In their aggressive encounters, animals communicate with each other through signals that can be visual and acoustic (for example, a gorilla would try to intimidate and show dominance to others through blows to the chest and grunts), but also with chemical signals.
And it is this type of signal that a team of researchers from the Institute of Ecology and Evolution, of the University of Bern (Switzerland), has studied in the Neolamprologus pulcher , a species of fish from the endemic cichlid family of Lake Tanganyika ( East Africa) . Their findings have recently been published in the journal Behavioral Ecology and Sociobiology .
After observing these fish, they wondered if these cichlids urinated simply because they had to or if this was actually a way of communicating their aggressiveness to rivals . To measure their level of interaction at the chemical level, the researchers injected a special dye into the fish, thanks to which their urine could be traced in a striking blue color, and carried out two actions with them in a special double tank, divided by a plate. transparent: in the first, this plate contained holes that put the waters of both tanks in communication; in the second, the glass was solid, it did not have any holes.
As soon as the animals could be seen through the glass, they swam to the dividing screen and urinated. They developed this behavior in aggressive interactions. Interestingly, when the plate that separated them did not have holes, not being able to detect the opponent’s urine, they urinated even more , in an attempt to convey their message. In this way, the fish that only maintained visual contact with each other significantly increased their frequency of urination and had a more aggressive behavior than those that maintained not only visual, but also chemical contact.
According to the researchers, these results highlight the need to study the role of chemical communication in aggressive encounters between animals , even when other signals are produced that may be more obvious to the human observer, such as visual and acoustic signals. .
