<p> The larval nutritional mode of marine invertebrates is an important life history trait that has strong effects on their ecology and evolution. Increases in egg size and transitions from feeding to nonfeeding larvae have happened repeatedly. In Spiralia, a change in cytoplasm allocated to macromeres at the 8-cell stage (that could delay the development of a functional gut) may accompany these transitions. The first part of this thesis describes the development of the gastropod <i>Crepidula williamsi</i> and compares it to the closely related <i>C. fornicata,</i> with a focus on changes in allocation to macromeres and the development of a functional gut. The second part is a phylogenetic comparison of egg size and allocation to macromeres in 44 species of spiralians, which revealed a significant correlation between the two. A phylogenetic comparison like this one has not previously been done on the development of such diverse marine invertebrate taxa.</p>

<p> This study examines how the different behavioral, environmental and physiological factors might be influencing the essential physiological trait of erythrocyte mean cell diameters (MCD). At present no other study has explored the effects of these factors. Erythrocyte MCD for 153 species were collected from recent literary sources and compared to erythrocyte MCDs collected by Gulliver (1875), genome sizes and spleen sizes were also collected from a variety of literary sources. This data was analyzed using R with phylogenetic generalized least square analyses against several different behavioral, environmental and physiological factors. From these analyses, I found that as mammal mass and length increase the erythrocyte MCD also increases and as mammals move into higher elevations and warmer climates erythrocyte MCD decreases. All other behavioral, environmental, and physiological factors did not have an influence on erythrocyte MCD. These data did not support hypotheses previously offered by the other studies done on erythrocytes. Further research needs to be conducted on this topic because other factors that influence erythrocyte MCD may still exist that were not examined in this study.</p><p>

<p> Interpreting the taxonomic and behavioral implications of variation in the inferred limb proportions of fossil hominin taxa is contingent upon assessing how much variation exists in extant primate taxa and, by extension, how much of that variation is associated differences in their locomotor behaviors. However, the majority of evidence linking limb proportions to behavior in extant primates is based on taxonomically-restricted samples, or on species means as opposed to individual values, or does not account for field observations that capture the complexity of locomotor behavior in a primate taxon (see Napier &amp; Napier, 1967; Fleagle, 1988; see also Preuschoft, 2002). With regards to extinct taxa, the problem is compounded by a necessary reliance on relatively few associated skeletons, most of which are incomplete, or fragmented or both. </p><p> This thesis addresses the aforementioned issues using a) multivariate methods to quantify the relationships between limb proportions and behavioral repertoires in extant anthropoids; b) machine-learning methods to select relevant extant models with which to interpret the limb proportions of extinct taxa; and c) resampling methods to evaluate hypotheses regarding major adaptive shifts in inferred locomotor behavior.</p><p>

<p> The earliest-diverged multicellular animals are decentralized organisms capable of growing to indeterminate sizes and highly variable morphologies. These organisms must coordinate activity among their constitutive cells at the scale of the organism in order to to leverage the benefits of multicellularity, and must do so using decentralized mechanisms that are robust to uncertainty in size and shape. This thesis investigates how coordination within the Placozoa&mdash;arguably the simplest animals&mdash;scales with organism size, quantifies the extent to which different developmental processes affect size regulation, and creates a framework for measuring morphological variability in what had been considered amorphous animals. In Chapter 1 I develop a method by which one can measure coordination and information propagation within an animal's body plan, and investigate how this propagation is affected by changes in size. I argue that such animals are poised at criticality, with evidence presented to suggest that this facilitates optimal information transmission, but that the physical constraints of multicellularity create a size-coordination trade-off in such decentralized organisms. The presence of size-induced trade-offs brings forth the question of how size is regulated, which in Placozoa occurs through growth and asexual fission. In Chapter 2 I investigate whether size is regulated in response to changing environmental nutrient conditions and find that animals adjust their sizes to match their environments. I further find that this change comes about primarily due to changing dynamics of growth rather than fission, and identify that growth is highly dependent on nutrient conditions, but find evidence that asexual fission could be an emergent phenomenon of poor coordination beyond certain sizes. Finally, in Chapter 3 I investigate the morphological variability in Placozoa and find evidence for allometric growth in such animals. In addition, Chapter 3 sets the groundwork for future comparative morphological studies between individuals and for behavioral stereotyping by developing a size and rotation invariant shape representation, which I use to identify the presence of idiosyncratic morphologies. I close the thesis with some remarks regarding future directions in exploring the effects of scaling on coordination, morphology, and behavior in this small yet evolutionarily significant Metazoa phylum.</p><p>

