Researchers have discovered that snakes lack the gene for ghrelin, a hormone that typically helps control hunger in many animals. This absence is significant, as it changes how we think about how snakes survive long periods without food and raises questions about the evolution of metabolism in reptiles.
Across 112 reptile genomes, scientists found the same genetic gap where the ghrelin gene should be. Rui Resende Pinto from the Interdisciplinary Centre of Marine and Environmental Research documented that this gene has vanished entirely in snakes. It’s also missing or damaged in 32 other species but still exists in crocodiles, which can go weeks without eating. This raises intriguing questions about the genetic changes in snakes.
Interestingly, studies show that simply knocking out the ghrelin gene in mice doesn’t significantly affect food intake. This suggests that ghrelin’s role is not just as a hunger signal but also in metabolism. After eating, the active form of ghrelin can increase, particularly in response to dietary fats. This could mean that losing the ghrelin system changes energy regulation more than appetite alone.
The loss of both the ghrelin hormone and its activating enzyme in snakes is a clear example of evolutionary gene loss. Researchers describe this as “paired disappearance,” where useful genetic instructions decay over time. In snakes, the remnants show signs of natural selection no longer preserving the gene. This pattern strongly supports the idea that a significant evolutionary shift has occurred.
Many snakes go weeks between meals, sometimes consuming prey that weighs up to half their body weight. This cycle of feast and famine means their bodies must quickly adapt to digesting large meals, which requires a lot of energy and resources. Burmese pythons, for example, switch thousands of genes on after eating, indicating a major overhaul in their systems. This substantial metabolic swing suggests that a continuous hunger signal might not be as necessary as previously thought.
Moreover, after eating, a snake’s metabolism can spike for several days to deal with the large food intake. Compared to other cold-blooded reptiles, snakes show a particularly high metabolic response. During fasting, they reduce movement and conserve energy, marking a substantial shift between low-energy waiting and high-energy digestion.
Interestingly, other reptiles like chameleons have also lost the ghrelin system, particularly those that hunt by ambushing prey. When animals rely on patience rather than active hunting, not having a constant hunger signal makes sense, as it allows energy conservation.
Crocodiles complicate this narrative. Even though they can fast for long durations, they retain the ghrelin genes, which suggests that there’s more to the relationship between feeding habits, energy use, and gene loss across species. This highlights the need for further research to understand these genetic dynamics better.
Future studies could involve deleting these genes in crocodiles to see if their fasting behavior changes to resemble snakes. Similarly, giving snakes the hormone and observing changes in their feeding and metabolism might clarify how appetite and energy regulation are connected.
These findings could also have implications for human health. As scientists study snake biology, it could reveal new insights into metabolic diseases like obesity and diabetes. Todd Castoe, an evolutionary geneticist at the University of Texas at Arlington, suggests that this research could lead to fresh avenues for understanding these conditions in humans. The genes that have vanished from snakes might indicate deeper metabolic rewrites rather than simply hunger signals.
This study opens up a fascinating area for exploration—one that may ultimately connect snake survival strategies with human health challenges. The original study was published in Open Biology.
For further reading, you can explore more about the research here.
