Variation in the mating and sexual signaling systems of African cichlids has likely contributed to the diversification of this fish family, which numbers more than 1,600 species. Studies of sexual selection—the evolution of features that influence mate choice—in these multicolored fishes have largely focused on visual signaling. In a recent paper, however, researchers have turned their attention to the overlooked role of sound as a matchmaking tool.
Karen P. Maruska and colleagues at Stanford University, California, tested sound production and hearing abilities in captive-reared Astatotilapia burtoni, a cichlid originally native to Lake Tanganyika. They placed males and females in tanks and used hydrophones and video cameras to record the sounds emitted by the fish and the associated courtship behavior. The team also determined the sensitivity of males of different social statuses and females at different stages of their breeding cycle to sounds of a range of frequencies, by playing back sounds and recording the fish’s auditory evoked potentials—brain electrical response—through thin electrodes inserted near the braincase.
In close proximity to receptive females, dominant males produced low-frequency sounds as they displayed quivering movements—a courtship behavior. Those females, in turn, preferred playback of male sounds to control noise. Hearing in females was strongly affected by breeding stage: those ready to lay eggs were two to five times more sensitive to low-frequency sounds than those that had already spawned and were in the mouthbrooding phase.
Interestingly, subordinate males were more sensitive to frequencies characteristic of smaller, rather than larger, dominant males. That sensitivity might explain how subordinates manage to dash into a courting scene and spawn just ahead of a small dominant male—while not risking a challenge to a larger rival. (PLoS One)