Behavior, Eusociality, and Kin Selection

OLD:

Today: Behaviors Vary

Behaviors are Relevant to Fitness

…and genes can influence Behaviors

Nikolaas Tinbergen’s Four Questions Proximate PerspectiveUltimate Perspective Static Perspective Mechanistic Cause (i.e. hormonal cascades) Adaptive Function (i.e. evolved to combat hunger) Dynamic Perspective Ontogenetic (i.e. developmental conditions) Phylogenetic (i.e. inherited from related ancestors)  How should ethologists “explain” behavior?

A cautionary note: “Our closest relatives, the chimpanzees, live in promiscuous societies in which females seek as many sexual partners as possible and a male will kill the infants of strange females with whom he has not mated. There is no human society that remotely resembles this particular pattern: Why not? Because human nature is different from chimp nature.” ― Matt Ridley, The Red Queen: Sex and the Evolution of Human NatureMatt RidleyThe Red Queen: Sex and the Evolution of Human Nature “Half the ideas in this book are probably wrong.” ― Matt Ridley, The Red Queen: Sex and the Evolution of Human NatureMatt RidleyThe Red Queen: Sex and the Evolution of Human Nature  Anthropomorphism: Ascribing human motives or cultural characteristics to natural phenomena such as animal behavior

Do not necessarily need a brain to “behave”

Do not necessarily need a brain to “behave” Karban et al. 2000

Behavior and Cooperation in unicellular organisms Dictyostelium discoides  Amoeboid cells -- aggregate under starvation  Form a “slug” to traverse faster  Fruiting body with “stalk” (~20%) and “spore” (~80%) guilds  Unicellular cooperation as precursor to multicellularity?

Dicty aggregation video

Cooperating vs. Cheating  Amoeboid cell fate (spore or stalk) determined at slug formation  Positional response to cell signalling – quantitative trait!  cthA allele confers a spot in the stalk  One cthA amoeba in 1000 wild-type cells:

Why Cooperate When You Can Cheat? Does selection favor individuals that behave at the expense of their groups?  Group Selection: Groups of cooperative individuals will outcompete and displace groups of selfish individuals  Evolutionary Stable Strategy: A balance of behavior(s) that, when adopted by a population of players, cannot be invaded by an alternate strategy

ARE MAJOR TRENDS IN THE FOSSIL RECORD DUE TO SELECTION OPERATING AT THE LEVEL OF SPECIES?  The possibility that long-term trends in the fossil record are due to differential survival of species raises the question of whether selection can operate at multiple levels. CONDITIONS NECESSARY FOR SPECIES SELECTION  The character shows “heritability” through speciation events. For example, species with larger than average body size tend to give rise to new species with larger than average body size. OLD:

 Game Theory: An approach to studying behavior that solves for the optimal payoff strategy, depending on the choice of other players.

Sometimes Sociality benefits vastly outweigh the costs

Obvious Group Advantages: Teamwork in the Wild

Obvious Group Advantages: Safety in Numbers

Obvious Group Advantages: Team Defense

Sometimes Sociality benefits vastly outweigh the costs, cont.  Connection with mates / offspring can be a significant benefit of maintaining social groups.

 Inclusive Fitness: Direct Fitness + Indirect Fitness  Kin Selection: Selection arising from indirect benefit to one’s own alleles from helping relatives. Coefficient of relatedness (r)  Self – parent: 0.5  Self – sibling: 0.5  Self – offspring: 0.5  Self – grandparent: 0.25  Self – grandoffspring: 0.25  Self – 1 st Cousin:  …..

When To Be Self-Sacrificial?  Hamilton’s Rule: When r * Benefit > Cost, an altruistic allele can spread under selection.

Barriers to Kin Selection:  Kin Recognition  Uncertain Paternity  Hindsight is 20/20. How to accurately gauge Benefit, Costs of helping behaviors?  …Calibration of help response to individual cost/benefit values.

Eusociality: The extreme of social organization Social systems in which reproduction and labor are divided into strict castes

Eusociality: The extreme of social organization  Haplodiploidy: Mechanism of sex determination in which males are haploid and females are diploid. - Females lay haploid eggs  If eggs are fertilized by haploid sperm, They become diploid females  If eggs are not, Remain haploid and develop into males.

Eusociality: The extreme of social organization  How does Hamilton’s Rule operate under haplodiploidy?  Queen mates with one or more males  Son’s entire genetic make-up from queen  Daughters’ r = 0.75 with one another  Offspring more heavily invested in queen’s reproduction than their own r * Benefit > Cost

Eusociality: The extreme of social organization  Development of hymenopteran castes:  Queens  Workers  Drones  Soldiers (sometimes)  Superorganism: Any such “organism” consisting of many organisms