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Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen
Odum School of Ecology, University of Georgia, Athens, GA 30602, USA
Department of Biology, Emory University, Atlanta, GA 30322, USA
Current address: Department of Genetics, University of Georgia, Athens, GA 30602, USA
* Author to whom correspondence should be addressed.
Received: 15 May 2013; in revised form: 14 August 2013 / Accepted: 15 August 2013 / Published: 28 August 2013
Abstract: Monarch butterflies (Danaus plexippus) throughout the world are commonly infected by the specialist pathogen Ophryocystis elektroscirrha (OE). This protozoan is transmitted when larvae ingest infectious stages (spores) scattered onto host plant leaves by infected adults. Parasites replicate internally during larval and pupal stages, and adult monarchs emerge covered with millions of dormant spores on the outsides of their bodies. Across multiple monarch populations, OE varies in prevalence and virulence. Here, we examined geographic and genetic variation in OE spore morphology using clonal parasite lineages derived from each of four host populations (eastern and western North America, South Florida and Hawaii). Spores were harvested from experimentally inoculated, captive-reared adult monarchs. Using light microscopy and digital image analysis, we measured the size, shape and color of 30 replicate spores per host. Analyses examined predictors of spore morphology, including parasite source population and clone, parasite load, and the following host traits: family line, sex, wing area, and wing color (orange and black pigmentation). Results showed significant differences in spore size and shape among parasite clones, suggesting genetic determinants of morphological variation. Spore size also increased with monarch wing size, and monarchs with larger and darker orange wings tended to have darker colored spores, consistent with the idea that parasite development depends on variation in host quality and resources. We found no evidence for effects of source population on variation in spore morphology. Collectively, these results provide support for heritable variation in spore morphology and a role for host traits in affecting parasite development.
Keywords: monarch butterfly; Danaus plexippus; neogregarine; Ophryocystis elektroscirrha; aspect ratio; spore size; parasite load
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Sander, S.E.; Altizer, S.; de Roode, J.C.; Davis, A.K. Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen. Insects 2013, 4, 447-462.
Sander SE, Altizer S, de Roode JC, Davis AK. Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen. Insects. 2013; 4(3):447-462.
Sander, Sarah E.; Altizer, Sonia; de Roode, Jacobus C.; Davis, Andrew K. 2013. "Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen." Insects 4, no. 3: 447-462.