Comparison of the jamming avoidance responses in Gymnotoid and Gymnarchid electric fish: A case of convergent evolution of behavior and its sensory basis

Abstract

Summary. 1. A behavioral response conforming to defining features of the jamming avoidance response (JAR) previously reported in Eigenmannia and Apteronotus of the Cypriniformes is found in Gymnarehus of the Mormyriformes.2. Other parallel specializations of these groups are noted, of which the most relevant is the character of the electric organ discharge (EOD); it is quasisinnsoidal, high in repetition rate and highly regular in each of the genera. The same features are found in Sternopygus but it lacks a JAR.3. The EOD is compared in Gymnarchus, Eigenmannia, Apteronotus and Sternopygus, in respect to power spectrum and regularity.4. Other special features of the EOD in Gymnarchus are described, including "singing"and a miniature EOD of a different frequency from the main EOD.5. The JAR in Gymnarchus, compared to Eigenmannia and Apteronotus is longer in latency, slower in reaching plateau, smaller in maximum frequency shift and best excited by a stimulus frequency closer to its own. The voltage gradient threshold (<2.5 ~tV/cm) is higher and the dynamic range smaller. Some correlations with habit of life are suggested. 6. Two types of electroreceptors seem particularly relevant to the JAR. They are similar to the T and P units already reported in Eigenmannia but substantial differences require separate designations; we call them Type S and Type 0 units. 7. Type S units are like T units but spontaneous at high rates and phase coding over a limited intensity range near threshold. Over a wide range of intensity, including much of the physiological range normally encountered the S unit cannot encode intensity.8. Type 0 units are like P units but usefully coding in a narrow intensity range; they are often unable to reach 1 : 1 following. The threshold is usually about 20 db higher than in S units.9. The filter properties of both types are those of a bandpass filter. Whereas the 0 units are sharply tuned to the EOD frequency, the S units have a fiat passband over a range of about 150 Hz, and sharp cutoffs (about 50 db/octave) on both the high and low frequency sides.

Representation of Accurate Temporal Information in the Electrosensory System of the African Electric Fish,Gymnarchus niloticus

“…EOD jitter measured in this study confirms the measurement of EOD jitter by Bullock et al (1975). The frequency "singing" described in Bullock et al (1975), however, was not observed, and all individuals showed stable EOD in a given measurement period (10 sec).…”

“…The behavioral sensitivity to microsecond time disparities is not unique to Gymnarchus; similar or even better temporal sensitivity has been shown in the electrosensory system of a gymnotiform electric fish as well as other vertebrate auditory systems (Rabizza and Masterton, 1972;Brown et al, 1978;Knudsen et al, 1979;Simmons et al, 1983). Despite independent evolution of the electrosensory and electrogeneric systems (Lauder and Liem, 1983), gymnotiform electric fish Eigenmannia performs JARs that are very similar to those of Gymnarchus (Bullock et al, 1975) using identical computational algorithms, consisting of multiple steps of amplitude and phase processing (Bullock et al, 1975;Heiligenberg et al, 1978;Heiligenberg and Bastian, 1980b;Heiligenberg, 1991;Kawasaki, 1993aKawasaki, , 1996. Eigenmannia exhibits comparable phase sensitivity to that found in this study (Rose and Heiligenberg, 1985b;Carr et al, 1986a).…”

“…The frequency "singing" described in Bullock et al (1975), however, was not observed, and all individuals showed stable EOD in a given measurement period (10 sec).…”

“…An electric field is thus established around the body, and its distortion by objects is detected by electroreceptors located over the body surfaces (Lissmann and Machin, 1958). When two fish with similar discharge frequencies meet, they shift their discharge frequencies away from each other to avoid mutual jamming of their electrolocation systems (Bullock et al, 1975). This jamming avoidance response (JAR) requires the detection of time disparities between sensory signals at different electroreceptors (Kawasaki, 1993a).…”

Elementary Motion Detection

“…One of the fish usually shows a so-called jamming avoidance behavior and changes its EOD frequency to improve object localization (Bullock et al, 1975;Bullock et al, 1972;Watanabe and Takeda, 1963). This example illustrates a completely different aspect of behavioral modulation of sensory processing because sensory information is actively changed before even reaching the receptors.…”