The dilution effect hypothesis, which suggests greater host biodiversity can reduce infectious disease transmission, occurs in many systems but is not universal. Most studies only investigate the dilution of a single parasite in a community, but many host communities have multiple parasites circulating. We studied a zooplankton host community with prior support for a dilution effect in laboratory- and field-based studies of a fungal parasite, Metschnikowia bicuspidata. We used paired experiments and field studies to ask whether dilution also occurred for a bacterial parasite, Pasteuria ramosa. We hypothesized that the similarities between the parasites might mean the dilution pattern seen in Metschnikowia would also be seen in Pasteuria. However, because Daphnia–Pasteuria interactions have strong host–parasite genotype specificity, dilution may be less likely if diluter host genotypes vary in their capacity to dilute Pasteuria. In a lab experiment, Pasteuria prevalence in susceptible Daphnia dentifera was reduced strongly by higher densities of D. pulicaria and marginally by higher densities of D. retrocurva. In a second experiment, different D. pulicaria genotypes had a similar capacity to dilute both Metschnikowia and Pasteuria, suggesting that Pasteuria’s strong host–parasite genotype specificity should not prevent dilution. However, we found no evidence of an impact of the dilution effect on the size of Pasteuria epidemics in D. dentifera in Midwestern U.S. lakes. Our finding that a second parasite infecting the same host community does not show a similar dilution effect in the field suggests the impact of biodiversity can differ even among parasites in the same host community.

稀释效应假说表明宿主生物多样性的增强可以减少传染病的传播，该假说存在于许多系统中，但并不普遍。大多数研究仅调查社区中单一寄生虫的稀释情况，但许多宿主社区有多种寄生虫在传播。我们研究了浮游动物宿主群落，并事先支​​持了真菌寄生虫实验室和现场研究中的稀释效应，Metschnikowia bicuspidata。我们使用配对实验和现场研究询问细菌寄生虫巴斯德氏菌是否也发生稀释。我们假设寄生虫之间的相似性可能意味着在 Metschnikowia 中看到的稀释模式也会在巴斯德氏菌< /span> 的能力。 a> 美国中西部湖泊。我们的发现是，感染同一宿主群落的第二种寄生虫在田间并未表现出类似的稀释效应，这表明即使同一宿主群落中的寄生虫之间，生物多样性的影响也可能有所不同。D 地区流行病的规模产生影响。 dentifera巴氏杆菌强大的宿主-寄生虫基因型特异性不应阻止稀释。然而，我们没有发现任何证据表明稀释效应对巴斯德氏菌，表明MetschnikowiaPasteuriaPasteuriaPasteuria 和 Metschnikowia 基因型具有相似的稀释 D。 pulicaria。在第二个实验中，不同的D。逆曲 和稍高密度的 D 的密度更高。 pulicaria的患病率大幅降低水蚤易感人群巴氏杆菌的能力不同，则稀释的可能性可能较小。在实验室实验中，巴斯德氏菌相互作用具有很强的宿主-寄生虫基因型特异性，如果稀释宿主基因型稀释巴斯德氏菌–水蚤。然而，由于