Violeta Pantaleón

Organism Research Paper

General Biology 106 Lab 12

TA Nora Marchiando

November 13, 2001

Socio-Behavioral Development and Pyshio-Morphological Adaptations in the Spotted Hyaena

Spotted hyaenas are unique gregarious carnivores used in extensive studies for two main reasons; they have a highly socio-behavioral development and the female spotted hyaena have an unusually high concentration of androgenic hormone. In addition the female spotted hyaena exhibits masculinized reproductive organs, is larger and more aggressive than males, and is socially dominant to the male spotted hyaena. Spotted hyenas members establish a strict hierarchy system that is dominated by females. The socio-behavioral development and morphological adaptations in hyaenas have been a progressive result of their evolution.

Spotted hyaenas are only found in Africa south of the Sahara (see figure 1, page 10). Here lies their only natural predator, the lion. Contrary to popular belief that portrays lions as noble hunters and hyaenas as only scavengers, is mostly the other way around. Nearby clans of lions and spotted hyaenas wage war that surprisingly enough is not over food. These eternal rivals tend to set up boundary marks against each other. Hyaenas are only afraid of the male lion pride and they could easily kill a lioness. On the other hand lions kill both juvenile and adult hyaenas. Members of the Crocuta crocuta live in social matrilineal clans that consist approximately 8 to 80 individuals. Spotted hyaenas exhibit behavioral displays of submission and dominance through an array of vocal and olfactory modes. The females maintain a strict social hierarchy organization, which is more similar to that baboons and macaques, rather than lions.

Hyaenas belong to the hyaenidae family that consists of only four living species; spotted hyaena (Crocuta crocuta), brown hyaena (Hyaena brunnea), stripped hyaena (Hyaena hyaena), and the insectivorous aardwolf (Proteles cristatus). Hyaenas evolved from civet-like animals and display a true-backbone, mammalian reproductive system, carnivorous nutrition mode, and while it appears to be dog-like it is more closely related to cats. Hyaenas are the most recent addition to the order carnivora. The scientific name of the spotted hyaena is Crocuta crocuta, meaning “provided with the color or saffron and utus (saffron and utus indicates the spotted hyaenas reddish-brownish color). Crocuta crocuta have a body length from 37-65 inches, the shoulder height is from 32-35 inches, and the weight range is from 105-121lbs. The females are about 10% larger than the males. Each member has a coat of dark brown with a unique pattern of dark spots over the back. The spotted hyaenas exhibit the following physical characteristics; sloping shoulder, carry low head, have low-set powerful hind legs, a round head with a strong jaw (see figure 2, page 10). Based on the previously mentioned general characteristics the classification of the spotted hyaena is as follows:

The goal of this paper is to discuss the survival of the spotted hyaena through three inter-related subtopics socio-behavioral development, reproductive adaptations, and physio-morphological structures. The crocuta species exhibit social behavioral development stages and well-developed vocal sounds that maintain their survival as a clan and as predators of large mammals and prey to the lion. Like other gregarious carnivorous animals the spotted hyaena have discrete life stages that enhance their socio-behavioral development and influence their dominance status. The following are the five crucial stages in the crocuta social development:

Stage 1: Natal Den

A newborn is born with full eruption of incisors and canines, open eyes, movement capabilities, and weights about 1.5kg. The cub spends the first four weeks in an isolated natal den that serves a primary shelter and protection. The natal den is an abandoned aardwolf hole with a small aperture that leads to a channel. The opening is inaccessible to the mother, who guards the aperture from other adult crocuta members. Within a few days of birth natal aggression begins with the emergence of a dominant cub. Either the dominant cub kills the subordinate or deprives the subordinate from access to the mother’s teat by blocking the entrance. Thus, the dominant cub grows faster and stronger. Natal aggression occurs between siblings of the same sex. Therefore the natal aggression is directed from female-female or male-male. Cubs only emerge when the mother calls them with a soft groan.

Stage 2: Communal Den

Approximately from 1-8 months the cubs are moved from the natal den to a communal den, which is complex channel with many networks. Here the cubs initiate playful activities, mate mocking, and recognition establishment of other members. Playing stimulate growth and motor development in the cubs. Spotted hyaena exhibit unusual social behavioral patterns for recognition that re-enforce dominance and subordination. The members tend to introduce each other by smelling the urogenital area, licking the urogenital area, and smelling the scents from pasting. The pseudo penis of the female also functions in social hierarchy greetings. Hyaenas lick and sniff each other’s penises in order to show dominance or subordination. The young cubs frequently tried to do the pasting ceremony without secretion. This mock pasting is stimulated by the smell of another hyena’s anal gland excretion (see figure 3, page 10).

