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Why do males cooperate when resources, namely females and conceptions, are scarce and hard to secure (Krutzen et al. 2003)? Hamilton introduced the idea that related individuals may increase their inclusive fitness by cooperation, even if the increased reproductive benefits only apply to one of the individuals in his theory of kin selection (Hamilton 1964).
In 1964, W. D. Hamilton published two papers titled The Genetical Evolution of Social Behavior in the Journal of Theoretical Biology to explain the theory of kin selection. He formulated a mathematical relationship that could explain how individuals could increase their own fitness by helping their relatives. An actor will only perform a costly action if the relationship C<R*B , where C is cost in fitness to the actor, R is genetic relatedness of the actor to the recipient, and B is the fitness benefit to the recipient, holds true. This relation explains the driving force for many seemingly altruistic behaviors of related organisms and is the basis for the kin selection theory.
To test whether alliance formation in male bottlenose dolphins was influenced by kinship, Krutzen et al. tested relatedness in primary, secondary, and super-alliances. It was found that males in primary and secondary alliances were more closely related than expected by chance. However, super-alliance members were not significantly related. Relatedness of primary and secondary alliances may be explained by the theory of kin selection. Since super-alliances are not based on genetic relatedness, a large group must present other advantages for members. It is highly probable that super-alliances can compete more strongly against smaller primary and secondary alliances to secure more females (Krutzen 2003). [link] shows a high correlation between association coefficient and relatedness in bottlenose dolphins (p<0.01), which supports the idea that alliances are related.
In bottlenose dolphins, alliances form to help each other in foraging, predation, consorting females, and caring for young. This system of mutual assistance can be described by the theory of reciprocal altruism (Connor&Norris 1982).
Reciprocity can occur independent of genetic relatedness (Trivers 1971). The model of reciprocal altruism consists of two parties, X and Y. X performs an altruistic act for Y, expecting that in return Y will perform an altruistic act for X. This increases the inclusive fitness of X (Connor&Norris 1982). However, what happens if X helps Y, but Y does not reciprocate? In order to prevent this situation of cheating, there must be a method for discriminating against a cheater (e.g. a partner who will not reciprocate). In a social society, like that of bottlenose dolphins, individuals communicate about the altruistic and cheating tendencies of other individuals. In a study by Marino et al., it was shown that dolphins demonstrate social knowledge, showing awareness of the behaviors and identities of others (2007). Because of the size of the society and the intermingling of individuals, dolphins must be able to recognize a high volume of individuals and identify them as ally or cheat. By sharing information on cheaters, bottlenose dolphins are able to discriminate against them. Consequently, the cheater’s inclusive fitness decreases and the cheating gene will be selected against.
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