"The capacity of a virus to propagate upon a novel host apparently is conditional on the recent experience of preceding generations," explain John J. Dennehy (Yale University), Nicholas A. Friedenberg (Dartmouth College), Robert D. Holt (University of Florida), and Paul E. Turner (Yale University). "This is intrinsically interesting, suggesting a kind of complexity in pathogen population dynamics that has not been widely regarded."
The researchers observed viral populations on host bacteria, specifically situations where virus populations were sustained on the original hosts, but went extinct on the new hosts. Observing transmission rates, they found that viruses previously reared on an original host showed greater productivity on the new host than viruses previously reared on the new host.
"In this critical region, periodic exposure to native hosts allowed the viruses to survive on novel hosts, an unanticipated result," explain the authors.
The researchers infer that the mechanism behind this phenomenon may be the "host-legacy" effect. If this is the case, according to the authors, the total viral population experiencing the new environment is greater than previously expected, allowing for increased chances of adaptive evolution to the new host.
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Dennehy, John J., Nicholas A. Friedenberg, Robert D. Holt, and Paul E. Turner. "Viral ecology and the maintenance of novel host use," The American Naturalist 167:3.