Biology subjects

Roper, M.

Publications and source records attributed to Roper, M..

10 recordsLinked to original sources

bioRxiv2026

Life history stage-dependent nuclear selection in chimeric fungi

A single hyphal compartment of the filamentous fungus Neurospora crassa may contain tens or hundreds of nuclei, sharing macromolecules with each other, and, via a continuous cytoplasm, with the nuclei in other compartments. Nuclear lineages acquire mutations with each mitosis, which, combined with the autonomous mitosis of nuclei, has fueled speculation that multilevel selection may occur, both upon the mycelium, and upon individual nuclear populations. Here, we combine experiments on fungal chimera formed from two auxotrophically and epitopically labeled nuclear populations, with specially created microscopy toolkit for extracting the proportions of the two nucleotypes to analyze the strength of nuclear-level selective forces at different stages in the fungal life history. We find strong nucleotype-selective forces during spore-germination and establishment of the mycelium, and no evidence of selection on nuclei inside a growing mycelium. The kinetics of mycelial initiation from individual spores therefore allow for the selection of nuclear compositions best adapted to the fungus environment, in accordance with the hypothesized function of unicellular life history stages for purging deleterious mutations.

evolutionary biology↗

bioRxiv2023

A neuromorphic model of active vision shows spatio-temporal encoding in lobula neurons can aid pattern recognition in bees

Bees' remarkable visual learning abilities make them ideal for studying active information acquisition and representation. Here, we develop a biologically inspired model to examine how flight behaviours during visual scanning shape neural representation in the insect brain, exploring the interplay between scanning behaviour, neural connectivity, and visual encoding efficiency. Incorporating non-associative learning, adaptive changes without reinforcement, and exposing the model to sequential natural images during scanning, we obtain results that closely match neurobiological observations. Active scanning and non-associative learning dynamically shape neural activity, optimising information flow and representation. Lobula neurons, crucial for visual integration, self-organise into orientation-selective cells with sparse, decorrelated responses to orthogonal bar movements. They encode a range of orientations, biased by input speed and contrast, suggesting co-evolution with scanning behaviour to enhance visual representation and support efficient coding. To assess the significance of this spatiotemporal coding, we extend the model with circuitry analogous to the mushroom body, a region linked to associative learning. The model demonstrates robust performance in pattern recognition, implying a similar encoding mechanism in insects. Integrating behavioural, neurobiological, and computational insights, this study highlights how spatiotemporal coding in the lobula efficiently compresses visual features, offering broader insights into active vision strategies and bio-inspired automation.

neuroscience↗

bioRxiv2022

Inclusive fitness forces of selection in an age-structured population

Current evolutionary theories of senescence predict that the force of selection on survival will decline from maturity to zero at the age of last reproduction, and the force of selection on reproduction will decline monotonically from birth. These predictions rest upon the assumption that individuals within a population do not interact with one another. This assumption, however, is violated in social species, where an individuals survival and/or reproduction may shape the fitness of other group members. In such species, it is inclusive fitness that natural selection optimises. Yet, it remains unclear how the forces of selection on survival and reproduction might be modified when inclusive fitness, rather than population growth rate, is considered the appropriate metric for fitness. Here, we derive inclusive fitness forces of selection for hypothetical populations of social species. We show that selection on survival is not always constant before maturity, and can remain above zero in post-reproductive age classes, contrary to conventional models of senescence. We also show how the trajectory of the force of selection on reproduction does not always decline monotonically from birth, as predicted by classical theory, but instead depends on the balance of benefits to direct fitness and costs to indirect fitness. Our theoretical framework provides the unique opportunity to expand our understanding of senescence across social species, with important implications to species with variable life histories.

evolutionary biology↗

bioRxiv2022

Bumblebees retrieve only the ordinal ranking of foraging options when comparing memories obtained in distinct settings

Are animals preferences determined by absolute memories for options (e.g., reward sizes) or by their remembered ranking (better/worse)? The only studies examining this question suggest humans and starlings utilize memories for both absolute and relative information. We show that bumblebees make decisions using only memories of ordinal comparisons. After learning to discriminate pairs of different flowers by sucrose concentration, bumblebees preferred flowers (in novel pairings) with 1) higher ranking over equal absolute reward, 2) higher ranking over higher absolute reward, and 3) identical qualitative ranking but different quantitative ranking equally. Despite these suboptimal choices, bumblebees found the optimal option in an ecologically relevant foraging task. Our results illuminate a divergent mechanism of learned preferences that may have arisen from adaptations to bumblebees natural environment.

