Lecture 5:
Unit of Selection
•Who/what benefits from adaptation?
Nucleotide – Gene – Cell – Organism – Group – Species
•What is the unit of selection?
•Can a benefit at one level be detrimental to
other levels? Conflict?
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Unit of Selection - Evolution - Lecture Slides, Slides of Theory of Evolution
Unit of Selection, Benefits from Adaptation, Segregation Distorter Genes, Cell Lines, Reproductive Restraint, Northern Flicker, Altruism, Florida Scrub Jay, Interdemic Selection Model are the key important points of lecture slides of Evolution.
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Lecture 5:
Unit of Selection
- Who/what benefits from adaptation?
Nucleotide – Gene – Cell – Organism – Group – Species
- What is the unit of selection?
- Can a benefit at one level be detrimental to other levels? Conflict?
Examples
- Segregation distorter genes
- Benefit one gene at expense of others
- Cell lines vs. rest of body
- Must be able to reproduce from >1 cell line
- Theoretical at the moment
Interdemic/ Interpopulational
Selection
VC Wynne-Edwards :
- Non-breeding in seabirds – how explain?
- NS acts on the level of group
- Social behaviour regulates pop’n density
Reproductive restraint
Evidence:
Northern Flicker :
avg: 6-8 eggs can lay up to 71
- Infer: restraint evolves through
pop’n selection not ind. selection
- Why? Unrestrained pop’n growth depletes resources & leads to extinction
- Implication: selection operates to the detriment of the ind. but benefit of the group
- How likely is this really?
Interdemic Selection Model
Selfish gene (S) = ↑↑ repro rate
Initial success, ultimate failure
A A A S A A A A
S S S S S S S S S
EXTINCT
Patch Model
(Maynard-Smith)
Alleles: A = altruistic S = selfish
S
empty
A
Overuse resources
Extinct unless migrate
Infected by S Goes to fixationDocsity.com
Group Selection
- Weak force
- Only if migration is very low & group extinction rates very high
- Group selection may exist, it just cannot counteract individual selection
Life History Trade-offs
- Current vs. Future reproduction
- “cost of repro” hypothesis
Invest now
Future Reproduction
Future Survival
Evidence: future fecundity
- Collared flycatcher:
Gustaffson & Part (1990)
- Manipulated clutch size,
- birds with ↑ clutches had
↓ clutches for next 3 years
Kin Selection
Altruism: incur cost ( c ) to bestow benefit ( b )
Contradicts Darwinism: Unlikely NS fix altruistic allele
Nepotistic alleles: tend to help sibling
Should feed own offspring or sibling?
Offspring p(n) = 0.5 (meiosis)
Sibling p(n) = 0.
Allele says either because they are equal
Hamilton’s Rule of Inclusive Fitness
If : rb > c or r > c/b then help r = degree of relatedness b = benefit (#surviving offspring) c = cost (#lost offspring) e.g. Costs c to help sister ( r = 0.5), each gene suffers c but gains b x 0. If b /2 > c help b/c ↑ inclusive fitness N.B. r = probability that two individuals have homologous alleles identical by descent
Beldings Ground Squirrel
Alarm calling:
Cost: ↑ predation risk Benefit: ??? Likelihood of calling depends on knowledge of relatedness (philopatry?)…. thus ↑ inclusive fitness
Spadefoot Toad Cannibalism
- Two morphs: omnivore vs. cannibal
- Cannibals tended not to eat their siblings (Pfennig 1999)
- Calculated that rb > c
European Wood Mouse Sperm
- Promiscuous females
- Sperm trains: faster than single sperm
- Release before reaching egg…many unsuccessful, but improves brothers’ chances