Sneaky Male Fish With Giant Testes Act and Look Like Females to Snag Mates

Underwater mating habits can actually teach us humans a thing or two about how to get the girl. Research from the University of Otago, in New Zealand, has shown that some male bluehead wrasses, colorful fish found in parts of the Atlantic Ocean, disguise themselves as females to find a mate.

It seems there are no lengths that males will stop at to attract the opposite sex—including masquerading as a female (if you're a fish, that is).

Research from the University of Otago in New Zealand has shown that some male bluehead wrasses, colorful fish found in parts of the Atlantic Ocean, disguise themselves as female to find a mate. And to do this, the fish manage to switch specific genes in their brains and gonads on or off.

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In the realm of strange but true phenomena, past research on the fish, which are found in the Atlantic from Florida to the Gulf of Mexico, Bermuda and South America, has shown that certain males act like females in order to go undetected by other males to avoid competition.

"There are two types of males—large, aggressive blue-headed males that openly court females, and smaller 'sneaker' males that look, and act, like females in order to sneak in matings," study co-author Erica Todd said in a statement.

Scientists have now determined how the two types of male bluehead wrasse are able to appear more female by essentially flipping a switch on their gonads using certain genes in the brain. The team drew on RNA-sequencing to compare the brains of sneaker males to their more aggressive male fish counterparts. They also compared the brains of those tricky bluehead wrasses to females.

Todd and her team found that the sneaky bluehead wrasses had gene patterns that were almost identical to females. However, their genes were vastly different from the more aggressive male fish.

"Males of many species use bright colors and other ornamentation to attract mates and compete with rivals, which are often regulated by male sex hormones produced in the testes. In sneaker male testes, we found that many of the genes critical for male sex hormone production were turned off—making them look female," said Todd in a press release from the University of Otago.

Though they may have similar genetics to females, the sneaker males are actually more fertile than territorial males, producing 60 percent more sperm, thanks to larger testes. Aside from their mating abilities, sneaker males benefit from being less stressed too.

"Sneaker males express genes for neuroplasticity that may help them elude territorial males and steal mating opportunities with females. Territorial males express genes associated with stress and protection against cellular damage, suggesting that life is tough at the top of the social hierarchy," said Todd in the statement.

While this study is in fish, there may be a lesson that human males can take from the study, too. Prior research has shown that women don't necessarily prefer macho, dominant males, suggesting that guys can act more feminine and still attract women.