Infectivity, multiple infections, and the genetic correlation between within-host growth and parasite virulence: A reply to Hochberg

摘要

Two experimental studies, Ebert (1994) and Ebert and Mangin (1997), described a genetic correlation between parasite virulence and the number of transmission stages found in the hosts. It was concluded that this correlation is evidence that within-host growth rate of the parasite is positively correlated with virulence. Hochberg (1998) has criticized this interpretation, arguing that differential infectivity and density-dependent parasite growth could confound the results. Here I point out that density dependence is unlikely to have confounded the results, but, at least for Ebert (1994), differential infectivity is likely to have been a confounding factor. However, Ebert and Mangin (1997) measured infectivity and showed that strains with higher infectivity had lower virulence, which is contrary to Hochberg's hypothesis. In summary, I conclude that differential infectivity played a role in the assessment of the correlation between parasite reproduction and virulence, but that differential within-host growth remains the most likely explanation for the correlation observed in Ebert and Mangin (1997). [References: 21]