Cichlid males "breed" large-finned females

First voucher for influence of mate choice also on appearance of females

Cichlid females (front) have developed large ventral fins during evolution © University of Bonn
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The fact that sexual selection through mate choice affects the appearance of males in the animal kingdom is nothing new. However, this effect also works in reverse: cichlids develop larger and larger pelvic fins, because it makes this attractive to the males of their species. This is reported by researchers in the journal "BMC Evolutionary Biology".

Charles Darwin still thought that only the females in the animal kingdom were picky. The males would take anybody who could get them. That this is not always true is only known since the late 1980s. At that time it was shown in experiments that at least in some species also the males look carefully at the mate choice. The fact that the choice affects the appearance of the partners, already suspected Darwin. For example, in the course of evolution, the peacock has developed a magnificent plumage to impress the females.

Mate choice also affects females

Now, biologists from the University of Bonn, using the example of the cichlid species Pelvicachromis taeniatus, discovered that even the ladies change their appearance to please the gentlemen. So far, this is the first empirical proof of this connection. For their study, the researchers x-rayed 73 female cichlids and used the bone beams to determine the size of the fins. With an interesting result: "The abdominal fin is particularly large compared to other fins, " explains Sebastian Baldauf, a researcher at the Institute for Evolutionary Biology and Ecology at the University of Bonn.

But why is that? The belly fin is conspicuously colorful in cichlid females. During the courtship the females set them up and wave them in front of the males. Therefore, the researchers suspected that the fin plays a role in and is influenced by the partner choice.

The size is what matters

To test this thesis, the researchers conducted a partner election trial using computer animation. Aquariums with one male each were placed between two computer monitors. On the one screen, a virtual female with a small belly fin swam back and forth, on the other exactly the same female with a large fin. display

The males always decided in the experiments for the partner with the larger belly fin.

Females with large pelvic fins tend to find it easier to find a sexual partner and have offspring with them. In the course of evolution, the fins should therefore continue to increase. But at some point the conclusion is: "Too large fins hinder the fish while swimming and complicate, for example, the flight from enemies", so Baldauf. Therefore, the fin can not take on an exaggerated amount in nature, as it is more often found in fish farms.

Great fin as a sign of fitness

Of course, just out of sheer vanity, the male cichlids do not choose the partner with the largest fins. The Bonn biologists were able to show that a large belly fin in females signals a good fitness of the wearer. As a result, the chances of survival of the young bass born of her are increasing: "Young women with good physical condition can carry out intensive brood care", the researcher explains. "In addition, there is no danger that they will eat their own brood for lack of food."

(University of Bonn, 12.10.2010 - NPO)