Krebs Bethany L, Anderson Tavis K, Goldberg Tony L, Hamer Gabriel L, Kitron Uriel D, Newman Christina M, Ruiz Marilyn O, Walker Edward D, Brawn Jeffrey D
School of Integrative Biology, University of Illinois, Urbana, IL 61801, USA
Department of Biology, Georgia Southern University, Statesboro, GA 30460, USA.
Proc Biol Sci. 2014 Dec 7;281(1796):20141586. doi: 10.1098/rspb.2014.1586.
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 inside roosts seroconverted to WNV more slowly than those outside of roosts, suggesting that social groups decrease per capita exposure to infected mosquitoes. These results therefore support the encounter-dilution hypothesis in a vector-borne disease system. Our results suggest that disease-related selective pressures on sociality may depend on the mode of disease transmission.
动物可以通过形成群体来降低个体被捕食的风险。遭遇稀释假说将群居的潜在益处扩展到叮咬昆虫和媒介传播疾病，该假说预测在较大的宿主群体中，人均被昆虫叮咬的次数应该会减少。尽管媒介传播疾病很常见，并且会对宿主施加强大的选择压力，但在自然系统中对遭遇稀释效应的测试却很少。我们使用美洲知更鸟（旅鸫）对遭遇稀释假说进行了实验测试，美洲知更鸟是西尼罗河病毒（WNV，一种由蚊子传播的病原体）的常见宿主物种。通过将哨兵宿主（家麻雀）关在芝加哥郊区自然形成的群居栖息处的笼子里，我们评估了栖息处内外哨兵宿主感染西尼罗河病毒的风险。我们还估计了栖息处内外宿主人均接触感染媒介的情况。关在栖息处内笼子里的哨兵鸟感染西尼罗河病毒后血清转化的速度比栖息处外的鸟慢，这表明社会群体减少了人均接触感染蚊子的机会。因此，这些结果支持了媒介传播疾病系统中的遭遇稀释假说。我们的结果表明，与疾病相关的对社会性的选择压力可能取决于疾病传播的方式。
