Nature Genetics pp1326 - 1329

A study to be published in the December issue of Nature Genetics is the first to correlate mating behavior across a range of diverse species to changes in the sequence of a gene involved in reproduction. Bruce Lahn and colleagues show that the rate of evolution of the gene encoding semenogelin II (SEMG2), a component of semen coagulum, correlates with the degree of female promiscuity in at least some primates.

Sexual selection is defined as the competition for mates between individuals of the same sex, and was proposed by Darwin to be a powerful force driving evolution. Postcopulatory sperm competition is a well-studied example of sexual selection, and has been shown to affect the evolution of traits associated with reproductive physiology, such as testis size and sperm count (the greater the number of potential competitors, the larger the number of sperm it is desirable to have). Semen coagulum, a component of the seminal fluid, has also been shown to be critical in preventing fertilization of a recently inseminated female by other males. Lahn and co-workers show that SEMG2 is evolving fastest in primate species in which females are the most sexually promiscuous (chimpanzees and macaques). Humans fall in the middle of the range, but are difficult to assess given the cultural influences on mating behavior. Presumably, the rapidly evolving versions of SEMG2 in chimpanzees are being selected for effectiveness in preventing fertilization by competing sperm, although this has not yet been demonstrated directly.

Nature Genetics pp1259 - 1267

John Parkinson and colleagues in the transatlantic nematode genome project report in the December issue of Nature Genetics a genetic characterization of nematodes, a highly diverse group of organisms ranging from free-living worms to human parasites. The authors have identified and characterized sequences in over 30 nematode species, defining over 90,000 new nematode genes, and find a surprisingly high degree of diversity between species. Nematodes contribute to a high burden of disease, particularly in the developing world.

The authors in the nematode genome project generated over 250,000 short sequences from a wide range of species. Analysis showed a high degree of novelty, such that over 50% of genes were found only in nematodes, and over 23% were unique to their species. The identification of both nematode and species specific genes will be important in driving drug and vaccine development.

Nematodes are highly abundant, accounting for 80% of all individual animals on earth, as well as diverse, with estimates of 100,000 to 1 million species. With 2.9 billion human infections, nematodes contribute to a high level of morbidity and mortality worldwide, with an estimated 100,000 deaths annually.