Ecoacoustical constraints shape sound communication in lake Malawi Cichlids [abstract]

Van Staaden, M, Wysocki, L E & Ladich, F (2012). Ecoacoustical constraints shape sound communication in lake Malawi Cichlids [abstract]. Bioacoustics, Volume 21 (1): 84

As with other African great lakes, Lake Malawi exhibits an explosive radiation of several hundred cichlid species, most of which are endemics. Although visual communication is widely considered the predominant force driving species recognition and mate choice in this radiation, recent studies highlighted a potential role for acoustic signals. To corroborate this proposition, we are analyzing internal and external constraints on acoustic communication in several species from different tribes. Here we focus on the correlation between characteristics of species-specific vocalizations, auditory sensitivity, and eco-acoustical constraints shaping this communication system. Ambient noise in Lake Malawi is characterized by a steep increase to 800 Hz and a slow decline up to several kilohertz. This increase is particularly pronounced during windy conditions creating a low frequency sound window. Interestingly, hearing sensitivity in Melanochromis johanni and Metriaclima callainos revealed by auditory evoked potential measurements, is maximally sensitive at 150-200 Hz and lowest at 800-1000 Hz. Moreover, this is true whether sensitivity is measured in terms of acoustic pressure or particle acceleration. All genera investigated to date produce pulsed sounds during agonistic and reproductive interactions with energies concentrated between 200-300 Hz. Thus, the main frequencies for sound communication are concentrated both at the maximum auditory sensitivity, and within the ambient noise window of the lake. These results indicate that sound communication in Lake Malawi cichlids is facilitated by both internal sensory and eco-acoustical conditions in the lake, and could play a major role in speciation.