Does genetic diversity protect host populations from parasites? A meta-analysis across natural and agricultural systems

If parasites transmit more readily between closely related hosts, then
parasite burdens should decrease with increased genetic diversity of host
populations. This important hypothesis is often accepted at face value -
notorious epidemics of crop monocultures testify to the vulnerability of
host populations that have been purged of diversity. Yet the relationship
between genetic diversity and parasitism likely varies across contexts,
differing between crop and non-crop hosts and between experimental and
natural host populations. Here, we used a meta-analytic approach to ask if
host diversity confers protection against parasites over the range of
contexts in which it has been tested. We synthesized the results of 102
studies, comprising 2,004 effect sizes representing a diversity of
approaches and host-parasite systems. Our results validate a protective
effect of genetic diversity, while revealing significant variation in its
strength across biological and empirical contexts. In experimental host
populations, genetic diversity reduces parasitism by ~20% for non-crop
hosts and by ~50% for crop hosts. In contrast, observational studies of
natural host populations show no consistent relationship between genetic
diversity and parasitism, with both strong negative and positive
correlations reported. This result supports the idea that, if parasites
preferentially attack close relatives, the correlation of genetic
diversity with parasitism could be positive or negative depending upon the
potential for host populations to evolve in response to parasite
selection. Taken together, these results reinforce genetic diversity as a
priority for both conservation and agriculture and emphasize the
challenges inherent to drawing comparisons between controlled experimental
populations and dynamic natural populations.

若寄生虫在亲缘关系相近的宿主间更易传播，则宿主种群的遗传多样性越高，其寄生虫负荷量（parasite burdens）应越低。这一重要假说常被直接采信——臭名昭著的作物单作流行病，印证了遗传多样性丧失的宿主种群极易受寄生虫侵害。然而，遗传多样性与寄生作用间的关联很可能因情境而异，在作物宿主与非作物宿主之间、实验宿主种群与自然宿主种群之间均存在差异。
本研究采用元分析（meta-analytic）方法，在已开展相关检验的各类情境中，探究宿主多样性是否能为宿主抵御寄生虫提供保护。我们整合了102项研究的结果，涵盖2004个效应量（effect sizes），涉及多种研究方法与宿主-寄生虫系统（host-parasite systems）。
研究结果证实了遗传多样性的保护作用，同时揭示其保护强度在不同生物学与实证情境中存在显著差异。在实验宿主种群中，遗传多样性可使非作物宿主的寄生水平降低约20%，使作物宿主的寄生水平降低约50%。与之相对，针对自然宿主种群的观测研究并未显示遗传多样性与寄生水平间存在一致关联，已有研究报道过二者间极强的负相关与正相关关系。
这一结果支持如下观点：若寄生虫优先侵染亲缘关系相近的宿主，则遗传多样性与寄生水平间的相关性可为正或负，具体取决于宿主种群应对寄生虫选择压力的演化潜力。
综上，本研究结果凸显了遗传多样性在保护生物学与农业领域的优先地位，同时也强调了将受控实验种群与动态自然种群进行对比时所固有的挑战。