animal behavior and cognition↗

bioRxiv2022

Discrimination of edge orientation by bumblebees

Simple feature detectors in the visual system, such as edge-detectors, are likely to underlie even the most complex visual processing, so understanding the limits of these systems is crucial for a fuller understanding of visual processing. We investigated the ability of bumblebees (Bombus terrestris) to discriminate between differently angled edges. In a multiple-choice, "meadow-like" scenario, bumblebees successfully discriminated between angled bars with 7{degrees} differences, significantly exceeding the previously reported performance of eastern honeybees (Apis cerana, limit: 15{degrees}). Neither the number of choices required to learn, nor the bees final discrimination performance were affected by the angular orientation of the training bars, indicating a uniform performance across the visual field. Previous work has found that, in dual-choice tests, eastern honeybees cannot reliably discriminate between angles with less than 25{degrees} difference, suggesting that performance in discrimination tasks is affected by the training regime, and doesnt simply reflect the perceptual limitations of the visual system. We used high resolution LCD monitors to investigate the limits of bumblebees angular resolution in dual-choice experiments. Bumblebee could still discriminate 7{degrees} angle differences under such conditions (exceeding the previously reported limit for Apis mellifera, of 10{degrees}, as well as that of A. cerana), eventually reaching similar levels of accuracy, but required longer learning periods than under multiple-choice conditions. Bumblebees show impressive abilities to discriminate between angled edges, performing better than two previously tested species of honeybee. This high performance may, in turn, support complex visual processing in the bumblebee brain.

animal behavior and cognition↗

bioRxiv2021

RNA-specific condensation promotes auto-regulation of polyQ RNA-binding protein Whi3

RNA-binding proteins are frequently seen to be capable of auto-regulation by binding their own transcripts. In this work, we show that in the multinucleated fungus Ashbya gossypii, the phase-separating RNA-binding protein Whi3 binds and regulates its own transcripts in distinct condensates from its other targets. Failure of Whi3 to bind its own transcript leads to a reduction in Whi3 protein level and its inability to properly regulate its other targets, leading to defects in nuclear cycling, polarized growth, and transcription of START-regulated genes. These results present a role for auto-regulation and condensate formation triggered by an RNA-binding protein interacting with its own coding transcript. Given the propensity of RNA-binding proteins to interact with their own coding mRNAs, this may be a wide-spread mechanism of feedback that utilizes biomolecular condensates.

cell biology↗

bioRxiv2021

Automated video tracking and flight analysis show how bumblebees solve a pattern discrimination task using active vision

Active vision, the ability of the visual system to actively sample and select relevant information out of a visual scene through eye and head movements, has been explored in a variety of animal species. Small-brained animals such as insects might rely even more on sequential acquisition of pattern features since there might be less parallel processing capacity in their brains than in vertebrates. To investigate how active vision strategies enable bees to solve visual tasks, here, we employed a simple visual discrimination task in which individual bees were presented with a multiplication symbol and a 45{degrees} rotated version of the same pattern ("plus sign"). High-speed videography of unrewarded tests and analysis of the bees flight paths shows that only a small region of the pattern is inspected before successfully accepting a target or rejecting a distractor. The bees scanning behaviour of the stimuli differed for plus signs and multiplication signs, but for each of these, the flight behaviour was consistent irrespective of whether the pattern was rewarding or unrewarding. Bees typically oriented themselves at ~{+/-}30{degrees} to the patterns such that only one eye had an unobscured view of stimuli. There was a significant preference for initially scanning the left side of the stimuli. Our results suggest that the bees movement may be an integral part of a strategy to efficiently analyse and encode their environment. Summary statementAutomated video tracking and flight analysis is proposed as the next milestone in understanding mechanisms underpinning active vision and cognitive visual abilities of bees.

animal behavior and cognition↗

bioRxiv2021

Circadian rhythm shows potential for mRNA efficiency and self-organized division of labor in multinucleate cells

