"In 2011, a captive lioness called Emma at the National Zoological Gardens of South Africa developed a mane. Tests revealed high levels of testosterone due to a problem in her ovaries, and once they were removed she reverted to a typical lioness."
https://www.newscientist.com/article/2106866-five-wild-lionesses-grow-a-mane-and-start-acting-like-males/
They aren't natural.