Showing 1971 - 1980 of 2040 Items
De novo assembly of a transcriptome for the cricket Gryllus bimaculatus prothoracic ganglion: An invertebrate model for investigating adult central nervous system compensatory plasticity
Date: 2018-07-01
Creator: Harrison P. Fisher
Micah G. Pascual
Sylvia I. Jimenez
David A. Michaelson
Colby T., Joncas
Eleanor D. Quenzer
Andrew E. Christie
Hadley W. Horch
Access: Open access
- The auditory system of the cricket, Gryllus bimaculatus, demonstrates an unusual amount of anatomical plasticity in response to injury, even in adults. Unilateral removal of the ear causes deafferented auditory neurons in the prothoracic ganglion to sprout dendrites across the midline, a boundary they typically respect, and become synaptically connected to the auditory afferents of the contralateral ear. The molecular basis of this sprouting and novel synaptogenesis in the adult is not understood. We hypothesize that well-conserved developmental guidance cues may recapitulate their guidance functions in the adult in order to facilitate this compensatory growth. As a first step in testing this hypothesis, we have generated a de novo assembly of a prothoracic ganglion transcriptome derived from control and deafferented adult individuals. We have mined this transcriptome for orthologues of guidance molecules from four well-conserved signaling families: Slit, Netrin, Ephrin, and Semaphorin. Here we report that transcripts encoding putative orthologues of most of the candidate developmental ligands and receptors from these signaling families were present in the assembly, indicating expression in the adult G. bimaculatus prothoracic ganglion.
Interaction of stretch feedback and beat regularity in response to AMGSEFLamide in the heart of Homarus americanus
Date: 2020-01-01
Creator: William Allen
Access: Open access
- Central pattern generators (CPGs) are neural circuits whose component neurons possess intrinsic properties and synaptic connections that allow them to generate rhythmic motor outputs in the absence of descending inputs. The cardiac ganglion (CG) is a nine-cell CPG located in the American lobster, Homarus americanus. Stretch of the myocardium feeds back to the CG through mechano-sensitive dendrites and is thought to play a role in maintaining regularity in the beating pattern of the heart. The novel peptide AMGSEFLamide has been observed to induce irregular beating patterns when applied at high concentrations. This study investigated the interaction between stretch-related feedback and AMGSEFLamide modulation in generating irregular beating patterns in the whole heart of Homarus americanus. It was hypothesized that greater longitudinal stretch of the heart would result in greater regularity in the instantaneous beat frequency, based on previous findings that stretch-sensitive dendrites play a role in the regulation of the heartbeat. Furthermore, it was predicted that the elimination of stretch feedback via deafferentation of the heart would augment the irregularity induced by AMGSEFLamide. Data showed significantly increased irregularity in beating in response to 10-6 M AMGSEFLamide application. Longitudinal stretch did not reliably alter baseline variability in frequency, nor did it influence the modulatory effect of AMGSEFLamide. Deafferentation did not significantly alter baseline irregularity. Deafferented preparations did exhibit a trend of responding to AMGSEFLamide with a greater percent increase in irregularity compared to when afferents were intact, suggesting a potential role of stretch-stabilization in response to modulatory perturbations in the Homarus heart.
Demography of a Collapsing Aerial Insectivore Population
Date: 2017-05-01
Creator: Liam Taylor
Access: Open access
- Aerial insectivores have been declining across northeastern North America since the end of the 20th century. The mechanisms and demographic patterns of this decline are unclear. On Kent Island, New Brunswick, Canada, an isolated population of Tree Swallows (Tachycineta bicolor) collapsed between 1987 and 2010. To explore how demographic rates (i.e., survival, reproduction, and immigration) drove the population dynamics of these northeastern aerial insectivores, we combined productivity, population survey, and capture-recapture data in an integrated population model analysis. Neither consistently low juvenile survival rates, adult survival rates, nor clutch size were correlated with population growth rate across years. Alternatively, male and female immigration, hatching success, and fledging success rates were correlated with population growth rate. Because local hatching and fledging success rates cannot influence a population without local recruitment, we argue that the demography of these Tree Swallows is mainly structured by immigration. Parameter-substitution simulations revealed that overall decline was likely even if the population had avoided the worst years of demographic collapse. Breeding Bird Survey comparisons demonstrated how the Kent Island population represents both a demographic and geographical extreme at the edge of a declining region. These demographic patterns highlight the sensitivity, even to the point of local extinction, of some isolated populations to region-scale patterns in the production of potential immigrants.
