Download Chapter 7- Ecology of Phenotypic Plasticity

Chapter 7- Ecology of Phenotypic Plasticity
Why Ecology Distinct roles of plasticity in contrasting ecological scenarios
1. Stress-tolerant
2. competitive
3. ruderal
 Organisms that adjust to their environment through plasticity alter their own
relationship with the environment
(Ted 1) How can you tell if organisms are ecotypes or have an adaptively plastic
genotype and why can't the latter be the cause of the former?
Phenotypic Plasticity as an Adaptive Strategy
 Approached to the study of Phenotypic Plasticity
 Historical-comparative analysis of plasticity in different species who phenotypic
relationships are known
 Fitness-correlate- adaptiveness of any trait within a given environment
 Optimality- predicting which phenotype should be favored by natural selection in
each environment
(Marty 3) Why is there always a negative correlation between
plasticity and fitness? Couldn't there be a situation where a plastic
genotype is more fit in environment A and B as opposed to a nonplastic
genotype? (pg 161)
(Justin 2) Pigliucci states that "there may be constraints or costs affecting plasticity
acting simultaneously with natural selection..." Do costs (and/or benefits) "act" on a
phenotype or is phenotypic expression a result of varied environmental parameters,
costs, benefits, constraints, limits, etc.?
(pg 162)
(Justin 1) How do we address the evolution of plasticity for a trait whose expression may
be controlled via multiple pathways? (pg 163-164)
(Jon 1) Does Pigliucci really feel that the large amount of genetic variation for plasticity
is regrettable? Or do you think he means that if the genetic variation were just a little less
rampant then it would be easier to interpret? (pg163)
Empirical studies of Adaptive Plasticity
(Willow 1) According to Pigliucci when should a behavior be regarded as Plastic? (pg
169)
(Jon 3) ) Are all behavioral changes examples of plasticity? It appears that the daily
behavioral change of the spider is similar to many behavioral changes that occur in other
animals between day and night. Are all of these changes examples of plasticity? If so, are
they really 'equivalent to heterophylly in plants? (pg 169)
Plasticity Integration and the Bradshaw-Sultan effect
 Situations in which across-environment stability of a given phenotypic trait is
achieved because of marked plasticity in another trait
(Willow 2) Pigliucci implies that fitness can be considered a
phenotypic trait in its own right. Fitness of the whole organism would appear to a
somewhat unquantifiable quantity, made up of the combination of
fitnesses for a number of individual traits. Can just fitness be
considered a trait on its own? (pg 172)
(Will 2) Don't you always expect an organism to skimp on less important traits and
maintain consistency on important traits? Could you not phrase any
adaptive plasticity as an example of the B-S effect?
Are There Costs to Plasticity and DeWitt’s Paper
 If there were no costs or limits to plasticity then there would be the evolution of a
Darwinian Monster
 Costs of plasticity
1. Maintenance
2. Production
3. Information acquisition
4. Developmental instability
5. Genetic
 Limits to plasticity
1. Information reliability
2. Lag time
3. Developmental range
4. Epiphenotype problem
(Willow 3) Is it valid, when the field of phenotypic plasticity is still quite young,
to use model organisms to make generalizations about plasticity? (pg 468)
(Jon 4) DeWitt measures fecundity as total number of egg masses produced during the
course of the experiment. Should the quality of the eggs be taken into account when
measuring fecundity? DeWitt measure of growth rate is simply the shell profile. By
ignoring any internal structural changes, how can we be certain that he is actually
measuring shell production costs?
(Greg 1) Dewitt uses the developmental range hypothesis in the snail experiment. Does
this hypothesis really provide an appropriate test for this system, since only a single
population was sampled that is presumably exposed to both types of predators? (page
472)
(Marty 1) Why aren't costs of plasticity measured in the ultimate context-that
of annual or lifetime production of offspring? DeWitt tests family fecundity, but doesn't
say if that is lifetime fecundity or not. Even if there is no cost directly to
fitness, it might be the best place to start looking for costs if we're
to assume the Bradshaw-Sultan effect.
(Marty 2) Why is it not intuitive that there might be production costs? How does
one arrive at production costs and maintenance or genetic costs being
equal?
(Will 1/ Greg 2) Is Pigliucci correct to say that expressing the wrong phenotype in a
given environment is not a cost of plasticity? Is it possible that this signal detection
constraint is the most significant cost of all in phenotypic plasticity? If a plastic
individual has lower fitness than a non-plastic individual in a given environment, isn't
that the definition of a cost? (pg 179)
(Amber 1) Dewitt suggests in the discussion that it "appears at present as if such
constraints are neither universal nor great in magnitude. Costs and limits of plasticity may
only be present for some plastic traits and for some organisms or populations." If so, how
does this affect the way we think about "Darwinian monsters?" What would keep them
from evolving? (p. 478)
(Amber 2) Neither Dewitt nor Pigliucci give an example of Epiphenotype problem. Is
there one? If not, how did Dewitt come up with this? Is it testable?
