Pierce Amanda A, de Roode Jacobus C, Altizer Sonia, Bartel Rebecca A
Biology Department, Emory University, Atlanta, Georgia, United States of America.
Odum School of Ecology, University of Georgia, Athens, Georgia, United States of America.
PLoS One. 2014 Jun 13;9(6):e100061. doi: 10.1371/journal.pone.0100061. eCollection 2014.
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.
宿主的移动和空间结构会对传染病的生态和进化产生重大影响，宿主移动受限可能导致感染出现高度的空间异质性。黑脉金斑蝶（Danaus plexippus）最为人所知的是在北美东部进行壮观的长途迁徙；然而，它们也形成了非迁徙种群，在夏威夷和其他热带地区等气候较为温和的地方全年繁殖。先前的研究表明，黑脉金斑蝶的迁徙倾向与原生动物寄生虫微孢子虫（Ophryocystis elektroscirrha）的流行率呈负相关。在这里，我们从四个夏威夷岛屿中的每个岛屿的重复地点采集了黑脉金斑蝶样本，以探究这些种群是否像其他一些非迁徙种群的黑脉金斑蝶那样，寄生虫原生动物的流行率始终很高。与我们的预测相反，我们观察到寄生虫流行率存在显著的空间异质性，每个地点的感染率在4%至85%之间。接下来，我们使用微卫星标记来探究观察到的感染差异是否可以用宿主移动受限和各地点之间的空间亚结构来解释。我们的结果表明，夏威夷群岛上的黑脉金斑蝶形成了一个混合种群，这支持了各地点之间的高基因流动。此外，个体水平的遗传多样性指标并不能预测宿主的感染状态，而如果近亲繁殖程度更高的宿主携带更高的寄生虫负荷，情况可能会是这样。这些结果表明，其他因素，如景观水平的环境变化或定殖 - 灭绝过程，可能反而导致了这里观察到的黑脉金斑蝶感染的极端异质性。
