| Summary: | For decades, social amoebae have served as a model supporting broader
theories of social behavior. Owing to their peculiar aggregative life cycle, it
has seemed reasonable altruism in social amoebae is possible because of
adaptive mechanisms of kin discrimination, and kin discrimination evolves
to maintain this altruistic behavior. Nonetheless, these hypotheses have not
withstood critical tests in social amoebae or other organisms. As a result,
general theories of social evolution have rested on a few abstract theoretical
assumptions.
I here use social amoebae as a model system to examine these
assumptions through empirical study. First, I focus on the natural context of
social evolution in the social amoeba Dictyostelium discoideum. I establish
D. discoideum occurs frequently in a state of clonality during the social stage
and that obligate cheaters (non-altruists) are not present in nature (Chapter
1). I then show that kin discrimination in D. discoideum has only a weak
effect on genetic relatedness in the social stage (Chapter 2). Upon this
finding, I propose a hypothesis that kin recognition evolves in response to
facultative rather than obligate cheating (Chapter 2). I generalize this
argument in Chapter 3, where I propose a new "selfish genome" model of
kin recognition. This model is unique in that it accounts for the effects of
genome-wide relatedness between individuals on one another's fitness. This
model explains the adaptive basis of kin recognition-a trait thought to be
crucial for major evolutionary transitions.
I also describe two additional studies of social amoebae. In the first, I
report on the finding of a large clonal patch of a social amoebae. This is the
first example of such a phenomenon in a microorganisms (Chapter 4). In the
second, compare two forms of migration and development in social amoebae
(Chapter 5). This study shows social amoebae can be studied in a similar
way to animals, with a focus on the multicellular phenotype. I argue the
production of stalk during migration is an example of altruistic behavior.
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