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Biochemical and Immunological Systematics of Some Ascaridoid Nematodes: Genetic Divergence between Congeners

1987; American Society of Parasitologists; Volume: 73; Issue: 4 Linguagem: Inglês

10.2307/3282419

1937-2345

Steven A. Nadler,

Coccidia and coccidiosis research

Vertical starch gel electrophoresis and trefoil immunodiffusion were used to study the systematics of some ascaridoid nematodes.Within the Ascarididae, the time scale of divergence was too great for intergeneric electrophoretic comparisons.Congeneric electrophoretic comparisons of Baylisascaris procyonis (host-raccoon) versus Baylisascaris transfuga (host-black bear), and Toxocara canis (host-domestic dog) versus Toxocara cati (host-domestic cat) yielded Nei genetic distance coefficients of 1.21 and 1.55, respectively.Estimates of times of divergence made from 1 electrophoretic clock calibration suggest that the Baylisascaris species have not shared a common ancestor for 25 million years (Myr), and that the Toxocara species diverged 33 Myr ago.The Baylisascaris divergence estimate corresponds to host-family divergence estimates based on immunological and paleontological evidence, which suggests that cospeciation has occurred.In contrast to this, Ascaris suum (host-pig) and Ascaris lumbricoides (host-human) have a distance coefficient of 0.09.This indicates that these species diverged comparatively recently and may represent a case of host range expansion.Trefoil immunodiffusion comparisons of ascaridoid albumins yielded reactions of identity for A. suum, A. lumbricoides, Parascaris equorum, B. procyonis, B. transfuga, T. canis, and T. cati.This confirms that these taxa are members of a monophyletic group.Comparisons of proteins by electrophoretic and immunologic techniques have proven useful for estimating levels of genetic similarity and in reconstructing phylogenetic relationships among taxa (Wilson et al. , 1977).Molecular data can provide a basis for analysis in groups where other methods are of limited usefulness because structural-gene and organismal-level evolution appear to be independent processes (King and Wilson, 1975;Wilson, 1976; Wilson et al., 1977).Most assessments of ascaridoid relationships have depended upon evaluation of a few qualitative characters (Hartwich, 1974;Sprent, 1980Sprent, , 1983;;Gibson, 1983).In the present investigation, relationships among some members of the Ascarididae sensu Sprent (1983) were studied using starch gel electrophoresis in a multilocus enzymatic approach in order to determine the systematic value of isoenzyme studies at the intergeneric and congeneric levels.In addition, an immunodiffusion study of ascaridoid albumins was undertaken to address the question of monophyly among these taxa.The results indicate that although the ascaridoid taxa examined are members of a monophyletic group, genetic di-