Robert Ricklefs

Biologists from the University of Missouri–St. Louis and Mississippi State University have discovered a way to better determine the evolutionary timeline for microscopic malaria parasites. Having a better understanding of the origins of new pathogens lineages, such as malaria, is fundamental to understanding emerging diseases, according to the researchers. In particular, the time of the origin of falciparum malaria in humans has been dated to as few as 10,000 years and as old as several million years.

Robert Ricklefs, Curators’ Professor of Biology at UMSL, and Diana Outlaw, a former postdoctoral fellow at UMSL and now an assistant professor of biology at MSU in Starkville, wrote the paper “A Molecular Clock for Malaria Parasites,” which will be published in the July 9 issue of Science Magazine and provides a well-supported time calibration for the evolution of malaria parasites.

“Because the single-cell malaria parasites leave no fossil record, one has to estimate their rate of evolution by comparison with their hosts,” said Ricklefs, of University City, Mo. “Previously, this had been done under the assumption that parasites evolve at the same rate as their hosts and thus were the same age as their hosts.”

Ricklefs and Outlaw’s research suggests these parasites jump to new, unrelated hosts at any time.

“Thus, one cannot equate parasite evolution with its host’s evolution,” Ricklefs said.

By marrying DNA research to a new statistical approach, they were able to get a better handle on the timeline of parasite evolution. The scientists found that a key gene in the malaria parasites evolved at 60 percent of the rate of the same gene in their hosts. Knowing the rate of gene evolution of the vertebrate hosts, they were able to estimate that modern malaria parasites began to diversify across mammals, birds and reptiles about 16 million years ago and that ancestors of humans gained the parasite 2.5 million years ago.

Ricklefs said, “Malaria parasites undoubtedly were relatively benign for most of that history, becoming a major disease only after the origins of agriculture and dense human populations.”

More information:
http://www.umsl.edu/~ricklefsr/
http://www.sciencemag.org/