Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen

• Type of Material: Article
• Authors: Sarah E. Sander, University of Georgia; Sonia Altizer, University of Georgia; Jacobus De Roode, Emory University; Andrew K. Davis, University of Georgia
• Language: English
• Date: 2013-08-28
• Publisher: MDPI
• Publication Version: Final Published Version
• Copyright Statement: © 2013 by the authors
• License: Creative Commons Attribution 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.3390/insects4030447
• Title of Journal or Parent Work: Insects
• ISSN: 2075-4450
• Volume: 4
• Issue: 3
• Start Page: 447
• End Page: 462
• Grant/Funding Information: National Science Foundation Graduate Research Fellowship to SES.; National Science Foundation grant (DEB-1019746) to JCdR; National Science Foundation grant (DEB-0643831) to SA
• Keywords: parasite load; spore size; neogregarine; Danaus plexippus; aspect ratio; Ophryocystis elektroscirrha; monarch butterfly
• Research Categories: Biology, Ecology; Biology, Genetics

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.