mg in
  their leaf tissue when grown on serpentine soil
  supplemented with Ca.

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Hypothesis 3 Mg toxicity
n11, one-tailed t-test, experiment-wise P
0.05, Bonferroni corrected
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Conclusions for M. guttatus
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg High Mg requirement Mg
toxicity avoidance
? ? ?
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg Mg toxicity susceptibility
? ?
? hypothesis not supported by data ?
hypothesis supported by data
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Hypothesis 4 Heavy metal toxicity

• Mechanistic
• SP exclude potentially toxic heavy metals present
  at high levels in serpentine soil (Cr, Ni) better
  than NP.
• Prediction SP maintain lower levels of toxic
  heavy metals in their leaf tissue than NP when
  both are grown on serpentine soil.

Ca-limiting b. Supplementing Ca to serpentine
soil decreases the quantity of potentially toxic
heavy metals taken up by NP, thus ameliorating
the serpentine effect. Prediction NP
contain lower levels of heavy metals in their
leaf tissue when grown on serpentine soil
supplemented with Ca.
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Hypothesis 4 Heavy metal toxicity
n11, one-tailed t-test, experiment-wise P
0.05, Bonferroni corrected
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Conclusions for M. guttatus
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg High Mg requirement Mg
toxicity avoidance Heavy metal toxicity
avoidance
? ? ? ?
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg Mg toxicity susceptibility Heavy metal
toxicity susceptibility
? ? ? Cr ? Ni
? hypothesis not supported by data ?
hypothesis supported by data
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Conclusions for M. guttatus
Mechanistic SP are able to survive on serpentine
soil because they are equipped with one or more
of the following traits, which NP lack
Tolerance of low CaMg High Mg requirement Mg
toxicity avoidance Heavy metal toxicity
avoidance
? ? ? ?
Ca-limiting Supplementing serpentine soil with
Ca ameliorates serpentine conditions for NP by
altering the following
Low CaMg Mg toxicity susceptibility Heavy metal
toxicity susceptibility
? ? ? Cr ? Ni
? hypothesis not supported by data ?
hypothesis supported by data
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More than one way to solve a problem Nectar
feeding birds
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More than one way to solve a problem Serpentine
tolerance

• Likely to be more than one physiological
  mechanism that confers tolerance to serpentine
  soil.
• Ion uptake discrimination
• Ion translocation and/or sequestration properties
• Chelation

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• Future Work
• Investigate serpentine tolerance at the root
  level using chemically-defined nutrient
  solutions.
• What is happening at the root-soil interface?
• How does membrane permeability differ between
  serpentine and non-serpentine plants?
• How are elements stored in the root?
• Investigate genetic component of serpentine
  tolerance.
• Generate a QTL map
• Develop NILs

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• Future Work
• Investigate evolutionary trajectories of
  different serpentine populations.
• Do different populations arrive at the same
  solution to the serpentine problem or are there
  multiple pathways to tolerance within a species?

• In California, USA, serpentine soil comprises
  1.5 of landscape, but hosts 13 of endemic
  plant species.
• 11 of CA plant taxa listed as threatened or
  endangered are serpentine endemics.

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Many Thanks!
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Soil Elemental Differences (Complete Table)
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