Successful preservation of Earth’s biodiversity requires an understanding of the processes that generate new species. The generation of species without gene exchange is considered predominant; however, a growing body of evidence indicates that populations can diverge while exchanging genes, and that this may be common. Previous research hypothesized that blue-footed (Sula nebouxii) and Peruvian (S. variegata) boobies diverged from their common ancestor while exchanging genes. Here, I combine ecological and genetic perspectives to thoroughly evaluate this hypothesis. Using a panel of eight molecular markers, I estimate population differentiation for each species. I find evidence of weak population differentiation for both species, an uncommon pattern in seabirds, and argue that specialization to an unpredictable food resource has shaped contemporary population differentiation. Next, I use molecular markers and morphology to evaluate the hybrid status of five morphologically aberrant individuals. I report that all are likely F1 (first generation) hybrids, and are the product of crosses between female Peruvian boobies and male blue-footed boobies. Sex biases in pairing may occur because of an underlying preference for elaborate courtship displays. I then expand the dataset to 19 loci and use cline theory and Bayesian assignment tests to characterize the hybrid zone, to examine introgression, and to evaluate the hybrid status of the aberrant individuals. The hybrid zone is most likely maintained by strong endogenous and exogenous selection against hybrids and dispersal of parentals into the hybrid zone (a tension zone), and introgression is low for nuclear loci and absent for mitochondrial loci. Finally, I test the hypothesis that this species pair diverged from their common ancestor with gene flow using recently developed analyses and multiple loci. Divergence without gene flow is rejected and unidirectional introgression of sex-linked loci during divergence is reported. The results of this study support the hypotheses that: 1) populations can diverge while exchanging genes; 2) the Z chromosome may play a role in avian speciation; and 3) organisms specialized to variable foraging environments should exhibit low population differentiation. This study adds to our understanding of both population differentiation and speciation in seabirds, and the generation of new species more generally. / Thesis (Ph.D, Biology) -- Queen's University, 2011-04-06 13:55:32.151

<p>Under the increasing threat of climate change, it is imperative to understand the impact that environmental phenomena have on the demography and behavior of natural populations. In the last few decades an ever increasing body of research has documented dramatic changes in mortality rates and breeding phenology for a large number of species. A number of these have been attributed to the current trends in climate change, which have been particularly conspicuous in bird populations. However, datasets associated to these natural populations as well as to the environmental variables that affect their biology tend to be partial and incomplete. Thus, ecological research faces the urgent need to tackle these questions while at the same time develop inferential models that can handle the complex structure of these datasets and their associated uncertainty. Therefore, my dissertation research has focused on two main objectives: 1) to understand the relationship that demographic rates and breeding phenology of a colony of seabirds has with the environment in the context of climate change; and 2) to use and develop models that can encompass the complex structure of these natural systems, while also extending the process not only to inference but to building predictions. I divided this work in three research projects; for the first one I developed a hierarchical Bayesian model for age-specific survival for long lived species with capture-recapture data that allows the use of incomplete data (i.e. left-truncated and right-censored), and builds predictions of years of birth and death for all individuals while also drawing inference on the survivorship function. I compared this method to more traditional ones and address their limitations and advantages. My second research chapter makes use of this method to determine the age-specific survivorship of the Dry Tortugas sooty tern population, and explores the effect of changes in sea surface temperature on their cohort mortality rates. Finally, my third research chapter addresses the dramatic shift in breeding season experienced by the Dry Tortugas sooty tern colony, the most unprecedented shift reported for any bird species. I explore the role of climatic and weather variables as triggering mechanisms.</p> / Dissertation