In situ HCR in non-traditional arthropods
Date: 2024-01-25
Creator: Heather Bruce
Hadley Wilson Horch
Access: Open access
- Visualizing the expression of genes is a fundamental tool in molecular biology. Traditional colorimetric in situ hybridization using long RNA probes has been a staple for visualizing gene expression but has many drawbacks. In situ HCR v3.0, developed by Choi et. al. 2018, offers improvements over traditional in situs in nearly every aspect: probes can simply be ordered rather than painstakingly cloned and transcribed, which also makes them cost-effective; an HCR takes just three days to complete rather than five or more days; HCR is robust and works well for first-time users; and HCR probes can be multiplexed, allowing four to eight genes to be visualized in a single sample. HCR has been used successfully in many arthropods, including insects (Drosophila, Tribolium), crustaceans (Parhyale, Daphnia, Artemia), and chelicerates (Limulus horseshoe crab, Acanthoscurria tarantula). In this demo, you will learn how to design and order HCR probes as well as best practices for experimental design.
Characterizing the influence of Atlantic water intrusion on water mass formation and phytoplankton distribution in Kongsfjorden, Svalbard
Date: 2019-12-01
Creator: Courtney M. Payne
Collin S. Roesler
Access: Open access
- Warm water intrusion into Arctic fjords is increasingly affecting polar ecosystems. This study investigated how Atlantic water intrusion and tidewater glacial melting impacted water mass formation and phytoplankton distribution in Kongsfjorden, Svalbard. Field data were collected over a 2-week period during the height of the melt season in August 2014 and were contextualized within an 18-year regional MODIS satellite record. Since 1998, intruding waters have warmed by 4–5.5 °C, which has prevented sea ice formation and changed the characteristics of fjord bottom waters. Modeled light fields suggest that suspended sediment in this glacial meltwater has reduced the euphotic zone close to the ice face, contributing to lower phytoplankton concentrations in both persistent and intermittently sediment-laden meltwater plumes. However, measurements collected close to terrestrially terminating glaciers indicate that turbidity is significantly lower in the meltwater plumes, resulting in deep euphotic zones and high phytoplankton concentrations. The results of this study support a three-part conceptual model of the effects of warm-water intrusion on water mass formation and primary production within 10 km of tidewater glaciers. Initially, warm water intrusion reduces sea ice coverage, which increases the euphotic depth and increases phytoplankton biomass. Warm water intrusions may also result in increased melting of tidewater glaciers, enhanced sediment release, reduction in euphotic depth and reduction in phytoplankton biomass. Ultimately, as tidewater glaciers retreat and become terrestrially terminating, the sediment load decreases, the euphotic zone again increases, and phytoplankton biomass increases.
Pandemic as method
Date: 2019-10-01
Creator: Belinda Kong
Access: Open access
- This essay deploys the concept of pandemic as a set of discursive relations rather than a neutral description of a natural phenomenon, arguing that pandemic discourse is a product of layered histories of power that in turn reproduces myriad forms of imperial and racial power in the new millennium. The essay aims to denaturalize the idea of infectious disease by reframing it as an assemblage of multiple histories of American geopower and biopower from the Cold War to the War on Terror. In particular, Asia and Asian bodies have been targeted by US discourses of infection and biosecurity as frontiers of bioterrorism and the diseased other. A contemporary example of this bioorientalism can be seen around the 2003 SARS epidemic, in which global discourses projected the source of contagion onto Asia and Asians. Pandemic as method can thus serve as a theoretical pathway for examining cultural concatenations of orientalism and biopower.
