Cooperation and Death in Evolutionary Biology

Cooperation and Death

  • The textbook discusses various behaviors related to cooperation and death, including:
      - Migration
      - Signaling through visual or chemical communication
      - Learning
      - Mating
      - Parenting

  • Emphasizes that in externally-fertilizing animals, male parenting is as prevalent as female parenting.

  • Parenting involves significant investment in the protection and nourishment of offspring, raising the question of whether parenting is a selfish or selfless act.

Types of Interactions

  • Cooperation: A mutualistic interaction providing fitness benefits to all parties involved.

  • Altruism: A behavior where one party sacrifices its own fitness for the benefit of others.

  • Selfishness: A behavior where one party benefits at the expense of others.

  • Spite: A behavior resulting in fitness loss to all involved parties.

The Paradox of Altruism

  • Darwin viewed selfless acts as potentially contradictory to his theories of evolutionary fitness.

  • Inclusive Fitness: Understanding altruism hinges on this principle:
      - Acts favoring the survival or reproduction of close relatives might be selected for because genes from relatives are seen as extensions of the individual's own genes from an evolutionary perspective.

  • William Hamilton's Model: Analyzes how relatedness among individuals favors altruistic behavior.

Hamilton’s Rule

  • Formula: B imes r > C or equivalently r > rac{C}{B}
      - Where:
        - BB = Benefit to the recipient.
        - CC = Cost to the actor.

  • Example: "I’d give my life for two siblings … or eight cousins."

  • Indirect fitness may be gained by assisting relatives, making altruistic acts evolutionarily beneficial.

Coefficients of Relatedness

  • Coefficient (r) Calculation:
      - Parent-offspring relation: r=rac12r = rac{1}{2}
      - Grandparent-offspring relation: r=rac14r = rac{1}{4}
      - Cousin-cousin relation: r=rac18r = rac{1}{8}.
      - Total genetic contribution to offspring includes:
        - 50 ext{ ext{% of genes}} from parents to offspring.

Kin Selection: Potential Products

  • Developments and patterns arising from kin selection include:
      - Multicellularity
      - Coloniality in invertebrates
      - Sterile castes in haplodiploid insects
      - Family helper associations in birds and mammals
      - Human social structure
      - Parenting behaviors in organisms like the Portuguese man o' war.

Alarm Calling in Belding’s Ground Squirrels

  • These squirrels exhibit sentry behavior in “prairie dog towns.”

  • Alarm calls are made at a high risk of attracting predators, particularly by females when close relatives (mother, sister, daughter) are nearby:
      - Call frequency increases by 3-5 times when kin are present compared to non-relatives.

  • Females collaborate to drive out intruding squirrels, especially among closely related individuals.

  • Types of calls include whistles and trills.

Natal Habitats and Male Migration

  • Data shows extensive male migration correlated with alarm calling frequency among different age and gender groups, noting:
      - Adult females are more likely to call than males.

Cannibalistic Tadpoles

  • Ambystoma tigrinum (Tiger Salamander):
      - Exhibits phenotypic plasticity, with two morphs:
        - Cannibal morph: feeds on other tadpoles rather than algae.
      - Benefits of cannibal morph:
        - Useful in scarcity of algae.
        - Provides a high protein diet.
      - Costs include:
        - Extra growth cost.
        - Higher parasite risk.
        - Potentially consuming relatives.

Frequency of Cannibal Morph

  • Altered based on:
      - Food availability (normal food: algae)
      - Abundance of competitors (other tadpoles).
      - Relatedness to other tadpoles.

  • In small ponds with few colonizers, cannibal behavior may be less favorable due to potential relative consumption.

Kin-Recognition and Discrimination

  • Research by Pfennig et al. showed genetic variation in kin recognition:
      - Some cannibals strictly avoided relatives, leading to trade-offs between growth rate and inclusive fitness.

Model for Sociality: Slime Molds

  • Dictyostelium:
      - Lives as single amoebae but aggregates under stress (starvation).
      - Slug Stage: Mobile phase seeking optimal reproductive conditions.
      - Fruiting Body Formation: For spore dispersion.
      - Genetic Chimeras: Diminished performance due to selfishness among cells, reflecting conflict.

Portuguese Man o' War

  • This organism exemplifies eusociality,
    characterized as a ‘superorganism’ with caste systems resembling organs in a body:
      - Cooperative offspring care.
      - Sterile castes comprised of workers and warriors that sacrifice personal reproduction.
      - Observed in certain insects, one crustacean species, and one mammal species (e.g., naked mole rats).

Hamilton & Hymenopteran Relatedness

  • Haplodiploid Sex-Determination System:
      - Males develop from unfertilized eggs (haploid).
      - Females are diploid, originating from fertilized eggs by the queen.

  • Hamilton’s conclusion:
      - Females are evolutionarily incentivized to help rear sisters over producing their own offspring.

Inclusive Fitness in Hymenoptera

  • Workers demonstrate greater relatedness to sisters than to their own offspring (r=0.5r=0.5).

  • Kin selection theory predicts that workers preferentially care for the queen’s daughters:
      - Queens lay equal numbers of male and female eggs, but workers manipulate sex ratios, often culling male embryos.
      - In single-queen species, sex ratios can approach 1:3 due to this culling process.