Patterns of variation in prevalence and load of the Junonia coenia densovirus (JcDV) across wild populations of a western North American Lycaenid

Kelli J. McKeegan and Angela M. Smilanich, Biology, University of Nevada, Reno, Reno, NV, Matthew L. Forister, Department of Biology, University of Nevada, Reno, Reno, NV, Mike B. Teglas, University of Nevada, Reno, Reno, NV, Nadya D. Muchoney, Biology, University of Nevada, Reno, Zachary H. Marion, Biology, University of Nevada, Reno, NV

Background/Question/Methods
Identifying the patterns of pathogen abundance in nature is important for understanding host-pathogen dynamics, especially in the case of non-model systems. The Junonia coenia densovirus (JcDV) is a small, non-enveloped, single-stranded DNA virus that infects multiple species of Lepidoptera. JcDV was first described in the common buckeye (Lepidoptera: Nymphalidae) in the 1970s and has been primarily cultured and studied in a lab setting since. The Melissa blue butterfly (Lycaeides melissa) is a multivoltine, sexually dimorphic member of the Lycaenidae family that is located in patches across western North America. The native host plant diet of L. melissa contains species of the Lupinus, Glycyrrhiza, or Astragalus genera, but there is evidence of a recent expansion to the use of feral alfalfa (Medicago sativa) as a novel host plant. We were first interested in whether JcDV was found in wild L. melissa, and if so, whether host diet had an effect on viral prevalence (i.e., frequency) or load. Adult L. melissa DNA from 19 populations was screened for JcDV presence with the use of qPCR and a standard curve.
Results/Conclusions
This study represents the first record of JcDV occurring in wild L. melissa, with 34.5% of individuals overall and 17 of 19 populations testing positive. While there was only a weak association of host plant (native or novel) and sex with viral abundance, there was significant variation in virus frequency and load across populations and a positive correlation between the two metrics. To explore whether these intriguing patterns were due to genetic variation of the virus itself, a segment of the capsid gene (VP4) was amplified from wild-caught individuals using Sanger sequencing. Although there were instances of single segregating sites, very few were shared and there was no apparent pattern explaining variation across L. melissa populations, and even between host species. This confirms that JcDV is highly genetically conserved and introduces follow-up questions about other sources of heterogeneity viral prevalence and load across hosts. By investigating the drivers of disease variation within and among host species, we can begin to explain host range evolution of a generalist virus.