Biology subjects

Walker, N. D.

Publications and source records attributed to Walker, N. D..

4 recordsLinked to original sources

bioRxiv2025

On the imbalance between production and exploitation of marine fish assemblages: a case study from the Celtic Seas

Sustainable management of marine ecosystems has to take into account the conservation of many species that are not themselves targets of fishing, in addition to those that are commercially exploited. Dynamic size-spectrum models suggest that fishing which leads species to have similar ratios of yield to production (i.e. similar exploitation ratios) is not sufficient to protect those that are rare: these species need to experience lower exploitation ratios. Here, the status of the demersal fish assemblage in the Celtic Seas is examined from the perspective of yield and production, using survey data collected over the period 2012 to 2016, and incorporating both common and rare species. The results give no evidence that rarer species have lower exploitation ratios than common ones. This suggests that current management methods are not not operating in a way that conserves the fish assemblage as a whole.

ecology↗

bioRxiv2022

Volumetric microscopy of CD9 and CD63 reveals distinct subpopulations and novel structures of extracellular vesicle in situ in triple negative breast cancer cells

Secreted extracellular vesicles (EVs) are now known to play multifaceted roles in biological processes such as immune responses and cancer. The two primary classes of EVs are defined in terms of their origins: exosomes are derived from the endosomal pathway while microvesicles (ectosomes) bud from the cell membrane. However, it remains unclear whether the contents, sizes, and localizations of subpopulations of EVs can be used to associate them with the two primary classes. Here, we use confocal microscopy and high-resolution volumetric imaging to study intracellular localization of the EV markers CD9 and CD63 prior to EV export from cells. We find significantly different spatial expression of CD9 and CD63. CD9 is primarily localized in microvesicles, while CD63 is detected exclusively in exosomes. We also observe structures in which CD63 forms a shell that encapsulates CD9 and interpret them to be multi-vesicular bodies. The morphology and location within the endoplasmic reticulum of these shell-like structures are consistent with a role in differential sorting and export of exosomes and microvesicles. Our in situ imaging allows unambiguous identification and tracking of EVs from their points of origin to cell export, and suggest that CD9 and CD63 can be used as biomarkers to differentiate subpopulations of EVs.

biophysics↗

bioRxiv2021

The Effect of COVID-19 on the Postdoctoral Experience: a comparison of pre-pandemic and pandemic surveys.

In the interest of advocating for the postdoctoral community in the United States, we present results from survey data collected before and during the COVID-19 pandemic on the same population of postdocs. In 2019, 5,929 postdocs in the US completed a comprehensive survey, and in 2020, a subset completed a follow-up survey several months into the pandemic. The results show that the pandemic has substantially impacted postdocs mental health and wellness irrespective of gender, race, citizenship, or other identities. Postdocs also reported a significant impact on their career trajectories and progression, reduced confidence in achieving career goals, and negative perceptions of the job market compared to pre-COVID-19. International postdocs also reported experiencing distinct stressors due to the changes in immigration policy. Notably, having access to Postdoctoral Associations and Postdoctoral Offices positively impacted postdocs overall well-being and helped mitigate the personal and professional stresses and career uncertainties caused by the pandemic. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=137 SRC="FIGDIR/small/468693v2_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@174d7e3org.highwire.dtl.DTLVardef@9893dorg.highwire.dtl.DTLVardef@114470org.highwire.dtl.DTLVardef@1a4278f_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract of survey responses to: Why or how has your research been disrupted or not disrupted due to the pandemic? Overall, postdocs responded with feelings of loss of control as the pandemic was acting upon them and taking away their ability to complete their work. C_FIG

scientific communication and education↗

bioRxiv2018

Ensemble projections of global ocean animal biomass with climate change

Climate change is shifting the abundance and distribution of marine species with consequences for ecosystem functioning, seafood supply, management and conservation. Several approaches for future projection exist but these have never been compared systematically to assess their variability. We conducted standardized ensemble projections including 6 global fisheries and marine ecosystem models, forced with 2 Earth-system models and 4 emission scenarios in a fished and unfished ocean, to derive average trends and associated uncertainties. Without fishing, mean global animal biomass decreased by 5% ({+/-}4%) under low and 17% ({+/-}11%) under high emissions by 2100, primarily driven by increasing temperature and decreasing primary production. These climate-change effects were slightly weaker for larger animals and in a fished ocean. Considerable regional variation ranged from strong biomass increases in high latitudes to strong decreases in mid-low latitudes, with good model agreement on the direction of change but variable magnitude. Uncertainties due to differences among ecosystem or Earth-system models were similar, suggesting equal need for model improvement. Our ensemble projections provide the most comprehensive outlook on potential climate-driven ecological changes in the ocean to date. Realized future trends will largely depend on how fisheries and management adapt to these changes in a changing climate.

ecology↗