Ecological genetics Flashcards
Lecture 4
Darwin’s theory of natural selection
The structure and function of an organism reflects its adaptations to its environment
organisms become better adapted* to their environments through differential success (survival and reproduction) of individuals within the population.
What is an adaption?
a heritable trait that develops in response to environmental conditions.
Genotyps and phenotypes.
What is natural selection?
Is driven by the success or failure of
individuals
– The population reflects the collective successes and failures through time.
Survival of the fittest (individuals that contribute most to future generations)
Occurs when there has been a gradual shift in the phenotype (appearance) over time
What is evolution?
The process by which the properties of populations change over generations.
What is needed for natural selection to take place?
- Variation in phenotypes.
- Variation must be heritable
- Variation must influence behaviour
Galapagos finch example
Finches with bigger beaks can eat larger food, leaving behind more offspring. The population of finches’ beak sizes increased.
How does the change in the environment influence natural selection?
Favors certain phenotypes - shifts the distribution of the phenotypes
Increases the average fitness of some individuals in a population over time.
What is the target of selection?
Phenotype
What is the selection agent?
Environmental pressure.
How does natural selection result in genetic differentiation?
A wider geographic range includes a
broader range of environmental conditions
– Can lead to phenotypic variation among neighbouring populations
– The greater the distance between populations, the more pronounced the phenotypic differences
▪ Clines, ecotypes, geographic isolation
What is a cline?
Natural selection resulting in genetic differentiation
Measurable, gradual change in the
average of a phenotypic trait over a geographic region
– usually associated with an environmental gradient
E.g., North American white-tailed deer.
What is the ecotype?
Natural selection resulting in genetic differentiation
Population adapted to its
unique local environmental conditions
– Changes among nearby populations can be abrupt
E.g., Aspalanthuslinearis(Rooibos)
▪ five ecotypes depending on environmental conditions
African fruit fly example
Cline
Flies living at lower altitudes have smaller wing and different shape, than flies living at high altitudes.
Rooibos Example
Ecotype
different ecotypes were found with different kinds of environmental conditions.
depending on altitude and rainfall have different distributions of the rooibos plant.
What are geographic isolates?
When gene flow among sub- populations is prevented
▪ Isolation seldom complete
– isolated sub-populations ~subspecies
▪ Each has set of unique characteristics
▪ Subspecies defined by distribution limits
▪ In complete isolation, speciation can occur
– Allopatric
African leopard example.
Is it a cline, ecotype or subspecies?
Cline, because they are genetically the same species and they gradually change, it is not an abrupt change.
What is adaptive radiation?
When one species gives rise to
multiple species that exploit different features of an environment (food, habitat)
– Sympatric speciation
Why do organisms respond to environmental variation at
the individual and population levels?
Individuals can respond to temporal (time) and spatial (space) changes in the environment
– By moving to a more suitable location
– By a direct influence of environment on gene expression (phenotypic plasticity).
What is phenotypic plasticity?
Organisms Respond to Environmental Variation at the Individual and Population Levels
The ability of a single genotype to give rise to different phenotypes under different environmental conditions.
– Improves the individual’s ability to survive, grow, and reproduce under the prevailing environmental conditions.
Phenotypic plasticity
Organisms Respond to Environmental Variation at the Individual and Population Levels
Developmental plasticity – change in the allocation of biomass to different tissues during growth and development due to differences in environmental conditions
– Irreversible
Acclimation– phenotypic changes in an individual in response to changing environmental conditions
– Reversible
– Seasonal responses
Why taxonomy is important?
Just know of
When phenotypic plasticity and wide environmental tolerances are really hiding multiple species.
The taxonomic impediment
Just know of
Taxonomic expertise has declined, ‘nearing
complete demise’
▪ Taxonomists are ‘stamp collectors’, or ‘bureaucratic accountants’
▪ Taxonomy is not trendy and intellectually unchallenging (i.e., descriptive)
▪ Research does not attract large grants and can’t be published in high impact journals
▪ Taxonomy not taught at universities
▪ interest in field not fostered
Most biological disciplines are built on Taxonomy.
A species identification is not just about its name.
Strength of conclusions depends on accuracy of identification.
Better data will be collected when taxonomists & ecologists collaborate
Just know of
For the ecologist: accurate species identifications can highlight patterns that would have been overlooked if taxa were misidentified or only identified to higher taxonomic levels, and/or if (pseudo-) cryptic diversity is not detected.
For the taxonomist: ecological and biological data (biogeographical, behavioural, reproductive,
trophic) reliably linked to species increase the value of the research.
