Extreme heterogeneity in parasitism despite low population genetic structure among monarch butterflies inhabiting the Hawaiian Islands

• Published in: PloS one Vol. 9; no. 6; p. e100061
• Main Authors: Pierce, Amanda A, de Roode, Jacobus C, Altizer, Sonia, Bartel, Rebecca A
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 13.06.2014; Public Library of Science (PLoS)
• Subjects: Animal behavior; Animal Migration; Animals; Biological evolution; Biology and Life Sciences; Butterflies; Butterflies & moths; Butterflies - genetics; Butterflies - parasitology; Climate; Colonization; Danaus plexippus; Ecological effects; Ecology; Ecology and Environmental Sciences; Evolution; Female; Gene flow; Genetic diversity; Genetic Heterogeneity; Genetic markers; Genetic structure; Genetic Variation; Genetics, Population; Habitats; Hawaii - epidemiology; Health aspects; Heterogeneity; Host-Parasite Interactions - genetics; Inbreeding; Infection; Infections; Infectious diseases; Insect migration; Islands; Male; Medicine and Health Sciences; Microsatellite Repeats - genetics; Microsatellites; Migration; Monarch butterfly; Parasites; Parasitism; Population genetics; Populations; Prevalence; Protozoa; Protozoan Infections, Animal - epidemiology; Protozoan Infections, Animal - genetics; Protozoan Infections, Animal - parasitology; Protozoan Infections, Animal - transmission; Spatial heterogeneity; Species extinction; Hawaii; Atlanta Georgia; Georgia; United States > US; North America
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0100061

Host movement and spatial structure can strongly influence the ecology and evolution of infectious diseases, with limited host movement potentially leading to high spatial heterogeneity in infection. Monarch butterflies (Danaus plexippus) are best known for undertaking a spectacular long-distance migration in eastern North America; however, they also form non-migratory populations that breed year-round in milder climates such as Hawaii and other tropical locations. Prior work showed an inverse relationship between monarch migratory propensity and the prevalence of the protozoan parasite, Ophryocystis elektroscirrha. Here, we sampled monarchs from replicate sites within each of four Hawaiian Islands to ask whether these populations show consistently high prevalence of the protozoan parasite as seen for monarchs from several other non-migratory populations. Counter to our predictions, we observed striking spatial heterogeneity in parasite prevalence, with infection rates per site ranging from 4-85%. We next used microsatellite markers to ask whether the observed variation in infection might be explained by limited host movement and spatial sub-structuring among sites. Our results showed that monarchs across the Hawaiian Islands form one admixed population, supporting high gene flow among sites. Moreover, measures of individual-level genetic diversity did not predict host infection status, as might be expected if more inbred hosts harbored higher parasite loads. These results suggest that other factors such as landscape-level environmental variation or colonization-extinction processes might instead cause the extreme heterogeneity in monarch butterfly infection observed here.