Although evolution by natural selection has often been depicted as favoring ruthless, selfish behavior, cooperation is actually widespread in nature. Consequently, the evolution of cooperative behavior has become a central problem in biology. The present research examines the evolution of a particular form of cooperation, cooperative nest building in an African bird. Communal nests represent a public goods dilemma: each individual benefits directly from the communal nest, but would benefit more if it could refrain from contributing to nest-building as long as others continued to maintain the nest. Such public goods dilemmas are common in human societies but have rarely been explored in non-human animals.
This research will investigate cooperative nest construction behavior of a Namibian bird, the sociable weaver. Observations of nest construction in nature will examine relative contributions of the sexes and of individuals to test whether cooperation in this instance can be explained via kin selection. Simply, kin selection is a type of natural selection favoring aid to genetic relatives. An agent-based model will be used to further explore the possibility that cooperative nest building can be sustained through kin selection. The computer code used to implement the model will be made available to other scientists, thus facilitating future modeling efforts in social evolution.
In addition, an experiment will test whether individuals that forego cooperative nest construction are punished by others; such punishment is a common explanation for contribution to public goods in human societies. Thus the research will test whether theories explaining contribution to public goods in human societies explain cooperation in this model system. The project will also contribute to the development of the next generation of scientists and engineers. The project includes undergraduate mentoring and training in genetic analyses and behavioral observation, thus providing useful research experience for the next generation of American scientists.
The National Science Foundation Doctoral Dissertation Improvement Grant #1210500 investigated how large-scale cooperative behaviors can be maintained in animal societies despite short term benefits of exploitation. We utilized sociable weavers (Philetairus socius) as a model system, and we specifically focused on the cooperative nest construction behavior that these birds perform. The communal nest is a particularly useful system because the weavers must maintain the nest, but an individual bird would be better off if it took advantage of the cooperative effort of other individuals in the group without working itself. Therefore, we would expect that a selfish strategy would outcompete the cooperative strategy, leading to a reduction or extinction of cooperative nest construction in nature. Since cooperative nest construction stably exists, we hypothesized that evolutionary mechanisms exist that maintain the cooperative behavior, preventing exploitation. We specifically tested two mechanisms that have been theorized to stabilize cooperation: kin selection and punishment. We found evidence that kin selection helps maintain cooperative nest construction in sociable weavers. We found that the degree of relatedness of an individual to other colony members predicted how much that individual invested in cooperative nest construction. Working to help genetic relatives can explain the evolutionary maintenance of cooperative behavior, because individuals with genes promoting cooperation will aid others that share those same genes. Therefore the genes underlying cooperation can be maintained in the population since the benefits of cooperation are directed towards the same genes in other individuals. Kin selection prevents exploitation because it assures that the benefits of cooperation are received by the genes that underlie cooperation. We subsequently tested whether sociable weavers punish the selfish behavior of others. We found evidence that cooperative individuals are more aggressive towards individuals that work on individual chambers in the nest, which we consider a more selfish type of nest construction. After suffering aggression, these selfish individuals shifted to helping construct the exterior of the nest, a more cooperative type of nest construction. This aggressive behavior allows cooperative individuals to help limit exploitation of their cooperative output because individuals switch to a more cooperative behavior after suffering aggression. In total, we find support for both kin selection and punishment, the two mechanisms that according to theory should stabilize large-scale cooperative behavior. While investigating sociable weavers in the field, the Co-PI designed and implemented software that will help introduce individuals from the public to concepts in evolution and behavior. The Co-PI published curriculum material describing this software in an open-access journal (Evolution: Education and Outreach, article in press, 2014) that can be used by instructors at both the high school and undergraduate levels. The Co-PI has utilized the software at University of Miami alumni events and has begun the process of using the software to teach individuals about public goods and the evolution of cooperation. To complement more traditional academic publications, the Co-PI has also utilized established media platforms to discuss the topic of study and introduce the system to the public. Specifically, the Co-PI is currently writing for the National Geographic Explorer’s Journal Blog (http://newswatch.nationalgeographic.com/2014/07/09/to-study-bird-societies/) and is documenting interesting behaviors studied during the project. Given the global presence of National Geographic the Co-PI is able to reach a large audience by this means. The Co-PI has also worked with an NSF Post-doctoral fellow at the University of Miami Rosenstiel School of Marine and Atmospheric Science to directly communicate research findings to the public. Specifically, the website www.publiscize.com was created by NSF fellow Robert Seigel to facilitate the transmission of research findings to the public. To this end the Co-PI has written scientific synopses about research supported by the NSF doctoral dissertation grant. These synopses are edited and published at the website for consumption by the public. In addition to the digital methods of communicating science, the Co-PI has also given a lecture at a local community college (Broward Community College). During the lecture the Co-PI described central results of the project to local students. After the lecture the Co-PI discussed with the science club of Broward Community College how to begin a career in science.
