Our understanding of the genetic population structure and evolution of free-living organisms has been greatly advanced by the application of molecular techniques. However, the genetic structure of parasitic species has been almost completely ignored. It is proposed to initiate studies of the genetic structure of populations of the human-parasitic nematode Ascaris lumbricoides. Because so much is known about the biology of this A. lumbricoides and its host, Homo sapiens, these species could serve as a model system for studies relating host and parasite population structures. The following scientific questions will be addressed: 1. Are genetically similar or geographically close populations of humans parasitized by genetically similar populations of Ascaris? Or is there genetic evidence for transfer of parasites among geographically separated human populations? Answers to these questions will provide evidence on how long particular host-parasite associations have persisted at the population level. 2. What is the local (within villages) genetic structure of Ascaris populations? For instance, are the worms harbored by a single family representative of a random sample of worms present throughout the village, or do host families harbor their own genetic subpopulations of parasites? Such information will provide clues about major routes of parasite transmission within a population, and thus indicate ways that people could reduce their worm burdens. 3. What are the genetic relationships among parasites derived from different host species (humans and pigs)? Specifically, do these worms represent different species? This information will shed light on the evolution of host specialization in parasitic species. If the worms in pigs and humans are indeed the same species, as we suspect, our results will be of significance for animal husbandry and for reducing rates of infection of humans that live in association with pigs.
