Adding of methyl groups to a DNA molecule or methylation has the interesting ability to alter the activity of a DNA segment without changing the sequence. In this behind the scenes look, Zachary Laubach and colleagues test if this valuable biomarker is impacted by differences in hyena social status or other ecological factors early in life. What’s particularly impressive is that they garnered insights into methylation from a wild population. They find some surprising results, such as that high ranking mums can confer higher levels of methylation to their cubs that disappears when they get older. Why? Find out below and read the full article here.
What led to your interest in this topic / what was the motivation for this study?
Across a broad taxonomic spectrum, social experiences, particularly those early in life, seem to have a profound impact on organisms’ development. The idea that during sensitive periods of development, social experiences and early life environment can have lasting impacts on the later life phenotype and health is known as the Developmental Origins of Health and Disease (DOHaD) hypothesis, and was formalized in the 1980s by epidemiologists, namely David Barker and his research on cardiovascular disease. Among social mammals, including humans and non-human primates, an individual’s social rank affects their behavior, physiology, and related health outcomes. For example, in humans, low socioeconomic status is widely recognized as a risk factor for cardiovascular complications and other chronic diseases. In non-human primates, low social rank is risk factor for elevated chronic stress and immune dysregulation. So, although we observe that social status affects biology, we still know little about how this all works. To better understand a potential mechanism for how early life environment affects biology, we investigated possible early environmental determinants of a molecular biomarker (DNA methylation) over the course of development in a population of wild spotted hyenas. Similar to many primates, hyenas live in groups organized by a social dominance hierarchy, and whether or not a hyena is born high or low ranking has lifelong consequences.
What difficulties did you run into along the way?
In this study, we focused on measuring DNA methylation, which is generally of interest to researchers because it is responsive to environmental stimuli and associated with gene expression. Still, while spotted hyenas present a unique opportunity to investigate how various social experiences and ecological factors early in life are associated with biological characteristics later in life, there were no previous studies (at least of which we were aware) that measured DNA methylation in this species. In other words, this was not like working with a well characterized molecular biology model organism, like fruit flies or lab rats. In fact, when we were conducting our lab work there was no publicly available draft hyena genome. In our attempt to assess a potentially informative biomarker in hyenas, we measured multiple types of DNA methylation with varying degrees of success. Finally, the hyenas we study live freely in a large reserve in Kenya, so much of our data were observational and collected under a variety of field conditions making collection of samples non-trivial.
What is the biggest or most surprising innovation highlighted in this study?
This work represents one of a handful of studies conducted in a wild population that measures DNA methylation to better understand how early life environment may influence organisms’ biology over the course of development. Taking advantage of our approximately 30 years’ worth of continuously collected data on individually recognizable hyenas from the Masai Mara Hyena Project, we not only amassed a particularly large sample size for a long-lived, wild mammal, but we were also able to compare patterns of DNA methylation at various stages of development with respect to multiple early life environmental factors. We found that being born to a higher-ranking mom corresponded with greater global DNA methylation in young but not older hyenas. One interpretation of this result is that high ranking moms confer some advantage to their cubs early in life, but that the effect of maternal rank per se is not evident in global DNA methylation of subadult or adult hyenas. We also found some associations between global DNA methylation and litter size, human disturbance, and prey availability in the year a hyena was born, and these associations were strongest in the youngest age group of hyenas.
Moving forward, what are the next steps in this area of research?
In our next steps we are working to understand whether specific types of early life social environments, like maternal care and how well socially connected an animal is within its group, correspond with variation in DNA methylation and adult stress. We are also utilizing more advanced techniques for measuring DNA methylation, so that we might home in on functional pathways that are involved in the development of an adverse stress phenotype. As part of our broader research agenda looking at general biological principles related to DOHaD hypothesis, we have also teamed up with epidemiologists to ask how social status in humans affects biology. In fact, we have recently published another a paper looking at the associations between maternal socioeconomic status and patterns of DNA methylation over the course of development in children who are part of the Project Viva pre-birth cohort study (check out the paper here).
What would your message be for students about to start developing or using novel techniques in Molecular Ecology?
This project was part of my PhD work, and from this experience I have learned just how fast molecular biology advances as a field. Given that this technology is constantly changing, it is critical to find mentors and collaborators with up-to-date expertise who are willing to support you. I was fortunate to work in a cutting-edge molecular laboratory, and to receive training from internationally recognized experts in Dr. Dana Dolinoy’s lab who specialize in studying DNA methylation. Additionally, in studies like these that involve large observational data sets and that aim to understand biological mechanisms, the value of clearly defined study questions, hypotheses and a complimentary analytical strategy cannot be understated. In my opinion, novel technology will not substitute for a thoughtful and well-planned analysis.
What have you learned about methods and resources development over the course of this project?
Working in a novel system, like investigating DNA methylation in wild spotted hyenas, presents challenges and limitations that are unique from those encountered in laboratory settings and when working with model organisms. However, there are deep insights and rich perspective to be gained at the three-way interface between molecular biology, behavioral ecology and evolutionary biology from study populations with intact life histories and that are subject to natural selection. I have also learned that long-term field studies with uninterrupted data collection, like the Masai Mara Hyena Project, provide an invaluable resource and an unmatched opportunity to combine molecular techniques with vast collections of behavioral, demographic and ecological data. In addition, while long-term field studies represent a substantial investment of time and resources, they also present a chance for comparative research that can help elucidate basic biological principals that span taxa, like the DOHaD hypothesis. As such, I believe I have been fortunate to work with Dr. Kay Holekamp’s hyenas and that these types of long-term field studies are an asset to be prioritized and preserved.
Describe the significance of this research for the general scientific community in one sentence.
Social and ecological factors experienced early in life can correspond to changes in molecular biomarkers, like DNA methylation, that are detected over the course of development, and that may affect patterns of gene expression.
Describe the significance of this research for your scientific community in one sentence.
Findings from this research suggests that maternal rank, anthropogenic disturbance, and prey availability around the time of birth are associated with later life global DNA methylation in spotted hyenas, particularly in cubs.
Citation: Laubach, ZM, Faulk, CD, Dolinoy, DC, et al. Early life social and ecological determinants of global DNA methylation in wild spotted hyenas. Mol Ecol. 2019; 28: 3799– 3812. https://doi.org/10.1111/mec.15174