Multiple mechanisms of partner regulation may maintain symbiont densities at beneficial levels in a cleaning symbiosis
Results/Conclusions Similar to previous experiments, we saw clear evidence that crayfish removed excess large branchiobdellidans early in the experiment. Worms in all treatments laid their cocoons in a synchronized pulse during the first 3 weeks. During that period, we saw evidence of an Allee effect, i.e., highest total and per capita cocoon production at intermediate worm densities. This resulted in more juvenile worms on the 5 worm crayfish later in the experiment. However, treatments did not differ in total branchiobdellidan number by the end of the experiment. There was no significant relationship between worm treatment and the proportion of worms lost during the crayfish molt. Instead, the best predictor of the number of worms on a crayfish after the molt was the number of worms it had prior to molting. Our results suggest that worm removal by the crayfish in conjunction with an Allee effect in branchiobdellidan reproduction maintain branchiobdellidan densities at those which benefit the crayfish in this cleaning symbiosis.