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Abstract Determining the genetic architecture of traits involved in adaptation and speciation is one of the key components of understanding the evolutionary mechanisms behind biological diversification. Hybrid zones provide a unique opportunity to use genetic admixture to identify traits and loci contributing to partial reproductive barriers between taxa. Many studies have focused on the temporal dynamics of hybrid zones, but geographical variation in hybrid zones that span distinct ecological contexts has received less attention. We address this knowledge gap by analyzing hybridization and introgression between black-capped and Carolina chickadees in two geographically remote transects across their extensive hybrid zone, one located in eastern and one in central North America. Previous studies demonstrated that this hybrid zone is moving northward as a result of climate change but is staying consistently narrow due to selection against hybrids. In addition, the hybrid zone is moving ~5× slower in central North America compared to more eastern regions, reflecting continent-wide variation in the rate of climate change. We use whole genome sequencing of 259 individuals to assess whether variation in the rate of hybrid zone movement is reflected in patterns of hybridization and introgression, and which genes and genomic regions show consistently restricted introgression in distinct ecological contexts. Our results highlight substantial similarities between geographically remote transects and reveal large Z-linked chromosomal rearrangements that generate measurable differences in the degree of gene flow between transects. We further use simulations and analyses of climatic data to examine potential factors contributing to continental-scale nuances in selection pressures. We discuss our findings in the context of speciation mechanisms and the importance of sex chromosome inversions in chickadees and other species. 

Abstract Retaining information in working memory is a demanding process that relies on cognitive control to protect memoranda-specific persistent activity from interference^1,2. However, how cognitive control regulates working memory storage is unclear. Here we show that interactions of frontal control and hippocampal persistent activity are coordinated by theta–gamma phase–amplitude coupling (TG-PAC). We recorded single neurons in the human medial temporal and frontal lobe while patients maintained multiple items in their working memory. In the hippocampus, TG-PAC was indicative of working memory load and quality. We identified cells that selectively spiked during nonlinear interactions of theta phase and gamma amplitude. The spike timing of these PAC neurons was coordinated with frontal theta activity when cognitive control demand was high. By introducing noise correlations with persistently active neurons in the hippocampus, PAC neurons shaped the geometry of the population code. This led to higher-fidelity representations of working memory content that were associated with improved behaviour. Our results support a multicomponent architecture of working memory^1,2, with frontal control managing maintenance of working memory content in storage-related areas^3–5. Within this framework, hippocampal TG-PAC integrates cognitive control and working memory storage across brain areas, thereby suggesting a potential mechanism for top-down control over sensory-driven processes. 

Beginning from the shallow water equations (SWEs), a nonlinear self-similar analytic solution is derived for barotropic flow over varying topography. We study conditions relevant to the ocean slope where the flow is dominated by Earth's rotation and topography. The solution is found to extend the topographic β-plume solution of Kuehl (2014) in two ways. (1) The solution is valid for intensifying jets. (2) The influence of nonlinear advection is included. The SWEs are scaled to the case of a topographically controlled jet, and then solved by introducing a similarity variable, η = cx^n_xy^n_y. The nonlinear solution, valid for topographies h = h₀ − αxy³, takes the form of the Lambert W-function for pseudo velocity. The linear solution, valid for topographies h = h₀ − αxy^−γ, takes the form of the error function for transport. Kuehl's results considered the case −1 ≤ γ < 1 which admits expanding jets, while the new result considers the case γ < −1 which admits intensifying jets and a nonlinear case with γ = −3. 

his project is supported by an NSF BPE grant. Career choices, such as engineering, are influenced by a number of factors including personal interest, ability, competence beliefs, prior work-related experience, and financial and social supports. However, financial and social support, a particularly significant factor for rural students’ career decisions, is often overlooked in the literature exploring career choice. Moreover, little work has explored how communities serve as key influencers for supporting or promoting engineering as a career choice. Therefore, the goal of this study is to explore the ways in which communities provide support to students deciding to pursue engineering as a college major. To better understand how students from selected rural area high schools choose engineering as a major, we conducted focus group discussions consisting of 4-6 students each from selected schools to talk collectively about their high school experiences and their choice to major in engineering. Choosing focus group participants from different schools enabled us to elicit tacit perceptions and beliefs that may not be evident when students from the same community talk with one another. That is, as students share their experiences across schools, they may recognize differences in their experiences that, though otherwise unconscious or unacknowledged, proved significant in their choice of college and major. We expect that certain community programs and the individuals involved will have some influence on students’ decisions to study engineering at [University Name]. We anticipate that the results will yield two key outcomes: 1. A holistic understanding of the communities that effectively support and encourage engineering major choice for rural students. 2. Locally driven, contextually relevant recommendations for policies and programs that would better enable economically disadvantaged, rural schools in southwestern Virginia to support engineering as a career choice for high school students. By understanding the ways some economically-disadvantaged rural communities support engineering as a career choice and linking a broad spectrum of rural communities together around this issue, this project will broaden participation in engineering by increasing support for students from these areas. By shifting our focus from students to communities, this research broadens our understanding of career choice by capturing the perspectives of community members (including not only school personnel, but also community leaders, students’ families, business owners and others) who often play a key role in students’ decisions, particularly in rural communities. Our research will bring these voices into the conversation to help scholars learn from and respond to these essential community perspectives. In doing so, we will provide a more nuanced model of engineering career choice that can then be explored in other rural contexts. This work thus contributes to the research on career choice, rural education, and engineering education. © 2018 American Society for Engineering Education