Sound production in longear sunfish (Lepomis megalotis): Acoustic behavior and geographic variation

Acoustic communication during reproductive behavior of longear sunfish (Lepomis megalotis aquilensis, Centrarchidae) was studied in streams in central Texas. Longear sunfish, with documented ecology and behavior, are an ideal model system to study geographic divergence and the forces driving it. Calls collected from five streams around Austin, TX (L. m. aquilensis) and from Brier Creek, OK (L. m. breviceps) were used to examine variation within individuals, among individuals from the same population, among populations of the same subspecies and between subspecies. Analysis of animal calls that are low frequency and short duration can be imprecise using traditional Fourier-based techniques. The results from wavelet and Fourier transforms were compared using a variety of animal calls and synthetic signals in order to assess accuracy and precision. Longear sunfish parental males produce both courtship and pursuit calls while nesting. Courtship calls are directed toward females and are given in conjunction with a distinctive visual courtship display. Pursuit calls are typically directed toward ‘raiders’ and are given during pursuits. The amount of variation in pulse rate and frequency differs between contexts, with pursuit calls exhibiting more variation. Ambient noise and acoustic signal propagation were measured at each of the study sites, with urban sites having higher ambient noise than sites in nature preserves. A series of pure tones and longear sunfish call exemplars were played at each site to assess signal propagation. In general, 75–200 Hz attenuated least in all these shallow streams indicating a ‘window’ for signal propagation. Fish appear to take advantage of signal propagation windows generated by near field effects for acoustic communication. Nested MANOVAs reveal significant differences among males within a population and among populations for both pursuit and courtship calls. Pursuit calls from males appear to be less different than courtship calls among sites. Microgeographic variation in acoustic signals has not been documented in fish before.