Publication Date

2015-03-06

Availability

Embargoed

Embargo Period

2016-03-05

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biology (Arts and Sciences)

Date of Defense

2015-03-05

First Committee Member

William A. Searcy

Second Committee Member

J. Albert C. Uy

Third Committee Member

Donald L. DeAngelis

Fourth Committee Member

Richard R. Tokarz

Fifth Committee Member

Dustin R. Rubenstein

Abstract

The evolutionary maintenance of cooperative behaviors, i.e. those behaviors that increase the fitness of other individuals, is difficult to explain because natural selection should eliminate behaviors that reduce an individual’s fitness. Despite this seeming disadvantage, cooperative behaviors permeate nature; indeed, many of the major evolutionary transitions require cooperation. The prevalence of cooperative behaviors suggests that mechanisms exist that allow for the evolution and maintenance of cooperation. In this dissertation I investigated the cooperative nest construction of sociable weavers Philetairus socius. Sociable weavers are colonial birds that roost and breed in large, communal nests; the communal nests provide thermal buffering, and thus fitness benefits, to colony members. The communal nest therefore represents a public good, and as such should be susceptible to exploitation. Given the potential risk of exploitation, I tested whether certain evolutionary mechanisms are responsible for limiting the exploitation of public good and thus for maintaining cooperation; specifically, I tested both kin selection and punishment as potential forces for maintaining cooperative nest construction. Observations of nest building combined with next-generation sequencing data on relatedness demonstrate that the relatedness of an individual to its colony of residence is positively associated with cooperative investment in the public good. This result supports the importance of kin selection in maintaining cooperative building. Other results support a role for punishment in maintaining cooperation. Sociable weavers that focus their nest construction efforts on interior nest chambers (a less cooperative behavior) suffer aggression from weavers that focus their construction efforts on the nest exterior (a more cooperative behavior). The individuals that suffer aggression subsequently increase their cooperative investment in exterior construction. The totality of the evidence thus suggests that both kin selection and punishment contribute to the evolutionary maintenance of cooperation in this system.

Keywords

Cooperation; Sociable Weavers; Kin Selection; Animal Behavior; Punishment

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