Biology subjects

Bach, M.

Publications and source records attributed to Bach, M..

4 recordsLinked to original sources

bioRxiv2023

Coordinated electrical and chemical signaling between two neurons orchestrates switching of motor states

To survive in a complex environment, animals must respond to external cues, e.g., to escape threats or to navigate towards favorable locations. Navigating requires transition between motor states, e.g. switching from forward to backward movement. Here, we investigated how two classes of interneurons, RIS and RIM, fine-tune this transition in the nematode C. elegans. By Ca2+ imaging in freely moving animals, we found that RIS gets active slightly before RIM and likely biases decision-making towards a reversal. In animals lacking RIS, we observed lowered Ca2+-levels in RIM prior to a reversal. Combined photo-stimulation and voltage imaging revealed that FLP-11, a neuropeptide released by RIS, has an excitatory effect on RIM, while tyramine, released from RIM, inhibits RIS. Voltage imaging of intrinsic activity provided evidence for tight electrical coupling between RIS and RIM via gap junctions harboring UNC-7 innexins. Asymmetric junctional current flow was observed from RIS to RIM, and vice versa. We propose that the interplay of RIS and RIM is based on concerted electrical and chemical signaling, with a fast junctional current exchange early during the transition from forward to backward movement, followed by chemical signaling, likely during reversal execution.

neuroscience↗

bioRxiv2020

Interaction of habitat isolation and seasonality: impact of fragmentation in dynamic landscapes on local and regional population variability in meta-food chains

While habitat loss is a known key driver of biodiversity decline, the effect of habitat fragmentation per se is far less clear. Environmental perturbations, e.g. due to seasonality, potentially interact with effects of habitat fragmentation, thus making the latter even more difficult to assess. In order to analyze how the dynamic stability of local and metapopulations is affected by habitat fragmentation, we simulate a meta-food chain with three species on complex networks of habitat patches and evaluate the average variability of the local populations and the metapopulations as well as the level of synchronization between the patches. To account for environmental perturbations, we contrast simulations of static landscapes with simulations of dynamic landscapes, where 30 percent of the patches periodically become unavailable as habitats. We find that it depends on the parameterization of the food chain whether higher dispersal rates in less fragmented landscapes synchronize the dynamics or not. Even if the dynamics synchronize, local population variability can decrease due to indirect effects of dispersal mortality, thereby stabilizing metapopulation dynamics and reducing the risk of extinction. In dynamic landscapes, periodic external perturbations often fully synchronize the dynamics even if they act on a much slower time scale than the ecological interactions. Furthermore, they not only increase the variability of local and metapopulations, but also mostly overrule the effects of habitat fragmentation. This may explain why in nature effects of habitat fragmentation are often small and inconclusive.

ecology↗

bioRxiv2020

The Rotating Snake Illusion is a straightforward consequence of non-linearity in arrays of standard motion detectors

The Rotating Snakes illusion is a motion illusion based on repeating, asymmetric luminance patterns. Recently, we found certain grey-value conditions where a weak, illusory motion occurs in the opposite direction. Of the four models for explaining the illusion, one (Backus and Oruc, 2005) also explains the unexpected perceived opposite direction. We here present a simple new model, without free parameters, based on an array of standard correlation-type motion detectors with a subsequent non-linearity (e.g., saturation) before summing the detector outputs. The model predicts (1) the pattern-appearance motion illusion for steady fixation, (2) an illusion under the real-world situation of saccades across or near the pattern (pattern shift), (3) a relative maximum of illusory motion for the same grey values where it is found psychophysically, and (4) the inverse illusion for certain luminance values. We submit that the models sparseness of assumptions justifies adding a fifth model to explain this illusion.

neuroscience↗

bioRxiv2018

Resource co-limited growth in fluctuating environments

Variability in the supply of limiting resources determines consumer-resource interactions. Yet, how consumers are affected by variability when multiple resources co-limit growth remains unknown. We use a two-resource DEB model to predict how consumer somatic growth rate responds to the temporal structure (i.e. fluctuation frequency, phase and covariance) of single and co-limiting resources supply. Subsequently, we experimentally test the model predictions using Daphnia magna (co-)limited by dietary phosphorus and cholesterol supply. Both model and experiments indicate that for certain fluctuation frequencies, resource fluctuation phase and (co)variance can heavily affect somatic growth. The model suggests that dynamic resource storage and assimilation efficiency adjustment are key for predicting the frequencies at which the growth rate is mostly affected by (co)variance and phase. In a context of ongoing anthropogenic landscape homogenization, our results offer novel insights on how co-occurring perturbations to the temporal structure of resource supply can affect consumer performance.

ecology↗