BIOL300 - Macroevolutionary Strategies Notes

Environment: Behaviors induced by environmental conditions.
- Example: A chameleon changing color to absorb more heat when it's cool. This isn't genetically controlled each time, nor is it learned.
Cultural: Learned behavior.
- Example: White-crowned sparrows have regional dialects; many birds learn songs or portions of songs from others in the community.
Genetic: "Hard-wired" behavior.
- Example: The release of eggs at a certain time of day by a female oyster is clearly genetic.
All behaviors have some genetic component. The ability to change color and the ability to learn songs are genetic.

Complex behavior is influenced by both nature and nurture.
Behaviors (and strategies) have genetic, cultural, and environmental components.
All three interact in complex ways. The ability to learn or change environmentally may be genetic.
Subject to evolution (selection, drift, mutation, etc.).

Fitness: An individual’s contribution of alleles to the next generation.
Genetically controlled animal behaviors evolve to optimize individual fitness.
Competition is a method for optimizing fitness.
Cooperation: Giving up one’s own fitness (at least in part) for the benefit of another’s fitness.
Cooperation increases the reproductive success of the allele that confers cooperative behavior (individual carrying that allele).
Cooperation is a form of competition when it benefits the individual that cooperates; better cooperation is better competition.

Solitary (Presocial): Individuals do not associate except to mate.
Subsocial: Parental care is provided, but there are no other associations.
Parasocial: Individuals live in groups with different degrees of cooperation.
- Examples: Cooperative foraging, protection, care of offspring.
Eusocial:
- Cooperative brood care.
- Cooperative foraging.
- Overlapping generations.
- Reproductive division of labor.

Herds, prides, shoals, colonies, associations.
Safety in numbers:
- Collective vigilance: More eyes, ears, and noses for predator detection.
- Dilution effect: Less likely to be “picked off”.
- Greater ability to find resources, including mates.
- Improved movements (thermoregulation, drafting in birds, etc.).
Individuals benefit from living near others in groups.
Costs may include competition with others in the group.

Live in "towns."
"Bark" when predators are around.
- Warning their mates?
- But… exposes them to predators. Altruism?
- Or… Telling predators, “You see me, and I see you?”

Example: Vampire bats and reciprocal feeding.
- Bats must feed every couple of nights.
- Successful feeders regurgitate for unsuccessful feeders.
Reciprocation: An organism temporarily reduces its fitness while increasing another’s fitness with the expectation that the other will act in a similar manner at a later time.
What about cheaters (e.g., get food but don’t provide food)?
- Individual recognition and policing.

Most (all) examples benefit the individual and help individuals reproduce.
However, eusociality exhibits:
- Cooperative brood care
- Cooperative foraging
- Overlapping generations
- Reproductive division of labor
Examples:
- Ants, bees, wasps
- Termites
- Beetles, few other insect groups
- Pistol shrimp, other crustaceans
- Naked mole rats
- Plants? Staghorn ferns

Multiple castes: different individuals with specialized roles.
- Workers: forage, tend nest (cleaning, etc.), take care of eggs and larvae, do not reproduce.
- Soldiers: protect nest, do not reproduce.
- Drones: males, only reproduce (die after mating).
- Queen: one female, mates with drones, lays eggs.

Altruism: Behavior that has a cost to the self but benefits another.
Hamilton’s Rule: “An altruistic trait can increase in frequency if the benefit ( $b$ ) received by the donor’s relatives, weighted by their relationship ( $r$ ) to the donor, exceeds the cost ( $c$ ) of the trait to the donor’s fitness.”
- r b > c
“Benefits” and “costs” are in terms of the number of copies of alleles (on average) passed on to the next generation.
$r$ = coefficient of relationship: fraction of donor’s genes that are identical by descent with any of the recipient’s genes.

Your reproductive success + reproductive success of your relatives, weighted by how related they are to you.
“I would lay down my life for two brothers or eight cousins because of the average degree of relatedness."
Your fitness includes the fitness of others including offspring, but other relatives, too.

Benefits may include Direct fitness (individual) and Indirect fitness (fitness of other individuals that carry the same allele).
Alleles that can affect their own frequency in the population (e.g., by affecting their own fitness in other individuals) will gain selective advantage.
Kin selection: Other individuals with shared alleles are “kin,” and their reproductive success affects indirect fitness.
Parental care, altruism? Reproduction benefits parental alleles.

Females (queens and workers) are diploid; males are haploid (haplodiploid sex determination).
Daughters (workers) share 100% of their father’s alleles and 50% of their mother’s (queen’s) alleles.
Workers share 75% of alleles with each other.
Would only share 50% of alleles with offspring.
Better for their alleles to help raise sisters.

Sisters only share 25% of their alleles with brothers.
The average relatedness to siblings is actually only 50% ( $(75\% + 25\%) / 2$ ).
Helping is only beneficial if helping sisters.
- Would drive the proportion of males to females to 1:3, but males would then be more reproductively valuable (because they are rare).
Also, most Hymenoptera are not eusocial, and most eusocial species are not haplodiploid.

Kin selection may be only part of the story.
The queen controls development and uses pheromones to control the hive - selection on queens.
Females (queens):
- Behavioral suppression
- Physiological suppression

Castes:
- Workers (juveniles)
- Soldiers (juveniles)
- King(s)
- Queen
King(s) and queen live in the colony and continue to mate; they are the only reproductives.

Termites and wood roaches exhibit cooperative foraging.
Wood as a resource necessitates symbiosis.
Proctodeal trophallaxis: Offspring need gut microbes, transmitted socially, encourages communal living
Cooperative defense of resources.
Kin selection (limited relatedness with others in the colony).

Two species of eusocial mammals.
- One female, 2-3 males reproduce.
- Others are workers of various types.
Explanation:
- A harsh environment with rare resources (underground tubers) encourages cooperative foraging.
- Risky dispersal and mate finding.
- Close relatedness (kin selection).
- Benefit to staying with relatives and raising offspring.

Platycerium bifurcatum (Staghorn fern):
- Grow on slopes.
- Individuals at the bottom of the slope produce sterile fronds that collect nutrients and water that is shared with the group.
- Also have overlapping generations.

Darwin on sterile castes… the "one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory"
- Kin selection
- Queen manipulation (selection of manipulative individuals)
- Ecological situations and stepwise evolution
- Other?