Eizaguirre Christophe, Lenz Tobias L, Traulsen Arne, Milinski Manfred
Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, 24306 Plön, Germany.
Ecol Lett. 2009 Jan;12(1):5-12. doi: 10.1111/j.1461-0248.2008.01247.x.
Speciation and the maintenance of recently diverged species has been subject of intense research in evolutionary biology for decades. Although the concept of ecological speciation has been accepted, its mechanisms and genetic bases are still under investigation. Here, we present a mechanism for speciation that is orchestrated and strengthened by parasite communities acting on polymorphic genes of the immune system. In vertebrates, these genes have a pleiotropic role with regard to parasite resistance and mate choice. In contrasting niches, parasite communities differ and thus the pools of alleles of the adapted major histocompatibility complex (MHC) also differ between niches. Mate choice for the best-adapted MHC genotype will favour local adaptations and will accelerate separation of both populations: thus immune genes act as pleiotropic speciation genes--'magic traits'. This mechanism should operate not only in sympatric populations but also under allopatry or parapatry. Each individual has a small subset of the many MHC alleles present in the population. If all individuals could have all MHC alleles from the pool, MHC-based adaptation is neither necessary nor possible. However, the typically small optimal individual number of MHC loci thus enables MHC-based speciation. Furthermore, we propose a new mechanism selecting against species hybrids. Hybrids are expected to have super-optimal individual MHC diversity and should therefore suffer more from parasites in all habitats.
几十年来，物种形成以及最近分化出的物种的维持一直是进化生物学中深入研究的主题。尽管生态物种形成的概念已被接受，但其机制和遗传基础仍在研究之中。在此，我们提出一种物种形成机制，该机制由作用于免疫系统多态基因的寄生虫群落精心策划并强化。在脊椎动物中，这些基因在抵抗寄生虫和选择配偶方面具有多效性作用。在不同的生态位中，寄生虫群落不同，因此适应的主要组织相容性复合体（MHC）的等位基因库在不同生态位之间也有所不同。选择最适应的MHC基因型作为配偶将有利于局部适应，并加速两个种群的分离：因此免疫基因充当多效性物种形成基因——“神奇性状”。这种机制不仅应在同域种群中起作用，也应在异域或邻域情况下起作用。每个个体拥有种群中众多MHC等位基因的一小部分子集。如果所有个体都能拥有基因库中的所有MHC等位基因，基于MHC的适应既无必要也不可能。然而，通常MHC位点的最佳个体数量较少，这使得基于MHC的物种形成成为可能。此外，我们提出一种针对物种杂交体的新选择机制。杂交体预计具有超最佳个体MHC多样性，因此在所有栖息地中应更容易受到寄生虫的侵害。
