Branchiobdellid annelids and their freshwater crayfish hosts are generally thought to have a commensal relationship. Branchiobdellids of the genus Cambarincola exploit their hosts through a variety of mechanisms; however, an effect of branchiobdellids on crayfish has not been conclusively demonstrated. We investigated whether branchiobdellids positively affect the host crayfish Cambarus chasmodactylus in the New River, North Carolina. In a laboratory experiment, we placed 0, 3, or 6 branchiobdellids on C. chasmodactylus and observed a significant effect of branchiobdellid presence on both growth and mortality of host crayfish; crayfish with branchiobdellids exhibited faster growth and lower mortality with increasing branchiobdellid density. A tracer experiment demonstrated that branchiobdellids feed on items found in the branchial chamber of C. chasmodactylus. We hypothesize that such feeding activity by branchiobdellids reduces fouling of crayfish gills by epibionts and particulate matter and could lead to the reduced mortality and increased growth rates observed in the laboratory experiment. Specifically, Cambarincola may improve the ventilatory and excretory fitness of C. chasmodactylus by cleaning gill filaments. Field data support this hypothesis by demonstrating that branchiobdellids are found disproportionately at sites proximal to the branchial chamber in the New River. This study provides evidence that the relationship between C. chasmodactylus and Cambarincola may be a cleaning symbiosis, at least in environments where gill fouling is a problem for C. chasmodactylus.
Microphiopholis gracillima can autotomize and then regenerate the autotomized central disc, including integument, gut, and gonads. Experiments were carried out to determine the relative importance of internal nutrient reserve translocation and exogenous nutrient uptake during the regeneration process. Approximately 60% of the dry body weight of M. gracillima is organic material. Intact animals held for three weeks in natural seawater did not change significantly in weight, caloric content, or relative concentration of protein, carbohydrates, or lipids. Intact animals held for three weeks in artificial seawater devoid of nutrients lost weight and caloric content. The rate of loss was rapid initially, but slowed after about eight days. Animals regenerated in natural seawater lost weight initially, then regained the lost weight. Animals regenerated in artificial seawater lost weight constantly and at a higher rate than either the artificial seawater control or natural seawater regenerated animals. All weight losses were attributable to significant changes in the protein and carbohydrate fractions of the organic body component. The lipid fraction and ash components did not change significantly in any treatment. M. gracillima appears to be adapted to regenerate the lost disk rapidly, even under conditions of food deprivation.
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