Transcript Adaptation with stomata

Announcements
• Next week: THANKSGIVING, NO CLASS!
• Work on Group Project Presentation
(p170—checklist p 171-172)
• In 2 weeks, Functional Response Lab
Today’s Objectives
• Examine examples of adaptation &
convergent evolution in the greenhouse
• Explore the relationship between stomata
density and climate—a study of adaptation?
• Consider how adaptations are studied and
the link between ecology and evolution
Adaptation
Heritable characteristic that improves organism’s fitness
(survival & reproduction)
Schemske et al.
Why do organisms ‘match’ their environment?
• the ‘match’ is genetic
fitness
Natural selection:
differential survival and reproduction of individuals
based on genetic differences in some trait(s)
adaptation
• the ‘match’ is induced by environment
Adaptation
• Any heritable characteristic of an organism
that improves its ability to survive and
reproduce in its environment.
• Also used to describe the process of
genetic change within a population, as
influenced by natural selection.
Adaptation ≠ Acclimation
• Acclimation
– individual changes over short period of time to
survive better in environment
– Ex: shed winter fur in summer
• Adaptation
– a population evolves to be better suited to its
environment via natural selection
& genetic change over
multiple generations
– Ex: evolution of cryptic coloring
to avoid predation
flickr
Natural Selection
• Selection acts on phenotypes
– If brown beetles are less visible to predators
than green beetles
– Then brown beetles will be more likely to
survive & reproduce
• Evidence is seen in populations over
generations
evolution.berkeley.edu
Natural selection – key points
differential survival and reproduction of individuals
based on genetic differences in some trait(s)
• For adaptations to evolve:
- differences in the trait must cause differences in
fitness
- differences in the trait must be heritable
• Fitness depends on the environment.
local adaptation
Ecology & Evolution are interconnected
• Ecology
– study of interactions between organisms and
their environments
• Adaptation
– An evolved characteristic of an organism that
improves its fitness in its environment
• Thus, adaptations are both ecological &
evolutionary
Rainforest
Ecology
• Light competition
• Lots of rain
– Promotes fungal growth
• High biodiversity
• Adaptations include
– Epiphytes, vines, leaf
morphologies
Desert
Ecology
• Water limited
• Temperature extremes
• Adaptations include
– CAM, annual life cycle, water
storage
Stomata
• Structures on the
outer layer of
plants
• “Mouth” in Greek
• Allow gases such
as carbon dioxide,
water vapor and
oxygen to move
rapidly into and out
•Trade-off between
staying open and
obtaining CO2, and
staying closed to reduce
water loss
Stomata density varies across
plant species and habitats
http://www.scienceclarified.com/IoMa/Leaf.html
http://radioweblogs.com/0105910//20
http://www.microscopyuk.org.uk/micropolitan/botany/fra
Stomata study
• 1. Choose a plant in the greenhouse or outside.
Apply an even, thin layer of clear nail polish on to
the underside of the leaf surface.
• 2. Wait till the polish dries completely.
• 3. Gently lift the sides to peel off the nail polish
without tearing it.
• 4. Place the peeled layer onto a slide (without any
creases).
• 5. Observe under a 10 or 40x lens and count the
number of stomata. If the number of stomata is too
numerous to count, just count a portion of the field
of view and multiply the results accordingly.
• 6. Calculate stomatal densities per cm2.
Slide tips and greenhouse use
• Stay on path and be respectful of plants
• Use plant tips, or herbivore-attacked
leaves
• AVOID—small plants, healthy, centrallylocated leaves, and Wellwichia
• Do not choose fuzzy or moist leaves—nail
polish does not come off
At Greenhouse
• IN PAIRS: Use worksheet (pg 140) to tour
greenhouse & identify different adaptations
• Find examples of 10 adaptations on sheet
• INDIVIDUALLY: Make a stomata slide from
a species you can identify. Your group
must have at least one rep from desert,
temperate, and rainforest habitats
TAKE: p 140, a pencil, nailpolish
Find stomata densities
• Count all you see in a field at either 10x or
40x
• Divide your stomata number by the
approximate area of your field (for either
10x or 40x)
• Look up average temperature, rainfall,
humidity?, etc. of your plant’s habitat
• Put all information on the board
While you wait
• Answer the questions on the handout.
• For question 2, read up on an adaptation
you think is interesting (but not that we
have discussed) using the web. Consider
using You-Tube.
How do we know if a trait gradient
is caused by a local adaptation?
• Trait variation across the gradient is
greater than variation within the gradient
• Observed trait variation has a genetic
basis
• Trait variation must have evolved in that
location, and not be from an already
different founder population
• Variation must have an effect on survival
in that habitat
Testing for local adaptation
Observation: differences in stomata density is
correlated with humidity and temperature
Dry
Wet
How can we test whether the difference in stomatal density
is an adaptation? What other explanations are possible?
Testing for adaptation:
reciprocal transplant experiment
Dry Habitat
Wet Habitat
effective
predators
Plant Fitness
Prediction
Wet
Dry
Habitat
If we see this pattern….
Stomata density is likely to be an adaptive
trait.
•Plants with LOW stomatal density
have high fitness at DRY habitat
•Plants with HIGH stomatal density
have high fitness at WET habitat
Wrap-up the study
• IN PAIRS Use the info on the board. On a new sheet of paper,
make either 1 bar graph of the mean stomata densities and
standard errors from each climate AND 1 bar graph of the %
closed in each climate OR make line graphs comparing the 3
climate variables to stomata densities.
• Answer these questions on your separate sheet:
1) Using class data, do you think your prediction was right?
Why?
2) What is one flaw of this study?
3) Could a study like this one conclusively show stomata
densities are the result of a local adaptation? Explain.
4) Do you think plants grown in a greenhouse would have
different #s of stomata than the same species in nature? If
yes, does this support or refute the idea that s. densities are
adaptive? Explain.