Agonistic behaviour and electric signalling in a mormyrid fish, Gnathonemus petersii

Kramer, B.; Bauer, R.

Behavioural Ecol Sociobiol 11: 45-61


DOI: 10.2307/4599088
Accession: 037781944

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Agonistic motor behavior and concurrent electric signaling were studied in individually held, residential G. petersii. Aggressive behavior was elicited by presenting a specimen of a closely related species Mormyrus rume for 3 min a day. The principal agonistic motor patterns are described. Among them head butt, approach and lateral display were further analyzed. The electrical activity displayed during agonistic behavior differed fundamentally both from isolated resting and swimming conditions. The mean discharge rate recorded during aggressive behavior (31 Hz), is approximately twice the rate observed in an isolated swimming fish and 3 times the rate displayed by a resting animal. An attacking G. petersii exhibits a much greater range of electric organ discharge (EOD) intervals than isolated swimming or resting individuals. EOD-interval histograms recorded from attacking fish show 2 sharp modes at high discharge rate; there are no intermediate intervals. During the course of an attack, the initially low and variable discharge rate increases fairly linearly as the distance from the attacked fish diminishes. The EOD rate associated with physical contact (head butt) comprises between 60 and 80 Hz in 24 of 28 attacks analyzed; the dominant mode of the distribution is 61 Hz. During subsequent lateral display, G. petersii emits a high discharge rate pattern consisting of 2 types of "steady-state" activities which may last up to a few seconds: the 1st is a fairly regular alternation of approximately 16 and 8 ms intervals (paired pulses); this pattern gives rise to the 2 peaks of high discharge rate in the interval histogram. The 2nd is a regular sequence of either 16 or 8 ms intervals. The only female showed the same display but did not exhibit the highest possible discharge rate (i.e. a regular sequence of 8 ms intervals). The high discharge rate is terminated by a sudden discharge break. The attack-associated EOD rate increase may be a remnant of an ordinary locomotory pattern which has changed its function to a ritualized aggressive signal that occurs in a socially significant and well-defined context. The high discharge rate might serve 3 functions: behavioral isolation of closely related, sympatrically living mormyrids (perhaps by character displacement); recognition of sexes; synchronization of mates during courtship.

Agonistic behaviour and electric signalling in a mormyrid fish, Gnathonemus petersii