The evolution of communication in a complex acoustic environment

Animals use communicatory signals for species recognition, mate choice, and territory defense. In many cases, communication occurs in the presence of other species with similar signals, which can make it difficult to discriminate conspecific from heterospecific signals. To avoid interference from syntopic signals, species should partition communication space. I studied partitioning of acoustic space in the dawn chorus of birds in the Amazon basin, an example of communication in high levels of heterospecific background noise. My research analyzed bird songs to determine whether the timing of signal transmission, the structure of signals, or both, serve to partition the acoustic space among different species. I used a combination of acoustic censuses and field experiments to investigate acoustic partitioning. With the censuses, I documented the times and places at which species sing, and I measured the features of each species’ song to determine their locations in acoustic space. Playback experiments in the field enabled me to test predictions about partitioning of both acoustic signal space and acoustic perceptual space. The analyses of the acoustic censuses revealed that songs of species that used the same forest stratum and sang during the same 30-min intervals had more dispersed signals than other species. The first experiment indicated that signalers and receivers coordinate the timing of production and reception of signals within the dawn chorus. The second experiment revealed that, although the partitioning of acoustic signal space was disjunct, with gaps between nearest species’ signals, the partitioning of acoustic perceptual space was saturated. Since signals are degraded as they travel through the environment, receivers must respond to degraded signals mixed with background noise. As a consequence, receivers should allow for more variation in signals than signalers include at the source. The results of these censuses and experiments allowed me to examine the influence of background noise from heterospecific species on the evolution of acoustic communication. It is the first study to investigate acoustic perceptual space in a multispecies community. The results indicate that signalers and receivers have evolved distinct strategies to reduce errors in recognizing conspecific signals

Missed medical appointments during shifts to and from daylight saving time

Transitions into and out of Daylight Saving Time (DST) can provide insights into how a minor change to a regular sleep–wake cycle can inadvertently affect health. We examined the relationship between DST and missed medical appointments. Using a large dataset, the proportion of missed appointments were examined prior and post spring and autumn clock changes. As predicted, the number of missed medical appointments significantly increased following the spring (forward) clock change and the week of the clock change. This trend was reversed following the transition out of DST. The implications of scheduling appointments around DST to increase attendance are discussed

The Edge-Connectivity of Vertex-Transitive Hypergraphs

A graph or hypergraph is said to be vertex-transitive if its automorphism group acts transitively upon its vertices. A classic theorem of Mader asserts that every connected vertex-transitive graph is maximally edge-connected. We generalise this result to hypergraphs and show that every connected linear uniform vertex-transitive hypergraph is maximally edge-connected. We also show that if we relax either the linear or uniform conditions in this generalisation, then we can construct examples of vertex-transitive hypergraphs which are not maximally edge-connected.Comment: 8 page

Existential Closure in Line Graphs

A graph $G$ is $n$-existentially closed if, for all disjoint sets of vertices $A$ and $B$ with $|A\cup B|=n$, there is a vertex $z$ not in $A\cup B$ adjacent to each vertex of $A$ and to no vertex of $B$. In this paper, we investigate $n$-existentially closed line graphs. In particular, we present necessary conditions for the existence of such graphs as well as constructions for finding infinite families of such graphs. We also prove that there are exactly two $2$-existentially closed planar line graphs. We then consider the existential closure of the line graphs of hypergraphs and present constructions for $2$-existentially closed line graphs of hypergraphs.Comment: 13 pages, 2 figure

Microbial iron mats at the Mid-Atlantic Ridge and evidence that Zetaproteobacteria may be restricted to iron-oxidizing marine systems

