Appearance / variation of male zebra finches in nature
Male Competition for Mates
Male competition for mates is a source of intrasexual selection that can reduce variation among males.
Such competition may involve agonistic behavior, an often ritualized contest that determines which competitor gains access to a resource.
Males Compete - Agonistic interaction
Applying Game Theory
In some species, sexual selection has driven the evolution of alternative mating behavior and morphology in males.
The fitness of a particular phenotype (behavior or morphology) depends on the phenotypes of other individuals in the population.
Game theory evaluates alternative strategies where the outcome depends on each individualís strategy and the strategy of other individuals.
For example, each side-blotched lizard has a blue, orange, or yellow throat, and each color is associated with a specific strategy for obtaining mates. There is a genetic basis to throat color and mating strategy.
Like rock-paper-scissors, each strategy will outcompete one strategy, but be outcompeted by the other strategy. The success of each strategy depends on the frequency of all of the strategies; this drives frequency-dependent selection.
Male polymorphism in the side-blotched lizard (Uta stansburiana)
Inclusive fitness can account for the evolution of altruistic social behavior
Natural selection favors behavior that maximizes an individualís survival and reproduction.
These behaviors are often selfish.
On occasion, some animals behave in ways that reduce their individual fitness but increase the fitness of others.
This kind of behavior is called altruism, or selflessness.
Example of altruism / selfless behavior for the good of the group:
Under threat from a predator, an individual Beldingís ground squirrel will make an alarm call to warn others, even though calling increases the chances that the caller is killed.
Altruism can be explained by inclusive fitness.
Inclusive fitness is the total effect an individual has on proliferating its genes by producing offspring and helping close relatives produce offspring.