Host social behavior decreases exposure to vector-borne disease: a field experiment in a “hotspot” of West Nile virus transmission

Animals can decrease their individual risk of predation by forming groups. The encounter-dilution hypothesis extends the potential benefits of gregariousness to biting insects and vector-borne disease by predicting that the per capita number of insect bites should decrease within larger host groups. Although vector-borne diseases are common and can exert strong selective pressures on hosts, there have been few tests of the encounter-dilution effect in natural systems. We conducted an experimental test of the encounter-dilution hypothesis using the American robin (Turdus migratorius), a common host species for the West Nile virus (WNV), a mosquito-borne pathogen. By using sentinel hosts (house sparrows, Passer domesticus) caged in naturally occurring communal roosts in the suburbs of Chicago, we assessed sentinel host risk of WNV exposure inside and outside of roosts. We also estimated per capita host exposure to infected vectors inside roosts and outside of roosts. Sentinel birds caged ...动物可通过集群行为降低个体被捕食的风险。相遇稀释假说（encounter-dilution hypothesis）将集群性的潜在益处拓展至吸血昆虫与媒介传播疾病领域，该假说预测：宿主群体规模越大，单一个体遭遇的昆虫叮咬数量便越少。尽管媒介传播疾病分布广泛且可对宿主施加强烈的选择压力，但目前在自然系统中针对相遇稀释效应的实证检验仍较为匮乏。本研究以西尼罗河病毒（West Nile virus, WNV，一种蚊媒病原体）的常见宿主——美洲知更鸟（Turdus migratorius）为研究对象，对相遇稀释假说开展实验验证。我们将笼养的哨兵宿主（sentinel hosts）家麻雀（Passer domesticus）安置于芝加哥郊区自然形成的集群栖息点内及周边区域，以此评估栖息点内外哨兵宿主的西尼罗河病毒暴露风险；同时还估算了栖息点内外宿主个体接触感染媒介的概率。笼养哨兵鸟类……