Nature

In the mandrill species, if a beta male wins a fight, then it gradually transforms into an alpha male – gaining larger testicles, more colorful skin, and the ability to produce offspring with females. If an alpha male loses a fight, then the reverse happens.

Adult male mandrills with alpha status display vivid colouration on their skin, while those with beta status are more dull in colour. Both types of males engage in mating, but only the dominant alpha males have the ability to produce offspring. Male mandrills sometimes fight for breeding rights which results in dominance. Though conflicts are rare, they can be deadly. Gaining dominance, that is becoming the alpha male, results in an "increased testicular volume, reddening of sexual skin on the face and genitalia, and heightened secretion of the sternal cutaneous gland". When a male loses dominance or its alpha status, the reverse happens, although the blue ridges remain brightened. There is also a fall in its reproductive success. This effect is gradual and takes place over a few years. When beta males mate-guard a female, the competition between them allows the alpha males to have a greater chance of producing offspring, since betas outnumber alphas 21 to 1.