Experimental Evolution of Anticipatory Regulation in Escherichia coli

Environmental cues in an ecological niche are often temporal in nature. For instance, in temperate climates, temperature is higher in daytime compared to during night. In response to these temporal cues, bacteria have been known to exhibit anticipatory regulation, whereby triggering response to a yet to appear cue. Such an anticipatory response in known to enhance Darwinian fitness, and hence, is likely an important feature of regulatory networks in microorganisms. However, the conditions under which an anticipatory response evolves as an adaptive response are not known. In this work, we develop a quantitative model to study response of a population to two temporal environmental cues, and predict variables which are likely important for evolution of anticipatory regulatory response. We follow this with experimental evolution of Escherichia coli in alternating environments of rhamnose and paraquat for ∼850 generations. We demonstrate that growth in this cyclical environment leads to evolution of anticipatory regulation. As a result, pre-exposure to rhamnose leads to a greater fitness in paraquat environment. Genome sequencing reveals that this anticipatory regulation is encoded via mutations in global regulators. Overall, our study contributes to understanding of how environment shapes the topology of regulatory networks in an organism.

Why am I always late? Modeling the cognitive mechanisms underlying anticipatory timing under uncertainty

Responding to stimuli in a timely manner and anticipating the timing of future events both require us to internally track the passage of time. Models of timing on these tasks suggest that the subjective passage of time can be described as a noisy accumulation process driven by neural oscillations. In this paper, we show that the accuracy of these accumulators can be manipulated by occluding visual cues to the passage of time. Using a simple perceptual paradigm, we manipulate the total length of time that a stimulus must be tracked, the rate at which it moves, and the uncertainty that participants have about its position (length of occlusion). Participants consistently under-estimated the movement of the stimulus when it was occluded, corresponding to a drift rate in an accumulator model that was approximately half of what would be required to accurately track the passage of time. This results in consistently tardy anticipatory response times under uncertainty (Study 1) and an under-estimation of stimulus movement as it passes behind an occlusion (Study 2). Using a novel timing problems scale, we show that individual differences in model parameters representing subjective tracking of time under uncertainty predicted real-world difficulties managing time, tardiness, and procrastination.

Threat imminence reveals links among unfolding of anticipatory physiological response, cortical-subcortical intrinsic functional connectivity, and anxiety

Excessive expression of threat-anticipatory defensive responses is central in anxiety. Animal research indicates that anticipatory responses are dynamically organized by threat imminence and rely on conserved circuitry. Insight from translational work on threat imminence could guide mechanistic research mapping abnormal function in this circuitry to aberrant defensive responses in anxiety. Here, we initiate such research. Fifty pediatric anxiety patients and healthy-comparisons (33 females) completed a threat-anticipation task whereby cues signaled delivery of highly-painful (threat) or non-painful (safety) heat. Temporal changes in skin-conductance indexed defensive responding as function of threat imminence. Resting-state functional connectivity data were used to identify intrinsic-function correlates of anticipatory response within a specific functional network derived from translational research. Results indicate that anxiety was associated with greater increase in anticipatory response as threats became more imminent. Magnitude of increase in threat-anticipatory responses corresponded to intrinsic connectivity within a cortical-subcortical circuit; importantly, more severe anxiety was associated with greater connectivity between ventromedial prefrontal cortex and hippocampus and basolateral amygdala, a circuit implicated in animal models of anxiety. These findings link basic-translational and clinical research, highlighting aberrant intrinsic function in conserved defensive circuitry as potential pathophysiological mechanism in anxiety.

Predicting experimental designs leading to rewiring of transcription program and evolution of anticipatory regulation in E. coli

Environmental cues in an ecological niche are temporal. In response to these temporal cues, bacteria have been known to exhibit learning or conditioning, whereby they trigger response to a yet to appear cue, anticipating its actual arrival in the near future. Such an anticipatory response in known to enhance Darwinian fitness, and hence, is likely an important feature in the regulatory networks in microorganisms. However, the conditions under which an anticipatory response optimizes cellular fitness are not known. Nor has evolution of anticipatory regulation in laboratory conditions been experimentally demonstrated. In this work, we develop a quantitative model to study response of a population to two temporal environmental cues, and present the key variables in cellular physiology associated with response to the cues whose modulation is likely to lead to evolution of anticipatory regulatory response. We predict experimental conditions, which are likely to lead to demonstration of rewiring of regulation, and evolution of anticipatory response in bacterial populations. Using inputs from the modeling results, we evolve E. coli in alternating environments of the pentose sugar rhamnose and paraquat, which induces oxidative stress. We demonstrate that growth in this cyclical environment leads to evolution of anticipatory regulation. Thus, we argue that in niches where environmental stimuli have a cyclical nature, conditioning evolves in a population as an adaptive response.

Evaluation of Sheep Anticipatory Response to a Food Reward by Means of Functional Near-Infrared Spectroscopy

Anticipatory behaviour to an oncoming food reward can be triggered via classical conditioning, implies the activation of neural networks, and may serve to study the emotional state of animals. The aim of this study was to investigate how the anticipatory response to a food reward affects the cerebral cortex activity in sheep. Eight ewes from the same flock were trained to associate a neutral auditory stimulus (water bubble) to the presence of a food reward (maize grains). Once conditioned, sheep were trained to wait 15 s behind a gate before accessing a bucket with food (anticipation phase). For 6 days, sheep were submitted to two sessions of six consecutive trials each. Behavioural reaction was filmed and changes in cortical oxy- and deoxy-hemoglobin concentration ([ΔO2Hb] and [ΔHHb] respectively) following neuronal activation were recorded by functional near infrared spectroscopy (fNIRS). Compared to baseline, during the anticipation phase sheep increased their active behaviour, kept the head oriented to the gate (Wilcoxon’s signed rank test; p ≤ 0.001), and showed more asymmetric ear posture (Wilcoxon’s signed rank test; p ≤ 0.01), most likely reflecting a learnt association and an increased arousal. Results of trial-averaged [ΔO2Hb] and [ΔHHb] within individual sheep showed in almost every sheep a cortical activation during the anticipation phase (Student T-test; p ≤ 0.05). The sheep showed a greater response of the right hemisphere compared to the left hemisphere, possibly indicating a negative affective state, such as frustration. Behavioural and cortical changes observed during anticipation of a food reward reflect a learnt association and an increased arousal, but no clear emotional valence of the sheep subjective experience. Future work should take into consideration possible factors affecting the accurateness of measures, such as probe’s location and scalp vascularization.