Animals integrate physiological and environmental signals to modulate their food uptake. The nematode C. elegans, whose food uptake consists of pumping bacteria from the environment into the gut, provides excellent opportunities for discovering principles of conserved regulatory mechanisms. Here we show that worms implement a graded feeding response to the concentration of environmental bacteria by modulating a commitment to bursts of fast pumping. Using long-term, high-resolution, longitudinal recordings of feeding dynamics under defined conditions, we find that the frequency and duration of pumping bursts increase and the duration of long pauses diminishes in environments richer in bacteria. The bioamine serotonin is required for food-dependent induction of bursts as well as for maintaining their high rate of pumping through two distinct mechanisms. We identify the differential roles of distinct families of serotonin receptors in this process and propose that regulation of bursts is a conserved mechanism of behaviour and motor control.

We investigated the neural representation of locomotion in the nematode C. elegans by recording population calcium activity during movement. We report that population activity more accurately decodes locomotion than any single neuron. Relevant signals are distributed across neurons with diverse tunings to locomotion. Two largely distinct subpopulations are informative for decoding velocity and curvature, and different neurons’ activities contribute features relevant for different aspects of a behavior or different instances of a behavioral motif. To validate our measurements, we labeled neurons AVAL and AVAR and found that their activity exhibited expected transients during backward locomotion. Finally, we compared population activity during movement and immobilization. Immobilization alters the correlation structure of neural activity and its dynamics. Some neurons positively correlated with AVA during movement become negatively correlated during immobilization and vice versa. This work provides needed experimental measurements that inform and constrain ongoing efforts to understand population dynamics underlying locomotion in C. elegans.

Diversity is often associated with the functional stability of ecological communities from microbes to macroorganisms. Understanding how diversity responds to environmental perturbations and the consequences of this relationship for ecosystem function are thus central challenges in microbial ecology. Unimodal diversity-disturbance relationships, in which maximum diversity occurs at intermediate levels of disturbance, have been predicted for ecosystems where life history tradeoffs separate organisms along a disturbance gradient. However, empirical support for such peaked relationships in macrosystems is mixed, and few studies have explored these relationships in microbial systems. Here we use complex microbial microcosm communities to systematically determine diversity-disturbance relationships over a range of disturbance regimes. We observed a reproducible switch between community states, which gave rise to transient diversity maxima when community states were forced to mix. Communities showed reduced compositional stability when diversity was highest. To further explore these dynamics, we formulated a simple model that reveals specific regimes under which diversity maxima are stable. Together, our results show how both unimodal and non-unimodal diversity-disturbance relationships can be observed as a system switches between two distinct microbial community states; this process likely occurs across a wide range of spatially and temporally heterogeneous microbial ecosystems.

Power-law dwell times have been observed for molecular motors in living cells, but the origins of these trapped states are not known. We introduce a minimal model of motors moving on a twodimensional network of filaments, and simulations of its dynamics exhibit statistics comparable to those observed experimentally. Analysis of the model trajectories, as well as experimental particle tracking data, reveals a state in which motors cycle unproductively at junctions of three or more filaments. We formulate a master equation for these junction dynamics and show that the time required to escape from this vortex-like state can account for the power-law dwell times. We identify trends in the dynamics with the motor valency for further experimental validation. We demonstrate that these trends exist in individual trajectories of myosin II on an actin network.We discuss how cells could regulate intracellular transport and, in turn, biological function, by controlling their cytoskeletal network structures locally.Individual microscopic particles (beads [1,2] or fluorescently labeled molecules [3-5]) can now be tracked in cells. These studies reveal complex dynamics [6][7][8]. The resulting trajectories can be treated as random walks, and quantitative analysis of their statistics can provide insights into underlying mechanisms [1,9]. Often, the mean square displacement (MSD) exhibits a power-law (typically sublinear) dependence on the separation in time between two observations, known as the lag time (∆) [1,9,[11][12][13][14][15]. In certain cases [9,14], the MSD also decays as the amount of data included in averages (the measurement time, T ) increases; this trend indicates a power-law distribution of dwell times and is known as "aging" in theories of glassy dynamic [16].These correlations can have important biological implications [9,17]. For example, a recent study shows that the anomalous dynamics observed for insulin secretory vesicles (granules) can account for the biphasic kinetics of insulin release [9] without the need to invoke separate pools of granules, as previously [18]. In particular, the sustained release relies on the glassy dynamics. Glassy dynamics are often interpreted in terms of trapping in local minima of an energy landscape with an exponential or power-law distribution of depths [19,20]. However, how such a landscape could arise from typical biomolecular interactions is unclear. Crowding is insufficient, as it results in standard Brownian motion but with a reduced diffusion coefficient [21]. Because the moving vesicles are associated with molecular motors, which consume cellular energy stores (nucleotide triphosphates) for directed motion along cytoskeletal filaments, other, intrinsically nonequilibrium mechanisms of generating these statistics may exist.In the case of insulin release, the vesicles have both kinesin and dynein associated with them [22], which walk in opposite directions on microtubules [23]. More generally, many cytoskeletal assemblies in cells have multiple motors associated with ...

Our approach adds a powerful tool for studying pharyngeal pumping. It enhances the experimental versatility of assaying genetic and pharmacological manipulations and the ability to characterize the resulting behavior. Both the experimental setup and the analysis can be readily adapted to additional challenging motion detection problems.