Biology subjects

Cooper, C. E.

Publications and source records attributed to Cooper, C. E..

3 recordsLinked to original sources

bioRxiv2023

The influence of carbon dioxide on cerebral metabolism and oxygen consumption: combining multimodal monitoring with dynamic systems modelling

Hypercapnia increases cerebral blood flow, but the effect on cerebral metabolism in humans remains incompletely understood. Either increased or reduced oxygen consumption has been predicted from Fick models incorporating cerebral oxygen extraction fraction and cerebral blood flow. Hypercapnia also results in oxidation of cytochrome c oxidase, complex IV of the mitochondrial respiratory chain, implicating a change in cellular metabolism. The aim of this study was to combine systems modelling with non-invasive measurements of cerebral tissue oxygenation, cerebral blood flow, and cytochrome c oxidase redox state to evaluate any metabolic effects of hypercapnia. Cerebral tissue oxygen saturation and cytochrome oxidase redox state were measured with broadband near infrared spectroscopy and cerebral blood flow velocity using transcranial Doppler ultrasound. Data collected during 5-minutes hypercapnia in human volunteers were analyzed using a Fick model to determine changes in brain oxygen consumption and a mathematical model of cerebral hemodynamics and metabolism (BrainSignals) to inform on the potential mechanisms of any observed changes. Systemic physiology - blood pressure, arterial oxygen saturations and end-tidal carbon dioxide - served as model inputs. The extent of the hypercapnic oxidation of cytochrome oxidase required modifications of the BrainSignals model; simulations compared two possible modifications that could cause this oxidation - a decrease in metabolic substrate supply or an increase in metabolic demand. Only the decrease in substrate supply was able to explain both the enzyme redox state changes and the Fick calculated drop in brain oxygen consumption. These modelled outputs are consistent with, but do not prove, previous reports of CO2 inhibition of succinate dehydrogenase, complex II of the mitochondrial respiratory chain. These findings suggest that hypercapnia may have physiologically significant effects suppressing oxidative metabolism in humans and perturbing mitochondrial signaling pathways in health and disease.

physiology↗

bioRxiv2023

Stuck in the weeds: Invasive grasses reduce tiger snake movement

Wetlands are particularly vulnerable to degradation in urban environments, partially due to the introduction of non-native plants. Invasive weeds in wetlands can replace native plants leading to alterations in habitat composition and vegetation, in turn, animal movements and ultimately population dynamics might be affected. Here we investigate how home range size and movements of western tiger snakes (Notechis scutatus occidentalis) differ in wetlands dominated by invasive kikuyu grass (Cenchrus clandestinus) compared to wetlands dominated by native vegetation to understand if and how the movement ecology of this top-order predator is altered by vegetation homogenization. To do so, we used Autocorrelated Kernel Density Estimators (AKDE) to estimate home range size, dynamic Brownian Bridge Movement Models to document movement trajectory confidence areas, and compared movement distances using a Bayesian regression model. Home range sizes by tiger snakes were 14.59 {+/-} 9.35 ha smaller in areas dominated by invasive versus native vegetation. Moreover, within-day movement distances tended to be smaller in areas dominated by invasive versus native vegetation (mean {+/-} SD: 9 {+/-} 3 m versus 18 {+/-} 6 m), but there was considerable overlap between the 95% credible intervals between these two groups. Smaller home ranges by tiger snakes in areas dominated by invasive kikuyu grass were likely driven by thermoregulation, with snakes moving vertically between basking locations on top of kikuyu and shelter sites at the base, rather than travelling horizontally along the ground to open basking areas in sites dominated by native vegetation. Additionally, fragmentation of sites dominated by invasive vegetation might have contributed to the comparatively smaller home ranges of snakes there. These findings add to our understanding how changes in habitat composition driven by invasive vegetation can affect animal space use and emphasise the need for further studies to understand how these changes affect population dynamics.

ecology↗

bioRxiv2022

Quantifying the impacts of an invasive weed on habitat quality and prey availability for tiger snakes (Notechis scutatus) in urban wetlands

Invasive plants are a threat to natural ecosystems worldwide with urban wetlands being some of the most susceptible and highly modified environments of all. The tiger snake (Notechis scutatus) is a top predator that persists in urban wetlands in south-western Australia, many of which have been degraded by introduced kikuyu grass (Cenchrus clandestinus). To evaluate the potential impact of kikuyu grass on habitat quality for western tiger snakes we quantified the structural features of habitats within wetlands degraded by kikuyu grass and compared them to wetlands with native vegetation, examined tiger snake prey availability, assessed predation risk for juvenile snakes using clay models, and measured the thermal quality of the vegetation. Proliferation of kikuyu grass reduced habitat structural heterogeneity by reducing available bare ground and increasing vegetation density. This homogenisation of habitat structure had little effect on the predation risk for juveniles or the thermal properties of tiger snake shelter sites; however, one key snake prey species, the motorbike frog, had significantly lower abundance in the most impacted habitat. Habitat types with more structural complexity also offered tiger snakes more stable thermal regimes and lower predation risk. These findings indicate that the current extent of kikuyu grass invasion offers overall similar habitat quality for tiger snakes and may contribute to their persistence in urban wetlands, but they, along with their anuran prey, may befit from some increased habitat structural complexity in open areas.

ecology↗