Olof Leimar, Department of Zoology, Stockholm University

Biology and game theoryWhere are we now and how did we come here?

A biologist’s perspective

The Logic of Animal Conflict

Maynard Smith & Price (1973)

Mule deer males fighting Arabian oryx males fighting

“reducing intra-specific damage”

Julian Huxley (1966). Ritualization of behaviour in animals and man.

The logic of asymmetric contests

Maynard Smith & Parker (1976)

Papilio zelicaon male Hilltopping P. zelicaon male

“The resident always wins”Davies (1978). Territorial defence in the speckled wood butterfly (Pararge aegeria)

Typical habitat for speckled wood butterflies

Does the resident always win?

Does the resident always win?

The role of motivation

Christer Wiklund

Bergman, Olofsson & Wiklund (2010) Contest outcome in a territorial butterfly

Polymorphism and morph determination

Papilio dardanus

model mimicPapilio dardanus

model

model

mimic

mimic

Papilio dardanus

Batesian mimicry

Polymorphism

The Dobzhansky - Cain & Sheppard - Fisher polymorphism debate

Dobzhansky (1951) Genetics and the origin of species

Genetic polymorphism as such is frequently adaptive Theo. Dobzhansky

Cain & Sheppard (1954) The theory of adaptive polymorphism

"This interesting theory may be correct, but it is not clear what is meant by one population being more highly adapted than another to a particular environment"

Arthur Cain

A precursor of the group selection debate

Fisher concluded the debate

Dobzhansky is right, but the idea traces back to "a little-known book of nearly a hundred years ago, called The Origin of Species"

Fisher regarded polymorphism as an adaptive strategy

"one way of making this intelligible is by the analogyof games of skill, or to speak somewhat more pretentiously, of the Theory of Games"

Fisher (1958) Polymorphism and natural selection

"I would not have alluded to this storm in a tea-cup, but for the circumstance that I mean to put forward some ideas on this problem of the possible adaptive value of polymorphisms"

The “Darwin joke”

Phenotype determination

Schwander & Leimar (unpubl.)

Phenotype determination

Schwander & Leimar (unpubl.)

Sex determinationBulmer & Bull (1982). Models of polygenic sex determination and sex ratio control

Ouachita map turtle Baby

Sex determination

Van Dooren & Leimar (2003). The evolution of environmental and genetic sex determination in fluctuating environments.

Mechanisms of sex determination

Quinn et al. (2007). Temperature sex reversal implies sex gene dosage in a reptile.

Central bearded dragon lizard

Climate-driven population divergence in sex-determining systems

Pen et al. (2007)

Snow skink

Five rules for the evolution of cooperation

Nowak (2006)

From a biologist’s perspective some things are missing

• Biological markets

• Sanctions and partner choice

• By-product benefits

• Pseudoreciprocity

• Common interest

Leimar & Hammerstein (2010). Cooperation for direct fitness benefits.

Sanctions in legume rhizobium mutualism

Bacteria fix atmospheric nitrogen inside root nodules of leguminous plants

What if the bacteria do not fix nitrogen?

Experiments suggest that the plant then re-allocates its resources (Kiers et al. 2003)

Recent work claims that the role of sanctionsis small (Marco et al. 2009)

CommentSanctions are best understood as a by-product of an action that is of direct interest to the actor

Cleaning mutualism: by-product benefits

There are immediate benefits (food and removal of ectoparasites) for the partners

Ant-lycaenid mutualism: pseudoreciprocity

Lycaenid larvae invest in sweet secretion – ants forage and protect their food resource

Mycorrhizae: exchange of organic carbon and mineral nutrients between plants and fungi

Could it work like human trading and exchange?

Mutual investments in by-product benefits

Leimar & Connor (2003) Bever et al (2009)

Evolution of common interest

Contributing factors

• Cost of changing partners, resulting in partner fidelity

• Increased dependence on partners

Acacia plant housing mutualistic ants Extrafloral nectar is offered

The extrafloral nectar

• contains glucose and fructose

• is virtually void of sucrose

Ants of the genus Pseudomyrmex

• have lost the capacity to digest sucrose

• depend on this nectar (Kautz et al. 2009)

Possible evolution of increased dependence as a by-product of the advantage of being less attractive to non-mutualistic ants