Type of Document Dissertation Author McGhee, Katie E. URN etd-11062009-113936 Title Behavioral Types And Sexual Selection In The Bluefin Killifish Degree Doctor of Philosophy Department Biological Science, Department of Advisory Committee
Advisor Name Title David Houle Committee Member James Fadool Committee Member Thomas Hansen Committee Member Frank Johnson University Representative Keywords
- Behavioral Syndrome
- Lucania goodei
- Social Interactions
- Mating Behavior
Date of Defense 2009-09-24 Availability unrestricted AbstractIn many animal species there is pronounced and repeatable variation among individuals in their expression of suites of behaviors, resulting in consistent behavioral types. These behavioral types are characterized by measures like the degree of boldness, aggression, activity, and exploratory behavior. While the prevalence of behavioral types and their importance in terms of natural selection have become apparent in recent years, their importance in determining the outcome of sexual selection remains imperfectly understood. In this dissertation I examined the role of behavioral types in sexual selection in the bluefin killifish, Lucania goodei, as well as the influence of environmental and genetic factors on the expression of behavioral types.
In chapter two I investigated how female choice and male competition interact in the bluefin killifish in a 3-staged experiment where (1) females could choose between two males, (2) those males could interact in the presence of that female, and (3) females and males could freely interact and spawn. In the pairwise stages (1 and 2), females displayed pronounced preferences between males and male competition produced a distinctly dominant individual. None of the morphological traits, including color, measured in males were associated with either female preference or male dominance. When all three fish interacted (stage 3), male mating activity level (behavioral type) was the sole predictor of spawning success. Males with elevated activity levels were more aggressive toward males and females, exhibited intensified courtship, and obtained more spawns. Female preference did not predict the number of spawns with a male but it did predict her latency to spawn; females spawned more quickly with preferred males. Thus, male competition and female choice interact to determine reproductive success but there is evidence for conflict and a cost to females of associating with dominant males. Reproductive success in this species is not easily predicted from simple measures of morphology or female preference, and is influenced by complex social interactions, both between males, and between males and females. The outcomes of these social interactions are in turn influenced by the behavioral types of the participants.
In chapter three I examined whether repeatable personality differences among males are associated with repeatable outcomes of male-male interactions within the mating context. Specifically I examined the repeatability of individual differences in mating behaviors and the stability of dominance status, which partially determines mating success in the bluefin killifish. The expression of male behaviors in competition between males and female courtship was significantly repeatable over a five-week time period; the number of aggressive behaviors to males, to females, and the number of courtship bouts had significant repeatabilities of 0.71, 0.72, and 0.65 respectively. A maleís behavioral type within the mating context, as measured by a composite measure of the overall level of mating behavior activity, was significantly repeatable at 0.75. Males showed repeatable, linear dominance hierarchies and a maleís rank in the hierarchy was highly correlated with his behavioral type. Neither behavioral type nor dominance status was associated with body size or body condition. The repeatability of behavioral types and stability in the outcomes of aggressive interactions, suggest that these behavioral types are inherent characteristics of individuals rather than short-term responses to recent social experience or daily levels of food or stress.
In chapter four, I examined how differences between individuals in behavioral type arise. Specifically I examined whether nutritional and social conditions experienced by individuals early in life affect the development of behavioral type and behavioral expression later in life in the bluefin killifish. As fry, individuals experienced either high food or low food levels and within each food treatment, individuals experienced one of three social environments: they were reared with one adult male, one adult female, or no adult, producing six treatment combinations. Social treatments were removed at 5 months and food manipulations were ceased at 6 months, after which individuals were fed ad libitum until behavioral testing at 10 months. Males reared on high food and low food were paired with one another within a social treatment and tested in a female choice trial and male dominance trial. Food and social treatments produced strong, synergistic effects on growth; individuals raised at high food were larger than those raised at low food and high food individuals reared with an adult female grew faster than those in all other treatments. There was no evidence for compensatory growth after release from treatments imparting slow growth. Despite the effects of early experience on growth and body size, I was unable to detect any comparable effect on behavioral variation. Male behavioral type and behavioral expression were not significantly affected by food level and this did not vary across social treatments. High food and low food males did not differ significantly in their likelihood of becoming dominant as adults or of being preferred by females. These results suggest that an individualís early rearing environment, at least the particular aspects manipulated here, have little influence on the development of behavioral type in this species.
Given that personalities can affect fitness, understanding the environmental and genetic factors that influence personalities, as well as the associations among behaviors across different contexts are crucial to understanding the evolutionary response of personality to direct and indirect selection. In chapter five, I performed a series of paternal half-sib crosses to estimate the heritability of a number of distinct behaviors within and across three different contexts (mating, response to a predator, recovery from stress) as well as whether there are phenotypic and genetic correlations among behaviors exhibited within and across contexts. Despite the presence of strong phenotypic correlations among the behaviors exhibited in the mating context, my results indicate that only courtship behaviors appear to be significantly heritable and there is little evidence for significant additive genetic variance in aggressive behaviors. In addition, I found no evidence for phenotypic correlations among traits expressed outside the mating context, nor evidence for additive genetic variation for those behavioral traits.
The results of my dissertation point to more complex sources of individual variation in personality and, concomitantly, more complex patterns of selection. I found that while variation in three behaviors formed an integrated personality, in only one behavior was that variation based on substantial heritable genetic variation. What emerges as individual personality could be the result of individual variation in a single behavior and the network of provocation and response that is built by social interactions. This complexity opens new avenues for future empirical work and new possibilities for understanding the subtle interplay of genetic and environmental foundations for the behaviors seen in complex social systems.
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