# A four-oscillator model of seasonally adapted morning and evening activities in Drosophila melanogaster

## TL;DR

This paper proposes a new model with four oscillators to explain how fruit flies adjust their morning and evening activity patterns with changing seasons.

## Contribution

The paper introduces a novel four-oscillator model to explain seasonal adaptation of circadian activity rhythms in fruit flies.

## Key findings

- A four-oscillator model is proposed to regulate morning and evening activity peaks and midday and nighttime sleep.
- The model suggests that interactions among four oscillators explain flexible activity rhythms under different photoperiods.

## Abstract

The fruit fly Drosophila melanogaster exhibits two activity peaks, one in the morning and another in the evening. Because the two peaks change phase depending on the photoperiod they are exposed to, they are convenient for studying responses of the circadian clock to seasonal changes. To explain the phase determination of the two peaks, Drosophila researchers have employed the two-oscillator model, in which two oscillators control the two peaks. The two oscillators reside in different subsets of neurons in the brain, which express clock genes, the so-called clock neurons. However, the mechanism underlying the activity of the two peaks is complex and requires a new model for mechanistic exploration. Here, we hypothesize a four-oscillator model that controls the bimodal rhythms. The four oscillators that reside in different clock neurons regulate activity in the morning and evening and sleep during the midday and at night. In this way, bimodal rhythms are formed by interactions among the four oscillators (two activity and two sleep oscillators), which may judiciously explain the flexible waveform of activity rhythms under different photoperiod conditions. Although still hypothetical, this model would provide a new perspective on the seasonal adaptation of the two activity peaks.