Dissertation/Thesis Abstract

Essays on biological cooperation
by Akcay, Erol, Ph.D., Stanford University, 2008, 132; 3313805
Abstract (Summary)

The evolution of cooperation has been a major question in evolutionary biology for over 40 years. This dissertation develops new theoretical approaches to the question. It adopts a conceptualization of social evolution that operates at two separate, but connected tiers. Behavior is modeled at the time-scale it happens, i.e. within the lifetime of the interacting individuals, while evolutionary change is between generations. This two-tiered approach allows new modeling tools at the behavioral tier that will contribute to our understanding of how cooperation and social behavior in general function and have evolved.

The chapters of my dissertation deal with four separate systems. In chapter 2, I present a model of the symbiosis between nitrogen-fixing rhizobia and legume plants. The model describes a mechanistic negotiation process occurring in behavioral time, which leads to a mutually beneficial outcome. In so doing, it goes beyond the question of why cheaters do not take over the system, and generates testable predictions about the division of benefits from the interaction. It also illustrates that stable agreements can be negotiated even between bacteria and plants that lack any cognitive complexity or legal system.

Chapters 3 and 4 deal with a phenomenon in bird reproductive behavior called extra-pair paternity, which is the presence of offspring in a nest that is not sired by the male tending the nest. Previous hypotheses for why this occurs have focused on the females "cheating" on the males to obtain genetic benefits for their offspring. In chapter 3, I review the large number of studies testing this hypothesis and find that they do not lend support for genetic benefits as a major cause of extra-pair paternity. Then, in chapter 4, I present a model that provides a new explanation, namely that extra-pair paternity arises as a result of negotiations between males for opportunities to pair with particular females. I model this hypothesis in behavioral time, using a new modeling tool, cooperative game theory. This model explains currently documented patterns of extra-pair paternity, while at the same time generating new empirical predictions.

Chapter 5 deals with biparental care. So far, models of biparental care have focused on the conflicts of interests between parents, but the predictions from these models have not been confirmed in experimental studies. In chapter 5, I develop a model that does not assume conflict of interests, but instead considers the behavioral decisions of two parents that both aim to maximize their joint nest production. This model can explain observed patterns in empirical data and provides a way of testing whether parents act as together as a team or individually.

The last chapter, chapter 6, returns on the evolution of cooperation problem in the abstract, and brings the two tiers together for the first time. We model the evolution of internal motivations of animals engaged in an interaction which involves conflict of interests, but also offers the possibility of cooperation. We find that animals can evolve motivations that are non-selfish: they care of each other's payoff as well. This provides a new explanation for how cooperation can evolve and function.

Overall, this dissertation demonstrates how the study of social behavior will benefit from a two-tiered approach. Models of interactions at the behavioral tier such as the ones presented here will help our understanding the functioning of social behavior and guide the empirical and evolutionary questions we need to ask.

Indexing (document details)
Advisor: Roughgarden, Joan
School: Stanford University
School Location: United States -- California
Source: DAI-B 69/05, Dissertation Abstracts International
Subjects: Ecology, Zoology
Keywords: Biological cooperation, Cooperation, Evolutionary game theory, Extra-pair paternity, Legume-rhizobium symbiosis, Parental care, Social evolution theory
Publication Number: 3313805
ISBN: 978-0-549-62961-0
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