Understanding Animal Behavior During Feeding Time

Genetic components regulating daily eating patterns have been studied by Tokyo Metropolitan University using fruit flies. The quasimodo (qsm) gene was found to align feeding with the light/dark cycle. In constant darkness, these patterns were maintained by the genes clock (clk) and cycle (cyc), particularly in metabolic tissues. Moreover, it was discovered that nerve cell "clocks" are vital in co-ordinating eating patterns with daily changes in light. This research is significant for our understanding of circadian rhythms in feeding behaviour and might aid in the development of treatments for eating disorders.

A study conducted by researchers at Tokyo Metropolitan University has used fruit flies to gain insights into the regulation of daily eating patterns. It was revealed that the synchronization of feeding with the light/dark cycle is dependent on the quasimodo (qsm) gene. However, this gene doesn't function in complete darkness. Under those conditions, eating and fasting cycles are maintained by the genes clock (clk) and cycle (cyc).

Besides, other "clocks" present within nerve cells adjust these cycles in accordance with day-night changes. Understand the molecular mechanisms which govern eating cycles will further our understanding of animal and human behaviour.

It is common for most animals to eat at similar times each day. This trend arises from their need to adapt to different environmental factors like light, temperature, food availability, and possibility of predators, all crucial for survival. Proper digestion and metabolism, and therefore general well-being, also rely on this.

In the study, the team discovered that qsm regulated alignment to light/dark cycles, whereas molecular clocks in neurons took over this role in complete darkness. The clk/cyc genes, on the other hand, helped maintain feeding/fasting cycles.

But how do such diverse organisms know when to eat? One crucial aspect is the circadian rhythm, a near-daily physiological cycle common to organisms like animals, plants, bacteria, and algae. It works as a "master clock" regulating rhythmic behavior. However, animals also possess other "peripheral clocks" which are based on different biochemical pathways. These can be reset by external elements such as feeding. They way they govern animal feeding habits is unclear.

To explore this, a team led by Associate Professor Kanae Ando of Tokyo Metropolitan University used fruit flies, which exhibit many characteristics common to more complex animals, including humans. They employed a CAFE assay, where flies are fed via a microcapillary to measure their food intake at different times. They then studied how flies adjust their eating habits to light.

Previous study on flies feeding in a light/dark cycle demonstrated that flies eat more during the day, even with introduced mutations to circadian clock genes, period (per) and timeless (tim). The team focused on quasimodo (qsm), a gene coding for a light-responsive protein controlling the firing of clock neurons. Knocking down qsm affected the daytime feeding patterns of the flies. It was found for the first time that the alignment of feeding to a light-mediated rhythm is impacted by qsm.

This effect was absent for flies feeding in constant darkness. Here, flies with mutations in their circadian clock genes had their daily feeding patterns severely disrupted. Of the genes involved, period (per), timeless (tim), cycle (cyc) and clock (clk), loss of clk and cyc had the most severe impact. It was revealed that clk/cyc is needed to create eating and fasting periods, especially in metabolic tissues. But how these cycles were synced with days was due to molecular clock genes in nerve cells rather than metabolic tissues.

The findings of the team are the first insight into how varying clocks in different parts of an organism regulate feeding/fasting cycles and their alignment with diurnal rhythms. Understanding the mechanisms behind feeding behaviours can shed light on animal behaviour, and potentially lead to the development of new treatments for eating disorders.

Reference: The study named “Dissecting the daily feeding pattern: Peripheral CLOCK/CYCLE generate the feeding/fasting episodes and neuronal molecular clocks synchronize them” was published in iScience on 7 October 2023.

This study received support from the Farber Institute for Neurosciences and Thomas Jefferson University, the National Institutes of Health, a Takeda Foundation Grant, and the TMU Strategic Research Fund.