Video: Cichlid fish have a bizarre mating ritual that involves males discharging their sperm into a female鈥檚 mouth
Men may be intrigued to hear that researchers have pinpointed a gene that makes females suck up sperm through their mouths.
The gene was found in the cichlid fish, where the males have evolved a way to lure females close so that they can squirt sperm into their mouths.
As is the case in many fish species, the sight of a brightly coloured male somehow triggers females with ripe eggs to start releasing them. But in cichlids, there is a twist. Females hold their eggs in their mouths and incubate them there after fertilisation 鈥� a behaviour that is thought to have evolved to protect the eggs from predators.
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As soon as a female has spawned her eggs, she collects them up in her mouth. Normally, sperm released into the water by a male nearby will then fertilise the eggs.
But males of certain cichlid species in east Africa have evolved a way to increase the odds that females take up their sperm. Oval yellow markings resembling the eggs are found on the anal or pelvic fins. When a female approaches the male, she thinks she sees an egg on its fin, so tries to vacuum it up in her mouth 鈥� and get a mouthful of sperm from the canny male in the process.
鈥楾urned on鈥�
鈥淚t looks like she鈥檚 eager to pick up the 鈥榚gg dummy鈥� because she thinks she鈥檚 forgotten one of her own eggs,鈥� says at the University of Lausanne, Switzerland, who led the study.
鈥淭he females actually seem to be turned on by the egg dummies,鈥� comments Sigal Balshine at McMaster University in Hamilton, Ontario, Canada. 鈥淎nd the amazing thing is that they match the egg colour shade within each species.鈥�
Salzburger鈥檚 team believes it has now identified the gene that makes this bizarre mating behaviour possible.
They suspected a gene called csf1ra 鈥� short for colony-stimulating factor 1 receptor a, was responsible 鈥� because they knew that zebrafish lacking this gene failed to produce a yellow pigment similar to the shade of the cichlid fin spots.
The researchers extracted DNA samples from 19 cichlid species 鈥� nine that had egg spots on their fins and 10 that did not. They found the species that had evolved most recently had a mutation in the csf1ra linked to the egg spots.
Salzburger says this shows that the dummy egg spots are a genetic trait that provides a selective advantage because they encourage females to participate in oral mating.
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