Role of larval release pheromones and peptide mimics in abdominal pumping and swimming behavior of ovigerous blue crabs, Callinectes sapidus

Blue crabs Callinectes sapidus, like most decapods, synchronously hatch eggs and release larvae over a very short time period. Synchrony is achieved though vigorous abdominal pumping in response to pheromones from hatching eggs. We hypothesized that these or related pheromones stimulate vertical swimming associated with larval release and ebb-tide swimming during the last few days before egg hatching. We used abdominal pumping and swimming assays to investigate the roles of pheromones. We tested responses of crabs to egg extract containing pheromones, trypsin (an enzyme that generates peptide pheromones), and bradykinin (a peptide pheromone mimic). We delivered test substances directly into the egg mass via capillary tubing. In response to egg extract, ovigerous crabs increased abdominal pumping and vertical swimming, showing native pheromones evoke both behaviors. Delivery of trypsin and bradykinin caused increased pumping but not vertical swimming. These results suggest that pheromones generated from eggs stimulate vertical swimming during ebb-tide transport, but that peptides that induce abdominal pumping are not sufficient to cause swimming. We hypothesize that swimming is stimulated by a blend of molecules that includes these peptide pheromones.