GASTRIC NEMATODE COMMUNITIES IN LIZARDS FROM THE GREAT VICTORIA DESERT, AND AN HYPOTHESIS FOR THEIR EVOLUTION

This study examines the biology of gastric nematodes in two communitie s of lizards from the Great Victoria Desert, and develops an hypothesi s for their evolution. Abbreviata antarctica A. hastaspicula, A, levic auda, A. tumidocapitis, Skrjabinoptera goldmanae, Kreisiella chrysocam pa, Physalopteroides filicauda, Wanaristrongylus ctenoti and W. papang awurpae were recovered from 3023 lizards of 45 species from two differ ent habitats. Genera in the Physalopterinae (Abbreviata, Skrjabinopter a and Kreisiella) exhibited narrow host specificities, Abbreviara and Skrjabinoptera occurring as adults only in larger host species (Varanu s gouldii, V. tristis and Pogona minor). P. filicauda and encysted lar vae of Physalopterinae occurred widely in the smaller lizard species i n all five families represented. Eight of the nine nematode species we re recovered from both lizard populations, and differences in prevalen ce and number of host species infected are discussed in terms of core hosts providing an infective pool. Associations were derived between p arameters of infection (prevalence, intensity and abundance) and host size across and within species; abundance of nematodes in Ctenotus ski nks correlated with host geographical range. Epidemiological evidence is presented that suggests that termites are intermediate hosts to spe cies of Physalopterinae, and that Orthoptera may be intermediate hosts to P.filicauda. It is suggested that species in the Physalopterinae a rose in smaller lizards (where they are now represented by the morphol ogically primitive Kreisiella), and that they were acquired by large p redatory species by host capture, and in which they are now speciating . The small lizards now act as paratenic hosts to their larvae, and th e niches left vacant have been occupied by P. filicauda. It is conclud ed that P.filicauda is at an early non-interactive phase and that Abbr eviata and Skrjabinoptera are at an evolutionary phase, and are evolvi ng along with their hosts. Thus, the two principal nematode groups aro se at different times in response to the radiation and ecology of thei r hosts, and are at different stages in their own evolution.