1. Chapter 6: Evolution and adpatation
Darwin’s finches

2. Heavy rains during El Nino events support lush plant growth in the archipelago.

4. What this does us? Finches do not survive or die at random
Because the average hardness of seeds increased as the drought intensified and the softest seeds were consumed  birds with larger beaks that could generate the forces needed to crack hard seeds survived better than those with smaller beaks
The average beak size of surviving individuals and their progeny increased significantly
What is necessary for such ‘evolution in action’?

5. Genetics review
The phenotype is the outward expression of an individual's genotype
Genotype: unique genetic constitution
Phenotype: outward expression of that genotype
A genotype = set of genetic instructions; blueprints
Phenotype = the expression of that genotype in the form of an organism
(is that enough? Are there external factors?)
Effects of environmental influences are like details in a blueprint that are left to the discretion of the building contractor.. What does that mean?

6. More genetics All phenotypic traits have: Phenotypic plasticity
Genetic basis + influence by variations in the environment
What kind of environmental variations?
Phenotypic plasticity
Capacity of an individual to exhibit different responses to its environment
How the individual responds to environmetnal variation

7. Genetic variation (review, right?)
Alleles
Different forms of a particular gene
Heterozygous
Two different alleles for a particular gene
Homozygous
Both copies of a gene are the same
Dominant… Recessive…
Gene pool
All the alleles of the genes of every individual in a population

8. Sources of genetic variation
How does genetic variation arise?
Mutation
Any change in the sequence of the nucleotides that make up a gene or in regions of the DNA that control the expression of a gene
Consequence?
Drastic – maybe lethal – changes in the phenotype
No detectable effect – silent mutations
New phenotypes produced  better suited to the local environment  phenotypes increase
Multiple effects  pleiotropy (effects of a single gene on multiple traits)

9. Genetic basis of continuously varying phenotypic traits
Many phenotypic traits with ecological relevance vary continuously over a range of values (eg: body size)

10. Adaptations result from natural selection on heritable variation in traits that effect evolutionary fitness
The most important consequence of genetic variation for the study of ecology is evolution by natural selection
Evolution
Any change in a population’s gene pool (what is a gene pool?)
Individuals whose traits enable them to have higher rates of reproduction have more offspring  alleles increase
Adaptations or evolutionary adaptation
Process = adaptation

11. Adaptation (process of evolution by natural selection)
Variation among individuals
Eg – bird beaks; different individuals have different-sized beaks
Inheritance of that variation
Size of bird’s beak has an existence of its own in a population; individual is borrowing that trait
Differences in survival and reproductive success (or fitness) related to that variation
Fitness: production of descendants over an individual’s lifetime.

12. Evolutionary change Change in a California citrus pest
Cyanide fumigation no longer effective

13. Stabilizing, directional, and disruptive selection
Stabilizing selection
Individuals with intermediate (average) phenotypes have higher reproductive success
Population moved towards an optimum point
Maintains a single fittest phenotype
When the environment of a population is relatively unchanging: dominant mode; little evolutionary change
Directional
Fittest individual have a more extreme phenotype;
When new optimum reached – becomes stabilizing selection
Disruptive
Increase genetic and phenotypic variation within a population and in the extreme case creates a bimodal distribution of phenotypes; relatively uncommon; eg: individuals specializing on one of a small number of food resources; strong competition among individuals

15. Example of Disruptive selection

16. Selection and change in melanistic moths (peppered moths)
Dark form: more popular in forests near industrialized regions
Industrial melanism

17. Criticism of Kettlewell’s research
Moths that were used for the mark – recapture experiments were reared in the lab
This might have affected their behavior – eg – choice of resting locations
Experimental moths released at unnaturally high densities – might have affected the behavior of predators
So?
But: with pollution control  forests became cleaner  frequencies of melanistic moths decreased (as predicted by evolutionary theory)

19. Population genetics and the prediction of evolutionary change
Study of the dynamics of natural selection and genetic change in populations
Populations are continually engaged in dynamic evolutionary relationships with their environment that shape their ecological interactions
(one) Goal of population genetics  to develop methods for predicting changes in gene frequencies in response to selection
Why?
Ability to predict them can tell us whether the genetic changes we observe are consistent with our understanding of evolution
(check out the ‘more on the web’ links)

20. Population genetics and ecologists
every population harbors some genetic variation that influences fitness .. Potential for evolution exists in all populations
Except?
Changes in the environment will almost always be met by an evolutionary response that shifts the frequencies of genotypes within the population. (translate?)
Magnitude of the evolutionary response depends on genetic variation present in the pop at a given time
Rapid environmental changes brought about by the appearance of new adaptations in populations of enemies or by human-caused changes in the environment (eg?) can exceed the capacity of a population to respond by evolution
So?

21. Individuals can respond to their environments and increase their fitness
Evolution: less fit individuals replaced by the progeny of more fit individuals in a population over time
Individual himself/herself does not benefit from evolution. Explain?
Still: individuals can undergo changes that help them cope with variation in their environment during their lifetime
 phenotypic plasticity  capacity to respond to environmental variation
How?

22. Cactus wren: adapted to the desert environment
Insectivorous bird that lives in deserts
No source of drinking water  must not get too much heat from the environment
In the desert: seeks favorable microhabitats
Cool mornings: forage;
Afternoon: finds cooler parts; shade

23. Temperature affects microhabitat use by cactus wrens

24. Orientation of cactus wren nest entrances changes over the breeding season Lengths of the bars represent relative number of nests with each orientation
Behavioral flexibility of the cactus wren in choosing where to forage and how to orient its nest is a good example of the more general ability of the phenotype to respond to variation in the environment

25. Phenotypic plasticity allows individuals to adapt to environmental change
Reaction norm  observed relationship between the phenotype of an individual and the environment

27. Phenotypic plasticity allows individuals to adapt to environmental change
Some reaction norms are a simple consequence of the influence of the physical environment on life (heat energy  accelerates most life processes  certain caterpillars grow faster at higher temperatures … but individuals of the same butterfly species from MI and AL have different relationships between growth rate and temperature…)

28. Reaction norms of populations adapted to different environments may differ

29. Reaction norms may be modified by evolution
May diverge when two populations of the same species exist for long periods under different conditions…

31. acclimatization
 a shfit in an individual’s range of physiological tolerances
 generally useful in response to seasonal and other persistent changes in conditions
 reversible
But – increased tolerance of one extreme often brings reduced tolerance of another extreme

32. A species’ capacity for acclimatization may reflect the range of conditions in its environment

33. Irreversible developmental responses
Developmental responses  when conditions persist for long periods – env may influence individual development so as to modify the size or other attributes of the individual for long periods
Striking example: the African grasshopper – changes color to match the color of their environment

34. Most grasshoppers complete their life cycle within a single season So in habitats where this color progression occurs – the pigment systems in the epidermis develop in such a way that the nymphs an adult grasshoppers match the background

35. Genotype – environment interaction
When the reaction norms of two genotypes cross for some aspect of performance, then individuals with each genotype perform better in one environment and worse in another environment (eg: swallowtail butterfly)
This relationship  genetoype – environment interaction because each genotype responds differently to environmental variations
How to identify them?  reciprocal transplant experiment