Biology subjects

Ramesh, D.

Publications and source records attributed to Ramesh, D..

6 recordsLinked to original sources

bioRxiv2026

Fluctuating hydrodynamic forces increase fish locomotor variability in turbulence

Turbulence has been shown to alter fish locomotion and increase the energetic cost of swimming, yet the mechanisms underlying these effects remain unclear. To address this, we studied giant danios (Devario aequipinnatus) swimming at multiple speeds in both laminar and turbulent flows. Within this turbulent regime, mean tail-beat kinematics were largely unchanged relative to laminar conditions, but cycle-to-cycle variability increased, with larger effects occurring at higher speeds, where the velocity fluctuations are stronger. Turbulence also increased the frequency of asymmetric tail beats, particularly under stronger fluctuations, providing further evidence of increased locomotor variability. A quasi-steady hydrodynamic model suggests that velocity fluctuations in this flow regime produce relatively small changes in mean thrust and drag, whereas thrust variance scales with the square of velocity fluctuation magnitude. These variable forces likely prompt fish to adjust locomotor output to maintain position, which could explain the observed increase in kinematic variability. We further show that mechanical swimming power can be increased through correlations between fluctuating hydrodynamic forces and tail velocity. Together, these results suggest a mechanistic link between turbulent velocity fluctuations, locomotor variability, and increased energy expenditure.

biophysics↗

bioRxiv2026

Beyond fish in formation: A two-tier approach for biomechanical studies of collective movement

Despite much of the literature perceiving fish schooling as an organized system with a focus on fixed formations for theoretical analyses, experimental observations suggest that frequent positional rearrangement commonly occurs. Previous studies have also demonstrated that fish schools reduce locomotor costs relative to individuals swimming alone. This introduces an intriguing dichotomy. How can individual fish within schools exhibit dynamic interactions while also saving energy? We hypothesize that schooling dynamics are the result of positional and kinematic modulation of individuals responding to fluid dynamic stimuli from the movement of neighbouring individuals. We propose a two-tier approach to studying kinematic modulation within fish schools. First, quantification of the variation of individual movement in a school relative to that of a solitary individual uses an analytical pipeline combining artificial-intelligence-enabled tracking and video processing. Second, the study of kinematic modulation in response to hydrodynamic stimuli uses a mechanical flapping mechanism coupled with an enclosure to control fish position. We discovered that fish in schools exhibit higher levels of positional and kinematic modulation than individuals swimming alone. Fish swimming in enclosures can robustly respond to fluid stimuli from either a simple robotic fish or other fish located in proximity. This two-tier approach allows high-resolution analysis of positional and kinematic modulation within fish schools and their impacts on energy conservation resulting from collective movement.

biophysics↗

bioRxiv2025

Phage-mediated lysis increases growth rate of surviving bacterial cells

Bacterial phage infection and subsequent lysis are traditionally considered mechanisms of bacterial mortality and viral propagation; additionally, emerging evidence indicates that they may also contribute to nutrient recycling in broader ecological systems. However, it remains unclear how the nutrients released during cell lysis affect the growth dynamics of the remaining bacterial population. Addressing this gap, we built a controlled system consisting of two Escherichia coli lysogenic strains: one carrying a wild-type{lambda} prophage and the other a temperature-inducible variant that can be induced to lyse at 38 {degrees}C. Using this system, we selectively induced phage lysis in a defined fraction of the population and quantified both total biomass and the biomass of surviving, non-lysed cells. We observed that the biomass loss was consistently smaller than expected based on the fraction of lysed cells, supporting the idea that some of the released biomass is rapidly recycled by the non-lysed population. To formalize the observed dynamics and obtain quantitative insight, we developed a mathematical model showing that nutrients released during lysis can transiently enhance the growth rate of the surviving, non-lysed cells. This effect emerges on a short timescale of minutes, consistent with the rapid onset of biomass compensation observed experimentally. The growth rate increase was confirmed in single-cell experiments using microfluidics and time-lapse microscopy, where we cultured wild-type lysogens in lysate-containing culture supernatants. In summary, the results suggest that nutrients released through lysis are rapidly consumed, leading to an acceleration in the growth rate of non-lysed cells. The consequent partial compensation for cell loss can substantially influence the population dynamics, highlighting phage lysis as a direct modulator of bacterial growth. Overall, our findings provide quantitative insights into how phage-mediated lysis affects the physiology of non-lysed bacterial cells, extending beyond its well-established role in biomass recycling.

