Natural selection & adaptation
Habitats
Fisheries Management
Changing World
Ecology & Evolution
Darwin’s dangerous idea
Identified a process that could explain the patterns of diversity on Earth and (even though he never spoke of speciation per se) could provide the ‘origin of species’ (the mystery of mysteries as he called it).
Darwin’s dangerous idea
Identified a process that could explain the patterns of diversity on Earth and (even though he never spoke of speciation per se) could provide the ‘origin of species’ (the mystery of mysteries as he called it).
Contentious then (and now) because the other proposed mechanism involves supernatural processes
Low rate of acceptance of evolution in the US
Response to the following true or false question: “human beings, as we know them, developed from earlier species of animals”
Researchers working in this area have identified lack of understanding of natural selection as a process as a source of ‘not sure’ and (at least some) of the ‘false’ responses.
Miller et al. 2006
Signatures of evolution
# 1: Major changes in traits come through gradual modification of existing forms
#2: Major change (e.g. complete speciation, reproductive isolation) takes thousands of generations, though important changes in trait size, shape, etc… (microevolution) can occur in only a few generations
The process; evolution by natural selection
Some complementary definitions of natural selection
Fitness!
“Something that everyone knows but can’t define precisely”- Steve Stearns, famous evolutionary biologist
Fitness!
“Something that everyone knows but can’t define precisely”- Steve Stearns, famous evolutionary biologist
“…if the variation were of a beneficial nature, the original form would soon be supplanted by the modified form, through the survival of the fittest.” Darwin in the Origin
Fitness!
“Something that everyone knows but can’t define precisely”- Steve Stearns, famous evolutionary biologist
“…if the variation were of a beneficial nature, the original form would soon be supplanted by the modified form, through the survival of the fittest.” Darwin in the Origin
(Darwinian ) fitness is thus a term that describes the ability of an individual to survive and reproduce
Population fitness is a measure of population growth potential (or growth rate, λ). Populations with high fitness are comprised by individuals with high Darwinian fitness
The logic behind natural selection
Premise 1: populations can produce many more individuals than the environment can support, therefore there is competition for limited resources, “struggle for existence”
The logic behind natural selection
Premise 1: populations can produce many more individuals than the environment can support, therefore there is competition for limited resources, “struggle for existence”
Premise 2: some individuals have traits that convey advantage in the struggle for resources and those individuals are more likely to survive and reproduce and produce more children than others, “survival of the fittest”
The logic behind natural selection
Premise 1: populations can produce many more individuals than the environment can support, therefore there is competition for limited resources, “struggle for existence”
Premise 2: some individuals have traits that convey advantage in the struggle for resources and those individuals are more likely to survive and reproduce and produce more children than others, “survival of the fittest”
Premise 3: if traits that convey advantage have a heritable (i.e. genetic) component they will be propagated in future generations and individuals will become adapted to their local environments, “adaptive evolution”.
The logic behind natural selection
Premise 1: populations can produce many more individuals than the environment can support, therefore there is competition for limited resources, “struggle for existence”
Premise 2: some individuals have traits that convey advantage in the struggle for resources and those individuals are more likely to survive and reproduce and produce more children than others, “survival of the fittest”
Premise 3: if traits that convey advantage have a heritable (i.e. genetic) component they will be propagated in future generations and individuals will become adapted to their local environments, “adaptive evolution”.
R = h2S (breeders equation)
In other words…
Premise 1: Competition
Premise 2: Trait variations allow some individuals to compete better than others (and thus have higher prob. of survival and reproduction
Premise 3: if random variation is genetic, then adaptive evolution occurs
A first example…brewer’s yeast
Fermentation occurs when yeast converts the glucose (sugar) in the grain mixture (wort) into ethyl alcohol and CO2
Fermentation ceases due to depleted sugar and toxicity of alcohol to yeast (the booze in your beer is a deadly by- product to the yeast)
Let’s provide an explanation for increased alcohol tolerance in yeast
Inspiring brew master PJ Clark is working on mastering his IPA recipe. With the goal of saving money he harvests the surviving yeast from his beer at the end of the fermentation step and uses those yeast to seed his next batch of brew. He measures the alcohol content (inferred through specific gravity) of each batch. The results are tabulated below:
Batch | Final* Specific gravity (P) | Alcohol % by volume |
1 | 22 | 4.89 |
2 | 20 | 6.06 |
3 | 18 | 7.22 |
4 | 15 | 8.93 |
5 | 14 | 9.50 |
6 | 12 | 10.6 |
Original SG = 30
Let’s take a few minutes in groups
Let’s provide an explanation for increased alcohol tolerance in yeast
Batch | Final* Specific gravity (P) | Alcohol % by volume |
1 | 22 | 4.89 |
2 | 20 | 6.06 |
3 | 18 | 7.22 |
4 | 15 | 8.93 |
5 | 14 | 9.50 |
6 | 12 | 10.6 |
Thoughts?
Group 1: Yeast genetically changes – outliving other yeast that aren’t as viable
Group 2: Yeast is evolving from batch to batch – getting stronger. Using more of the sugars to release more alcohol
Group 3: same yeast is producing enzymes better over time
Group 4: Stronger alcohol tolerance – leftover yeast
Group 5: Genetically advantageous to become more resistant.