The development of recognition is very important for young cubs. Upon extensive recognition, social ranks are established throughout the clan. In this stage the young crocuta starts directing aggression towards larger spotted hyaenas of lower ranks. The mother reinforces maternal ranks by joining her cub when the cub attacks a cub or an adult of a lower rank. The alpha female attacks any adult or cub that approximates her cub. Reinforcement of maternal ranks is a mechanism that promotes dominance and secures rank inheritance. The establishment of ranks will determine the cub’s access to food and critical resources.

Stage 3: Communal Den to Weaning

The subadults, now about 8-14 months, are introduced to their physical and environmental surroundings. Is critical for a young hyaena to become well aware of its surrounding, water supply, and how to access food. The cub also needs to distinguish the boundaries between its clans, other spotted hyaena clans, and overlapping lion prides. There is minimal nursing and the cubs are starting to feed on ungulate kills along with other members. At first the young spotted hyaenas are intimidated by the larger-feeding hyaenas and feed along side the mother. The alpha female respond with aggressiveness towards any other young spotted hyaenas that tries to eat from the side of her cub(s). The males are usually chased off when the females arrive to a feed.

Development of survival techniques is important for young spotted hyaenas. The young spotted hyaenas is too large to try to re-enter the communal den. The den no linger provides protection from lion(s) or spotted hyaenas from other clans.

Stage 4: Weaning to Reproductive Maturity

After 24-36 months the mother refuses to nurse the cub. Her refusal leads the young spotted hyaenas hyaena into a persistent tantrum that goes ignore. The young spotted hyaenas now encounters the challenge of obtaining fresh solid food. Young hyaenas are ineffective hunters and instead feed on carrion, hares, and gazelle fawns.

Stage 5: Reproductive Maturity to Death

The males become sexually mature before the females. Upon reaching sexual maturity at about the age of three the males leave their natal den and immigrate into other clans. Natal females act unresponsive to the sexual advances from natal males. This mechanism shapes the male behavior of leaving the natal clan in order to breed. The immigrant males display submissive behavior to its’ new clan. Natal males exhibit aggressive behavior towards the immigrant males and initiate fights. Regardless that natal males win all the fights the adult immigrants have a higher testosterone. Adult immigrant males carry out more sexual behavior with natal females.

Contrary to ancient popular belief the spotted hyaenas are not hermaphroditic animals. The female has a pseudo penis or phallus that is transverse by the vagina. Upon reaching maturity there is a striking resemblance between the male and female anatomy. The female spotted hyaena is polyestrous, with an estrous cycle of fourteen days. Female spotted hyaena usually has a litter of two. All the females within a clan produce offspring yearly with no seasonal preference and they usually mate with any immigrant male. The alpha female tends to reproduce more offspring over the years than any other female, having a smaller gestation period and producing 2.5 more sons and 2.75 more daughters (see figure 3, page 10). The gestation period usually lasts n average of 110 days. They suckled only their cubs for a period of about six months and don’t carry food back to the cubs. Due to their morphological adaptation of a pseudo penis, females have a high mortality rate from 9-18% when giving birth.

It is unknown why or how the developed a masculinized anatomy. Within the hyanidae family only the female crocuta displays this morphological adaptations. The females have a pseudo penis that is actually the enlarged clitoris. The clitoris is shaped like the penis and has circular blunt tip rather than a pointed tip. In place of the vulva there is a scrotum-like sac consisting of connective tissue and fat. After births the female develop tow large nipples that enables observers to distinguish the two solely on sight. The females mate and give birth through this urogenital canal (see figure 4, page 10). The canal increases in diameter and becomes elastic allowing the male to insert the penis. Retractor muscles pull the phallus to the base, like the sleeve of a shirt.

Previous hypotheses for the demand for an aggressive female were: to prevent infanticide deaths (kruuk), to prevent forced mating, and/or to allow the female to mimic the males. These theories have been disregarded respectively because; there are no evident observations to show that males are a threat to cubs, there is no evidence that rape occurs in any hyaena species, the adaptation of a masculinized anatomy has fatal consequences if the organs are wounded in aggression. Recent field studies findings hypothesize that the reproductive adaptation was a result of a selection that favored more aggressive females. Further laboratory studies based on the hormonal concentration suggest that prenatal exposure of a high concentration of androgenic hormone is responsible for the masculinized reproductive organs and aggressive behavior in the female crocuta. The males sometimes gang up on a single higher-ranking female in a pack of 3-8. They tend to bait and nip at her hind legs, resulting into injury or harassment.

