Animals contain billions of bacteria and most benefit the health of their animal hosts. Currently, the effects of symbiotic bacteria on the behavior of their animal hosts remain largely unexplored. Symbiotic bacteria potentially figure prominently in animal communication, especially among mammals. Many mammals communicate by scent-marking with products of specialized glands. These glands are highly conducive to bacterial proliferation, and it has been postulated that the volatile odorants the bacteria generate are used by their hosts in communication. This project uses current insights and tools of microbial ecology to elucidate the effects of symbiotic bacteria on the scent-marking system of the spotted hyena, a socially complex large carnivore found throughout Sub-Saharan Africa. Scent discrimination experiments with hyenas in Kenya will illustrate the information content of hyenas' scent-marks. Chemical analyses will further illustrate the information content of their marks and also reveal how that information is chemically coded. Culture-independent molecular surveys of the same scent-marks will indicate whether variation in symbiotic bacterial communities underlies the coding of information in scent-marks. Lastly, contemporary culturing techniques will be used to isolate prominent members of scent gland bacterial communities, and to ascertain whether they produce the odorants that, as indicated by the chemical analyses, likely code information in scent-marks. This project will enhance our understanding of the potential roles of bacteria in mammalian chemical communication systems. The project will involve the training of undergraduates across disciplinary boundaries, integrating cutting-edge advances in molecular biology into animal behavior research. It will result in public access to over one million molecular sequences from an entirely novel symbiotic environment, and should stimulate multi-disciplinary partnerships to generate a central online database enabling rapid access to molecular sequences from symbiotic systems. This project should be transformative, opening up a rich new field of study and altering our perceptions of symbiotic bacteria and the behavior of their animal hosts.
All animals harbor symbiotic microbes. Certainly, some are pathogenic, but many are beneficial to their hosts. For example, they are critical contributors to animal nutrition and immune health, and they serve as important catalysts for the effective development and functioning of animal tissues and neural connections, including in the brain. It is also becoming increasingly clear that they can contribute to animal behavior. This is important because behavior is one of the primary mechanisms animals have for mediating their positions and circumstances within the dynamic physical and social environments they inhabit. Recent research shows that symbiotic microbes can protect their hosts from predators, increase their hosts’ foraging efficiencies and reproductive outputs, and, as we showed in this project, it appears that they can mediate their hosts’ communication systems. An effective communication system is a critical component of each animal’s behavioral repertoire, and most animals rely, at least in part, on chemical signals. The symbiotic hypothesis for animal chemical communication posits that bacteria in the specialized scent glands of animals generate odorous metabolites that are used by their hosts for communication, and that variation in host chemical signals is often a product of underlying variation in the microbial communities inhabiting their scent glands. For mammals, fermentative bacteria in particular have been implicated. However, despite this hypothesis being at least 40 years old and it having been investigated using a dozen different mammals, limitations of the tools historically available for sampling bacterial communities in mammalian scent glands precluded effectively testing this hypothesis, and most studies consequently yielded ambiguous results. Contemporary advances in DNA sequencing technologies and their associated software tools have rectified this problem, affording us more accurate views of the bacterial communities associated with animals’ bodies. Using wild hyenas as model systems, the aim of this project was to effectively test this hypothesis using a multi-pronged approach that included accurate surveys of the bacterial communities inhabiting hyenas’ scent glands, complementary data on the odorant profiles of scent secretions, and investigations of the metabolic characteristics of hyenas’ scent gland bacteria. We studied two species of hyena, spotted and striped, each a large African carnivore that relies heavily on scent marking to mediate conspecific social interactions. Spotted hyenas live in large, highly complex societies, whereas striped hyenas are essentially solitary, interacting directly with conspecifics only infrequently. The project showed that 1) the scent glands of spotted and striped hyenas contain diverse bacterial communities dominated by fermentative odor-producers, 2) scent gland bacterial communities are markedly different between spotted and striped hyenas, 3) in both hyena species there is strong covariance between the bacterial and odor profiles of scent secretions, 4) among spotted hyenas scent gland bacterial communities vary among different social groups, 5) these communities vary with host characteristics—age, sex, reproductive state—within social groups, and 6) these bacterial communities differ from those inhabiting other hyena organs, suggesting that they function specifically in hyena communication. We anticipate that the symbiotic hypothesis for animal chemical communication will prove broadly applicable as others employ the technical and analytical approaches used in this project. In fact, the explanatory potential of the hypothesis is limited only by the capacity of animals’ physiological and social circumstances to alter the structure of their symbiotic microbial communities in ways that consequently affect their odor profiles in behaviorally-relevant ways. Evaluating its potential is therefore a critical step in elucidating the contributions of symbiotic microbes to animal behavior in general. This project crossed disciplinary boundaries, integrating cutting-edge advances in microbial ecology into animal behavior research. It provided opportunities for interdisciplinary training and professional development for two postdoctoral researchers and four undergraduate students, two of whom, both women, have already begun successful graduate careers in science. Collectively, project personnel have broadly disseminated research findings through peer-reviewed publications, conference presentations, research seminars at universities and colleges, interviews with the popular media, an entertaining blog detailing hyena research in the field, and talks given to tour groups in Africa. Throughout the duration of the project, the Principal Investigator voluntarily taught workshops and courses in microbial and ecological community analysis to students, postdoctoral researchers and faculty interested in elucidating the roles of microbes in their own study systems. In each instance, the approaches and findings of this project figured prominently.
