Browsing by Author "Sillett, T. Scott, committee member"
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Item Open Access Body size, first year breeding, and extra-pair paternity in an island endemic, the Island Scrub-Jay(Colorado State University. Libraries, 2014) Desrosiers, Michelle A., author; Angeloni, Lisa M., advisor; Ghalambor, Cameron K., advisor; Funk, W. Chris, committee member; Sillett, T. Scott, committee member; Crooks, Kevin R., committee memberBody size is a fundamental characteristic that shapes all aspects of an organism's biology. The advantages of large body size may include increased probability of territory acquisition, a critical component of fitness for species that require a territory to breed. Large body size, an indicator of quality, may also be advantageous to males in acquiring mates, including matings outside of a pair bond. Such advantages could be especially important in island systems because habitat saturation may result in strong intra-specific competition for territories, and females may be especially motivated to seek large extra-pair mates to increase the body size of their offspring. We tested the role of body size in determining the ability of an island-endemic bird, the Island Scrub-Jay, Aphelocoma insularis, to acquire a territory and breed in their first spring, as well as to sire extra-pair offspring. We compared the body size of individuals that obtained a territory and bred to those that did not, as well as the body size of social fathers to the extra-pair sires to whom they lost paternity. We found that large body size was important in the siring of extra-pair young. However, body size did not predict the ability of male or female Island Scrub-Jays to acquire a territory and breed in their first year. We suggest that year-to-year variation in environmental conditions and chance may be more important than a large body size or weapon performance in early territory acquisition. Our study provides evidence for a mechanism, specifically female preference for a large body size in males, that supports the observed rates of extra-pair paternity, and demonstrates the general difficulty, even for individuals with a relatively large body size, of acquiring a territory as a yearling in an island system with saturated habitat.Item Open Access Demography and parental investment in orange-crowned warblers: testing life history theory(Colorado State University. Libraries, 2012) Sofaer, Helen R., author; Ghalambor, Cameron K., advisor; Noon, Barry R., committee member; Sillett, T. Scott, committee member; Webb, Colleen T., committee memberUnderstanding the diversification of life history strategies is a major goal of evolutionary ecology. Research on avian life history strategies has historically focused on explaining variation in clutch size, and most studies have tested whether this variation can be explained by variation in a single ecological factor, such as food availability or mortality risk. However, relatively few studies have evaluated whether the causes of variation within populations are distinct from or similar to the causes of variation between populations. In my dissertation, I compare the life history strategies of orange-crowned warbler (Oreothlypis celata) populations and study the causes of variation in clutch sizes, incubation behavior, nestling provisioning rates, nestling growth rates, and breeding phenology. I tested alternative hypotheses for the ecological causes of divergent life histories, and assessed the consequences of these different reproductive strategies for parents and offspring. My results indicate that no single ecological factor can explain life history variation either within or between populations. Instead, life history and behavioral traits differ in their sensitivities to different ecological factors, and while differences between nearby populations can reflect plastic responses to ecological variation, populations that are more geographically and evolutionarily distant can differ in both their responses to ecological variation and in the consequences of variation in parental behavior for offspring growth and development.Item Open Access Evolutionary underpinnings of microgeographic adaptation in song sparrows distributed along a steep climate gradient(Colorado State University. Libraries, 2021) Gamboa, Maybellene Pascual, author; Ghalambor, Cameron K., advisor; Funk, W. Chris, advisor; Sillett, T. Scott, committee member; Wolf, Blair O., committee member; Hufbauer, Ruth A., committee member; Morrison, Scott A., committee memberUnderstanding how evolutionary processes interact to maintain adaptive variation in natural populations has been a fundamental goal of evolutionary biology. Yet, despite adaptation remaining at the forefront of evolutionary theory and empirical studies, there remains a lack of consensus about the evolutionary conditions that enable adaptation to persist in natural populations, especially when considering complex phenotypes in response to multivariate selection regimes. In my dissertation, I disentangle the evolutionary mechanisms that shape adaptive divergence in song sparrows (Melospiza melodia) distributed along a climate gradient on the California Channel Islands and nearby coastal California. First, I found evidence that climate, and neither vegetation nor selection for increased foraging efficiency, likely drive adaptive divergence in bill morphology among insular populations. Second, I used an integrated population and landscape genomics approach to infer that bill variation is indicative of microgeographic local adaptation to temperature. Lastly, I tested whether the distinct climate gradient facilitates adaptative divergence in other thermoregulatory traits and found evidence to support environmental temperatures result in fixed population differences in many complementary phenotypes, including plumage color, feather microstructure, and thermal physiology. Collectively, these results find support for microgeographic climate adaptation in a suite of complex phenotypes and demonstrate the utility of integrative