Biology subjects

Fenton, A.

Publications and source records attributed to Fenton, A..

26 records · Page 2Linked to original sources

bioRxiv2020

Spatiotemporal variation in drivers of parasitism in a wild wood mouse population

O_LIHost-parasite interactions in nature are driven by a range of factors across several ecological scales, so observed relationships are often context-dependent. Importantly, if these factors vary across space and time, practical sampling limitations can limit or bias inferences, and the relative importance of different drivers can be hard to discern. C_LIO_LIWe collected a replicated, longitudinal dataset of >1000 individual wood mice (Apodemus sylvaticus) encompassing 6 years of sampling across 5 different woodland sites to investigate how environmental, host and within-host factors determine infection intensity of a highly prevalent gastrointestinal nematode, Heligmosomoides polygyrus. C_LIO_LIWe used a Bayesian modelling approach to further quantify if and how each factor varied in space and time. Finally, we examined the extent to which a lack of spatially or temporally replication (i.e., within single years or single sites) and single (cross-sectional) versus repeated (longitudinal) sampling of individuals would affect which drivers were found to predict H. polygyrus infection. C_LIO_LISeason, host body condition, and sex were the three most important determinants of infection intensity; however, the strength and even direction of these effects varied in time, but not in space. Additionally, longitudinal datasets, in which we can control for within-individual variation through repeat observations, provided more robust estimates of the drivers of parasite intensity compared to cross-sectional data. C_LIO_LIThese results highlight the importance of accounting for spatiotemporal variation in drivers of disease dynamics and the need to incorporate spatiotemporal replication when designing sampling regimes. Furthermore, they suggest that embracing rather than simply controlling for spatiotemporal variation can reveal important insight into host-parasite relationships in the wild. C_LI

ecology↗

bioRxiv2020

Thermal sensitivity of the Spiroplasma-Drosophila hydei protective symbiosis: The best of climes, the worst of climes.

The outcome of natural enemy attack in insects has commonly been found to be influenced by the presence of protective symbionts in the host. The degree to which protection functions in natural populations, however, will depend on the robustness of the phenotype to variation in the abiotic environment. We studied the impact of a key environmental parameter - temperature - on the efficacy of the protective effect of the symbiont Spiroplasma on its host Drosophila hydei, against attack by the parasitoid wasp Leptopilina heterotoma. In addition, we investigated the thermal sensitivity of the symbionts vertical transmission, which may be a key determinant of the ability of the symbiont to persist. We found that vertical transmission was more robust than previously considered, with Spiroplasma being maintained at 25 {degrees}C, 18 {degrees}C and with 18/15 {degrees}C diurnal cycles, with rates of segregational loss only increasing at 15 {degrees}C. Protection against wasp attack was ablated before symbiont transmission was lost, with the symbiont failing to rescue the fly host at 18 {degrees}C. We conclude that the presence of a protective symbiosis in natural populations cannot be simply inferred from presence of a symbiont whose protective capacity has been tested under narrow controlled conditions. More broadly, we argue that the thermal environment is likely to represent an important determinant of the evolutionary ecology of defensive symbioses in natural environments, potentially driving seasonal, latitudinal and altitudinal variation in symbiont frequency, and modulating the strength of selection for symbiotic protective systems compared to defensive systems encoded in the nuclear genomes.

ecology↗

bioRxiv2020

Microbial grazers can control chytridiomycosis caused by aquatic zoosporic fungi

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores ([~]3 {micro}m), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d-1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 x 103 zoospores d-1, with a half saturation constant (k) of 5.75 x 103 zoospores ml-1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 104 sporangia host-1). However, simulated inferior micrograzers (0.7 x Imax and 1.5 x k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modelling disease dynamics for Bd and other zoosporic fungi.

microbiology↗

bioRxiv2019

Is the rat prefrontal cortex crucial for cognitive control during spatial cognition?

Cognitive control tasks require using one class of information while ignoring competing classes of information. The central role of the medial prefrontal cortex (mPFC) in cognitive control is well established in the primate literature, and largely accepted in the rodent literature because mPFC damage causes deficits in tasks that may require cognitive control, as inferred, typically from the task design. In prior work, we used an active place avoidance task where a rat or mouse on a rotating arena is required to avoid the stationary task-relevant locations of a mild shock and ignore the rotating task-irrelevant locations of those shocks. The task is impaired by hippocampal manipulations, and the discharge of hippocampal place cell populations judiciously alternates between representing stationary locations near the shock zone and rotating locations far from the shock zone, demonstrating cognitive control concurrently in behavior and the hippocampal representation of spatial information. Here we test whether rat mPFC lesion impairs the active place avoidance task to evaluate two competing hypotheses, a "central-computation" hypothesis that the mPFC is essential for the computations required for cognitive control and an alternative "local-computation" hypothesis that other brain areas can perform the computations required for cognitive control, independent of mPFC. Ibotenic acid lesion of the mPFC was effective, damaging the cingulate, prelimbic and infralimbic cortices. The lesion also altered the normal coordination of metabolic activity across remaining structures. The lesion did not impair learning to avoid the initial location of shock or long-term place avoidance memory, but impaired avoidance after the shock was relocated. The lesion also did not impair the alternation between task-relevant and task-irrelevant hippocampal representations of place information. These findings support the local-computation hypothesis that computations required for cognitive control can occur locally in brain networks independently of the mPFC.

neuroscience↗

bioRxiv2019

Learning to learn persistently modifies a neocortical-hippocampal excitatory-inhibitory subcircuit

