Understanding the dynamics of feeding as a random walk on the feeding-rate axis

Abstract

In animals, the presence of food stimulates appetite and induces feeding behaviors. This is an important mechanism, instrumental for animals’ competitiveness in fluctuating environment. To learn fundamental principles of feeding regulation, it is useful to study simple model organisms, whose feeding dynamics can be quantitatively measured. Recently, we measured the feeding dynamics of the nematode C. elegans, whose feeding consists of pumping bacteria from the environment into the gut, and demonstrated that it matches its feeding activity with the availability of food by modulating the frequency and duration of persistent fast pumping periods. Here, we develop an effective model that described these dynamics as a random walk on the pumping-rate axis, experiencing food-dependent transition probabilities. This model suggests the existence of two classes of fast pumping: the first is characterized by persistent fast-rate pumping, while the other exhibits only transient fast pumping. We show, however, that it is the dynamics of transient fast pumping that is governed by the presence of food. Furthermore, we use the model to show that serotonin is used by worms both in a food-independent mechanism that promotes acceleration of pumping and address the different roles of two pairs of serotonergic neurons.