BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution

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BIOL 4120 Principles of Ecology Lecture 2
Adaptation and Evolution

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

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• Evolutionary Ecology
• 2.1 Nature selection as a force of evolution
• 2.2 Heritability is the feature of Natural
  Selection
• 2.3 Genes are the units of inheritance
• 2.4 Genetic variation is the ingredient of NS
• 2.5 Evolution is the outcome of NS resulted from
  gene frequency change
• 2.6 Speciation and mechanisms

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Introduction to evolutionary ecology

• Major question in Ecology What determines
  distribution abundance of species?
• Two classes of answers
• Contemporary, local factors (domain of
  traditional Ecology, biomes and PPT and T)
• Historical factors ( evolutionary ones)
• Why different species live in different
  environments? (Adaptation)
• E.g., 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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2.1 Nature selection as a force of evolution

• 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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• Two conditions (assumptions)
• 1. There is variation in populations. Variation
  is heritable.
• 2. In every generation some organisms are more
  successful at surviving and reproducing than
  others. Survival and reproduction are not random,
  but are related to variation among individuals.
  Organisms with best characteristics are
  naturally selected.
• If 2 conditions are met then the population will
  change from one generation to the next. Evolution
  will occur.

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Evidence of natural selection

• Evolution of beak shape in Finches.
• Peter and Rosemary Grants (and colleagues) work
  on Medium Ground Finches 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, small seeds
declined more than large seeds. Small beak birds
have difficult 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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Types of natural selection
black bellied seed
cracker beak size
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2.2 Heritability is an essential feature of NS

• Heritability individuals characteristics are
  passed from one generation to the next. Measured
  as proportion of the variation in a trait in a
  population that is due to variation in genes.
• Mendels genetics and inheritance

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Mendles Pea experiment

• Mendles conclusions
• Flower color is a heritable trait
• For each inherited char, an organism has two
  units, one from each parent
• (one each from egg and sperm). The unit may
  be the same or different.
• 3. When the two units are different, one is fully
  expressed, another one has no
• noticeable effect of the organisms outward
  appearance.
• Dominant the unit is expressed (purple)
• Recessive not expressed (white).

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2.3 Genes are the units of inheritance
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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 alternate 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 ability of a genotype
to give a range of phenotypic expressions under
different environmental conditions.
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Norm of reaction
The set of phenotype across a range of
environmental conditions.
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2.4 Genetic variation is the ingredient for
Natural Selection

• 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)
• 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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What do we mean by genetic variation?

• Range (variance) of phenotypes, as in Darwins
  Finch example
• Different chromosomal arrangements (cytogenetics)
• DNA sequence differences among individuals
• Electrophoresis--gt electromorphs allozymes
• Molecular marks RFLP, RAPD, etc.

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2.5 Evolution is a change in gene frequency

• Evolution is a change of gene frequencies within
  a population (or species) over time
• Individuals do not evolve, populations evolve
• Focus on gene pool, collective
• But why do we see populations are still the
  same over many generations?

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The Hardy-Weinberg Principle

• The Hardy-Weinberg Principle
• Gene frequencies will remain the same in
  successive generations of a sexually reproducing
  population if the following five conditions hold
• Random mating
• There is no mutation
• The population is very large
• There is no selection
• There is no migrations (isolated from other
  populations)

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The Hardy-Weinberg Principle
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Five Causes of evolution

• Mutations
• Gene flow - Emigration and immigration of
  individuals (Flow of alleles)
• Genetic Drift Changes in the gene pool of a
  small population due to chance
• Nonrandom mating (AA mates AA, Aa)
• Natural selection

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One Example Genetic drift in a small population
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(No Transcript)
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2.6 Speciation and mechanisms

• Speciation splitting of one species into 2
  different species.
• Concept of species
• Biological Species a species is a group of
  organisms whose individual have the potential to
  interbreed and produce fertile offspring.
• Reproductively isolated dont produce fertile
  hybrids
• Natural conditions artificial breeding doesnt
  count. For example, artificial insemination,
  keeping 2 species locked up together.
• Morphological species members of the same
  species look similar to each other. Many
  examples of organisms that look similar but cant
  produce fertile offspring.
• No one species concept applies to all organisms

Flickers
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Genetic isolation mechanisms (reproductive
barriers)

• Premating mechanisms
• Habitat selection temporal isolation behavior
  or mechanical or structure incompatibility
• Postmating mechanisms
• Genetic barrier such as hybrids are sterile seed
  abortion hybrid inviability.

