Why did females with such heavily ‘masculinized’ genitalia evolve in spotted hyenas?
No one yet knows the answer to this question, but a number of different hypotheses have been offered as explanations. Although most of these hypotheses can be ruled out, at least two are still in the running. First, if these ‘masculinized’ genitalia have an adaptive function, they might play an important role in post-copulatory choice by female hyenas regarding which sperm will fertilize their eggs. Females in the wild often mate with multiple males when they are in estrus, and the sperm from these competing males must therefore often occur together in the female’s reproductive tract. The ovaries of the female spotted hyena are comprised mainly of stromal cells, and they contain very little follicular tissue, so the female hyena may have few ova relative to those produced, stored and released by other mammalian carnivores. In addition to being rather long and convoluted, the female’s reproductive tract contains vaginal lumen that are full of blind alleys and dead ends (Cunha et al 2003
