1. The Evolution-Ecology Connection
Lecture 2
The Evolution-Ecology Connection

2. ‘Nothing in biology makes sense, except in the light of evolution
‘Nothing in biology makes sense, except in the light of evolution.’ Dobzhansky

3. What is: ___________?
Evolution:
What evolves?
In order for evolution to occur what must happen, or what conditions must be met?
Why is it important for species to evolve?

4. Natural selection:
What two conditions must occur for natural selection to take place?
Fitness:
A gene for increased fitness would….

5. Are those with greater levels of fitness necessarily bigger, stronger or faster?
Natural selection involves a competition for:
Traits which give an individual who possesses them an increased level of fitness are known as ____________

6. What is the basis of adaptations?
Genetic information is carried in a code in DNA
Traits (they may be adaptations) involve information carried in specific genes
Gene:
A variant form of a gene is an ___________
What leads to the formation of these variant forms?
Gene expression results in a specific ______

7. How genes interact:
Single genes:
Dominant – recessive
Codominant -
Incomplete dominance
Phenotype: expression of genetic information – consequence of gene interactions

9. Incomplete Dominance
One gene is not completely dominant over another – result is an intermediate expression form in the heterozygous genotype
Example: Flower color in petunias

12. Quantitative traits:
Involve interaction of several (sometimes many) genes
Complicated by epistatic expression, epigenetic inheritance patterns and environmental interactions (multifactorial inheritance)
Accounts for continuous variation in phenotype form

13. How Polygenic Inheritance Works:
Several genes may influence ultimate phenotype :
Height
Hair and skin color
Continuous range (red to white) in flower color
Another example: Beak depth in Galapagos Finches

14. Fig. 5-3

15. Fig. 5-4

16. Fig. 5-8

17. Examples of Evolution
1. Gartersnake-Oregon Newt interaction
2. modification of beak size in Galapagos finches – studies of Peter and Rosemary Grant
No new species arose in either case
Species: ‘A group of similar appearing organisms that share the same gene pool’

18. Fig. 5-9

19. Selection pressure within a species
Selection for one extreme
Selection for the ‘average’
Selection for two extremes (bimodal)

20. 5.6 Several Processes Can Function to Alter Patterns of Genetic Variation
Not all phenotypes represent adaptations in response to natural selection
Factors other than natural selection affect changes in genetic variation within populations
Mutations are heritable changes in a gene or a chromosome
Genetic drift is the change in allele frequency due to random chance associated with sexual reproduction
Migration is the movement of individuals between local populations
Gene flow is the movement of genes between populations

21. 5.6 Several Processes Can Function to Alter Patterns of Genetic Variation
The Hardy–Weinberg principle of genetics states that under conditions of random mating, the allele frequency of a population remains constant through time
This occurs in the absence of natural selection, mutation, genetic drift, and gene flow
No evolutionary change occurs through the process of sexual reproduction itself

22. 5.6 Several Processes Can Function to Alter Patterns of Genetic Variation
Assortative mating occurs when individuals choose mates nonrandomly based on phenotype (and thus genotype)
Female mate choice
Positive assortative mating occurs when mates are more similar to each other than expected by chance
Increases homozygote frequency

23. 5.6 Several Processes Can Function to Alter Patterns of Genetic Variation
Negative assortative mating occurs when mates are less similar to each other than expected by chance
Increases heterozygote frequency

24. 5.6 Several Processes Can Function to Alter Patterns of Genetic Variation
Inbreeding is the mating of closely related individuals
Increases homozygosity at all loci
Offspring of closely related individuals are more likely to inherit rare, recessive, or deleterious genes that lower overall fitness
These consequences are referred to as inbreeding depression

25. Quantifying Ecology 5.1 Hardy–Weinberg Principle
Allele and genotype frequencies will remain the same in successive generations of a sexually reproducing population if certain criteria are met
Mating is random
Mutations do not occur
The population is large (genetic drift is minimal)
There is no migration
Natural selection does not occur

26. Quantifying Ecology 5.1 Hardy–Weinberg Principle
Two alleles at a locus
The sum of the allele frequency must equal one
p + q = 1
P (homozygote dominant) + H (heterozygote) + Q (homozygote recessive) = 1

27. 5.7 Natural Selection Can Result in Genetic Differentiation
The geographic range of a species can result in phenotypic variation of neighboring populations
A wider geographic range includes a broader range of environmental conditions
In general, the greater the distance between populations, the more pronounced the phenotypic differences

28. Geographic Variation in Species
Ecotype: Subpopulation of a species adapted to a specific environment
Cline: measurable change in a species characteristics over an environmental gradient
Variation in white tailed deer – larger animals at higher latitudes in NA

29. Genetic Variation of Ecotypes
An ecotype is a population adapted to its unique (often abrupt) local environmental conditions
Yarrow (Achillea millefolium) response to altitude
How much variation observable in the field is due to genetic variation and how much is due to impact of environment (phenotypic plasticity)?
Common Garden Experiment
Seed collected from plants of same species growing in different environments grow in same location(s) (p 85)

30. 5.7 Natural Selection Can Result in Genetic Differentiation
Geographic isolates result when gene flow among subpopulations is prevented
The isolation is rarely complete, and so these isolated subpopulations are often classified as subspecies because of a set of unique characteristics
Appalachian salamanders (Plethodon jordani)

31. Figure 5.14

32. How do new species arise?
Allopatric speciation: spatial isolation –geographic isolation
Spread of species into new areas
Founding population in isolated location
Geologic changes – gradual process
Sympatric speciation: different niches/same habitat or geographic area
Genetic changes (as ploidy levels in plants)
Disruptive selection: divergent genotypes favored

33. Species have become specialists feeding on seed providing optimal energy efficiency

34. Adaptive Radiation: Single ancestral from give rise to multiple ‘specialist’ forms

35. Summary:
Evolution involves heritable differences amongst individuals in a population which ultimately impact fitness
Organisms become ‘tailor made’ for their niche within an environment by processes of evolution
Characteristics of individuals making up current populations are a product of natural selection in ancestral populations
New species arise from preexisting species as populations become reproductively isolated