Transcript Genetics of Colonizing Species

Plasticity and local
adaptation in invasive
species
Recap of last time
We discussed THE ten hypotheses
We had a discussion about pre-adaptation..
Agreed that some level of preadaptation is
required for successful introduction
How do introduced species
succeed in new environments?
“Sorting” of pre-adapted
genotypes
Phenotypic plasticity allows
survival in multiple
environments
Post-introduction evolution of
locally adapted genotypes
Three questions:
Is there a relationship between plasticity and
invasiveness?
1. Are invasive species more plastic than
non-invasive species?
2. Does adaptive plasticity evolve in
invasive species?
3. Do invasive species become locally
adapted?
Phenotypic plasticity defined
The ability of a genotype to express different
phenotypes in different environments (Bradshaw
1965, Schlichting 1986, Scheiner 1993, Pigliucci 2001,
2005)
Genetically controlled
Refers to a specific trait, not an organism**
Not always adaptive, but adaptive plasticity is often
of interest to ecologists
11. General purpose
genotypes
Herbert Baker, 1965, Genetics of Colonizing Species
Species may become invasive BECAUSE they are
phenotypically plastic
-ORFollowing introduction, species may evolve
increased plasticity
Chlorophyll content
What does plasticity look
like?
Norm of reaction diagram
Chlorophyll content is a
plastic trait- phenotype
changes in response to
the environment
Trait plasticity can lead to
stable fitness across
environments
Fitness
Plasticity in traits,
constant fitness
Fitness is
maintained across
habitats
It is possible to have
plasticity for plant
traits, and no
plasticity in fitness
traits
Chlorophyll content
Not non-genetic
Heritability is as other
traits
Evidenced by genetic
variation for plasticity
Some families are more
plastic than others
Family x Environment interaction
Local adaptation
The existence of genotypes that are well
suited to local biotic and abiotic conditions
Created through the process of natural
selection
Local adaptation may require phenotypic
plasticity
e.g. highly variable environments
Fitness
What does it look like?
Each species has
higher fitness in the
area it is from
G x E interaction
Isn’t local adaptation
inevitable?
Not guaranteed:
selection too unpredictable
genetic variation too small
selection may be swamped by gene flow
adaptation may be prevented by phenotypic
plasticity
selection cannot act on genes it can’t “see”
Is there a relationship between
plasticity and invasiveness?
Two kinds of plasticity
Invasive
Non-invasive
1. Are invasive species more
plastic than non-invasive species?
Compare invasive exotic species with noninvasive exotic species + + + 0 0
Compare invasive exotic species with related
native species + + + 0
Compare invasive exotic species with
unrelated native species + + + + 0
11. YES
Jack-and-Master
2. Does adaptive plasticity
evolve in invasive
species?
Chlorophyll content
Not non-genetic
Family x Environment interaction
Would be expected to be
favored when:
Unpredictable environments (disruptive
selection in space and time)
Stabilizing selection on different genotypes in
a single environment- more than one
phenotype is adaptive
Strong directional selection on a trait for which
there is no genetic variation available
THE EVOLUTION OF
PLASTICITY
“chlorophyll”
+ or -
“plastic”
“chlorophyll
+”
One gene can be
expressed differently in
different environments
“chlorophyll
-”
Does adaptive plasticity
evolve in invasive
species?
Compare invasive populations with known
source of invaders no data??
Compare invasive populations with a
reasonable sample of native populations
+++++++000000-
+
Reasonable sample
Leger and Rice 2003
Master-of-some
Invasive
Native
3. Do invasive species
become locally adapted?
YES
Wing size
R.B. Huey and G.W. Gilchrist
Latitude
3. Do invasive species
become locally adapted?
YES
3. Do invasive species
become locally adapted?
YES
Does evolutionary
change CAUSE
invasion?
we don’t know
have to track
invasions as they
progress
Initial plasticity, followed by
adaptation
Chance mutations affect ability to plastically
respond to rare (or absent) stimuli
Selection does not remove these mutants from
the population
Eventually, may get plants with fixed response to
a particular condition
OR, there is a cost to maintaining plasticity,
therefore it is lost
Genetic assimilation
general purpose
genotype
“plastic”
“high”
“high”
“low”
“low”
“low”
PEAVINE PEAK
Are genotypes adapting to
high-elevation environments?
Results to date: no (but there is adaptation to lowelevation environments)
Survival at high elevations appears to be random
(not related to genotype or environment where you
were collected)
Once plants survive, fitness is identical to lowelevation sites
Seems like a great place for plasticity to evolve
Pre-adaptation
Adaptive plasticity = good
Local adaptation may follow
Summary
Introduced species can survive a complex new
environment if:
at least some pre-adapted genotypes are
introduced (“sorting”)
at least some genotypes can tolerate new
environments through phenotypic plasticity
species evolves increased plasticity postintroduction
species evolves locally adapted genotypes (?)