A potential response
The population of yeast used by PJ Clark had existing genetic variation in the resistance of yeast cells to different levels of alcohol. Cells that were more tolerant to alcohol survived whereas more susceptible cells died. The resistance to alcohol has a genetic basis and therefore resistance increases in subsequent generations of yeast.
Note: Increasing alcohol represents a change in the environment for yeast, making some individual maladapted to those conditions. Individuals with traits that allow them to survive in the new environment are favored.
The process of change is adaptive evolution by natural selection
The mechanism of selection was susceptibility of certain enzymes in the yeast to alcohol.
Process vs. mechanism
Natural selection is the process of change.
The mechanism favoring some individuals is ecological, physiological, behavioral, etc…
Predation by piscivorous fish eating the most conspicuously colored prey is an ecological mechanism of selection
What was the mechanism of selection in the yeast example?
Provide an explanation…
the short fin mako can burst speed to over 50 km/h, but its closest common ancestor can burst speed to only 30 km/h
Sources of variation
Two major sources of variation that is important for evolution of populations (one is contentious!)
For example: ATTCGCCCGGAATTAAGAGTGAGG
is changed to: ATTCGCCCGAAATTAAGAGTGAGG
This code gives the “blue print” for the protein dystophin
‘normal’ protein shape
‘normal’ protein shape
Hopeful mutants
Other types of variation
Former arm-wrestling world champion!
Raised without predator
Raised with predator
Protected bay
Exposed bay
Proc. R. Soc. B (2008) 275, 1081–1087
doi:10.1098/rspb.2007.1760
Published online 5 February 2008
Adaptive evolution or plasticity?
Let’s take a few minutes in groups
Provide a hypothesis for this observed pattern, and a potential way to test to see if you were right
This is what Chris Neufeld did!
Interpret the results
Protected
Exposed
Protected
Exposed
Growth Environment
Growth Environment
Came from: Exposed Protected
FTT Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Natural or artificial (unnatural)
Evolution of blindness in cave fishes
Evolution of blindness in cave fishes
Some facts
Cave form: Blind (no eyes), no pigment, heightened brain activity in region that controls olfaction (sense of smell) and loss of brain region controlling vision. Very efficient at building fat reserves. Non-schooling behavior.
Surface form: Acute vision, heavily pigmented, relatively large brain area for vision and relatively little for olfaction. Less efficient at storing fat reserves. Occur in large schools.
Cave form
Surface form
Provide an explanation
For the loss of eyes and pigmentation in cave-dwelling tetras, given that cave populations were colonized by surface dwelling individuals that had eyes and were pigmented.
Cave form
Surface form
Let’s take a few minutes in groups (3-4 people…you decide)
Thoughts?
For the loss of eyes and pigmentation in cave-dwelling tetras given that cave populations were colonized by surface dwelling individuals that had eyes and were pigmented.
Cave form
Surface form
Propose a way to determine
Whether the lack of eyes and pigmentation in cave-dwellers is primarily the result of the environment or genetics?
Cave form
Surface form
Let’s take a few minutes in groups (3-4 people…you decide)
Ideas on how to disentangle genes from the environment?
Common garden experiments
Logic: take groups of individuals that differ in traits of interest (in this case eyes and pigmentation) and let them grow and develop in the same environment. If surface forms maintain eyes (and pigment) and blind-forms remain blind (and lack pigment) then this is strong evidence for genetic control of these traits.
Genes or environment???
Same conditions
Modified common garden experiments
Logic: Rear surface-dwellers and cave-dwellers in conditions that are similar to their own and each other’s environment and measure ‘performance’ (traits linked to ‘fitness’: growth, survival, reproductive output, etc…) in each environment.
Hypothesis and predictions assuming adaptation: ???
Cave-like conditions
Surface-like conditions
Reciprocal transplants
Move surface-dwellers to cave environments and cave-dwellers to surface environments and quantify survival, growth, or other fitness-linked traits.
A much more realistic and powerful approach.
And much more difficult to do logistically!
Evolution of coloration in male guppies
Photos: A. Hendry
Started with an observation in nature
Photos by A. Hendry & P. Bentzen
Below waterfalls
Above waterfalls
Hypotheses?
Streams in Trinidad below waterfalls are dangerous places (for guppies)
Rivulus hartii, killifish
Occurs with guppies above waterfalls. Eats guppies but only very small ones (gape-limited predator)
Occurs with guppies below waterfalls. Loves to eat adult guppies. Any guesses what sense this predator uses most for hunting?
Crenicichla alta, pike cichild
Are predators driving the color patterns in guppies?
How might you design an experiment to test for effect of predation on guppy color?��Two minutes alone…
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Ideas??
One (good) approach
John Endler
Results from artificial streams
Endler 1980
Founding generation from Trinidad
Predators introduced
High predation habitats
No predation habitats
Low predation
~ 10 generations
Predation leads to less colorful guppies
But why do guppies get more colorful in absence of predation??
Sexual selection
The advantage of individuals over others of the same species with specific regards to reproduction
“Special means of defence may be given through means of sexual selection, as the mane to the lion, the shoulder-pad to the boar, and the hooked jaw to the male salmon…”
Darwin, the Origin
Summary