Individual specialization occurs when individuals selectively consume a subset of their population's diet. Intraspecific diet variation can stabilize population and community dynamics, promote species coexistence, and increase ecosystem productivity. Ecological variation also provides the variability necessary for natural or sexual selection to act. Individual threespine stickleback select different prey from a shared environment, and this variation is not simply a result of sex, size, or spatial heterogeneity. I use longitudinal observation of stickleback foraging microhabitat to support more commonly used cross-sectional metrics. Among recaptured individuals there were correlations between microhabitat use and functional morphology, and microhabitat use and long term dietary differences between individuals. I quantify individual specialization across populations using cross-sectional sampling to understand how and why ecological variation may itself be variable. All populations showed significant individual specialization. Specialization varied between populations and this variation seems to be a long-term property of populations. Overall morphological variance was positively correlated with ecological variation. Ecological variation, like all types of heritable variation, provides raw material for evolutionary change. For example, lacustrine populations of stickleback are commonly under disruptive selection due to intraspecific competition for prey resources. Speciation with gene flow may be driven by a combination of positive assortative mating and disruptive selection, particularly if selection and assortative mating act on the same trait. We present evidence that stickleback exhibit assortative mating by diet, using the isotopes of males and eggs within their nests. In concert with disruptive selection, this assortative mating should facilitate divergence. However, the population remains phenotypically unimodal, highlighting the fact that assortative mating and disruptive selection do not guarantee evolutionary divergence and speciation. There are several not-mutually-exclusive mechanisms by which assortative mating by diet may occur in these populations, such as shared microhabitat preference among individuals of similar diet. Stable isotopes reveal diet differences between different nesting areas and among individuals using different nest habitat within a nesting area. Spatial segregation of diet types may generate some assortative mating, but is insufficient to explain the observed assortment strength. We therefore conclude that sticklebacks' diet-assortative mating arises primarily from behavioral preference rather than from spatial isolation. / text

<p>The threats of human encroachment and climate change are increasing and understanding the interplay between genetic diversity, fitness, and ecological variation has become critical for predicting adaptive responses and species extinction risk. Decreasing genetic diversity, owing to population decline or inbreeding, can be detrimental at the level of the individual, population, or species. One of the major challenges for evolutionary and conservation biologists is identifying the specific genetic components that influence inter-individual variation in fitness remains. As a direct link between genetic-make up and individual fitness, the Major Histocompatibility Complex (MHC) is critical to the activation of the adaptive immune system. Biologist have suggested that in addition to influencing an individual's health, variation at the MHC may be related to an individual's survival and reproductive success. Here, I test this hypothesis using two populations of ring-tailed lemurs (<italic>Lemur catta</italic>) at long-term study sites to achieve individual and population-level comparisons of MHC diversity and to integrate new genetic technology with behavioral, ecological, and environmental data. First, I address the difficulty of genotyping large populations at hypervariable genes by using next generation sequencing and suggest improvements to current methods. Second, I describe patterns of variation at the MHC-DRB 2nd exon, including diversity between alleles, individuals, and populations. Next, I examine the relationship between MHC-DRB diversity and measures of immunocompetence, parasitism, and survival within a broader framework of ecological variability across captive and wild conditions. Because the MHC is also thought to be important in mate choice and reproduction, I use an experimental approach in captive individuals to investigate possible mechanisms of MHC-based signaling through olfactory communication. Lastly, I link a female's MHC genotype to her reproductive success in the wild and explore if this relationship is altered by environmental stressors. The results of this dissertation emphasize the increasing feasibility of using genetic approaches to investigate the fitness correlates of genetic diversity non-model systems. These advances are critical for future studies and the integration of behavioral, ecological, and genetic perspectives in semi-natural and wild environments.</p> / Dissertation

<p>Alternative reproductive tactics (ARTs) have been described across taxa numerous times, and are especially common in fishes. The advent of molecular techniques has enhanced our understanding of such mating systems, yet these techniques have only been applied to relatively few species. Furthermore, ecological variation has long since been recognized as an important factor influencing mating patterns and sexual selection, yet it is often ignored. In my thesis, I conducted field studies to investigate the reproductive ecology of a species with well characterized ARTs, the plainfin midshipman (<em>Porichthys notatus</em>), and to explore how these mating patterns varied across time and space. This species is characterized by two male tactics: guarders and sneakers. I show that both tactics are successful at gaining fertilization. Indeed, I found evidence for several behavioural adaptations by the guarder male tactic to gain fitness, including guarding, nest takeovers, and plastic cuckoldry behaviours. I also documented the lowest paternity for guarder males for a species with obligate male parental care. Paternity increased over the course of the breeding season, which was likely a result of a higher occurrence of nest takeovers early in the season. In a cross-population analysis of plainfin midshipman, I found significant differences in nest availability and density between two genetically distinct populations, but this did not translate into significant differences in mating patterns. Taken together, my thesis helps elucidate the reproductive ecology of a classic species with ARTs, and has important implications for our understanding of ecological influences on mating patterns and sexual selection.</p> / Doctor of Philosophy (PhD)