Geographic variation in acoustic signals of freshwater fishes

Abstract

Although well studied in other taxa, geographic variation in signal structure has been poorly studied in fishes. Signal divergence in marine fishes depends on larval form; pelagic larvae disperse more widely than demersal forms, limiting opportunities for isolation and subsequent divergence. Freshwater fishes, especially those restricted to headwater habitat, are isolated by drainage. There are many examples of species radiations in groups of North American freshwater fishes within drainage networks, including darters, minnows, and catfishes, some of which are restricted to single streams. Our data demonstrate divergence of acoustic signals among populations of stream and riverine fishes at multiple scales, and often in the absence of apparent morphological variation. Two model species, Longear Sunfish and Whitetail Shiner, differed in the temporal components of calls, while darter and sturgeon models showed variation in both temporal and spectral call components. In the case of the sturgeon, the populations were genetically distinct. Furthermore, data for Whitetail Shiner suggest that calls associated with courtship were strongly associated with geographic isolation, while divergence in those characteristics associated with aggression may be driven by genetic drift. We suggest that variation in acoustic signal structure may be common in freshwater fishes and discuss implications for mate choice.