Biology subjects

Stephens, G.

Publications and source records attributed to Stephens, G..

4 recordsLinked to original sources

bioRxiv2026

A lightweight deep-learning detector for the real-time monitoring of the invasive frogs Rhinella marina and Polypedates leucomystax

Early detection of invasive species is critical to efficiently managing biological invasions. Passive acoustic monitoring combined with deep learning has become an effective tool for identifying invasive anurans from their species-specific mating calls. In practice, however, these systems still depend on manually retrieving recordings and running inference on a dedicated workstation, which delays detection at invasion fronts, especially on remote islands where frequent travel is impractical. Here, we present a lightweight convolutional neural network for detecting Rhinella marina and Polypedates leucomystax that can be used with low-power microcontrollers, enabling continuous, real-time monitoring of these invasive species. Our model achieved a mean invasive-species F1 of 0.87 with precision higher than 0.88 for both species, comparable to the performance of substantially larger models at a fraction of the model size. Cross-domain evaluation confirmed reliable detection on two out-of-training locations: Iriomote Island, Japan, and on an independent dataset from Australia, demonstrating generalization across recording conditions and biogeographic contexts, albeit with local threshold calibration for P. leucomystax at Iriomote. Our results demonstrate that effective acoustic detection of invasive species is feasible on self-contained, battery-powered devices, removing the dependence on server infrastructure and enabling autonomous early warning systems in remote protected areas.

ecology↗

bioRxiv2026

Mice detect and discriminate temporal patterns of mesoscale optogenetic cortical stimulation

Optogenetic stimulation is widely used to establish causal links between neural activity, behavior, and sensory perception, yet animals may also perceive the neural stimulation itself, a phenomenon termed "optoception." We hypothesized that cortical optogenetic stimulation would generate an artificial percept that could be distinguished from externally evoked sensations and characterized psychometrically in an operant task. We tested this hypothesis using mesoscale cortical photostimulation delivered by a 3 mm, 459 nm LED implanted over auditory cortex. Four mice expressing Channelrhodopsin-2 (ChR2) in excitatory neurons learned a head-fixed go/no-go task in which 20 Hz cortical photostimulation served as the target. ChR2-positive mice detected cortical photostimulation relative to LED-off catch trials, distinguished it from both an external LED matched in wavelength and pulse rate and from an acoustic noise matched in amplitude-modulation rate, and discriminated between 20- and 10-Hz cortical photostimulation. Reducing implanted-LED optical power initially lowered rate-discrimination sensitivity, which then increased across training sessions, demonstrating perceptual learning. In two mice tested with 11 randomly interleaved rates spanning 10-20 Hz, lick probability followed a saturating rate-dependent function. Two ChR2-negative littermates failed to acquire photostimulation-locked behavioral responding. Together, these findings show that mesoscale cortical optogenetic stimulation generates a graded, learnable artificial percept whose behavioral readout depends on photostimulation rate and optical power. This single-LED preparation provides a cost-efficient and wavelength-extensible platform for psychometric analysis of optoception.

neuroscience↗

bioRxiv2023

Dynamics of dominance: maneuvers, contests, and assessment in the posture-scalemovements of interacting zebrafish

While two-body fighting behavior occurs throughout the animal kingdom to settle dominance disputes, important questions such as how the dynamics ultimately lead to a winner and loser are unresolved. Here we examine fighting behavior at high-resolution in male zebrafish. We combine multiple cameras, a large volume containing a transparent interior cage to avoid reflection artifacts, with computer vision to track multiple body points across multiple organisms while maintaining individual identity in 3D. In the body point trajectories we find a spectrum of timescales which we use to build informative joint coordinates consisting of relative orientation and distance. We use the distribution of these coordinates to automatically identify fight epochs, and we demonstrate the post-fight emergence of an abrupt asymmetry in relative orientations-a clear and quantitative signal of hierarchy formation. We identify short-time, multi-animal behaviors as clustered transitions between joint configurations, and show that fight epochs are spanned by a subset of these clusters, which we denote as maneuvers. The resulting space of maneuvers is rich but interpretable, including motifs such as "attacks" and "circling". In the longer-time dynamics of maneuver frequencies we find differential and changing strategies, including that the eventual loser attacks more often towards the end of the contest. Our results suggest a reevaluation of relevant assessment models in zebrafish, while our approach is generally applicable to other animal systems.

biophysics↗

bioRxiv2019

Optical interrogation of sympathetic neuronal effects on macroscopic cardiac monolayer dynamics

Alterations in autonomic function are known to occur in cardiac conditions including sudden cardiac death. Cardiac stimulation via sympathetic neurons can potentially trigger arrhythmias. Dissecting direct neural-cardiac interactions at the cellular level is technically challenging and understudied due to the lack of experimental model systems and methodologies. Here we demonstrate the utility of optical interrogation of sympathetic neurons and their effects on macroscopic cardiac monolayer dynamics to address research targets such as the effects of adrenergic stimulation via the release of neurotransmitters, the effect of neuronal numbers on cardiac wave behaviour and the applicability of optogenetics in mechanistic in vitro studies. We combine photo-uncaging or optogenetic neural stimulation with imaging of cardiac monolayers to measure electrical activity in an automated fashion, illustrating the power and high throughput capability of such interrogations. The methods described highlight the challenges and benefits of co-cultures as experimental model systems.

biophysics↗