<p> Over the last half-century, previously undescribed tick-borne pathogens including the Lyme disease bacteria, <i>Borrelia burgdorferi</i>, have rapidly spread across the Northeast and Midwest United States. Lyme disease is now the most commonly reported vector-borne disease in North America, with over 300,000 estimated cases each year in the United States. Despite its epidemiological importance, many questions remain about this ongoing invasion. Does the observed spread of human cases reflect the ecological spread of the Lyme disease bacteria or does it reflect changes in case reporting and recognition? How do ticks and tick-borne pathogens spread across space and why are tick-borne pathogens currently invading the US? A better understanding of the ecological and evolutionary history of Lyme disease in North America will inform predictions about its future spread and how control measures might be implemented.</p><p> Reconstructing the invasion of Lyme disease is challenging because <i> B. burgdorferi</i> circulates in an enzootic cycle; humans are only incidental hosts. This means that reported cases of disease may not reflect the underlying ecological spread of <i>B. burgdorferi</i>. Pathogen genomes offer an alternative data source for reconstructing the history of pathogen invasion. However, this requires large population-scale samples of pathogen genomes that are difficult to generate from field samples. Further, for pathogen genomes to be informative, pathogens must evolve on similar timescales to ecological spread.</p><p> My dissertation work integrates diverse data sources&ndash;human case reports and pathogen genomic data&ndash;to reconstruct the history of <i> B. burgdorferi</i> in North America. In Chapter One, I present a spatio-temporal model for the spread of human cases of Lyme disease and babesiosis, another tick-borne disease, across New England. Our model uses use the best available longitudinal data&ndash;human surveillance data&ndash;to model the underlying ecological spread of tick-borne pathogens. Our model predicts that tick- borne diseases spread in a diffusion-like manner, at approximately 10 km per year, with occasional long-distance dispersal, likely due to spread by avian hosts. The remaining studies rely on pathogen genomic data. In Chapter Two, I tackle the methodological challenge of generating genomic data from mixed template samples by developing a method to capture multiple pathogen genomes from individual field-collected tick samples. This approach allowed us to efficiently differentiate between pathogen DNA versus tick and other exogenous DNA, enabling efficient deep sequencing and population genomic study. In Chapter Three, I examined the genomic diversity of <i>B. burgdorferi</i> within individual field-collected ticks. I found that 70% of ticks are infected with multiple strains of the Lyme disease bacteria, indicating that humans may be exposed to and infected with more than one strain of the bacteria from a single tick bite. I also find evidence that the Lyme disease bacteria is evolving in response to the immune defenses of its natural hosts (including rodents and birds). Finally, in Chapter Four, I examined patterns of <i>B. burgdorferi</i> genomic variation across space. I find that <i>B. burgdorferi</i> diversity is ancient and predates not only the reported emergence of Lyme disease in humans over the last ~40 years, but also the last glacial maximum, ~20,000 years ago. Ultimately, population genomic data reveal that the recent emergence of Lyme disease in North America is not driven by a recent introduction or evolution of <i>B. burgdorferi</i>. Instead, the recent epidemic of human Lyme disease is likely driven by environmental and ecological changes that have increased the density of ticks, infected ticks, and/or frequency of human exposures to infected ticks in the past century.</p><p>

<p> The deep sea is the Earth&rsquo;s largest ecosystem and harbors a unique and largely endemic fauna. Although most research has focused on the ecological mechanisms that allow coexistence, recent studies have begun to investigate how this remarkable fauna evolved.. My work quantifies geographic patterns of genetic variation and investigates potential mechanisms that shape evolution in the deep ocean. </p><p> Bathymetric genetic divergence is common in the deep sea with population structure typically decreasing with depth. The evolutionary mechanisms that underlie these patterns are poorly understood. Geographic patterns of genetic variation indicated that the protobranch bivalve <i>Neilonella salicensis </i> was composed of two distinct lineages separated bathymetrically. Genetic diversity was greater in the lower-bathyal clade of <i>N. salicensis </i> than the upper to mid-bathyal clade. In a co-occurring mid-bathyal protobranch <i>Malletia johnsoni,</i> population differentiation was greater among samples than the confamilial lower-bathyal <i>Clencharia abyssorum,</i> though, genetic diversity was similar. These patterns suggest general trends do not always hold and fine scale patterns of gene flow need to be thoroughly investigated. </p><p> Little is known about the ecological or evolutionary mechanisms that might promote divergence or maintain population structure. Oxygen minimum zones (OMZs), which cover enormous regions of the deep ocean, might hamper gene flow by precluding larval dispersal. To test this, genetic patterns of the wood-boring bivalve <i>Xylophaga washington</i> were quantified across the northeastern Pacific OMZ. Results indicate two clades were apparent, one throughout the OMZ and one within and below it, possibly segregated by a historically stronger OMZ or other environmental factors that vary with depth. A similarly uninvestigated evolutionary factor with potentially large impacts is selection on mitochondrial DNA. Positive selection is apparent in the mitochondrial DNA of shallow water and deep-sea crabs, shrimp, and fishes, possibly related to any of the myriad factors that differ between the two habitats. </p><p> The deep sea is biogeochemically important and is highly impacted by climate change and anthropogenic factors. Genetic patterns in this habitat are very complex. This work suggests gene flow is inhibited at many scales, both across bathymetric gradients and within small bathymetric ranges.</p><p>