Reproductive Success of Eastern Bluebirds (Siala sialis) on Suburban Golf Courses

Understanding the role of green space in urban—suburban landscapes is becoming critical for bird conservation because of rampant habitat loss and conversion. Although not natural habitat, golf courses could play a role in bird conservation if they support breeding populations of some native species, yet scientists remain skeptical. In 2003–2009, we measured reproduction of Eastern Bluebirds (Siala sialis) in Virginia on golf courses and surrounding reference habitats, of the type that would have been present had golf courses not been developed on these sites (e.g., recreational parks, cemeteries, agriculture land, and college campus). We monitored \u3e650 nest boxes and 2,255 nest attempts (n = 1,363 golf course, n = 892 reference site). We used an information-theoretic modeling approach to evaluate whether conditions on golf courses affected timing of breeding, investment, or nest productivity compared with nearby reference sites. We found that Eastern Bluebirds breeding on golf courses reproduced as well as those breeding in other disturbed habitats. Habitat type had no effect on initial reproductive investment, including date of clutch initiation or clutch size ( = 4 eggs). During incubation and hatching, eggs in nests on golf courses had higher hatching rates (80%) and brood sizes ( = 4.0 nestlings brood-1) than nests on reference sites (75% hatching rate; = 3.8 nestlings brood-1). Mortality of older nestlings was also lower on golf courses and, on average, golf course nests produced 0.3 more fledglings than nests on reference sites. Thus, within a matrix of human-dominated habitats, golf courses may support productive populations of some avian species that can tolerate moderate levels of disturbance, like Eastern Bluebirds

Lipid Membranes: From Organizational Strategies in Cells to the Origins of Life

Thesis (Ph.D.)--University of Washington, 2020Lipids, a fundamental building block of cells, can spontaneously self-assemble into vesicles, which are spherical shells consisting of a lipid bilayer. The structure of lipid bilayers determines their biological function: membranes are elastic, selectively permeable, and fluid barriers that separate the internal components of a cell from its external environment. Historically, the cell membrane has been viewed as a passive medium in which biologically active proteins reside. In the past several decades, investigation of the unique physical properties of multi-component lipid bilayers has uncovered the active organizational role of lipids in the cell membrane. Through changes in temperature or lipid composition, model ternary lipid bilayers can phase separate into coexisting liquid phases. Similarly, the membrane of living unperturbed yeast vacuoles exhibits coexisting liquid phases under stress conditions. Lipid membranes also have a role in the origins of cellular life: prebiotically-feasible bilayers concentrate the building blocks of protein and RNA, catalyzing the formation of biological polymers. This text describes some physical properties of lipid membranes and their role in biological organization and the origins of cellular life. The chapters of this thesis start with (1) an introduction and then explore (2) the effect of general anesthetics on the phase behavior of synthetic and cell-derived membranes, (3) periodic small domains in synthetic and cell-derived membranes, (4) coexisting liquid phases on the submicron scale using cryo electron tomography, (5) miscibility transition temperatures of living, unperturbed yeast vacuole membranes, and (6) binding and stabilization of prebiotic fatty acid membranes by prebiotic amino acids. These examples demonstrate the importance of lipid membranes across many aspects of biology and the power of simple physical principles to explain complex phenomena

Remodeling of yeast vacuole membrane lipidomes from the log (one phase) to stationary stage (two phases)

Upon nutrient limitation, budding yeast of Saccharomyces cerevisiae shift from fast growth (the log stage) to quiescence (the stationary stage). This shift is accompanied by liquid-liquid phase separation in the membrane of the vacuole, an endosomal organelle. Recent work indicates that the resulting micrometer-scale domains in vacuole membranes enable yeast to survive periods of stress. An outstanding question is which molecular changes might cause this membrane phase separation. Here, we conduct lipidomics of vacuole membranes in both the log and stationary stages. Isolation of pure vacuole membranes is challenging in the stationary stage, when lipid droplets are in close contact with vacuoles. Immuno-isolation has previously been shown to successfully purify log-stage vacuole membranes with high organelle specificity, but it was not previously possible to immuno-isolate stationary-stage vacuole membranes. Here, we develop Mam3 as a bait protein for vacuole immuno-isolation, and demonstrate low contamination by non-vacuolar membranes. We find that stationary-stage vacuole membranes contain surprisingly high fractions of phosphatidylcholine lipids ( 40%), roughly twice as much as log-stage membranes. Moreover, in the stationary stage, these lipids have higher melting temperatures, due to longer and more saturated acyl chains. Another surprise is that no significant change in sterol content is observed. These lipidomic changes, which are largely reflected on the whole-cell level, fit within the predominant view that phase separation in membranes requires at least three types of molecules to be present: lipids with high melting temperatures, lipids with low melting temperatures, and sterols