Multinucleate cells occur in every biosphere and across the kingdoms of life, including in the human body as muscle cells and bone-forming cells. Data from filamentous fungi suggest that, even when bathed in a common cytoplasm, nuclei are capable of autonomous behaviors, including division. How does this potential for autonomy affect the organization of cellular processes between nuclei? Here we analyze a simplified model of circadian rhythm, a form of cellular oscillator, in a mathematical model of the filamentous fungus Neurospora crassa. Our results highlight the role played by mRNA-protein phase separation to keep mRNAs close to the nuclei from which they originate, while allowing proteins to diffuse freely between nuclei. Our modeling shows that syncytism allows for extreme mRNA efficiency -- we demonstrate assembly of a robust oscillator with transcription levels 104-fold less than in comparable uninucleate cells. We also show self-organized division of the labor of mRNA production, with one nucleus in a two-nucleus syncytium producing at least twice as many mRNAs as the other in 30% of cycles. This division can occur spontaneously, but division of labor can also be controlled by regulating the amount of cytoplasmic volume available to each nucleus. Taken together, our results show the intriguing richness and potential for emergent organization among nuclei in multinucleate cells. They also highlight the role of previously studied mechanisms of cellular organization, including nuclear space control and localization of mRNAs through RNA-protein phase separation, in regulating nuclear coordination. Author summaryCircadian rhythms are among the most researched cellular processes, but limited work has been done on how these rhythms are coordinated between nuclei in multinucleate cells. In this work, we analyze a mathematical model for circadian oscillations in a multinucleate cell, motivated by frequency mRNA and protein data from the filamentous fungus Neurospora crassa. Our results illuminate the importance of mRNA-protein phase separation, in which mRNAs are kept close to the nucleus in which they were transcribed, while proteins can diffuse freely across the cell. We demonstrate that this phase separation allows for a robust oscillator to be assembled with very low mRNA counts. We also investigate how the labor of transcribing mRNAs is divided between nuclei, both when nuclei are evenly spaced across the cell and when they are not. Division of this labor can be regulated by controlling the amount of cytoplasmic volume available to each nucleus. Our results show that there is potential for emergent organization and extreme mRNA efficiency in multinucleate cells.

cell biology↗

bioRxiv2019

Senescence: Still an Unsolved Problem of Biology

Peter Medawars An Unsolved Problem of Biology1 was one of several formal attempts to provide an explanation for the evolution of senescence, the increasing risk of mortality and decline in reproduction with age after achieving maturity. Despite ca. seven decades of theoretical elaboration aiming to explain the problem since Medawar first outlined it, we argue that this fundamental problem of biology remains unsolved. Here, we utilise demographic information2, 3 for 308 multicellular species to derive age-based trajectories of mortality and reproduction that provide evidence against the predictions of the classical, still prevailing, theories of ageing1, 4, 5, 6. These theories predict the inescapability of senescence1, 4, or its universality at least among species with a clear germ-soma barrier5, 6. The patterns of senescence in animals and plants that we report contradict both of these predictions. With the largest ageing comparative dataset of these characteristics to date, we build on recent evidence7, 8 to show that senescence is not the rule, and highlight the discrepancy between existing evidence and theory7, 8, 9. We also show that species age patterns of mortality and reproduction often follow divergent patterns, suggesting that organisms may display senescence for one component but not the other. We propose that ageing research will benefit from widening its classical theories beyond merely individual chronological age; key life history traits such as size, the ecology of the organism, and kin selection, may together play a hidden, yet integral role in shaping senescence outcomes.

evolutionary biology↗

bioRxiv2018

Gene expression patterns in synchronized islet populations

In vivo levels of insulin are oscillatory with a period of ~5-10 minutes, implying that the numerous islets of Langerhans within the pancreas are synchronized. While the synchronizing factors are still under investigation, one result of this behavior is expected to be coordinated intracellular [Ca2+] ([Ca2+]i) oscillations throughout the islet population. The role that coordinated [Ca2+]i oscillations have on controlling gene expression within pancreatic islets was examined by comparing gene expression levels in islets that were synchronized using a low amplitude glucose wave and an unsynchronized population. The [Ca2+]i oscillations in the synchronized population were homogeneous and had a significantly lower drift in their oscillation period as compared to unsynchronized islets. This reduced drift in the synchronized population was verified by comparing the drift of in vivo and in vitro profiles from published reports. Microarray profiling indicated a number of Ca2+-dependent genes were differentially regulated between the two islet populations. Gene set enrichment analysis revealed that the synchronized population had reduced expression of gene sets related to protein translation, protein turnover, energy expenditure, and insulin synthesis, while those that were related to maintenance of cell morphology were increased. It is speculated that these gene expression patterns in the synchronized islets results in a more efficient utilization of intra-cellular resources and response to environmental changes.

systems biology↗