Drawing a Triangle on the Thurston Model of Hyperbolic Space

In looking at a common physical model of the hyperbolic plane, the authors encountered surprising difficulties in drawing a large triangle. Understanding these difficulties leads to an intriguing exploration of the geometry of the Thurston model of the hyperbolic plane. In this exploration we encounter topics ranging from combinatorics and Pick’s Theorem to differential geometry and the Gauss-Bonnet Theorem

Analysis of Brevundimonas subvibrioides developmental signaling systems reveals inconsistencies between phenotypes and c-di-GMP levels

© 2019 American Society for Microbiology. All Rights Reserved. The DivJ-DivK-PleC signaling system of Caulobacter crescentus is a signaling network that regulates polar development and the cell cycle. This system is conserved in related bacteria, including the sister genus Brevundimonas. Previous studies had shown unexpected phenotypic differences between the C. crescentus divK mutant and the analogous mutant of Brevundimonas subvibrioides, but further characterization was not performed. Here, phenotypic assays analyzing motility, adhesion, and pilus production (the latter characterized by a newly discovered bacteriophage) revealed that divJ and pleC mutants have phenotypes mostly similar to their C. crescentus homologs, but divK mutants maintain largely opposite phenotypes than expected. Suppressor mutations of the B. subvibrioides divK motility defect were involved in cyclic di-GMP (c-di-GMP) signaling, including the diguanylate cyclase dgcB, and cleD which is hypothesized to affect flagellar function in a c-di-GMP dependent fashion. However, the screen did not identify the diguanylate cyclase pleD. Disruption of pleD in B. subvibrioides caused no change in divK or pleC phenotypes, but did reduce adhesion and increase motility of the divJ strain. Analysis of c-di-GMP levels in these strains revealed incongruities between c-di-GMP levels and displayed phenotypes with a notable result that suppressor mutations altered phenotypes but had little impact on c-di-GMP levels in the divK background. Conversely, when c-di-GMP levels were artificially manipulated, alterations of c-di-GMP levels in the divK strain had minimal impact on phenotypes. These results suggest that DivK performs a critical function in the integration of c-di-GMP signaling into the B. subvibrioides cell cycle. IMPORTANCE Cyclic di-GMP and associated signaling proteins are widespread in bacteria, but their role in physiology is often complex and difficult to predict through genomic level analyses. In C. crescentus, c-di-GMP has been integrated into the developmental cell cycle, but there is increasing evidence that environmental factors can impact this system as well. The research presented here suggests that the integration of these signaling networks could be more complex than previously hypothesized, which could have a bearing on the larger field of c-di-GMP signaling. In addition, this work further reveals similarities and differences in a conserved regulatory network between organisms in the same taxonomic family, and the results show that gene conservation does not necessarily imply close functional conservation in genetic pathways

Soiling experiment

The losses that occur annually to our farmers from the drying up of their pastures in July, August, and September, induced us to grow a few acres of green feed, and ascertain to what extent such feed, of different kinds, can be had from an acre of land; how much a cow requires of each kind, and the effect of such feeding on quantity and quality of milk, compared with well watered, well shaded, good blue grass pastures. Our dairies are mostly idle because the cows have gone dry. and the cows have gone dry because their pastures have failed and provision was not made on a large majority of farms to furnish them with something on which they could give milk. A succession of dry summers has regularly shortened our pastures, and made cows unprofitable, when all the elements of growth are present except moisture, or an arrangement of different crops sown at different times so that some one may always be at its best for cutting for green feed

Indications of a positive feedback between coastal development and beach nourishment

Beach nourishment, a method for mitigating coastal storm damage or chronic erosion by deliberately replacing sand on an eroded beach, has been the leading form of coastal protection in the United States for four decades. However, investment in hazard protection can have the unintended consequence of encouraging development in places especially vulnerable to damage. In a comprehensive, parcel-scale analysis of all shorefront single-family homes in the state of Florida, we find that houses in nourishing zones are significantly larger and more numerous than in non-nourishing zones. The predominance of larger homes in nourishing zones suggests a positive feedback between nourishment and development that is compounding coastal risk in zones already characterized by high vulnerability

Genome-scale fitness profile of Caulobacter crescentus grown in natural freshwater