Cognitive control, the judicious use of relevant information while ignoring distractions, is a feature of everyday cognitive experience, but its neurobiology is understudied. We investigated whether cognitive control training (CCT) changes hippocampal neural circuit function in mice, beyond the changes caused by place learning and memory formation. Mice learned and remembered a conditioned place avoidance during CCT that required ignoring irrelevant locations of shock. They were compared to controls that learned the same place avoidance under lower cognitive control demands. Weeks after CCT, mice learn new tasks in novel environments faster than controls; they learned to learn. We investigated entorhinal cortex-to-dentate gyrus neural circuit changes and report that CCT rapidly changes synaptic circuit function, resulting in an excitatory-inhibitory subcircuit change that persists for months. CCT increases inhibition that attenuates the dentate response to medial entorhinal cortical input, and through disinhibition, potentiates the response to strong inputs, pointing to overall signal-to-noise enhancement. These neurobiological findings support a neuroplasticity hypothesis that, beyond storing item/event associations, CCT persistently optimizes neural circuit information processing.

neuroscience↗

bioRxiv2019

Beyond the ecology of fear: non-lethal effects of predators are strong whereas those of parasites are diverse

The ecology of fear demonstrates how prey responses to avoid predation cause non-lethal effects at all ecological scales. Parasites also elicit defensive responses in hosts with associated non-lethal effects, which raises the longstanding, yet unresolved question of how non-lethal effects of parasites compare with those of predators. We developed a framework for systematically answering this question for all types of predator and parasite systems. Our framework predicts that trait responses and their non-lethal effects should be strongest from predators and parasites that do not kill individuals to feed on them, but which nevertheless damage fitness. Analysing trait response data on amphibians, which have been well-studied for this area of research, showed that individuals generally responded more directly to short-term predation risks than to parasitism. Apart from studies using amphibians, there have been few direct comparisons of responses to predation and parasitism, and none have incorporated responses to micropredators, parasitoids, or parasitic castrators, or examined their long-term consequences. Addressing these and other data gaps highlighted by our general framework can advance the field toward understanding how non-lethal effects shape real food webs, which contain multiple predator and parasite species.

ecology↗

bioRxiv2017

On how the dentate gyrus contributes to memory discrimination

SummaryThe dentate gyrus (DG) is crucial for behaviorally discriminating similar spatial memories, predicting that dentate gyrus place cells change (\"remap\") spatial tuning (\"place fields\") for memory discrimination. This prediction was never tested, although DG place cells remap across similar environments without memory tasks. We confirm this prior finding, then demonstrate that DG place fields do not remap across spatial tasks that require DG-dependent memory discrimination. Instead of remapping, place-discriminating discharge is observed transiently amongst DG place cells, particularly where memory discrimination is most necessary. The DG network signals memory discrimination by expressing distinctive sub-second network patterns of co-firing amongst principal cells at memory discrimination sites. This is accompanied by increased coupling of discharge from excitatory principal cells and inhibitory interneurons. Instead of remapping, these findings identify that memory discrimination is signaled by sub-second patterns of correlated discharge within the dentate network.\n\neTOC blurbvan Dijk and Fenton report that dentate gyrus place cells signal memory discrimination not by remapping, but by variable sub-second patterns of coordinated place cell network discharge and enhanced discharge coupling between excitatory and inhibitory neurons, at sites of memory discrimination.\n\nHighlightsO_LIDentate gyrus-dependent memory discrimination does not require place cell remapping\nC_LIO_LIDentate neural correlates of pattern discrimination are transient, lasting seconds\nC_LIO_LISub-second dentate network discharge correlations signal memory discrimination\nC_LIO_LIDentate excitatory-inhibitory coupling is increased at memory discrimination sites\nC_LI

neuroscience↗

bioRxiv2017

Analysis of hippocampal transcriptomic responses to technical and biological perturbations

Cost-effective next-generation sequencing has made unbiased gene expression analysis possible. Single-neuron gene expression studies may be especially important for understanding nervous system structure and function because of the neuron-specific functionality and plasticity that defines functional neural circuits. Cellular dissociation is a prerequisite technical manipulation for single-cell and single cell-population studies, but the extent to which the cellular dissociation process cells affects neural gene expression has not been determined, nor has it been determined how gene expression is altered by the stress that accompanies many of the behavioral manipulations that are required to study learning and memory and other cognitive functions. Here, we determined to which extent cellular dissociation-induced changes in hippocampal gene expression might confound studies on the behavioral and physiological functions of the hippocampus. We processed tissue punch samples from the dentate gyrus (DG), CA3, and CA1 hippocampus subfields using either a tissue homogenization protocol or a cellular dissociation protocol in preparation for RNA sequencing analysis to evaluate the impact of the tissue preparation. Then, we evaluated the effect of stressful experience and cognitive training on hippocampus subfield specific gene expression and determined to which extent these response overlap with the cellular dissociation response. Finally, we assessed the extent to which the subfield-specific gene expression patterns are consistent with those identified in a recently published hippocampus subfield-specific gene expression database. We report substantial differences in baseline subfield-specific gene expression, that 1% of the hippocampal transcriptome is altered by the process of cellular dissociation, that an even weaker alteration is detected 24 h after stressful experience, and that while these alterations are largely distinct from the subfield specific response of the hippocampus transcriptome to cognitive training, there is nonetheless some important confounding overlap. These findings of the concordant and discordant effects of technical and behavioral manipulations should inform the design of future neural transcriptome studies and thus facilitate a more comprehensive understanding of hippocampal function.

neuroscience↗