Blood cues sex choice for parasites
By John Travis
For a man, four gals for every guy sounds like a dream night at a singles bar. For the parasites that cause malaria in people and other vertebrates, such sex ratios were thought standard. “You generally find in all species of malaria parasites that there are many more females than males,” notes Richard E.L. Paul of the Pasteur Institute in Paris.
Paul and his colleagues, however, wondered whether that sex ratio varies during the course of an infection. The investigators now report in the Jan. 7 Science that in chickens, as malaria infections progress, the sex ratio usually changes so that male and female forms of the parasite become almost equally represented. Paul’s team also describes evidence that a protein that stimulates red blood cell production may trigger this sex-ratio shift.