• Actions taken at a cost to an individual which are beneficial to another
• Usually in nature these are related organisms which share part of their geonome
• Difference from Facilitation - this usually refers to interspecies interactions, but cooperation can be within OR between species

Altruistic cooperation

• Benefits others but is costly for the actor, such as decreasing their reproductive output

Coefficient of Relatedness $r$

General method:

This describes meiosis.
Where $L$ is the generation link, and 0.5 is the probability that a copy of a particular gene will be passed on.

Hamilton's Rule

In order for altruism to evolve:

Where:

• $r$ is coefficient of relatedness
• $b$ is the benefit to recipients
• $c$ is the cost to the actor

Example: Long-tailed Tits

• If a nest is failed, some individuals might decide to not try again, but instead assist a close relative in raising their offspring
• They recognize offspring by similar calls and behaviour

Example: Meerkat helpers

• Subordinate members ("helpers") provide altrustic care to the pups
• It's costly to "babysit" instead of foraging (they can lose up to 8% of their body weight)
  !course cooperation 071024_Van Meyel, p.3
• But there must be some advantage in order for this to evolve:
  !course cooperation 071024_Van Meyel, p.4
• Overall, the daily weight gain of pups is increased by having more members watching out for predators

Cost-Benefit Ratio and environment

• Generally, we find more cooperative behaviours in harsh or unpredictable conditions
• It was long thought that harsh conditions select for this behaviour
• In 2017, a new phylogenetic study of cooperative breeding in birds showed that this is a bit misleading and in fact the causality is opposite:
  • Species with cooperative behaviours are more likely to be able to colonize harsh environments

Example: Pine Sawflies and cooperative defense in larval stage

• They live and feed in very dense groups in larval stage
• They raise their heads and puke a foamy fluid at the same time when one is being predated on
  • They sequester defensive compond from compounds in pine needles (in their diet)
• This is more advantageous to the group if they all contribute to the defense
• They cause economic damage to pine trees:
  • Host plant defends against pine sawflies by producing toxic chemicals like terpene
  • The sawflies need to invest into protecting themselves from this compound
  • They have evolved to use this compound against predators
• We can study how this collective defense under different conditions

Amount of contribution

• There is a lot of variation in how much an individual contributes to the group
• There are some individuals who do not defend at all, even just against themselves

Experiment in diet variation

• Phenoloxidase activity: Higher values have higher immune defense
• Given low-resin and high resin diet, and also simulated a predator attack (high attack intensity vs low intensity), stimulating a defensive reaction
  • The Trade-off here is:
    • low-resin diet is less toxic, but they can produce fewer defenses
    • high-resin diet
• Within the high-resin diets, there was more variation between high and low intensity attack behaviour
  • Environment is an important factor in cooperative behaviour
• Larvae who did not defend were not "out of" defensive fluid, they just chose not to cooperate

Benefits of freeloading?

• Non-defending males grew faster than defending males
  • Not as significant in females

How does cooperation evolve?

Kin Selection is often a mechanism to evolve cooperation, but not the only one.

!Cooperation benefits flowchard

Heritability of Competition

• Quantitative evidence of heritability of behavioural traits are often lower than morphological traits (based on meta-analysis)
• Most are due to environmental/Maternal effect (social environment)
  • The genotypes of other individualsin the environment is called Indirect Genetic Effects (IGE) that need to be taken into account
• However there is some genetic variation that is part of this - this is difficult to quantify though

Example in animal breeding:

• In animal agriculture, they are sometimes selecting for animals that grow as fast as possible
  • In piglets, selecting only for growth rate can result in piglets that are less competitive for certain teats
  • Similarly in plant breeding, if you have plants in kin groups you might get faster responses in terms of selection?? Less variation?

Applied Example:

• Antimicrobial resistance of pathogens
• How is resistance evolved?
  • Biofilms are tolerant to antimicrobials
  • Inhibiting biofilm formation makes them more susceptible to antimicrobials
• We need to be able to limit evolution of resistance
• Some biofilm forming agents are "public goods" like EPS
  • EPS is costly to producing cells
• Some strains are non-EPS producers, others are EPS resistanct
• Adding EPS inhibitors on surfaces will make it harder for biofilms to form
  • Evolution of resistance to EPS inhibition, since in this case the resistant strain is outcompeted by the strains which are non-producers but are susceptible to other antimicrobials