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Cichlid egg-spot gene found

Picture by Neil Hepworth.

German scientists have revealed a gene with a key responsibility in the success of haplochromine cichlid breeding.

Walter Salzburger, Ingo Braasch and Axel Meyer from Konstanz University studied 19 haplochromine cichlid species and found that a gene known as colony-stimulating factor 1 receptor a (csf1ra) was expressed in the egg-spots or anal occeli of males of every species.

Egg spots on the anal fin are a characteristic of haplochromine cichlids and play an important role in the breeding system of these fish.

Haplochromine cichlids are maternal mouthbrooders. Once a female has laid her eggs, she picks them up in her mouth. A male will manoeuvre himself so that she is then attracted to the faux eggs on his fin. When she approaches him to gather the ‘eggs’ into her mouth, the male will then discharge his sperm into her mouth and the existing eggs.

In humans, csf1r is a major regulator of macrophage and tissue development and is often associated with prostate, breast and ovary cancers.

However, here molecular evolutionary analyses showed that the domain of this gene underwent adaptive evolution at the same time as the emergence of the egg-dummies.

It was also found that csf1ra is expressed in the egg-dummies of a distantly related cichlid species, Ophthalmotilapia ventralis, in which markings with similar functions evolved on the pectoral fin in convergence to those of the haplochromines.

There are around 1800 species of cichlids in East Africa, 80% of which are members of the extremely diverse haplochromine group.

The group is an amazing example of rapid evolution and adaptive radiation, where a single line evolves to fill a series of very different niches. Indeed, most of the cichlids found in Lake Malawi and Lake Victoria are haplochromines.

For more information see: Meyer A, Salzburger W and I Braasch (In press) - Adaptive sequence evolution in a color gene involved in the formation of the characteristic egg-dummies of male haplochromine cichlid fishes. BMC Biology (in press).

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