The Effects of the Parasite Probopyrus Pandalicola (Packard, 1879) (Isopoda, Bopyridae) on the Behavior, Transparent Camouflage, and Predators of Palaemonetes Pugio Holthuis, 1949 (Decapoda, Palaemonidae)

The bopyrid isopod Probopyrus pandalicola (Packard, 1879) is a large, noticeable, hematophagous ectoparasite of palaemonid shrimps, including the daggerblade grass shrimp Palaemonetes pugio Holthuis, 1949. Bopyrids affect grass shrimp physiology and may also affect predator-prey dynamics. The purpose of this study was to determine whether the isopod affected the behavior and/or camouflage of grass shrimp, thereby altering the predation preferences of the mummichog Fundulus heteroclitus (Linnaeus, 1766). To determine whether the isopod affected predator preference through behavioral and/or camouflage alterations, paired combinations of unparasitized, parasitized, and marked shrimp were presented to mummichogs. One branchiostegite of some of the unparasitized shrimp was marked with black paint to mimic the bopyrid parasite. Mummichog predation preference and shrimp behavior immediately prior to predation events were recorded. All shrimp behavior was classified as motionless, walking, swimming, or backward thrusting. Immediately prior to predation, parasitized shrimp swam more (p = 0.0477) and backward thrusted less (p = 0.0272) than unparasitized shrimp. Mummichogs exhibited a preference for the more active shrimp (80.7% of shrimp; p<0.0001), and also for the less camouflaged (parasitized or marked) shrimp (81.5% of shrimp; p = 0.0011) if there was no difference in shrimp behavior. Parasitized shrimp were preferentially consumed (51/85 shrimp) when paired with unparasitized shrimp (p = 0.0089), but not with marked shrimp (p = 0.0837). A 30-min activity budget was created for each type of shrimp both in the presence and absence of predators; neither the parasite nor marking affected their behavior over 30 min (p = 0.1005). The major finding of this study was that P. pandalicola affected the predation preferences of F. heteroclitus by altering the behavior and/or camouflage of the grass shrimp. Parasitization alters predator-prey dynamics by decreasing the camouflage and the frequency of backward-thrusting behavior by the host when it is threatened by predation, which thereby decreases the ability of shrimp to escape from predators.