Genetic Tricks of Parasites Parasites typically don’t have as
many genes as their free-living relatives do. Life is simple
because their hosts do the hard work of moving about, getting
food, and avoiding predators. Consider the nematodes (aka
roundworms). The common free-living soil dweller Caenorhabditis
elegans—which in 1998 became the first multicellular animal ever
to have its genome decoded—has about 20,000 genes, whereas
Brugia malayi, the parasite that causes the tropical disease
filariasis, has just 11,500. Yet in the course of parasite
evolution, genomes may need to grow before they can shrink. Ralf
J. Sommer and Christoph Dieterich of the Max-Planck Institute
for Developmental Biology in Tübingen, Germany, along with
fifteen colleagues, have sequenced the genome of Pristionchus
pacificus, a nematode that invades the bodies of beetles but
does not live off them. Instead, it waits in a state of
suspended animation for its host beetle to die of natural causes
before popping out and feeding on bacteria