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Mechanisms of speciation

• Several are well documented
• Allopatric speciation (probably most vertebrates)
• allopatric species occupy areas separated by time
  or space.
• Sympatric speciation (especially plants and
  insects)
• Sympatric species occupy the same place at the
  same time

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• Allopatric Speciation
• Geographic isolation, Easy to understand.

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Allopatric speciation Ring species
salamander
San Joaquin Valley, CA
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Speciation via geographic isolation and divergence
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Sympatric speciation (e.g Speciation by
Polyploidy)

• About half of all flowering plants are polyploid
  more than 2 copies of each gene.
• Polyploids are the result of failure of cell
  division (mitosis or meiosis) to separate the
  chromosomes into 2 cells.

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2.4 Adaptations reflect trade-offs and constraints

• Adaptation Individuals of a species have certain
  characteristics that enable an organism to thrive
  in a given environment.
• Adaptations maintain or increase fitness of an
  organism in a given environmental conditions.

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Tradeoff

• Evolution is reflected in changes in gene
  frequencies and phenotypes
• However, changes in gene frequencies involve
  tradeoffs
• Giraffes do not graze well on grass due to their
  long necks
• Snow leopards can hide in snowy mountains,
  ordinary leopards can hide well in green trees.

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Constraint

• There are many other factors that can influence
  species adaptation.
• For example, response of an organism to an
  environmental gradient such as temperature.
• All these factors influence species adaptation.

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The End
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Brief history of integration of Genetics into
Ecological studies

• Natural SelectionDarwin (1859) The Origin of
  Species
• Particulate genetics inheritanceGregor Mendel
  (1856-1864)
• Mutations chromosomesHugo Devries others
  (1901)--sources of variation in populations
  rediscovery of Mendels work
• The Modern Synthesis (Dobzhansky, Wright,
  Fisher, Haldane, Mayr, Simpson--1930s 1940s)
• Integration Natural Selection mutation genetic
  drift migration
• Appreciation of genetic variation within
  populations in nature
• DNA structure/importance elucidated by Watson
  Crick (1953) double helix structure of DNA
• Molecular variation in natural populations
  (Harris Lewontin Hubby 1966)--using starch gel
  electrophoresis ? molecular biology.
• Synthesis of Ecology with Genetics --gt
  Evolutionary Ecology (starting in 1970s)!

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Evolution by Natural Selection

• The major factors affecting the organisms
  survival in the system is Fitness
• Darwinian fitness ability of an organism to
  survive and reproduce in its environment.
• Adaptation is a characteristic or trait of an
  organism that increases its fitness relative to
  individuals that do not possess it. It is an
  inherited characteristic that increases the
  ability of an organism to survive and reproduce.

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• The traits selected for by natural selection need
  to be inheritable so that the next generation
  after selection retains the change
• Three types of selection
• Directional
• See finches
• Stabilizing
• Long necks in giraffes
• Disruptive
• Sexual dimorphism

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Fig. 5-6 An example of microevolution
directional selection
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Summary

• What is natural selection?
• Different types of NS
• Gene and genetic variation
• Evolution
• Hardy-Weinberg principle
• Concept of species.
• Speciation and mechanisms
• Adaptation and trade-offs

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What is a species

• Ecology is based on the idea that we can identify
  different groups of organisms within an ecosystem
• These groups are generally called species
• There are three specific means of defining a
  species
• Morphological species concept
• A species is defined as a morphologically
  consistent group of organisms than can be
  distinguished from all other species
• Can fail. So called cryptic species
• Biological species concept
• A group of populations whose individuals can
  interbreed and produce fertile offspring and
  cannot interbreed with other species
• Reproductive isolation
• Still fails. If you cannot tell the individuals
  apart morphologically, how can you tell if they
  are interbreeding or not
• Also, some species can interbreed and produce
  viable offspring
• Bontebok and Blesbok in South Africa
• Genetic species concept
• A group of populations whose individuals have a
  distinct genetic makeup and who do not interbreed
  with others groups of populations for some reason
• Bontebok and Blesbok are genetically distinct as
  well as being morphologically different. Do not
  naturally overlap in range

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• Geographical isolates

Salamanders
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Adaptations of Honeycreepers on the island of
Hawaii
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Recap

• Whats Nature selection? 2 assumptions?
• Three types of natural selection
• Concept in genetics gene, chromosome, DNA,
  allele, locus, genotype, phenotype, dominance,
  incomplete dominance etc