Discover Why All Spotted Hyenas Have External Genitalia
The animal kingdom is wild to study. Over our years of having close interactions with wildlife – and observing it from a distance – we have gotten to witness some of the strangest evolutions and behaviors. We watch spiders cannibalize one another after breeding. We note selective evolutions for protective breeding in ducks. Some researchers even get the opportunity to see how larger mammals interact and breed. In one case, a species of animal goes above and beyond. Hyenas are a matriarchal species, that wander in packs called “cackles” or “clans”. One thing that makes these animals distinct from others is their genitalia. All hyenas have external genitalia, and we’re going to explore this today. We’ll start with the pack structure of hyenas and move on to how their genitalia impact their social order.
We will specifically be looking at the most common of the four species of hyenas – the spotted hyena (Crocuta crocuta).
Social Structure of Hyenas
Hyenas have a complex and strange social order deeply linked with their biology. All hyena clans are matriarchal and ruled by alpha females. This is true matriarchy – it isn’t just the strongest alpha that rules the pack, it’s a bloodline. The power structure is strict and competitive. In this social structure, males are at the bottom of the food chain. This is in definitive contrast to the social structures of most other vertebrates. We’ve tried to put together a comprehensive social rank below. Keep these inheritance rules in mind: mothers outrank their daughters but younger daughters often outrank older daughters.
So, first, there is the alpha female leader, followed by the other mothers of the clan. Let’s go from there in list form.
- Alpha female
- Female young of the alpha female
- Younger daughters
- Older daughters
- Clan-born males
- Highest-ranking itinerant males
- All other males
Clans of hyenas form in sizes of up to 130 members in total. This structure is usually comprised of around 50 adult females 40 adult males, and the rest being offspring of various sexes. Daughters most frequently stay in their birth clan for the entirety of their lives, while males will wander to other clans when they reach adulthood at about 3.5 years of age. These solo travelers will struggle to establish themselves in a new clan when they find one and usually end up at the bottom of the pecking order. Once established, the itinerant male can raise his status in the clan.
External Genitalia on Female Spotted Hyenas
Female spotted hyenas are visually hard to distinguish from males. For one, female and male spotted hyenas share a very similar body shape and size. Females are slightly larger than males on most occasions, but the difference is hard to distinguish with the naked eye. Next, the sexual organs of female hyenas have been “masculinized”. What does this mean? Well, female hyenas are the only mammals in the world that lack an external vaginal opening.
In place of the classic external vaginal opening, female hyenas are equipped with elongated external clitorises that deeply resemble the penises of their male counterparts. This clitoris has the size and shape of a regular male hyena penis, and is known as a “pseudo-penis”. The hyena pseudo-penis is comprised of a fused urinary and reproductive tract. The female hyena has to urinate, breed, and give birth from her external clitoris. This poses several unique challenges that we will address in a later section.
Additionally. female hyenas have “pseudo-scrotums”. These false scrotums are tissue-filled outer labia. With both the external clitoris and the pseudo-scrotum, the female hyena is nearly a spitting image of the male. It is very hard to tell the sex of a hyena without a physical examination, especially when the hyenas are still in their youth. Because of this phenomenon, hyenas used to be mythical hermaphrodites. Experts in the field believed this myth for several years before they could observe hyenas more closely.
Let’s Talk Hormones
It isn’t just the visible exterior reproductive organs that matter here. Female hyenas also have distinct chemical and hormonal makeups that impact the way they interact with the world. Female hyenas, on average, produce about three times more testosterone than their male counterparts. This difference is especially clear for alpha and high-ranking mothers of a hyena clan. The alpha female of a clan is a hormonal giant. What do we mean by this? Female hyenas produce large amounts of testosterone and other chemicals most commonly observed in males of a species. The alpha female passes her leadership down through her bloodline based on these hormones.
Let’s refer to the National Science Foundation for more information on this topic. In 2006, an article on their website talked about how hyena cubs are put on a road to success before they are even born. High levels of specific hormones give hyena cubs – specifically females – a distinct advantage in growth. These hormones make young hyenas more aggressive, assertive, sexually advanced, and motivated. This is the first observation of social rank influencing behavior within mammals.
A study, called “Phylogenetic Comparisons Implicate Sex Hormone-Binding Globuline in “Masculinization” of the Female Spotted Hyena (Crocuta crocuta)”, reveals more information on the incredibly complex hormonal and steroidal systems in place for the masculinization of female hyenas. The study explores the hypothesis that these hormones and androgens directly influence the anatomy and social dominance of the female spotted hyena.
At What Cost?
The biological structure of hyena reproductive systems is complex and takes a toll on the spotted hyena females. The first thing we’ll note when we talk about this is that high levels of testosterone can – and do – damage female reproductive organs and make childbirth more dangerous and complicated. The higher the levels of hormones, the more of a struggle the birth can be. Additionally, this effect builds up over multiple pregnancies to a point where a mother hyena – and particularly the alpha – risks her life and the life of her potential young every time she gives birth.
Next, let’s look at the physical repercussions. Since a female hyena gives birth through her external phallic clitoris, it is a very painful and complex birthing scenario. Young females are likely to lose cubs during childbirth and, while this likelihood goes down with multiple pregnancies, the risk doesn’t ever disappear. This is especially true when birthing twins. The first of the two cubs is often stillborn. This is due to the lack of elasticity in the pseudo-penis.
Hyena litters are usually made up of two to four cubs, of which 60 percent do not survive the birthing process. In a later section, we’ll look at the other struggles young hyena cubs face in their youth.
