Altered Behavior in Isopods (Armadillidium vulgare) Infected with the Nematode Dispharynx nasuta

Abstract

position of papillae pair VI, no post-anal ventral tubercles) differs markedly from that of A. hastaspicula. There is therefore displacement of these secondary sexual characters in A. levicauda when the 2 nematodes occur together. However, these differences in the morphology of A. levicauda appear to be related to host species and not directly to the presence of A. hastaspicula. In an earlier study on V. gouldii (Jones, 1983, loc. cit.), 1 lizard was infected with A. levicauda only, and 1 was infected with A. levicauda concurrently with A. antarctica, and in both these hosts the morphology of A. levicauda was consistent with that described above from V. gouldii. Abbreviata hastaspicula is uncommon and may be an accidental parasite in V. tristis. Although there were no observable differences in this parasite from the 2 host species, in 1 of the 5 V. tristis infected the 2 male and 2 female A. hastaspicula present showed multiple structural abnormalities involving the esophagus, vulva and male tail, and the eggs were degenerate, possibly indicating poor adaptation to this host. Ecological factors may also have a role in determining the prevalence and intensity of these parasites. Both lizard species are opportunistic carnivores, feeding on a wide range of invertebrates and small vertebrates (Pianka, 1970, Western Australian Naturalist 11: 141-144; Pianka, 1971, Western Australian Naturalist 11: 180-183; King and Green, 1979, Copeia 1: 64-70), but V. tristis is largely arboreal whereas V. gouldii is largely terrestrial. The arthropod intermediate hosts of these parasites are not yet known. Thus displacement of 2 secondary sexual characters occurs in male A. levicauda when present in V. gouldii, in which host it almost always occurs with the more numerous A. hastaspicula. The morphology of the latter species, which is uncommon in V. tristis and in which it might be poorly adapted, is unaltered. This character displacement is presumed to be of importance in species recognition during copulation. I thank Dr. Eric Pianka for making his material and collection data available to me, and Dr. R. Black for his comments on an earlier draft of this manuscript.