Signaling via water currents in behavioral interactions of snapping shrimp(Alpheus heterochaelis)

The snapping shrimp Alpheus heterochaelis produces a variety of different w ater currents during intraspecific encounters and interspecific interaction s with small sympatric crabs (Eurypanopeus depressus). We studied the mecha nisms of current production in tethered shrimp and the use of the different currents in freely behaving animals. The beating of the pleopods results i n strong posteriorly directed currents. Although they reach rather far, the se currents show no distinctions when directed toward different opponents. Gill currents are produced by movements of the scaphognathites (the exopodi tes of the second maxillae) and can then be deflected laterally by movement s of the exopodites of the first and second maxillipeds. These frequent but slow lateral gill currents are most probably used to enhance chemical odor perception. The fast and focused, anteriorly directed gill currents, howev er, represent a powerful tool in intraspecific signaling, because they reac h the chemo- and mechanosensory antennules of the opponent more often than any other currents and also because they are produced soon after previous c ontacts between the animals. They may carry chemical information about the social status of their producers since dominant shrimp release more anterio r gill currents and more water jets than subordinate animals in intrasexual interactions.