Where do the poor live in cities? Revisiting the role of public transportation on income sorting in US urban areas
Date: 2020-06-03
Creator: Erik Nelson
Access: Open access
- Glaeser et al. (2008) argue that the relative distribution of poor and rich households (HHs) in American cities is "strongly" explained by the spatial location of the cities' public transportation (PT) networks. Among their claims: 1) The broad distribution of poor and rich HHs in the typical American city is consistent with a basic monocentric city model that includes commute technology speeds; 2) Poor commuters will overwhelmingly transition from commuting by PT to car if they experience a substantial increase in their HH’s income; 3) areas in American cities that receive new PT infrastructure become poorer over time. Using 2017 data I find empirical evidence that partially or wholly contradicts these three claims. First, as of 2017, the observed concentration of poor HHs in the inner city and rich HHs in the suburbs of the US’ smaller cities cannot be explained by monocentric model that includes commute speeds. Second, as of 2017, significant increases in poor HHs’ incomes were not expected to lead to a "massive shift" towards car commuting in these HHs; most of these poor workers commute by car already. Third, using data from four cities that expanded their light-rail and rapid-bus network in the early 2000s, I find that neighborhoods surrounding new light-rail or rapid-bus stations either saw little change in their income patterns or became slightly richer after station opening. In conclusion, as of 2017, the spatial distribution of HH incomes within American urban areas is not as intricately linked to the location of PT networks as Glaeser et al. (2008) would have us believe. As an addendum to the analysis I add some thoughts on how the COVID-19 pandemic might affect commuting behavior and income distributions within urban areas over the next decade.
The first formed tooth serves as a signalling centre to induce the formation of the dental row in zebrafish
Date: 2019-06-12
Creator: Yann Gibert
Eric Samarut
Megan K. Ellis
William R. Jackman
Vincent, Laudet
Access: Open access
- The diversity of teeth patterns in actinopterygians is impressive with tooth rows in many locations in the oral and pharyngeal regions. The first-formed tooth has been hypothesized to serve as an initiator controlling the formation of the subsequent teeth. In zebrafish, the existence of the first tooth (named 4 V1) is puzzling as its replacement is induced before the opening of the mouth. Functionally, it has been shown that 4 V1 formation requires fibroblast growth factor (FGF) and retinoic acid (RA) signalling. Here, we show that the ablation of 4 V1 prevents the development of the dental row demonstrating its dependency over it. If endogenous levels of FGF and RA are restored after 4 V1 ablation, embryonic dentition starts again by de novo formation of a first tooth, followed by the dental row. Similarly, induction of anterior ectopic teeth induces subsequent tooth formation, demonstrating that the initiator tooth is necessary and sufficient for dental row formation, probably via FGF ligands released by 4 V1 to induce the formation of subsequent teeth. Our results show that by modifying the formation of the initiator tooth it is possible to control the formation of a dental row. This could help to explain the diversity of tooth patterns observed in actinopterygians and more broadly, how diverse traits evolved through molecular fine-tuning.
Does Productivity Respond to Exchange Rate Appreciations? A Theoretical and Empirical Investigation
Date: 2010-12-15
Creator: Yao Tang
Access: Open access
- Although real currency appreciations pose direct difficulties for exporters and import-competing firms as they will face more intense competition, is it possible that such competition spurs firms to improve productivity? To answer this question, the paper first constructs a theoretical model to show how the competitive pressures of currency appreciations induce firms to improve productivity by adopting new technologies. In addition, the model predicts that during appreciations there will be a positive relation between market concentration and improvements in productivity for industries highly exposed to trade, because the marginal benefits of productivity improvement will be bigger for firms with a larger market share. The paper then examines Canadian manufacturing data from 1997 to 2006, and finds evidence consistent with model predictions. I find that growth rates of labor productivity were on average higher during the Canadian dollar appreciation between 2002 and 2006, after controlling for industry characteristics. Within the group of highly traded Canadian industries, the more concentrated ones experienced larger growth in labor productivity.