Nucleotide sequence data will be used to estimate phylogenetic relationships among ascaridoid nematodes. This parasite phylogeny then will serve as a framework for testing hypotheses concerning the evolution of morphological characters and life history attributes. Initial research involving direct sequencing of ribosomal-RNA and maximum parsimony analysis of these data indicates that ribosomal-RNA sequences provide a large number of informative characters and a robust phylogenetic hypothesis for ascaridoid nematodes. A more inclusive phylogeny of ascaridoids will be useful for testing competing hypotheses for the evolution of morphological characters and life cycle attributes. Analysis of evolutionary patterns for characters and attributes will be performed by applying Farris optimization to map these characters on the species cladogram inferred from the sequence data. An independent phylogenetic hypothesis based on cladistic analysis of documented morphological characters will also be developed. In addition, the molecular and morphological data sets will be used for a combined (and unweighted) phylogenetic analysis. The implications of the morphologically based and "combined" phylogenetic hypotheses for the evolution of life history attributes will also be explored by mapping. Finally, specific area of congruence and dissimilarity between the molecular and morphological data sets will be identified and examined, and the relative efficiency of phylogenetic hypotheses proposed by other researchers will be assessed independently for each data base (morphological, molecular, and combined).