Conclusions
(Will 3) . Where should the field go in terms of
studies of the ecology of plasticity? What are the important unanswered
questions? What types of studies need to be done?
Full Questions:
Marty
1) Why aren't costs of plasticity measured in the ultimate context-that
of annual or lifetime production of offspring? Even better- why not
look at the output of these offspring as the ultimate expression of
fitness (in order to correct for some of the Bradshaw-Sultan effect).
Throughout Pigliucci's section on costs and the paper, a wide variety of
options for measuring costs are included- the van Tienderen method (and
derivations thereof), molecular over- and underexpression of a trait
(does molecular biology still only 'inform' us here?), and reduced
fitness studies in wrongly expressed traits. He never actually forwards
the idea of measuring fitness as it is typically thought of (some
function of survival and fecundity). I know that the Bradshaw-Sultan
effect is supposed to cover this, but it might not. DeWitt seems to
address this in testing family fecundity, but doesn't say if that is
lifetime fecundity or not. Even if there is no cost directly to
fitness, it might be the best place to start looking for costs if we're
to assume the Bradshaw-Sultan effect.
2) Along the lines of testing for costs, why is it not intuitive that
there might be production costs? It seems that production costs would
be a) the easiest to test and b) more common than either Developmental
Instability or Genetic costs. I can think of some pretty simple ways to
test for production costs in plastic genotypes. They might not reveal
any costs, but they aren't necessarily hard to test for, and they
certainly are distinct from any of the other costs of Plasticity. How
one arrives at production costs and maintenance or genetic costs being
equal is not at all intuitive or obvious to me.
3) I am a little confused by Pigliucci's argument about the Silver Spoon
effect. First- why is there always a negative correlation between
plasticity and fitness? Couldn't there be a situation where a plastic
genotype is more fit in environment A and B as opposed to a nonplastic
genotype? In this case, wouldn't the correlation be positive? Secondin Pigliucci's example (pg. 161) he compares relatively larger leaves in
a stressed environment with absolutely larger leaves in a 'good'
environment. Shouldn't he be comparing either relative size or
absolute size, but not both? Also, it doesn't seem like this is relavent
at all to a negative correlation. As long as more plastic genotypes
exhibit higher fitness in both environments.
Willow
1. In Pigliucciís discussion of ìwithin-individual plasticityî (p. 169),
he seems to be accepting spider web building as an example of
behavioral plasticity. This confused me, since it seems like he is
somewhat reluctant to discuss behavioral plasticity. Where does
he draw the line and term a behavior plastic?
2. On p. 172 Pigliucci implies that fitness can be considered a
phenotypic trait in its own right (ìThis is a situation in which
across-envirinment stability of a given phenotypic trait (e.g.
fitness)Öî) Fitness of the whole organism would appear to a
somewhat unquantifiable quantity, made up of the combination of
fitnesses for a number of individual traits. Can just ìfitnessî be
considered a trait on its own?
3. At the top of p. 468, DeWitt describes his choice of a snail to test
several hypotheses about costs and limits of phenotypic plasticity.
Is it valid, when the field of phenotypic plasticity is still quite young,
to use model organisms to make generalizations about plasticity?
It seems to me that plasticity is such a complex topic, which has
importance consequences for other areas of biological inquiry
and, since plasticity is difficult to tease apart as an individual trait,
that it might be premature to draw conclusions about plasticity
between groups of species. There seem to be a lot of theories
about the effects of plasticity on fitness, without much data to back
them up. Shouldnít we wait until we understand how plasticity
functions in more species before trying to draw broad conclusions
between groups?
Amber
1. Pigliucci brings up the relationships among plasticity, genotypes, generalists, and specialists in this chapter. An
organism that has plasticity for a focal trait and is adapted to a range of environments is termed a generalist (p. 160). On
p. 174, however, he is careful to point out that plasticity must have costs and limits, or else we'd expect to see the
evolution of "Darwinian monsters." In the paper, though, Dewitt suggests in the discussion (p. 478) that it "appears at
present as if such constraints are neither universal nor great in magnitude. Costs and limits of plasticity may only be
present for some plastic traits and for some organisms or populations." If so, how does this affect the way we think about
"Darwinian monsters?" What would keep them from evolving?
2. One of the limits of plasticity suggested by Dewitt is the "Epiphenotype problem" in which "add-on phenotypes may be
less effective than developing the phenotype during early ontogeny (p. 467)." Neither Dewitt nor Pigliucci give an example
of this type of limitation. Is there one? If not, how did Dewitt come up with this? Is it testable?
Jon
Pigliucci:
1) A silly question to start with; Do you think Pigliucci really feels
that the large amount of genetic variation for plasticity is
regrettable(pg163)? Would his book have been written if it were otherwise?
Or do you think he means that if the genetic variation were just a little
less rampant then it would be easier to interpret?
2) What is a Pindaric flight of imagination (pg163)?
