BIOL300 Evolution - Macroevolutionary patterns

Definition: A strategy that, if adopted by all members of a population, cannot be invaded by any mutant strategy under natural selection.
Source: John Maynard Smith (1982).
Natural selection often favors fitness optima, such as in stabilizing and directional selection.
Examples:
- Cheetahs: Optimal running ability to catch prey.
- Bull elk: Optimal ability to mate with female elk.

Concept introduced by Sewall Wright.
Fitness in populations is visualized as peaks (higher fitness) and valleys (lower fitness).
Natural selection tends to make populations "climb peaks." Example: Selection for the fastest cheetahs.
Some peaks are "suboptimal," representing local fitness maxima that are not the highest possible fitness.
Transitions between peaks can be difficult due to fitness valleys.
Example: The backwards retina of vertebrates is considered suboptimal compared to the cephalopod eye.

Males and females face decisions about investing in current offspring versus creating new offspring.
Parental investment has benefits but also costs.
Investment asymmetry: Generally differs based on sex.
Strategic decision-making involves balancing benefits and costs.

As effort by one parent increases, the other's effort may decrease.
Optimal effort levels exist for both males and females, leading to an Evolutionarily Stable Strategy (ESS).

John Maynard Smith initially envisioned single strategies but ESSs are often mixed, with variable individual behavior (e.g., in parental care).
Hawk vs. Dove game:
- Models competition for resources.
- Involves the choice between fighting (Hawk) and fleeing (Dove).

Hawk always fights, even against other hawks.
Dove always backs down from a fight.
$C$ = cost of fighting.
$V$ = value of the resource.
Outcomes:
- Hawk meets Dove: Hawk gets full resource ( $V$ ).
- Hawk meets Hawk: Each has an equal chance of winning ( $(V-C)/2$ ) in a symmetrical contest where the loser is the first one injured but survives.
- Dove meets Hawk: Dove gets nothing ( $0$ ) but isn't hurt.
- Dove meets Dove: Shares the resource ( $V/2$ ) or engages in a war of attrition (waiting and display).

	Hawk	Dove
Hawk	$(V-C)/2$ , $(V-C)/2$	$V$ , $0$
Dove	$0$ , $V$	$V/2$ , $V/2$

Consider a population of all doves where each dove wins 50% of meetings without injury.
A hawk mutation can invade this strategy by winning every contest without suffering any cost.

In a population of all hawks, frequent fighting leads to injuries and reduced fitness.
A dove can invade if the costs of fighting and low reward from the resource (e.g., females) offset the benefits of fighting.
Dove's success is closely associated with the probability of encountering a hawk.
The ESS is a mixed strategy.

If encounters don't escalate, how is ownership of a resource decided?
- Sharing (dividing the resource).
  - Equity issues, potential for cheating, and future interactions must be considered.
- War of attrition.

Each player bids for a resource of value $V$ .
Each player pays the lowest bid $a$ .
Waiting game (persistence) where waiting costs fitness and increases over time.
The winner is the one who persists longer and gets the entire resource.
Potentially infinite number of waiting times, resulting in no dominant strategy.
Players may bid more than $V$ ; if both bid > $V$ , the winner loses less (Pyrrhic victory).
Players should not betray their intent due to symmetry.

Dominant male: Fights other males, competitively excludes them from females and resources.
Satellite/sneaker male:
- Typically smaller and non-aggressive.
- Hangs around edges, attempts to mate.
- May mimic females.

Benefits:
- No territorial defense or parental care.
- Fertilizes multiple females.
- Invests less in development and fighting, may live longer.
Costs:
- Possibly fewer eggs fertilized overall.
- Attacked by large territorial males.
Sneakers often have higher average individual fitness but depend on the dominant male strategy.
May invest more in testes and sperm.

Three forms (Gross & Charnov 1980):
- Large, territorial parent: Courts female, tends/defends nest; young depend on him.
- Smaller satellite cuckolder: Mimics females, confuses dominant male, fertilizes eggs.
- Even smaller sneaker cuckolder: Dives in and squirts sperm.
Each has equal average fitness over time (ESS).
Dominant male can exist without others; others cannot.
Dominant males take 6 years to mature; others 2-3 years.
Condition dependence: Poor condition males become one of the "parasites"; good condition males become dominant.

Uta stansburiana (Sinervo & Lively 1996).
Three genetically controlled forms:
- O form (orange throated): Ultra-dominant, roams and fights.
- B form (blue throated): Mate guarder, cooperative, beaten by O lizards.
- Y form (yellow throated): Creeper, sneaks copulations with O's females.
Cyclical dominance: O beats B, Y beats O, B beats Y.

Referencing Sheldon Cooper's expansion of Rock/Paper/Scissors to include Lizard and Spock.
- Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and rock crushes scissors.
Listing of other possible expanding strategies.