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Macho Males Deliver Sickly OffspringBecause of too much testosterone |
By Stefan Anitei, Science Editor
11th of January 2007, 12:00 GMT
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We, humans, say that women are the beautiful gender.
But in most animals is exactly
the opposite.
Males present the most showy looks and weapons. They bear huge antlers, horns, manes, the glossiest plumage/fur, the most spectacular adornments. All these traits are linked to testosterone levels.
That's because most animals are polygamous: a male will mate with as much females as possible, so HE must be attractive; while, in humans, they form monogamous bounds, in which a woman must be attractive in order to keep her man.
Of course, showier traits are linked to higher levels of testosterone, not to mention that higher levels of testosterone also induce a higher aggressiveness, and more aggressive males find it easier to get access to more females.
But a new study done by Judith Mank (Uppsala University, Sweden) warns that, in fish, choosing a flashier mate may cause trouble for future generations, as they turn more susceptible to pathogens.
Repeated mating over the generations with males displaying the most impressive traits, like bright scales or longer tails and fins, leads to generations of males with much higher testosterone levels.
Because male and female testosterone levels are genetically linked in each species, this also leads to increased female testosterone levels. But testosterone acts like an immune suppressor, and high testosterone levels can decrease an individual's capacity to fight infections. "Therefore, a female's choice of a male with exaggerated ornaments may make her daughters and granddaughters less able to resist pathogens," said Mank.
But, as natural selection has not eliminated this trend, there must be a trade-off. Higher testosterone amounts make females larger than males in many fish species, which stimulate them to produce much higher amounts of roe. "The benefits of increased body size to roe production and mate selection may, at least in some cases, counter the immunosuppressive effects of elevated testosterone in females", explained Mank.
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