The effects of familiarity on competitive interactions between threespinedsticklebacks

In this study, pairs of juvenile sticklebacks either familiar with each oth er or pairs unfamiliar with each other met to share a food source. The stud y showed that sticklebacks were less aggressive towards a partner when shar ing a common food source with a familiar conspecific, compared to when shar ing a food source with an unfamiliar conspecific. The results showed that t he aggressive behaviour was built up and broken down gradually depending on how long the two competitors had been together or apart. A decrease in agg ressiveness was found after the sticklebacks had been together two weeks, w ith a further decrease after four weeks together. Conversely there was an i ncrease in aggressiveness after the sticklebacks had been parted for two we eks or four weeks. The chance of food being equally distributed between the competing pairs increased with time spent together and decreased with time parted. The observed decrease or increase in the amount of aggression is d iscussed as a build-up or a breakdown of rank knowledge or of a co-operativ e partnership.