Spotted Hyena Research Paper

Amongst social mammals, spotted hyaenas (crocuta crocuta) display a number of unusual traits, including high maternal investment, strong sibling rivalry that may lead to siblicide, female dominance, and masculinization of female genitalia. (1) This paper will concentrate on the masculinization of female genitalia but will also touch on the other traits listed.

Taxonomic Hierarchy

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Infraclass: Eutheria

Order: Carnivora (cats, dogs, bears, raccoons, weasels, civets, mongooses, hyenas)

Suborder: Feliformia (cat-like carnivores)

Family: Hyaenidae (hyenas)

Genus: Crocuta

Species: Crocuta crocuta (Erxleben, 1777) - spotted hyena

The Spotted Hyaena In the barren landscape sub-Saharan Africa, one

Spotted hyenas are members of the family Hyaenidae, a lineage of carnivores that split from ancestral viverrids 25-30 million years ago. (2) Hyaenid is succeeded by four species, the smaller carnivore family existing today from the discovered 69 fossilized species. The four species left in the family are; striped hyenas (Hyaena hyaena), brown hyaenas (Parahyaena brunnea), spotted hyenas (Crocuta crocuta) and a small termite-eating outlier, the aardwolf (Proteles cristatus). (8) Amongst these species, only female Spotted Hyaenas display masculinization of genitalia. Closest living members of Hyaenas currently are civets and mongooses. It is quite remarkable, the evolution of modern hyaenas compared to its ancestors and relatives. The rise of Hyeanidea dates back 18-17 million years ago. The first known hyena, Protictitherium gaillardi resembled a civet rather than a large primitve dog. Protictitherium g is thought to have spent most of its times in trees due to its retractable claws. It is thought to have eaten birds, smaller mammals and insects. Various species of Protictitherium survived over millions of years and only died out between 5.3-4.2 million years ago. Other Hyaenids spent more of their time on the ground such as the first known European hyaenas, Plioviverrops orbignyi which resembled a mongoose and was specialized in eating insects. Its claws could

In order to understand the the reason behind the evolution of the pseudo-penis, the general “hyperaggresiveness” and complete dominance of female spotted hyenas must be understood as the masculinization of genitalia in Crocuta crocuta is in my understanding correlated with the masculinity of the female itself. (9) One theory suggest that female dominance in Spotted hyena clans could be due to the selection of aggressive females who successfully competed with males over the kills, ensuring there would be enough milk for the cubs who are dependent on their mothers for over a year. (4)Another theory suggests that aggressive female spotted hyaenas were selected because the cubs jaws are not fully developed for over a year since birth, so it is completely dependent on the mother for food. This aggressiveness has been hypothesized due to increased hormones such as testosterone. In turn the development of a pseudo-penis in females is theorized to be a by product of hormones due to hyperaggrresiveness. (4,5) However when proper studies were done, blood samples taken from Serengeti population (2) Hormones: testosterone (T), 5a-dihydrotestostrone (DHT), androstenedione (AE). Significantly lower (T) and DHT observed in females. (AE) little difference in female and postdispersal males but significantly lower in predispersal males. (9) Data shows hormones are