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 10 (2015): e0119284, doi:10.1371/journal.pone.0119284 .Chemolithoautotrophic iron-oxidizing bacteria play an essential role in the global iron cycle. Thus far, the majority of marine iron-oxidizing bacteria have been identified as Zetaproteobacteria, a novel class within the phylum Proteobacteria. Marine iron-oxidizing microbial communities have been found associated with volcanically active seamounts, crustal spreading centers, and coastal waters. However, little is known about the presence and diversity of iron-oxidizing communities at hydrothermal systems along the slow crustal spreading center of the Mid-Atlantic Ridge. From October to November 2012, samples were collected from rust-colored mats at three well-known hydrothermal vent systems on the Mid-Atlantic Ridge (Rainbow, Trans-Atlantic Geotraverse, and Snake Pit) using the ROV Jason II. The goal of these efforts was to determine if iron-oxidizing Zetaproteobacteria were present at sites proximal to black smoker vent fields. Small, diffuse flow venting areas with high iron(II) concentrations and rust-colored microbial mats were observed at all three sites proximal to black smoker chimneys. A novel, syringe-based precision sampler was used to collect discrete microbial iron mat samples at the three sites. The presence of Zetaproteobacteria was confirmed using a combination of 16S rRNA pyrosequencing and single-cell sorting, while light micros-copy revealed a variety of iron-oxyhydroxide structures, indicating that active iron-oxidizing communities exist along the Mid-Atlantic Ridge. Sequencing analysis suggests that these iron mats contain cosmopolitan representatives of Zetaproteobacteria, but also exhibit diversity that may be uncommon at other iron-rich marine sites studied to date. A meta-analysis of publically available data encompassing a variety of aquatic habitats indicates that Zetaproteobacteria are rare if an iron source is not readily available. This work adds to the growing understanding of Zetaproteobacteria ecology and suggests that this organism is likely locally restricted to iron-rich marine environments but may exhibit wide-scale geographic distribution, further underscoring the importance of Zetaproteobacteria in global iron cycling.This work was supported by grants from the National Science Foundation [grants OCE-0926805 (DE and JAB), OCE-1155754 (DE), and OCE-1131109 (GWL)] and the National Aeronautics and Space Administration [NNX12AG20G (GWL and DE)]

Ground state phases of the Half-Filled One-Dimensional Extended Hubbard Model

Using quantum Monte Carlo simulations, results of a strong-coupling expansion, and Luttinger liquid theory, we determine quantitatively the ground state phase diagram of the one-dimensional extended Hubbard model with on-site and nearest-neighbor repulsions U and V. We show that spin frustration stabilizes a bond-ordered (dimerized) state for U appr. V/2 up to U/t appr. 9, where t is the nearest-neighbor hopping. The transition from the dimerized state to the staggered charge-density-wave state for large V/U is continuous for U up to appr. 5.5 and first-order for higher U.Comment: 4 pages, 4 figure

Engineering the Interface between Inorganic Nanoparticles and Biological Systems through Ligand Design

Nanoparticles (NPs) provide multipurpose platforms for a wide range of biological applications. These applications are enabled through molecular design of surface coverages, modulating NP interactions with biosystems. In this review, we highlight approaches to functionalize nanoparticles with “small” organic ligands (Mw \u3c 1000), providing insight into how organic synthesis can be used to engineer NPs for nanobiology and nanomedicine

Effects of a regenerating matrix on the survival of birds in tropical forest fragments

Background Vast areas of lowland neotropical forest have regenerated after initially being cleared for agricultural purposes. The ecological value of regenerating second growth to forest-dwelling birds may largely depend on the age of the forest, associated vegetative structure, and when it is capable of sustaining avian demographics similar to those found in pristine forest. Methods To determine the influence of second growth age on bird demography, we estimated the annual survival of six central Amazonian bird species residing in pristine forest, a single 100 and a single 10 ha forest fragment, taking into consideration age of the surrounding matrix (i.e. regenerating forest adjacent to each fragment) as an explanatory variable. Results Study species exhibited three responses: arboreal, flocking and ant-following insectivores (Willisornis poecilinotus, Thamnomanes ardesiacus and Pithys albifrons) showed declines in survival associated with fragmentation followed by an increase in survival after 5 years of matrix regeneration. Conversely, Percnostola rufifrons, a gap-specialist, showed elevated survival in response to fragmentation followed by a decline after 5 years of regeneration. Lastly, facultative flocking and frugivore species (Glyphorynchus spirurus and Dixiphia pipra, respectively) showed no response to adjacent clearing and subsequent regeneration. Conclusions Our results in association with previous studies confirm that the value of regenerating forest surrounding habitat patches is dependent on two factors: ecological guild of the species in question and second growth age. Given the rapid increase in survival following succession, we suggest that the ecological value of young tropical forest should not be based solely on a contemporary snapshot, but rather, on the future value of mature second growth as well