evolution phenotypic plasticity

1. Assignment
Subject : Crop Evolution GPB821
Presented by: Mr. Indranil Bhattacharjee
Student I.D. No.: 17PHGPB102
Presented to : Dr. G.M. Lal
Sam Higginbottom University of Agriculture, Technology &
Sciences
Allahabad-211007

2. Phenotypic Plasticity
• Ability of an organism to express different
phenotypes depending on the biotic or abiotic
environment
• Involves regulatory genes that switch on
structural genes given the appropriate
stimulus

3. Many trees and shrubs produce shade
leaves and sun leaves
• Shade leaves are thinner and much greater in
surface area than sun leaves
• How is the type of leaf determined?
– The genes which determine the shape of a
particular leaf are sensitive to light
– Specifically, the portion of the plant is responsive
to the ratio of far red light to red light

4. – Red light is absorbed by leaves higher in the
canopy but far red light passes through to the
ground
– Therefore, the ratio of far red:red light increases in
more shaded areas
– When the FR:R ratio exceeds a critical value, a leaf
will be formed as a shade leaf, which is much
more efficient at gathering light under darker
conditions (high surface area)

5. “Talking trees”
• Sugar maple • Poplar

6. Some vascular plants are known to
produce herbivore-deterrent compounds
• There is evidence that the production of these
allelochemicals can be induced
• Producing these compounds only when needed
presumably saves the plant energy
– Many of these allelochemicals degrade quickly,
making an inducible response even more
economical

7. Some researchers at Dartmouth
tested some sugar maples and
poplars to see if the production of
allelochemicals can be induced by
herbivores

8. The experiment involved tearing off
7% of the leaf area of each tree
• The level of allelochemicals was measured
before the “artificial herbivory” and 52
hours later
• For both sugar maples and poplars, an
increase in the production of
allelochemicals was seen after 52 hours

9. But the really cool result was . . .
• Control trees in the same environmental
chamber increased their production of
allelochemicals too
• This result suggests that an airborne cue from
plants that have been grazed alerts
surrounding trees to step up their chemical
defense
• Hence, the “talking tree” metaphor

10. The dogwhelk, Nucella lamellosa, a
common rocky intertidal snail along
the western North American coast

11. Cancer productus, a predator on
Nucella lamellosa

12. Phenotypic plasticity in Nucella
• Workers exposed some Nucella to water in
which Cancer productus was present, some
Nucella to water in which the metabolites of
recently damaged Nucella was present and a
control of water without either type of
chemical signal

13. Dogwhelks exposed to Cancer or to
the metabolites of Nucella increased
the length of the apertural teeth

14. Daphnia (water flea)

15. A backswimmer, a potent predator on
Daphnia

16. Phantom midge larva, another potent
predator on Daphnia

17. Helmeted and normal Daphnia

18. On coral reefs, competition for space is
intense

19. • Some corals use
particularly virulent
nematocysts (specialized
stinging organelles) to kill
competitors

20. The coral Agaricia grows elongate
sweeper tentacles when a competitor
comes in contact

21. Sweeper tentacles in the coral Agaricia

22. • The sea fan
Erythropodium and
the anemone Palythoa
both induce the
growth of sweeper
tentacles in Agaricia

23. Sweeper tentacles from an anemone

24. Mechanisms of Evolutionary Change
• Mechanisms that change allele frequencies in
populations:
– Natural selection
– Mutation
– Gene flow (migration)
– Genetic drift (sampling error)

25. Genetic Structure of Populations
• All the genes contained by the individuals of
population constitute the gene pool
• To understand the genetics of evolution, we study
the gene pool of a population rather than the
genotypes of its individual members
• Quantitative measures of the gene pool
– Genotype frequencies
– Allele frequencies

26. Scarlet
Tiger Moth

27. Scarlet Tiger Moth Genotype
Frequencies
• Collection from one locality in England yielded
the following numbers of genotypes: 452 BB,
43 Bb and 2 bb for a total of 497 moths
– f(BB) = 452/497 = 0.909
– f(Bb) = 43/497 = 0.087
– f(bb) = 2/497 = 0.004
– Total 1.000

28. Allele Frequencies
• Used by most population geneticists instead
of genotype frequencies
• Allele frequency =
number copies of a given allele
sum of all alleles in the population

29. Calculation of allele frequencies
• When two alleles are present at a locus (let’s call it
the A locus), we can use the following formula to
calculate the allele frequency of A. The frequency of
A is abbreviated as f(A) or p.
• p = f(A) = (2 x number of AA homozygotes) +
(number of Aa heterozygotes)
(2 x total number of individuals)

30. Example calculation
• Imagine a population of 1000 individuals with 353 AA, 494 Aa
and 153 aa individuals
• Each AA individual has two A alleles while each heterozygote
has one A allele
• p = f(A) = [(2 x 353)+ 494]/(2 x 1000 individuals)
• p = 1200/2000 = 0.60
• The total of all allele frequencies must be 1.0
• Only two alleles are involved at this locus
• We can therefore calculate q = f(a) = 1.0 - 0.6 = 0.4

31. PHENOTYPIC PLASTICITY
Degree to which an organism's phenotype changes depending
upon its current or past environment. Two organisms with the
same genotype (e.g., identical twins) may have different
phenotypes (e.g., one may be taller or heavier) if raised in
different environments; those differences represent phenotypic
plasticity. All organisms exhibit some degree of phenotypic
plasticity (e.g., an animal that receives more food will generally
be heavier than a genetically identical animal that receives less
food), but sometimes phenotypic plasticity can be extreme
(e.g., some fish become either male or female depending upon
the temperatures they were exposed to as an egg).

60. Thank you

61. References
Quentin C.B. Cronk, Richard M. Bateman, Julie A.
Hawkins edited 2002 Developmental Genetics and Plant
Evolution. The Systematics Association Special Volume
Series 65 Taylor & Francis.
Robert J Henry 2005 Plant Diversity and Evolution -
Genotypic and Phenotypic Variation in Higher Plants
CABI Publishing
Smartt J & Simmonds NW. 1995. Evolution of Crop
Plants. Blackwell.