Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, UK.
Proc Biol Sci. 2010 Apr 7;277(1684):979-88. doi: 10.1098/rspb.2009.2084. Epub 2010 Jan 13.
Major histocompatibility complex (MHC) genes have been put forward as a model for studying how genetic diversity is maintained in wild populations. Pathogen-mediated selection (PMS) is believed to generate the extraordinary levels of MHC diversity observed. However, establishing the relative importance of the three proposed mechanisms of PMS (heterozygote advantage, rare-allele advantage and fluctuating selection) has proved extremely difficult. Studies have attempted to differentiate between mechanisms of PMS using two approaches: (i) comparing MHC diversity with that expected under neutrality and (ii) relating MHC diversity to pathogen regime. Here, we show that in many cases the same predictions arise from the different mechanisms under these approaches, and that most studies that have inferred one mechanism of selection have not fully considered the alternative explanations. We argue that, while it may be possible to demonstrate that particular mechanisms of PMS are occurring, resolving their relative importance within a system is probably impossible. A more realistic target is to continue to demonstrate when and where the different mechanisms of PMS occur, with the aim of determining their relative importance across systems. We put forward what we believe to be the most promising approaches that will allow us to progress towards achieving this.
主要组织相容性复合体（MHC）基因被提出作为研究遗传多样性如何在野生种群中维持的模型。病原体介导的选择（PMS）被认为产生了观察到的 MHC 多样性的非凡水平。然而，确定 PMS 的三种拟议机制（杂合优势、稀有等位基因优势和波动选择）的相对重要性已被证明极其困难。研究试图使用两种方法来区分 PMS 的机制：（i）将 MHC 多样性与中性条件下的预期多样性进行比较，（ii）将 MHC 多样性与病原体状态联系起来。在这里，我们表明，在许多情况下，这些方法下的不同机制会产生相同的预测，并且已经推断出一种选择机制的大多数研究并没有充分考虑替代解释。我们认为，虽然可能证明特定的 PMS 机制正在发生，但在一个系统中确定它们的相对重要性可能是不可能的。一个更现实的目标是继续证明 PMS 的不同机制何时何地发生，目的是确定它们在不同系统中的相对重要性。我们提出了我们认为最有前途的方法，这将使我们能够朝着实现这一目标前进。
