Dominance Relationships Between Male Territorial Neighbors in the Beaugregory Damselfish (Stegastes leucostictus)

Abstract

Using the permanently territorial beaugregory damselfish ( Stegastes leucostictus ), we examined behavioral differences between neighbors and how they relate to territory quality, male size, and social interactions. We manipulated territory quality by replacing some male's poor quality natural breeding sites with artificial sites. These artificial sites were known to rapidly increase a male's reproductive success. Three types of paired neighbors were tested: both males with high quality artificial sites (Group I); both neighbors with low quality natural sites (Group II); one male with a low quality natural site and his neighbor with a high quality artificial site (Group III). Because neighbors rarely interact, we stimulated interactions by placing a bottled male or a bottled female midway between the two breeding sites. The area between the 2 sites was rarely patrolled by either neighbor and we judged them to be outside of either male's territory. Although we found that both neighbors were in close proximity to each other while they simultaneously attacked a bottled male or courted a bottled female, the neighbors rarely interacted. Without one neighbor aggressively dominating the other neighbor, the neighbor that attacked or courted the bottled animal most intensively was termed 'dominant.' For pairs where both neighbors defended sites of similar quality (Group I and II), dominance was not related to male size. Reproductive success was only measured for Group I (both males with artificial sites) and relative reproductive success was not related to dominance. For heterogeneous pairs (Group III), dominance was related to territory quality (the male given the artificial site was always dominant when compared to his neighbor) but not male size. Irrespective of pair type (Groups I, II, or III), there was no inter-group differences in behavior among the dominants or among the subordinates. With the removal of the dominant individual, the remaining subordinates increased their aggressiveness toward bottled males and resembled the dominant individuals that were removed. Removing subordinate individuals caused no change in the behavior of remaining dominant individuals. Thus, the dominant males of all group types appeared to suppress the behavior of subordinates. We speculate that when neighbors have similar sites (Groups I and II), their past social interactions may be responsible for the development of the initial dominant-subordinate relationship. However, this dominant-subordinate relationship can be reversed by giving the subordinate male a higher quality breeding site ( i.e . Group III). We found no evidence that a subordinate's reproductive success was influenced by his more dominant neighbor and we speculate that it may influence his ability to secure a breeding site.