approaches to infer local adaptation in natural populations. Finally, by developing a more holistic understanding of climate adaptation in natural populations, my results inform conservation management of this species of special concern.Item Open Access Microgeographic divergence in a single-island endemic: evolutionary patterns and conservation implications(Colorado State University. Libraries, 2014) Langin, Kathryn M., author; Ghalambor, Cameron K., advisor; Crooks, Kevin R., committee member; Funk, W. Chris, committee member; Morrison, Scott A., committee member; Sillett, T. Scott, committee memberUnderstanding the processes that generate biological diversity is the central goal of evolutionary biology. Geographic isolation has traditionally been viewed as the primary scenario favoring evolutionary divergence. However, there is growing appreciation for the role of ecological variation and natural selection in driving adaptive differentiation, even in the absence of geographic barriers to gene flow. My dissertation tests for microgeographic patterns of local adaptation within one of the most range-restricted bird species in North America, the Island Scrub-Jay (Aphelocoma insularis). The species is restricted to Santa Cruz Island in southern California, USA, where it occurs in a diversity of habitat types within its narrow (250 km2) geographic range. Remarkably, I found that Island Scrub-Jays in three separate stands of pine habitat had longer, narrower bills than those in oak habitat, a pattern that mirrors adaptive differences between allopatric populations of the species' mainland congener (A. californica). Adaptive divergence was not constrained by genetic diversity, even though Island Scrub-Jays had much lower levels of neutral genetic diversity than A. californica. Genetic data indicate that Island Scrub-Jays in pine habitat were more closely related to individuals in adjacent oak habitat than to individuals in other pine stands, indicating that each pine stand can be considered an independent case where adaptive divergence has been maintained in the face of some gene flow with adjacent oak birds. Morphological differences were not abrupt across the pine-oak boundary, as bill length declined gradually with distance from pine habitat, a clinal pattern that is also consistent with a scenario of divergence-with-gene flow. Individuals mated non-randomly with respect to bill length within the population, which may be due to a combination of (1) isolation-by-distance (localized dispersal) across the landscape and spatial autocorrelation in bill morphology, and (2) assortative mating at a more local scale based on bill morphology or correlated acoustic signals. These findings provide strong support for the notion that microgeographic patterns of local adaptation may be more common than is currently appreciated, even in mobile taxonomic groups like birds. They also underscore the importance of conserving Island Scrub-Jays across the entire island in order to preserve the species' full range of biological diversity and to facilitate adaptive responses to future environmental changes.Item Open Access Reproductive ecology of the island scrub-jay (Aphelocoma insularis)(Colorado State University. Libraries, 2010) Caldwell, Luke, author; Angeloni, Lisa M., advisor; Sillett, T. Scott, committee member; Savidge, Julie A., committee memberThe small population size and limited range of the Island Scrub-Jay make it a species of conservation concern, yet its reproductive ecology is poorly known. From 2008 - 2010 I investigated factors influencing nest success, quantified annual fecundity per pair, and documented breeding behavior. Nest predation was the major factor influencing nest success, accounting for 92 percent of documented nest failures. Nests that were initiated earlier in the breeding season, nests that were higher and more concealed, and nests of breeding pairs that had smaller home ranges had higher daily nest survival. Despite a low estimated daily nest survival rate of 0.945 ± 0.004 SE, the high frequency of renesting allowed pairs to maintain a mean fecundity of 1.13 ± 0.15 SE. Island Scrub-Jays may benefit from an increase in breeding habitat and lower nest predation from the ongoing regeneration of woody vegetation and understory structure following the removal of exotic herbivores on Santa Cruz Island.Item Embargo The genomics of habitat-linked microgeographic adaptation in an island endemic bird(Colorado State University. Libraries, 2024) Cheek, Rebecca G., author; Ghalambor, Cameron K., advisor; Funk, W. Chris, advisor; Sillett, T. Scott, committee member; Aubry, Lise M., committee memberA fundamental goal of evolutionary biology is to understand the mechanisms that maintain adaptive diversity. This dissertation focuses on the interplay of two key evolutionary mechanisms - natural selection and gene flow. While natural selection is often portrayed as a driving force of adaptive evolution, gene flow is assumed to disrupt selection by introducing maladapted alleles into locally adapted populations. Yet this paradigm is beginning to shift as a growing appreciation for the role gene flow may play in concert with natural selection to facilitate adaptative divergence. I explore this interaction of selection and gene flow in island scrub-jays (Aphelocoma insularis), a highly mobile bird experiencing local adaptation at a microgeographic scale. First, I demonstrated that observed differences in bill morphology between pine-oak ecotones are likely genetically based despite overall limited population genetic structure. Second, I found that the genetic underpinnings of divergent bill morphologies are highly parallel at higher genetic levels, which is indicative of selection acting on shared, but highly polygenic, molecular pathways. Finally, I tested alternate dispersal mechanisms potentially impacting patterns of limited gene flow and found evidence for sex-biased natal habitat preference shaping limited dispersal. Collectively, these results show how gene flow can enhance adaptive divergence at microgeographic scales.