BIOL 4120: Principles of Ecology Lecture 6: Evolution and Adaptation

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BIOL 4120 Principles of Ecology Lecture 6
Evolution and Adaptation

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Introduction

• Major question in Ecology What determines
  distribution abundance of species?
• Two classes of answers
• Contemporary, local and regional factors (biomes
  and PPT and T)
• Historical factors ( evolutionary ones)
• Why different species live in different
  environments? (Adaptation and evolution)
• E.g., grasslands long necked giraffe in savannas
  of Africa (widely dispersed, umbrella-shaped
  trees) white coated polar bear in Arctic
  (invisible to prey)

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• Evolutionary Ecology (Chapter 6)
• 6.1 Phenotype is the outward expression of an
  individuals genotype
• 6.2 Adaptations result from natural selection on
  heritable variation in traits that affect
  evolutionary fitness
• 6.3 Evolutionary changes in allele frequencies
  have been documented in natural populations
• 6.4 Individuals can respond to their environments
  and increase their fitness
• 6.5 Phenotypic plasticity allows individuals to
  adapt to environmental change

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6.1 Phenotype is the outward expression of an
individuals genotype
Review concepts in Genetics 1. Gene and genetic
variation 2. Phenotype and genotype 3. Sources
of genetic variation 4. Qualitative and
quantitative traits
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What are genes?
Genes discrete subunit of chromosome, carry
genetic information Chromosomes the threadlike
structures where DNA is contained DNA
Deoxyribonucleric acid. All DNA is composed of
the same 4 nucleotide (ATGC), differ in
sequence. Alleles different forms of a gene (A,
a). Locus the position of an allele occupies on
a chromosome Homozygous (AA, aa) vs
heterozygous (Aa) Dominance (A vs a), incomplete
dominance (Aa shows different trait to AA or aa)
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How are genes transmitted?
Genotype the sum of genes carried by the
individual. Gene pool total collection of
genes across all individual in the population at
any one time Phenotype the observed expression
of genotype (color etc)
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Phenotypic plasticity
Phenotypic plasticity the capability of an
individual to exhibit different responses and
produce a range of phenotypic expressions under
different environmental conditions.
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Sources of genetic variation

• Genetic variation within a population is
  absolutely necessary for natural selection to
  occur
• If all individuals are identical within a
  population then their fitness will all be the
  same

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• Sources of genetic variation
• Mutation inheritable changes in a gene or a
  chromosome
• Gene mutation (point mutation) such as
  sickle-cell anemia, cystic fibrosis
• Chromosome mutation
• deletion, duplication, inversion, translocation
• Genetic recombination
• Sexual reproduction
• two individuals produce haploid gametes (egg
  or sperm) that combine to form a diploid cell
  or zygote.
• Reassortment of genes provided by two parents in
  the offspring
• Increases dramatically the variation within a
  population by creating new combinations of
  existing genes.
• Asexual reproduction less variation (only
  mutation)

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Genetic basis of continuously varying phenotypic
traits
Many phenotypic traits show continuous variation
(quantitative traits). Traits such as sizes and
rates of processes are often influenced by many
genes.
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6.2 Adaptation result from natural selection on
heritable variation in traits that affect
evolutionary fitness

• Evolution pertains to any changes in a
  populations gene pool. When genetic factors
  cause differences among individuals in survival
  and reproductive success, evolutionary change
  comes about through natural selection.
  Individuals whose traits enable them to achieve
  higher rates of reproduction leave more
  descendants, and therefore the alleles
  responsible for those traits increase in the
  gene pool of the population.
• The process is often referred to as Adaptation.

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Evolution by natural selection

• What is Darwins natural selection?
• The differential success (survival and
  reproduction) of individuals within the
  population that results from their interaction
  with their environment.
• Survival of fitness, elimination of
  inferior individual

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• Three main ingredients of evolution by natural
  selection
• 1. There is variation among individuals in a
  population.
• 2. The Variation is heritable.
• 3. Differences in survival and reproductive
  success, or fitness, related to that variation.
• Survival and reproduction are not random, but are
  related to variation among individuals.
  Organisms with best characteristics are
  naturally selected.
• If 3 conditions are met, the population will
  change from one generation to the next. Evolution
  will occur.

