Feeding rhythms: How do animals know when it's lunchtime?

How do animals innately know when it’s time to eat? To answer this question, researchers at Tokyo Metropolitan University investigated the feeding rhythms of fruit flies. 

Many members of the animal kingdom feed at roughly the same times each day. This punctual feeding routine is a response to environmental factors, such as light, temperature, availability of food, and potential predator threats. 

Circadian rhythm 

Ensuring that these feeding times align with optimal conditions is essential for survival, efficient digestion, and overall well-being. A key factor that governs the eating schedules of animals is the circadian rhythm. 

This physiological cycle is shared by a vast spectrum of organisms, ranging from animals and plants to bacteria and algae. It acts as the “master clock,” steering rhythmic behaviors.

Peripheral clocks 

Animals also possess “peripheral clocks” with unique biochemical pathways that can adjust based on external cues like feeding. However, the direct relation of these clocks to feeding behaviors has remained largely elusive.

Focus of the study

To investigate, Professor Kanae Ando and her team at Tokyo Metropolitan University used fruit flies as their model organism. Surprisingly, fruit flies share many characteristics with complex animals, including humans, making them an ideal subject for this study.

Through a method called CAFE assay, where the feeding amounts of individual flies can be meticulously measured, the researchers delved deep into understanding the flies’ eating patterns in relation to light. 

Circadian genes

Prior research revealed that flies primarily fed during the day even when mutations were present in their core circadian genes, period (per) and timeless (tim). Shifting focus to the quasimodo (qsm) gene, which produces a light-sensitive protein, the team made a groundbreaking discovery. 

When the expression of the quasimodo gene was reduced, the flies’ daytime feeding routine was drastically altered. This revelation highlights quasimodo’s important role in aligning feeding with light-based rhythms.

Constant darkness 

However, the rules changed when flies were feeding in constant darkness. Flies with mutations in their core circadian genes displayed erratic feeding behaviors. Among the primary genes, cycle (cyc) and clock (clk) stood out, with their loss causing the most significant disruptions. 

In essence, the clk/cyc combination was crucial for establishing clear eating and fasting intervals, especially in metabolic tissues. But the mystery of how these patterns aligned with days was solved when the team identified that molecular clock genes in nerve cells were the primary drivers.

Study implications 

The findings provide an initial understanding of how different internal clocks within an organism influence feeding cycles and align with daily rhythms. These insights into feeding behaviors may ultimately lead to innovative treatments for eating disorders.

“In summary, our results revealed novel pathways that regulate the formation of feeding rhythms in Drosophila,” wrote the study authors. “Feeding/fasting rhythms coordinate metabolism and affect aging and life span. Further studies of these axes may contribute to human health.”

The research is published in the journal iScience.

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