| Sociality varies greatly among animal species, ranging from completely solitary to highly gregarious. The evolution of this complex and widely diverse trait has long been a puzzle for behavioral scientists. Coalitions are a type of sociality that occurs when two or more individuals join together against a third; the evolution of this behavior is also not well understood. My dissertation focuses on developing a new way to understand coalitions. I develop a coalitionary trait metric, which uses the presence or absence of three traits, mutual tolerance, collaboration, and partner preference, to assess the level of social complexity possessed by the males of a species. I use this metric in a comparative study to determine what factors are the most correlated with increased coalition complexity and thus the most likely to have influenced the evolution of or coevolved with coalitions. I found that social factors such as estrus duration, group size, and dominance hierarchy were significantly correlated with coalition complexity, while environmental variables such as habitat type, diurnality, or diet type were not. I then tested the utility of the coalitionary traits metric on a model species, the yellow-bellied marmot. Using a combination of field and laboratory methods, I found that male marmots form rudimentary coalitions; they lack collaboration and partner preference, but possess mutual tolerance. I also found that male marmot sociality does not increase individual reproductive success, but is most likely a result of environmental constraints. Finally, I further explored the sociality of yellow-bellied marmots by examining the prevalence of inbreeding in my study population. I found that male marmots do not appear to discriminate against inbreeding, with approximately half of all breeding males siring at least one inbred offspring. I also found that inbreeding is costly, with the survival of inbred offspring significantly decreased. I conclude that inbreeding is maintained in the marmot population due to a large amount of variance in male reproductive success, so that the majority of males sire no offspring in their lifetime; this makes males who sire any offspring, even those that are inbred and less fit, achieve greater reproductive success. |
