Parasitized monarch butterfly

… our analyses suggest that parasite lifetime fitness would be maximized at an intermediate replication rate. Importantly, at this level of replication, the parasite causes considerable virulence to the host. … natural selection in this system favors parasite genotypes that cause significant damage to their hosts based on a trade-off between virulence and transmission.

–de Roode JC, Yates AJ, Altizer S (2008) Virulence-transmission trade-offs and population divergence in virulence in a naturally occurring butterfly parasite. Proc Natl Acad Sci U S A 105:7489–7494. DOI:10.1073/pnas.0710909105

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