microbiology↗

bioRxiv2025

Fish locomotor variation: connecting energetics and kinematic modulation

Analyses of vertebrate locomotion have frequently revealed variations in locomotor energetics and movement both among individuals and through time within an individual. This variation is often collapsed into mean values for broad comparative analyses of function. However, kinematic patterns of locomotion, even when animals move at a near-constant mean speed, frequently vary with both the physical and biological context. Here we demonstrate, using analyses of fish locomotion and energetics, how variation among individuals in kinematic gaits can manifest as changes in dynamics of metabolic rate (estimated from oxygen uptake). We present kinematic data from a small school of giant danio (Devario aequipinnatus) to show that fish within a school frequently modulate their kinematics and change position, even when the school moves at an overall constant mean speed. We show that rainbow trout (Oncorhynchus mykiss), swimming over a range of speeds, exhibit considerable variation in tail beat frequency and metabolic rate among speeds. By experimentally altering the fluid dynamic environment, we demonstrate that brook trout (Salvelinus fontinalis) show correlated modulation of both kinematics and metabolic rate. Simultaneous measurement of energetic and biomechanical characteristics can unveil the physiological, biomechanical, and fluid dynamic mechanisms that underlie dynamic changes in vertebrate locomotor gaits.

physiology↗

bioRxiv2025

When less is not more: Limits to the evolution of metabolic dependence in spatially structured microbial communities

In microbial communities, evolutionary processes can lead to loss of biosynthetic pathways, creating metabolic dependencies. The Black Queen Hypothesis suggests that such gene loss can confer a fitness advantage by reducing metabolic burden. However, how these dependencies evolve at the level of individual cells in spatially structured communities remains poorly understood. We used a combination of microfluidic single-cell imaging and mathematical modeling to examine the early fate of auxotrophic mutants within E. coli populations. We found that without external amino acids, auxotroph growth is strongly constrained by low amino acid leakage from wildtype neighbors, and further reduced when they form local clusters that drain this limited amino acid pool. A growth advantage was only observed when amino acids were added or when leakage from wildtypes exceeded a threshold. Together, our results reveal insights into determinants of mutant invasion fitness and the trade-offs between reducing metabolic costs and maintaining metabolic autonomy. HighlightsO_LISingle-cell imaging reveals how auxotrophs fare in spatially structured populations C_LIO_LIAuxotrophs grow slowly due to low amino acid leakage from wildtype neighbors C_LIO_LIMutant clustering intensifies local amino acid depletion and reduces auxotroph growth C_LIO_LIModel identifies leakage threshold required for auxotroph invasion from rare C_LI

evolutionary biology↗

bioRxiv2020

Search behavior of individual foragers involves neurotransmitter systems characteristic for social scouting

In honey bees search behavior occurs as social and solitary behavior. In the context of foraging, searching for food sources is performed by behavioral specialized foragers, the scouts. When the scouts have found a new food source, they recruit other foragers (recruits). These recruits never search for a new food source on their own. However, when the food source is experimentally removed, they start searching for that food source. Our study provides a detailed description of this solitary search behavior and the variation of this behavior among individual foragers. Furthermore, mass spectrometric measurement showed that the initiation and performance of this solitary search behavior is associated with changes in glutamate, GABA, histamine, aspartate and the catecholaminergic system in the optic lobes and central brain area. These findings strikingly correspond with the results of an earlier study that showed that scouts and recruits differ in the expression of glutamate and GABA receptors. Together, the results of both studies provide first clear support for the hypothesis that behavioral specialization in honey bees is based on adjusting modulatory systems involved in solitary behavior to increase the probability or frequency of that behavior.

animal behavior and cognition↗