Position of larval tapeworms, Polypocephalus sp., in the ganglia of shrimp, Litopenaeus setiferus

Abstract

Parasites that invade the nervous system of their hosts have perhaps the best potential to manipulate their host's behavior, but how they manipulate the host, if they do at all, could depend on their position within the host's nervous system. We hypothesize that parasites that live in the nervous system of their host will be randomly distributed if they exert their influence through non-specific effects (i.e., general pathology), but that their position in the nervous system will be non-random if they exert their influence by targeting specific neural circuits. We recorded the position of larval tapeworms, Polypocephalus sp., in the abdominal ganglia of white shrimp, Litopenaeus setiferus. Tapeworms are more common within ganglia than in the section of the nerve cord between ganglia, even though the nerve cord has a greater volume than the ganglia. The tapeworms are also more abundant in the periphery of the ganglia. Because most synaptic connections are within the central region of the ganglion, such positioning may represent a trade-off between controlling the nervous system and damaging it.

Fig. 1

Number of Polypocephalus sp. individuals in the anterior portion of the abdominal nerve cord of Litopenaeus setiferus. Square = average; horizontal line = median; box = 50% of data; whiskers = 95% of data; crosses = minimum and maximum.

Fig. 2

Positions of Polypocephalus sp. in a composite of abdominal ganglion 2 (n = 28 shrimp); arrowhead at anterior end of Polypocephalus sp. Thumbnails from each individual are shown below, arranged from fewest to most parasites.