Everyone defecates, as the saying goes. So it’s easy to think of feces as something that brings animals together across divides. Scientifically speaking however, hyenas are an exception. Research indicates that spotted hyenas of high and low social status have genetic differences that can be detected in their scat. In other words, biologists are able to tell the difference between high and low ranking hyenas by analyzing their feces, identifying “molecular signatures of social status,” according to a study published on March 28 in the journal Communications Biology. Communications Biology.
In hyena society, some individuals have power over others. The resulting hierarchy determines how animals interact and obtain food. Higher status hyenas can be seen as more popular, engaging in more frequent and successful social contact. They also have to put in less effort to eat. The new study shows that these social norms have wide-reaching effects, even causing changes in an animal’s DNA.
When the environment affects genes
These DNA alterations occur in the form of epigenetic changes, or shifts in how genes are expressed in response to environmental conditions. In gut cells extracted from scat samples, high status and low status hyenas show significant differences in 149 epigenetic sites. Between the two groups of animals, consistent variations in DNA methylation are detectable–a process where methyl groups bind to regions of the genome within a cell, silencing certain genes.
Things like food availability, activity level, stress, competition, or exposure to pollutants can all prompt changes in methylation, and thus gene expression. Once epigenetic changes have occurred, some can be passed down to the next generation.
Many things impact DNA methylation–much of it is inherited, but some of it is acquired throughout life. Factors such as food availability, activity level, stress, competition, or exposure to pollutants can all prompt changes in methylation, and thus gene expression. Once epigenetic changes have occurred, some can be passed down to the next generation.
In hyenas and a few other species Prior research has suggested that social status can lead to epigenetic shifts in other species. The new study further supports this idea, confirming the phenomenon in a pack of wild hyenas with new methods, identifying the genes influenced by methylation, and showing that changes persist from cubs to adults. The study adds to the growing body of evidence that the social environment plays a significant role in animal and human health and physiology, leaving a permanent mark on DNA.
It’s a “well done study” that improves on past work with more sensitive techniques, says Christopher Faulk, an associate professor of genetics at University of Minnesota who was uninvolved in the new research. Faulk previously contributed to research on DNA methylation in spotted hyenas, but he says that, thanks to advances in genetic science and the clever idea of turning to scat instead of blood or organ tissue, the new study represents “an impressive technical feat.”
“If we were to re-do our study today, we would have done it exactly this way. I think it [uses] excellent methods,” he adds.
Molecular evidence of social structure
Hyenas live in female-dominated packs organized under a strict social hierarchy. Higher-status individuals dominate lower-status ones, and rank is generally passed down from mother to daughter. The social order determines things like how conflicts are resolved and also how far an individual has to travel to forage–higher status animals have priority to closer food sources, while low-status hyenas have to commute longer distances.
“We didn’t have to interfere with the animals. This has never been done before [in the wild]… it opens up a big way forward for other researchers that work on wild species as well.”
The scientists think that the differences in access to resources are causing epigenetic changes in young cubs. Mothers with low status spend less time nursing their offspring when they have to travel for food, compared to mothers that can stay closer to the den, says senior study author Alexandra Weyrich. Alexandra Weyrich heads the wildlife epigenetics at the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany. She says that it's an early imprint of social status.The findings of Weyrich and her co-author support the idea. They collected and analyzed fresh scat samples from 42 hyenas of different ranks and found differences in DNA methylation between high and low status groups. By using feces, the researchers were able to avoid harming the study subjects.
The researchers identified genes related to energy conversion, the immune system, and gut-brain communication, indicating that food access and status differences have permanent effects on hyena metabolism and health. They also found that methylation differences in cubs continue into adulthood, with new epigenetic changes emerging in maturity. The authors were able to identify a hyena's rank solely from methylation signatures with 80% accuracy. However, the study needs to be tested on other populations to confirm the pattern, says Weyrich.
From hyenas to humans
Faulk says that wild hyenas are a great model for humans due to their complex social dynamics and behavior. He conducts many epigenetic studies in laboratory mice, but believes that hyenas offer a different level of insight because they are not manipulated by laboratory conditions or domestication.
There is a lot of research indicating that early life experiences can cause epigenetic changes in humans and rodents. The new study can be applied to people, says Weyrich, but more research is needed as the gene regions under epigenetic pressure may differ. The study suggests that social rank and resource access significantly affect mammal gene expression, which could also be the case for humans.
“Wild hyenas actually serve as a fantastic model for humans.”
The hyena research contributes to our understanding of how the human social environment might impact our health and risk of disease, according to Faulk. He considers this line of study to be very useful and important. Groups of hyenas have a strict social structure dominated by females, which affects their behavior and genetics.. Though it’s not a direct one-to-one comparison, the new study “can be extrapolated” to people, says Weyrich. “We have to be a bit cautious,” she adds–noting that more research would be needed and that the exact gene regions under epigenetic pressure may differ, but the study does suggest social rank and resource access have significant bearing on mammal gene expression. Despite the specifics of different species’ social hierarchies, if it’s happening in hyenas, it could be happening in humans too.
“This hyena research directly contributes to our understanding of how the human social environment might impact our health and risk of disease,” says Faulk. “It’s a very useful and important line of study.”