© 2018, International Society for Microbial Ecology. Bacterial genomes evolve in complex ecosystems and are best understood in this natural context, but replicating such conditions in the lab is challenging. We used transposon sequencing to define the fitness consequences of gene disruption in the bacterium Caulobacter crescentus grown in natural freshwater, compared with axenic growth in common laboratory media. Gene disruptions in amino-acid and nucleotide sugar biosynthesis pathways and in metabolic substrate transport machinery impaired fitness in both lake water and defined minimal medium relative to complex peptone broth. Fitness in lake water was enhanced by insertions in genes required for flagellum biosynthesis and reduced by insertions in genes involved in biosynthesis of the holdfast surface adhesin. We further uncovered numerous hypothetical and uncharacterized genes for which disruption impaired fitness in lake water, defined minimal medium, or both. At the genome scale, the fitness profile of mutants cultivated in lake water was more similar to that in complex peptone broth than in defined minimal medium. Microfiltration of lake water did not significantly affect the terminal cell density or the fitness profile of the transposon mutant pool, suggesting that Caulobacter does not strongly interact with other microbes in this ecosystem on the measured timescale. Fitness of select mutants with defects in cell surface biosynthesis and environmental sensing were significantly more variable across days in lake water than in defined medium, presumably owing to day-to-day heterogeneity in the lake environment. This study reveals genetic interactions between Caulobacter and a natural freshwater environment, and provides a new avenue to study gene function in complex ecosystems

Combined effects of heat waves and droughts on avian communities across the conterminous United States

Increasing surface temperatures and climatic variability associated with global climate change are expected to produce more frequent and intense heat waves and droughts in many parts of the world. Our goal was to elucidate the fundamental, but poorly understood, effects of these extreme weather events on avian communities across the conterminous United States. Specifically, we explored: (1) the effects of timing and duration of heat and drought events, (2) the effects of jointly occurring drought and heat waves relative to these events occurring in isolation, and (3) how effects vary among functional groups related to nest location and migratory habit, and among ecoregions with differing precipitation and temperature regimes. Using data from remote sensing, meteorological stations, and the North American Breeding Bird Survey, we used mixed effects models to quantify responses of overall and functional group abundance to heat waves and droughts (occurring alone or in concert) at two key periods in the annual cycle of birds: breeding and post-fledging. We also compared responses among species with different migratory and nesting characteristics, and among 17 ecoregions of the conterminous United States. We found large changes in avian abundances related to 100-year extreme weather events occurring in both breeding and post-fledging periods, but little support for an interaction among time periods. We also found that jointly-, rather than individually-occurring heat waves and droughts were both more common and more predictive of abundance changes. Declining abundance was the only significant response to post-fledging events, while responses to breeding period events were larger but could be positive or negative. Negative responses were especially frequent in the western U.S., and among ground-nesting birds and Neotropical migrants, with the largest single-season declines (36%) occurring among ground-nesting birds in the desert Southwest. These results indicate the importance of functional traits, timing, and geography in determining avian responses to weather extremes. Because dispersal to other regions appears to be an important avian response, it may be essential to maintain habitat refugia in a more climatically variable future

Effects of drought on avian community structure

Droughts are expected to become more frequent under global climate change. Avifauna depend on precipitation for hydration, cover, and food. While there are indications that avian communities respond negatively to drought, little is known about the response of birds with differing functional and behavioral traits, what time periods and indicators of drought are most relevant, or how response varies geographically at broad spatial scales. Our goals were thus to determine (1) how avian abundance and species richness are related to drought, (2) whether community variations are more related to vegetation vigor or precipitation deviations and at what time periods relationships were strongest, (3) how response varies among avian guilds, and (4) how response varies among ecoregions with different precipitation regimes. Using mixed effect models and 1989–2005 North American Breeding Bird Survey data over the central United States, we examined the response to 10 precipitation- and greenness based metrics by abundance and species richness of the avian community overall, and of four behavioral guilds. Drought was associated with the most negative impacts on avifauna in the semiarid Great Plains, while positive responses were observed in montane areas. Our models predict that in the plains, Neotropical migrants respond the most negatively to extreme drought, decreasing by 13.2% and 6.0% in abundance and richness, while permanent resident abundance and richness increase by 11.5% and 3.6%, respectively in montane areas. In most cases, response of abundance was greater than richness and models based on precipitation metrics spanning 32-week time periods were more supported than those covering shorter time periods and those based on greenness. While drought is but one of myriad environmental variations birds encounter, our results indicate that drought is capable of imposing sizable shifts in abundance, richness, and composition on avian communities, an important implication of a more climatically variable future