Differences in Caudal Morphology in Male Abbreviata levicauda (Nematoda: Physalopteridae) in Two Sympatric Species of Varanus (Reptilia: Varanidae)

Abstract

Abbreviata levicauda Jones, 1983 was described from lizards in the Varanus gouldii complex (including Varanus panoptes and Varanus rosenbergi) in Western Australia, occurring in these hosts with the more prevalent and numerous Abbreviata hastaspicula Jones, 1979 (Jones, 1983, Australian Journal of Zoology 31: 285298). Among the features which distinguish these 2 species of nematode in V. gouldii (sensu lato) are the spacing of the 3 pairs of caudal papillae and the extent of the bursal tubercles in the male. In A. hastaspicula the penultimate caudal papillae [VI of Chabaud (1956, Annale de Parasitologie 31: 29-52)] are closer to papillae pair V than to papillae pair VII (the more usual condition in this genus) and the tubercles extend, thickly set, to the level of papillae pair VII (Jones, 1979, Proceedings of the Helminthological Society of Washington 46: 1-14). In A. levicauda, papillae pair VI are placed further posteriorly, close to papillae pair VII, and the medial ventral surface of the tail is smooth and devoid of tubercles (Jones, 1983, loc. cit.). During further studies on gastric nematodes in this genus of lizards, the stomach contents were examined from an additional 20 V. gouldii and from 56 Varanus tristis collected by Dr. Eric Pianka from the arid region of Western Australia (most specimens from 122?50'E, 28?28'S and 123?36'E, 28?12'S), between October 1978 and March 1979. Both A. hastaspicula and A. levicauda were recovered from these 2 host species. In V. gouldii, A. hastaspicula was the dominant nematode (prevalence 100%, mean intensity 176), and A. levicauda occurred in 50% of hosts, at a mean intensity of 8. In V. tristis, A. levicauda was the dominant nematode (prevalence 96%, mean intensity 17), and A. hastaspicula occurred in only 9% (mean intensity 8). In A. levicauda recovered from V. tristis hosts, papillae pair VI were further anteriad than in those specimens recovered from V. gouldii hosts (t = 20.00; P < 0.0001; Fig. 1), and in all specimens there were small scattered tubercles on the ventral tail surface for some distance posterior to the anus. Thus in A. levicauda recovered from V. tristis the spacing of the caudal papillae is similar to the condition in A. hastaspicula, which occurs uncommonly and at low numbers in this host. In V. gouldii, on the other hand, in which these 2 species of nematode occur together frequently, the tail morphology of A. levicauda (posterior