The reproductive history of the spotted hyena is not their only unique feature. The physical morphological allow the spotted hyaena to be one of the most prolific hunters and feeders in Africa. The first impressive physio-morphological feature of the crocuta is the awkward appearance of a huge dog-like head on a small body and short hind legs. Hyaenas drop their hindquarter legs in order to protect them. The forequarters allow the hyaena to run at a high speed of 37mph and carrying a kill that weights 15 kg.

Spotted hyaenas have a round cranial skull with robust features and enlarged pre-molars that allow them to consume an entire carcass, the hoofs, the skin, and all the bones. Their diet is usually comprised of medium-sized ungulates such as wildebeest and zebra. Spotted hyaenas compete with each other for food by eating as much as possible as fast as possible. A pack of about 30 hyaenas can devour a 220 kg wildebeest in a few minutes and digest it within 24 hours. The third pre-molars in the upper and lower jaw allow hyaenas to crunch bones. The crania of the adult also exhibit elongated sinuses in the frontals and parietals that covered the entire brain (see figure 5, page 10). The constant biting and meat consumption affect the growth and development of the crania of a young cub. This physiological adaptation is also apparent in the brown hyaena, the stripped hyaena, and the extinct hyaenid (Adcrocuta eximia) Observers suggest that the enlarged sinuses offer a shock resistance when the hyaenas crunch bones. The carnassials provide a “carnassials shear” mechanism, that enable the spotted hyaena to crunch larger bones like no other member of the carnivora. Felidae (cats) and Canidae (dogs) have smaller carnassials that function the carnassials shearing mechanism. In addition, the enlarged frontal teeth and compressed back teeth enable the hyaenas to grasp the kill of another animal and run away with it.

The feces of the spotted hyaena are mainly a white-powdery substance due to their consumption of the bones and hair of an animal. Chemical analysis reveals that this white material consists of the formula of the indigestible material in bone, Ca3(PO4)2-1.5 Ca(OH)2. Hence, the morphological and physiological adaptation of a unique cranial and dentition structure allows the crocuta species, unlike any other species, to digest and use all parts of a carcass.

In conclusion the socio-development stages, physiological, morphological adaptations of the Crocuta crocuta, have shaped the consequent survival of this species in the deep forage of Sub-Sahara Africa. The socio-development stages are critical to the life of a cub. Without the proper acquisition of survival skills, rank recognition, and environmental knowledge, a cub can perish within the clan from lack of food and/or aggression by a more dominant hyaena. The early life stages also promote the development of vocal sounds that enable hyaena clan to survive as a whole. The early life stages are inevitably characterized by maternal rank acquisition and dominance of one cub over another. There is a high display of physical aggression or harassment from a few hours of birth for a spotted hyena. The reasons for the selection of an aggressive female, that is bigger than males and lack dimorphism enable the females to dominate males both socially and sexually. The birth of cubs to an alpha female enables the dominant cub to grow strong and enforces the inheritance of another strong female to lead the pack in a competitive world. Lastly, the physiological features of the exceptional pre-molar enlargement enable the spotted hyaena to be one of the most prolific hunter and feeder in Sub-Saharan Africa.

	Figure 1. This image shows the regional spread of the Spotted Hyena (Crocuta crocuta). This species is now only naturally found in Sub-Saharan African regions (note some regions overlap with other species and clans).	Figure 2. Adult spotted hyena showing general characteristics; Crocuta crocuta have a body length from 37-65 inches, the shoulder height is from 32-35 inches, and the weight range is from 105-121lbs. The females are about 10% larger than the males. Each member has a coat of dark brown with a unique pattern of dark spots over the back. The spotted hyaenas exhibit the following physical characteristics; sloping shoulder, carry low head, have low-set powerful hind legs, a round head with a strong jaw.
Figure 4
			Figure 3

Figure 5. Sideview of the skull of the spotted hyaena. The frontal and parietal skeletons are enlarged. Notice the enlargement of the third pre-molar that is essential for crunching bones and the large encompassing canines that are used for biting the kill.

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