Abstract
Many territorial animals reduce aggression toward their neighbours once territorial boundaries are established. This relationship is called the dear enemy phenomenon, hypothetically based on a conditional strategy like tit for tat (TFT). However, studies on territorial animals such as male songbirds do not fully support this hypothesis. We tested the TFT hypothesis in females of the territorial cichlid Neolamprologus pulcher, which exhibits dear enemy relationships, under laboratory conditions. Focal fish attacked invading neighbours as frequently as invading strangers, but they immediately stopped attacking the dear neighbour after the neighbour returned to its own territory, whereas they kept attacking strangers even after they stopped invading. These responses of territory owners are consistent with the predictions of TFT theory. Interestingly, fish were likely to remain vigilant toward the neighbour after its invasion and subsequent return to its own territory.
Highlights
In defending their territories, animals incur costs such as time, energy, and risk of predation and/or injury during aggressive fighting (e.g., Brown, 1964; Eberhard and Ewald, 1994; Temeles, 1994; Ydenberg et al, 1998)
Our experiments were conducted in compliance with the Guideline of Animal Welfare of the Japan Ethological Society, and were specially approved by the Animal Care and Use Committee of Osaka City University. Focal fish increased their aggression against neighbors that intruded into the center of their territory (Friedman, df = 5, P < 0.001; Welch pared t-test, t = 11.11, df = 7, P < 0.0001, n = 8; Figure 2), but decreased their aggression intensity immediately after neighbors stopped intruding and returned to their own territory (Welch pared t-test, t = 9.16, df = 7, P < 0.0001, n = 8; Figure 2)
Our results are consistent with the prediction and support the hypothesis that the dear enemy relationship between N. pulcher females is based on the tit for tat (TFT) strategy
Summary
Animals incur costs such as time, energy, and risk of predation and/or injury during aggressive fighting (e.g., Brown, 1964; Eberhard and Ewald, 1994; Temeles, 1994; Ydenberg et al, 1998). Studies have often documented that once a boundary has been established between adjacent territories, neighbors rarely invade each other’s territories, and owners become less aggressive toward their neighbors. This reduction in aggression is known as the dear enemy relationship, and is exhibited by a variety of vertebrates (e.g., Fisher, 1954; Getty, 1989; Temeles, 1994; Ydenberg et al, 1998; Frostman and Sherman, 2004; Briefer et al, 2008). Researchers expected that the dear enemy relationship between these birds would follow the rules for TFT: (1) avoid intruding when your honest neighbors do not intrude (original expectation from TFT: cooperate if your partner cooperates), (2) retaliate
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call