94 research outputs found
Microplastic-Associated Biofilms: A Comparison of Freshwater and Marine Environments
Microplastics (<5 mm particles) occur within both engineered and natural freshwater ecosystems, including wastewater treatment plants, lakes, rivers, and estuaries. While a significant proportion of microplastic pollution is likely sequestered within freshwater environments, these habitats also constitute an important conduit of microscopic polymer particles to oceans worldwide. The quantity of aquatic microplastic waste is predicted to dramatically increase over the next decade, but the fate and biological implications of this pollution are still poorly understood. A growing body of research has aimed to characterize the formation, composition, and spatiotemporal distribution of microplastic-associated (“plastisphere”) microbial biofilms. Plastisphere microorganisms have been suggested to play significant roles in pathogen transfer, modulation of particle buoyancy, and biodegradation of plastic polymers and co-contaminants, yet investigation of these topics within freshwater environments is at a very early stage. Here, what is known about marine plastisphere assemblages is systematically compared with up-to-date findings from freshwater habitats. Through analysis of key differences and likely commonalities between environments, we discuss how an integrated view of these fields of research will enhance our knowledge of the complex behavior and ecological impacts of microplastic pollutants
Functional Implications of Ubiquitous Semicircular Canal Non-Orthogonality in Mammals
The ‘canonical model’ of semicircular canal orientation in mammals assumes that 1) the three ipsilateral canals of an inner ear exist in orthogonal planes (i.e., orthogonality), 2) corresponding left and right canal pairs have equivalent angles (i.e., angle symmetry), and 3) contralateral synergistic canals occupy parallel planes (i.e., coplanarity). However, descriptions of vestibular anatomy that quantify semicircular canal orientation in single species often diverge substantially from this model. Data for primates further suggest that semicircular canal orthogonality varies predictably with the angular head velocities encountered in locomotion. These observations raise the possibility that orthogonality, symmetry, and coplanarity are misleading descriptors of semicircular canal orientation in mammals, and that deviations from these norms could have significant functional consequences. Here we critically assess the canonical model of semicircular canal orientation using high-resolution X-ray computed tomography scans of 39 mammal species. We find that substantial deviations from orthogonality, angle symmetry, and coplanarity are the rule for the mammals in our comparative sample. Furthermore, the degree to which the semicircular canals of a given species deviate from orthogonality is negatively correlated with estimated vestibular sensitivity. We conclude that the available comparative morphometric data do not support the canonical model and that its overemphasis as a heuristic generalization obscures a large amount of functionally relevant variation in semicircular canal orientation between species.Funding for this research was provided by grants NSFIIS-0208675 (http://www.nsf.gov/cise/iis/hcc_pgm.jsp), and EAR-0948842 (http://www.nsf.gov/awards/award_visualization.jsp?org=EAR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Geological SciencesAnthropologyEmail: [email protected]
Direct visualization of solute locations in laboratory ice samples
Many important chemical reactions occur in polar snow, where solutes may be
present in several reservoirs, including at the air–ice interface and in
liquid-like regions within the ice matrix. Some recent laboratory studies
suggest chemical reaction rates may differ in these two reservoirs. While
investigations have examined where solutes are found in natural snow and ice,
few studies have examined either solute locations in laboratory samples or
the possible factors controlling solute segregation. To address this, we used
micro-computed tomography (microCT) to examine solute locations in ice
samples prepared from either aqueous cesium chloride (CsCl) or rose bengal
solutions that were frozen using several different methods. Samples frozen in
a laboratory freezer had the largest liquid-like inclusions and air bubbles,
while samples frozen in a custom freeze chamber had somewhat smaller air
bubbles and inclusions; in contrast, samples frozen in liquid nitrogen showed
much smaller concentrated inclusions and air bubbles, only slightly larger
than the resolution limit of our images (∼ 2 µm). Freezing
solutions in plastic vs. glass vials had significant impacts on the sample
structure, perhaps because the poor heat conductivity of plastic vials
changes how heat is removed from the sample as it cools. Similarly, the
choice of solute had a significant impact on sample structure, with rose
bengal solutions yielding smaller inclusions and air bubbles compared to CsCl
solutions frozen using the same method. Additional experiments using
higher-resolution imaging of an ice sample show that CsCl moves in a thermal
gradient, supporting the idea that the solutes in ice are present in mobile
liquid-like regions. Our work shows that the structure of laboratory ice
samples, including the location of solutes, is sensitive to the freezing
method, sample container, and solute characteristics, requiring careful
experimental design and interpretation of results
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