Print PageInterspecific symbioses are rarely benign associations and opportunities often exist for symbionts to overexploit each other. Such possibilities necessitate partner control to prevent overexploitation of one symbiont by another. Previous research suggests that the ectosymbiotic worm Cambarincola ingens (Annelida: Branchiobdellidae) are engaged in cleaning symbioses with their crayfish hosts (Cambarus chasmodactylus). Specifically, the worms appear to remove detritus and epibionts from the crayfish gills which increases crayfish growth and decreases crayfish mortality. However, when worms are at high densities they can damage the crayfish gills which negatively affects crayfish growth. A second crayfish species (Orconectes cristavarius), which co-occurs with Cambarus, is host to many fewer worms. Here, we assess whether crayfish actively regulate their worm numbers. First, we examined the response of different sized Cambarus to the addition of 10 worms which typically exceeded observed worm loads for similarly-sized crayfish. Crayfish behavior was observed for 30 mins and final worm number on crayfish was determined after 72 hrs. In a second experiment, we compared attempts by both Cambarus and Orconectes to remove a single, stocked worm during 30-minute behavioral observations. We also compared worm retention on the two species after 24 hrs.
Results/Conclusions
In the first experiment, in which the Cambarus were stocked with 10 worms, removal rates by males were higher than females during the initial 30 minutes and larger males removed more worms than females. After 72 hrs there was a significant positive relationship between carapace length and number of worms remaining on females but not males. When stocked with a single worm, none of the Cambarus removed their worms after either 30 mins or 24 hrs. On the other hand, one quarter of the Orconectes removed stocked worms after 30 mins; after 24 hrs the proportion of Orconectes that had removed worms had increased to one third. We found that crayfish species may differ in their tolerance of ectosymbiotic worms. Orconectes, which does not exhibit a consistent association with worms, was more active in its attempts to remove worms. Cambarus, which appears to be engaged in a mutualism with C. ingens, removed worms down to a level that might maintain the mutualism. Our results suggest that in crayfish-branchiobdellid symbioses, crayfish play an active role in controlling worm loads which may prevent overexploitation of crayfish by their branchiobdellid symbionts.
