The Effects of Other Fish On the Reproductive Behavior of the Male Cyprinodon Variegatus (Pisces: Cyprinodontidae)

Abstract This study was conducted to investigate the effects of both inter- and intraspecific intruders on the reproductive behavior of Cyprinodon variegatus. Field observations suggested that the highly aggressive male Cyprinodon prefer to chase their own species, then Fundulus heteroclitus, followed by Lucania parva and Gambusia affinis last. In a series of laboratory experiments, in which dominant males were given various combinations of uni-specific and hetero-specific groups to chase, strong evidence was produced for the chase preferences predicted from field observations. The effects of intruders on the spawning behavior of the male were also recorded. In the field the female entered the male's territory, spawned an average of four times and then left. A female spent approximately 20 seconds in the male's territory. While other fish did interrupt spawning, only neighboring territorial males actually interfered physically. This interference occurred if the spawning pair ventured too close to the border (approximately seven cm). In the laboratory conspecific intruders significantly reduced both the number of spawns and the total duration of contacting (i.e., a side-by-side position of the pair, occurring just before spawning). These intruders also increased the probability of long spawning intervals following other long intervals. At the same time, intruders caused the pair to produce relatively more short intervals. Thus, when other Cyprinodon males were present, the pair had a tendency to perform a clustering of spawns which was separated by several long intervals. This resembled the field situation in which a female entered, spawned several times and quickly left. This study suggests that the effects of other interacting fish should be considered when analyzing reproductive behavior. The observation of laboratory fish in isolated pairs may produce misleading results as to the evolution and/or maintenance of behavior.