Large, slow changes in electric organ discharge associated with social context in Eigenmannia
Brian L. Keeley
The electric organ discharge (EOD) frequency of weakly electric fish is known to change over different time-scales. On the order of seconds, individuals with a difference in EOD frequency (Df) of 2-10 Hz will shift their EOD frequencies way from one another in a behavior known as the "jamming avoidance response" (JAR). On the time-scale of the life span of individuals, EOD frequencies change during the course of maturation. The work reported here focuses on changes that occur on the time-scale of weeks and months.
Eigenmannia virescens were investigated to determine whether EOD frequency changed as a function of social interaction, even when the interaction occurred between fish whose Dfs were significantly larger than needed to elicit a JAR. Two groups of five fish with similar distributions of EOD frequencies were placed alternately in two conditions for 21 days each. In condition 1 (Social), the five fish were placed together in a single aquarium. In condition 2 (Isolated), each of the five fish was placed in smaller, separate aquaria. EOD frequencies of individual fish were recorded daily 2.5-3.5 hours after lights went on in a 12hr-day/12hr-night cycle. It was observed that while in the Social condition, the total range and variance of EOD frequencies of a group of fish increased. While in the Isolated condition, the total range and variance of EOD frequencies of the fish decreased. This evidence suggests that social context has an effect on the distribution of EOD frequencies in a population of Eigenmannia.