Sexual mimicry
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Sexual mimicry is where one sex takes the characteristics of another sex within a species. Examples of animals it occurs in are the Spotted Hyena, bonobo chimp, spider monkey, lemur, european mole and sometimes humans.
Sexual mimicry can however have adverse reproductive costs, for example the spotted hyena has to copulate and give birth through the long peniform clitoris.
Clitoromegaly is an example of sexual mimicry and occurs in the Spotted Hyena as first noted by Aristotle. It results from natural high levels of testosterone in the female. In this case female external genitalia resembles that of the male, having a false penis from the clitoris and false scrotum from the vulva, this is a result of extreme hypertrophy. The females are also larger, more aggressive and dominant, a trait that is normally observed in males. More specifically, the unusual features are due to an increased production of androstenedione in the maternal ovaries during pregnancy. Androstenedione is an androgen and converted to testosterone by the enzyme 17β hydroxysteroid dehydrogenase in the placenta, then transported to the fetus. In most mammals, the placenta converts androstendione to oestrogen via the enzyme aromatase. Aromatase is deficient in the hyena placenta.
The european mole is another good example of sexual mimicry. The male testes are intraabdominal and the female ovaries are bilateral meaning the bipolar gonads have both male and female features, this makes the mole very difficult to sex. The females also appear to have an enlarged peniform clitoris, these characteristics are also due to testosterone.
Human girls suffering from congenital adrenal hyperplasia which is due to a deficiency in 21-hydroxylase in most extreme cases causes girls to be born with external male genitalia, in the case of the males they will undergo puberty much earlier than normal due to increased levels of testosterone.
[edit] References
Place NJ, Glickman SE. 2003 Masculinization of female mammals: lessons from nature. [1]