Answser (sort of): Pindar was a Greek poet, and Pindaric refers to the
style of poetry that he wrote which is apparently an ode with two metrical
forms. I'm guessing here that these were fanciful odes? My dictionary
doesn't say.
3) pg 169 Are all behavioral changes examples of plasticity? Or are they
restricted to examples like the spider where there is a physical product
(the web) that's changed in different environments. I think here I'm
slipping back into my old habits of "everything is plastic" because P.
doesn't do a very good job (in my mind) of explaining why these
within-individual changes are unique. It appears to me that the
daily behavioral change of the spider is similar to many behavioral
changes that occur in other animals between day and night. Are all of
these changes examples of plasticity? If so, are they really 'equivalent
to heterophylly' in plants?
DeWitt:
1) I have to take issue with at least two of DeWitt's measurements in this
study. The first is his measure of fecundity. He measured fecundity as the
total number of egg masses produced during the course of the experiment.
This ignores any within or between family variation in the number or
quality of the embryos within a mass. It may be that stressed individuals
produce smaller egg masses or fewer embryos/mass than do unstressed
individuals. I think to accurately measure fecundity costs this needs to
be addressed. Second, his measure of growth rate is simply the shell
profile. There may be changes to the internal structure of the shell which
reduce the susceptibility to predation, eg whorl number or shell
thickness. Neither of these is considered as a possibility and thus I am
left unconvinced that he's accurately measuring shell production costs .
Will
1. P. 179 - Pigliucci says that the consequences of expressing the wrong
phenotype in a given environment are not costs of plasticity. However, it
is simple to prove using signal detection analysis that any mechanism that
acts as a phenotypic switch will be constrained by the inability to
minimize missed detections and correct rejections simultaneously.
Therefore, any plasticity will have a cost for expressing the wrong
phenotype in a given environment.
Is he correct to say that expressing the wrong phenotype in a given
environment is not a cost of plasticity?
Is it possible that this signal detection constraint is the most
significant cost of all in phenotypic plasticity?
To quote Haven Wiley: "Everything is a signal detection problem."
2. I have a hard time understanding where the field should go in terms of
studies of the ecology of plasticity. What are the important unanswered
questions? What types of studies need to be done?
3. "The Bradshaw-Sultan Effect," where plasticity in one trait allows
stability in another trait (p. 172), does not seem surprising to me.
Don't you always expect an organism to skimp on less important traits and
maintain constistency on important traits? Could you not phrase any
adaptive plasticity as an example of the B-S effect?
e.g. - Caterpillars that can change from catkin to twig morph and do so
adaptively are plastic for that trait but stable in time to pupation and
egg production!!!! Another clear case of the B-S effect!
Greg
On page 472 of the Dewitt paper, he/she(?) discusses the developmental range
hypothesis and how it was tested in the snail experiment. Does this system
really provide an appropriate test for this system, since only a single
population was sampled that is presumably exposed to both types of
predators? It seems like it would be more appropriate to test this idea by
sampling both plastic populations and populations that are somewhat
genetically differentiated and that are only exposed to one type of predator
and therefore may be more specialized and less plastic (apologies for the
run-on).
On page 179 Pigliucci states that expressing a maladaptive phenotype in a
given environment is not a cost of plasticity. If a plastic individual has
lower fitness than a non-plastic individual in a given environment, isn't
that the definition of a cost?
Where the hell is the Arnold 1994 reference cited on page 476 of Dewitt?
Ted
I know an ecotype is a genetically specialized population that is adapted to
the local environment. Pigliucci tells us that an ecotype is at the opposite
end of the spectrum of an adaptively plastic genotype. Could somebody
explain that sentence to me. Does that mean that an ecotype, by definition
cannot express genes for plasticity? I've seen some species of gastropods
that are found both subtidally and intertidally. They lay different egg
clutch morphologies depending on the place and oxygen content. The egg cases
are molded by the mother's foot which has different musculature depending on
where she lives. So my question is... how can I tell if these snails are
ecotypes or have an adaptively plastic genotype and why can't the latter be
the cause of the former?
Justin
On page 163-164 P lists several of Sultan's points to consider as
students of the ecology of plasticity and adds a 6th of his own on pg.
164. This statement struck me as quite intriguing, in particular his
example re: temperature stress. If one is interested in organismal
response to environments that lie on a continuum, such as temperature,
yet the responses to these varied environments are distinct in the
manner suggested by P, then how do we define our trait of interest?
In this example, how do we determine the boundaries of temperature
response mediated by cold stress molecular machineries versus heat
stress mol. mach.? How do we address the evolution of plasticity for
a trait whose expression may be controlled via multiple pathways? I
don't have any answers to these questions but this topic seems quite
interesting.
My next question is more one of semantics. On pg. 162, P states
that "there may be constraints or costs affecting plasticity acting
simultaneously with natural selection..." Do costs (and/or
benefits) "act" on a phenotype or is phenotypic expression a result of
varied environmental parameters, costs, benefits, constraints, limits,
etc.?