Evolutionary Ecology

, Volume 23, Issue 4, pp 607–620 | Cite as

Sex differences in immune defenses and response to parasitism in monarch butterflies

  • Elizabeth Lindsey
  • Sonia Altizer
Original Paper


Host susceptibility and patterns of infection are predicted to differ between males and females due to sex-based tradeoffs between the demands of reproduction and costly immune defenses. In this study, we examined immune defenses and the response to experimental infection by a protozoan parasite, Ophryocystis elektroscirrha, in male and female monarch butterflies, Danaus plexippus. We quantified two measures of immunity in late instar larvae: the concentration of circulating hemocytes and mid-gut phenoloxidase activity, and also quantified final parasite loads, body size, longevity, and wing melanism of adult butterflies. Results showed that females had greater average hemocyte counts than males in the absence of infection; males, but not females, showed an increased concentration of hemocytes in the presence of infection. However, higher hemocyte concentrations in larvae were not significantly correlated with lower adult parasite loads, and mid-gut phenoloxidase activity was not significantly associated with hemocyte counts or parasite treatments. Among unparasitized females, greater hemocyte concentrations were costly in terms of reduced body size, but for parasite-treated females, hemocyte concentrations and body size were positively associated. Across all monarchs, unparasitized butterflies showed greater wing melanism (darker forewings) than parasitized monarchs. Overall, this study provides support for differential costs of immune defenses in male and female monarch butterflies, and a negative association between parasite infection and monarch wing melanism.


Hemocytes Insect immunity Phenoloxidase Danaus plexippus Ophryocystis elektroscirrha Tradeoffs 



We thank Laura Gold for assistance in rearing monarchs, Jaap de Roode for guidance in experimental design and comments on earlier drafts of the manuscript, and Andy Davis for advice on image analysis of monarch forewings. Mike Siva-Jothy and Richard Naylor provided guidance for protocols involving hemocyte counts and PO assays. Les Real provided access to greenhouse space. We thank Andrew Stoehr and Karen Oberhauser whose helpful suggestions significantly improved the manuscript. Support was provided from Emory University to S. A. and by the Graduate Division of Biological and Biomedical Sciences at Emory University and a PRISM Fellowship to E. L.


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Graduate Division of Biological and Biomedical Sciences, Population Biology, Ecology, and EvolutionEmory UniversityAtlantaUSA
  2. 2.Odum School of EcologyUniversity of GeorgiaAthensUSA

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