The Berkeley hyenas: an abbreviated memoir

I have not had the opportunity to know the Berkeley hyenas as individuals, but as a member of the scientific community, I am saddened by the loss of the Berkeley colony for both personal and scientific reasons. I’m a graduate student in Dr. Kay Holekamp’s lab at Michigan State University, which studies a wild population of hyenas in the Masai Mara in Kenya. Despite not having had the opportunity to see the Berkeley colony (I blame my sister, a graduate student in chemistry at Berkeley, for not being willing to use our vacation time together in San Francisco to chase down hyenas), members of my lab have enjoyed a strong collaboration over the years with Dr. Stephen Glickman and his cohort of hyena researchers at Berkeley.  Needless to say, we were distressed to learn that the colony had run out of funding, resulting in the euthanization of many of these amazing animals and the loss of an irreplaceable scientific resource.

One can’t help but be fascinated by spotted hyenas (Crocuta crocuta), which are some of the most flagrant “rule-breakers” of the class Mammalia. These are social carnivores that share a surprising amount of behavioral characteristics with old world primates, despite having diverged from them over 80 billion years ago. Like old world monkeys, they live in large groups (the largest of any carnivore), which are characterized by strict social hierarchies. Primates and hyenas also share some surprisingly advanced cognitive abilities, such as recognizing third party relationships. That means an individual doesn’t just know who tends to pick on him. He also knows who tends to pick on that poor other schmuck over there. By comparing the cognitive skills of hyenas and primates, we can better understand the forces behind the evolution of intelligence.

Hyenas also turn the general “rules” of mammalian sex differences on their head – that is, females  are highly masculinized – being bigger and more aggressive than males. This results in socially dominant females and added fun for researchers who get to watch the poor, terrified males actually attempt to mate with their aggressive, often uninterested, counterparts; their difficulty is no doubt expounded by the fact that the females possess masculinized genitalia, called pseudopenises. Due to these oddities, hyenas provide a powerful model system for the study of the physiological and evolutionary substrates of sexual differentiation in mammals. Meanwhile other fascinating attributes of the spotted hyena include their ability to crack bones and to eat diseased, rotting meat without succumbing to illness.  Spotted hyenas thus appeal to a broad range of interests- whether you’re into immunology, psychology, evolutionary biology, or just weird genitalia.

Dr. Kay Holekamp

Advances in many of these fields have been made with the help of the Berkeley hyenas. Researchers have carried out novel studies on problem-solving and cooperation in a social carnivore, engaging the hyenas in cognitively challenging tasks based on skills needed in cooperative hunting. They have also studied  personality types in the hyenas, finding individual differences on traditional scales such as assertiveness and curiosity. Of particular interest to me is the investigation into the hormonal mechanisms for masculinization of female behavior and genitalia. In a series of studies, Glickman et al. found that hyena fetuses are exposed to abnormally high concentrations of androgens – a hormone which masculinizes genitalia and increases aggression in other mammals. However, a later study showed pseudopenis formation does not actually require these high concentrations of androgens. This has led to further studies investigating the effects of other hormones in penis formation- research that may help to pinpoint causes of abnormal genitalia formation in humans. Meanwhile studies in the field led by Dr. Holekamp found high ranking pregnant females had higher androgen concentrations in their blood and more aggressive offspring than their lower ranking counterparts. Preliminary findings at Berkeley indicate this relationship is causal, as females given antiandrogen drugs in utero seem less aggressive.

Although work with wild populations of spotted hyenas is certainly valuable, the availability of captive hyenas has provided opportunities to validate and extend field studies. For instance, we can only dart hyenas in the field every few years since being shot in the butt too frequently can make the hyenas wary of us – which is problematic when we are trying to casually roll up and observe their behavior. Access to the captive colony allows us to take blood and tissue samples more frequently from the same animal, which provides an estimate of lifetime repeatability of certain physiological markers. Furthermore, research on sex differences at the Berkeley colony has inspired my own work: I am currently trying to unravel the role serotonin might play in behavioral sex differences, particularly in impulsive aggression across the lifespan of hyenas. I hope to make use of paired cerebrospinal fluid (CSF) and blood samples (from the same Berkeley hyena) to assess whether serotonin concentration in the brain correlates with that in the blood. This validation is very important – as I need to use blood samples rather than CSF for my project, since no one really wants a second year graduate student running amok in the field giving spinal taps to our poor, hapless study animals.

So thank you to the researchers and care-givers at Berkeley for maintaining this colony, and undoubtedly contributing greatly to the emotional and physical well being of these animals. My heart goes out to those of you who were intimately familiar with the hyenas and had to watch the end of the colony. And finally, thank you to the hyenas, whose existence contributed greatly to research and allowed many people to experience being close to such an amazing animal. It’s heartbreaking to hear that your reign over Berkeley’s hills ended in such a way, and I very much hope you are romping around happily in hyena heaven (or for some of you, in zoos) somewhere. You certainly deserve it.

Sarah Jones is a graduate student in zoology at Michigan State University.