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One example Evolutionary change in a population
may result from a change in the
environment. Cyanide fumigation to kill scale
insects Initially, very effective, killed most
non cyanide-resistant individuals Fumigation was
not effective Natural and artificial selection
(crops, domestic animals)
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Evidence of natural selection

• Evolution of beak shape in Finches.
• Peter and Rosemary Grants (and colleagues) work
  on Medium Ground Finch Geospiza fortis.

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Natural selection

• Darwins Finches
• Genetic studies show all arise from a single
  ancestral species.

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40-ha Daphne Major island
Rosemary Peter Grant
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Is there a phenotypic variation in beak size?
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Is variation in beak size correlated with
variation in fitness?
In 1978, there was a severe drought due to La
Nina, small seeds declined more than large
seeds. Small beak birds have difficulty to find
seeds, and suffered heavy mortality, especially
females.
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Beak size evolves
post-drought
pre-drought
Conclusion Nature selection indeed caused
evolution in beak size
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Three types of selection
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Disruptive selection increases phenotypic
variation in a population Black bellied
seedcraker
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6.3 Evolutionary changes in allele frequencies
have been documented in natural populations

• Cyanide resistance in scale insects
• Pesticide and herbicide resistance among
  agricultural pests
• Antibiotic resistance among pathogenic bacteria
  (superbug)

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Selection and change in frequency of melanistic
moths
Birds eaten Normal
Melanistic Unpollu- ted woods 26
164 Polluted 43
15 woods Kettlewell (1950s)
Early in the nineteenth century, occasional dark,
or melanistic, speciemens of the peppered moth
were collected. Over the next hundred years, this
dark form became increasing common in forests
near heavily industrialized region ? industrial
melanism.
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England, started pollution control in the 1950s
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6.4 Individuals can respond to their environments
and increase their fitness
Evolution occurs through the replacement of less
fit individuals by the progeny of more fit
individuals in a population over
time. Individuals do not benefit from evolution.
It is the gene pool of the population evolves,
not individuals. But individuals can undergo
certain changes over space and time and respond
to the environmental changes. E.g. Global
change or urbanization. Animal can move
around. Microhabitaes and microenvironments.
Example Responses of Catcus wren to
microhabitats.
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BIOL 4120 Principles of Ecology Lecture 6
Evolution and Adaptation

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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• Recap
• Evolution by natural selection
• Example of national selection Beak size
• Three types of selection
• Individuals can respond to environmental changes

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6.5 Phenotypic plasticity allows individuals to
adapt to environmental change
The set of phenotype expressed by a single
genotype across a range of environmental
conditions is referred to as the norm of reaction
Reaction norm.
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Norm of reaction
The set of phenotype expressed by a single
genotype across a range of environmental
conditions is referred to as the norm of reaction.
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The reaction norms of populations adapted to
different environments may differ Caterpillars
of swallowtail butterfly were obtained from two
populations one from Alaska and one in Michigan.
Grow in two temperature conditions High T
stimulated growth, but in cold T, caterpillars
from Alaska grow better under lower T.
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Norm of reaction
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Reaction norms may be modified by evolution
Reaction norms may diverge when two populations
of the same species exist for long periods under
different conditions. Very often, an increase in
performance under prevalent conditions is
accompanied by a decrease in performance when
exposed to conditions outside the populations
normal range .
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Acclimation
Adaptive phenotypic plasticity referred to as
Acclimation, such as growing thicker fur in
winter, producing smaller leaves during the dry
season, producing enzymes with different T optima
at different temperatures. Acclimation may be
thought as a shift in an individuals range of
physiological tolerances. It is useful in
response to seasonal and other persistent changes
in conditions Acclimation may takes days to
weeks Acclimation is reversible
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Blue 20oC Red 45oC
Larrea creosote bush, subtropical desert plant,
photosynthesis in both winter and summer Atriplx
saltbush, native to cool coastal region of
CA Tidestromia heat-loving, thermophilic species
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Irreversible developmental responses
Development responses When conditions persist
for long periods, the environment may influence
individual development so as to modify the size
or other attributes of the individual for long
periods, even for its remaining life time. These
changes are referred to as Development
Responses Coloration of African grasshopper
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Development responses are not reversible
Water fleas Left was exposed to predators and
survived, with a helmet.
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Genotype-environment interaction
Phenotypes Genotypes Environments How to
test if phenotypic variation is due to genotype
or environments? Reciprocal transplant
experiments
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Reciprocal transplant experiment are used to
investigate the causes of differences between
populations
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The growth rate of fence lizards reveal both
genetic determination and phenotypic plasticity
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The End