Benefits of This Structure
It isn’t all grim news for the female hyenas. Despite struggles with breeding and childbirth, there are some distinct advantages to both the pseudo-penis and the hormones that power pack structure. For example, female hyenas get to be highly selective when choosing a mate. They use this power to avoid incestuous relationships and to select appropriate mates that benefit the overall clan structure. Because of these physical and hormonal power dynamics, male hyenas have to work hard to find a female mate.
In essence, the entire social and mating structure is designed to be adaptive to a high level of intentional and selective breeding that attempts to guarantee the health and future of the hyena clan. Male hyenas, especially, have to adapt to these structures. Male hyenas, as we mentioned before, very much struggle to find a place in the clan and many become itinerant by adulthood. They go in search of other clans, which helps to guarantee that breeding will not end up incestuous.
Is Breeding Complicated?
The mating rituals of hyenas are incredibly complex. First, because female hyenas are so selective, it can take a very long time to create a pairing. In fact, some relationships between a male and a female hyenas take weeks, months, or years to develop. During this time, the male hyena will essentially “shadow” the female hyena and become close to her. Mates are most often created from these long-term friendly exposures, and “friendly” males are much more likely to find a mate and successfully breed. Friendly means more than cuddly or giving. Male hyenas that show less signs of aggression overall are significantly more likely to find a mate. It is hypothesized that this aspect of mate selection is a failsafe to protect the matriarchal nature of hyena clans.
This is not the only failsafe. Female hyenas select more than one mate in most cases and will mate with multiple males up to and following pregnancy. More than one-third of 75 litters of hyena cubs in one study had dual paternity. Male hyenas that were less aggressive and spent more time getting to know females sired more litters than ones that focused on dominance between males.
Past the social politics, the actual act of breeding is complex for hyenas. Because both the male and the female have awkward and external genitalia, it is actually quite hard for breeding to take place. Young hyenas spend months of their youth practicing breeding so they are more prepared for the future. Yes, in this case, practice does make perfect. The male hyena must perfectly position himself to align his penis with the pseudo-penis of the female. It’s an incredibly awkward angle that requires a large amount of dedication.
Challenges Faced by Hyena Cubs
If a hyena cub makes it through the complex and traumatizing experience of birth, it has other challenges to face. Infant hyenas have one of the highest rates of siblicide in any mammal species and begin attacking each other from the moment they are born. Baby hyenas are born with open eyes and full sets of teeth, so they are well-equipped to fight from the moment they arrive. It is hypothesized that baby hyenas experience a ten percent chance of death by siblicide within the first few weeks of their lives. That means that potentially one out of every ten hyena cubs is murdered by its sibling.
This aggression may be to establish pack order from a young age. It is also possible that this aggression is a training adaptation for the vicious and violent experience of a hunting-feeding frenzy. Since the most vicious hyenas get the food when they bring down prey, all hyenas need to be prepared to fight for their meal. This is also true in terms of fending off other predators – like lions – from stealing their food.
If the infant hyenas survive the first few weeks of life, they have another hurdle to face. Rival females within the hyena clan will try to raise their status in the clan by murdering the offspring of their opponents. Mother hyenas are loving and nurturing to their own cubs to a high degree. In fact, their love and care for their infants goes well beyond the expected in mammals. In order to protect their own cubs and maintain or elevate social standing, mothers take action against other cubs. Eli Strauss is a behavioral ecologist at the University of Nebraska-Lincoln. He and his colleagues have been observing and researching hyenas for decades. They found that infanticide was a leading cause of death for hyenas below one year of age. As many as 21 out of 99 observed deaths could be attributed to infanticide in this research.
Female hyenas use the same method of murder as they do for small prey. They get the head of the baby in their mouth and crush its skull. It seems no hyena baby is safe from this brutality – mothers will target any young hyena that isn’t her cub. This includes close familial relationships, such as the cubs of siblings or mothers.
Myths About Hyenas
We discussed earlier that we used to widely believe that hyenas were hermaphroditic. This isn’t the only myth we have come to believe about hyenas. The first one we’ll touch upon is the myth that hyenas are related to dogs or cats. This isn’t true, and hyenas are not really more related to one than the other. While hyenas do carry characteristics of both of these familial species, they are so distinct that they make up a family all of their own – the family Hyaenidae. This family is almost completely distinct from any other animal family on Earth. However, if we want to draw a comparison, we should look at the mongoose and the meerkat. These are two of the hyena’s closest relatives.
Next, we often think of hyenas as meek and easily bullied by other large predators. Whether we got this idea from the movie “The Lion King” or we just don’t know that much about the species, this is routinely false. Hyenas are actually one of the most vicious and strong mammals in the world. The spotted hyena is widely considered to be one of the most capable hunters of its size.
Speaking of being capable hunters, we often mistake hyenas for being scavengers. In fact, in clans with strong hunting parties, hyenas kill up to 95 percent of their food. Scavenging is a secondary adaptation for survival and is mostly limited to areas of food scarcity. Itinerant males are also more likely to scavenge than hunt.
Finally, let’s talk about their intellect and laughter. Hyenas are not the stupid, drooling, cowards of our human depictions. In fact, hyenas possess incredible intelligence that goes as far as solving complex puzzles and problem-solving. As for their laughter, we may believe that hyenas laugh uncontrollably. In truth, this laughter is specific and targeted. Most hyena laughter occurs surrounding a hunt, but it is also used to indicate frustration and a request for help.
Hyenas have adapted very special physical and sexual attributes to help ensure the success of their matriarchal social structure. The development of a pseudo-penis in female hyenas is one reflection of the effect of this adaptive pack order. High levels of hormones and androgens have created this effect over several generations. This is a phenomenon unique to some hyena varieties and cannot be found in mammals anywhere else on earth.