Life cycle variation and the genetic structure of nematode populations.

Few data are available on population genetic structure in nematode species, and little of the available data allows direct comparison of the genetic structures of species having different life cycles. Here we use mtDNA sequence data to describe the genetic structure of a heterorhabditid nematode, and compare results to published data on other nematode species. Heterorhabditis marelatus is a parasite of soil-dwelling insects. Its life cycle and local ecology should result in small effective population sizes and restricted gene flow. As predicted, H. marelatus shows much lower mtDNA diversity within populations and over the species as a whole, and has a much more strongly subdivided population structure, than parasites of mobile vertebrate hosts. From data such as these we can begin to generalize about the effects of life cycle variation on genetic structure in different nematode species.