Behavior/Humans

Piss Fight and Sex: Dominant Males Urinate More and Have Smellier Urine!

At least in African tilapias

By Stefan Anitei, Science Editor

17th of December 2007, 19:06 GMT

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In many cultures, pissing over the enemy is the supreme act of humiliation, and clearly proof of power and dominance. Some monkeys piss over their possible predators on the ground. But urine can also mix with sex. If you thought that only some human freaks can reach orgasm through urine (a sexual deviation called urolagnia, urophilia or undinism), you should know that our evolutionary relatives are 'better' than us: in capuchin monkeys this is practiced by the entire species!

These monkeys splash their feet and hands in urine to achieve comfort or to have sex. There are many species of monkeys that "recycle" their urine to wash their feet and hands, often taking a whiz on their hands and rubbing their feet. This affinity for the product of their own kidneys has been found even in chimps. Some African cattle raising tribes even use urinating cattle as... "living showers"! (see photo).

But the piss combat and sex goes much deeper in vertebrate evolution. A new Portuguese research published in BMC Biology shows that aggressive dominant territorial males of Mozambique tilapia fish (Oreochromis mossambicus) keep away potential rivals through chemical messages spread through their urine.

The dominant males were found to produce more urine, which is smellier than the less aggressive subordinate males. It was already known for some time that the urine of freshwater fish can spread sex pheromones in the water, changing the behavior and physiology of individuals of the opposite sex. But the new research shows that urine also affects the behavior of individuals of the same sex.

"Few studies have looked at the roles of pheromones in urine during competition between individuals of the same sex. We've found that tilapia dominant males store more urine in their bladders than subordinates, actively urinate during times of confrontation and the urine's olfactory potency or smell strength is even greater", said lead researcher Eduardo Barata.

Tilapias are lekking species: males gather in a breeding area (called lek) where they build their nests and they don't even feed during the breeding period. Social hierarchy determines which individuals occupy the best breeding spots. By pissing, males actively warn about their dominant status, controlling aggression in rival males through urine.

The research team assessed male urination frequency during competition, discovering that dominant males increased urination frequency when in the presence of 'intruders' from 10 times per hours to 60 times per hour. This high frequency urination ceased when their opponent submitted, thus aggressiveness/hierarchical behavior and urination rhythm were connected. Analyzing urine volume and olfactory potency (with an electro-olfactogram) over 5 days, the team found that low rank males not only stored less urine, but it was also less smelly than that of high rank males.

"We know pheromones are involved in reproductive and non-reproductive behaviors of fish, for example during migration, mating and schooling. While we do not yet know what these chemicals are, it is clear they play a major role in many aspects of tilapia social behavior by providing information about the fish's aggressive capabilities for instance. This is also probably not unique to tilapia, so we're touching the tip of the urinary pheromone iceberg!", said Barata.

TAGS:

fish | urine | dominant

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