ADAPTATIONS OF THE BRANCHIAL ECTOPARASITE PROBOPYRUS PANDALICOLA (ISOPODA: BOPYRIDAE) FOR SURVIVAL AND REPRODUCTION RELATED TO ECDYSIS OF THE HOST, PALAEMONETES PUGIO (CARIDEA: PALAEMONIDAE)

Abstract

ABSTRACT Survival of the branchial ectoparasite Probopyrus pandalicola through ecdysis of the host, Palaemonetes pugio, was studied by observing infected shrimps before and after ecdysis and directly with time-lapse video. The parasite pair retained its position through 97.3% of 112 host ecdyses. This observation and positive correlations between parasite and host size support the hypothesis that bopyrid isopods remain on and grow together with their host. Video recordings of shrimp ecdysis showed that the female and male maintain their position rather than being cast off and reentering the host branchial chamber. Observations on exuviae from parasitized shrimps and from video recordings suggest that the female parasite avoids being discarded with the molt skin by immediately attaching to the newly exposed inner lining of the gill cover as the shrimp backs out of its exuviae. Reproductive activities of the parasite relative to host molting were studied. Epicaridium larvae were released from the host branchial chamber several hours to 5 days before the host molt. Spawning by the parasite female took place within several hours (median = 12 h) after host ecdysis. Expulsion of exuvial fragments of female parasites from the host branchial chamber was observed in 2 video recordings prior to spawning. In several video recordings, the usually inactive male moved from its site on the female abdomen up to and inside the female marsupium after the host molt and before female spawning, presumably to inseminate the female. Females from which males had been removed failed to produce a brood after the next host molt, tentatively supporting the hypothesis that females must be inseminated prior to each spawning.