Hybridization is not always limited to two species; often multiple species are interbreeding. In birds, there are numerous examples of species that hybridize with multiple other species. The advent of genomic data provides the opportunity to investigate the ecological and evolutionary consequences of multispecies hybridization. The interactions between several hybridizing species can be depicted as a network in which the interacting species are connected by edges. Such hybrid networks can be used to identify ‘hub-species’ that interbreed with multiple other species. Avian examples of such ‘hub-species’ are Common Pheasant (Phasianus colchicus), Mallard (Anas platyrhynchos) and European Herring Gull (Larus argentatus). These networks might lead to the formulation of hypotheses, such as which connections are most likely conducive to interspecific gene flow (i.e. introgression). Hybridization does not necessarily result in introgression. Numerous statistical tests are available to infer interspecific gene flow from genetic data and the majority of these tests can be applied in a multispecies setting. Specifically, model-based approaches and phylogenetic networks are promising in the detection and characterization of multispecies introgression. It remains to be determined how common multispecies introgression in birds is and how often this process fuels adaptive changes. Moreover, the impact of multispecies hybridization on the build-up of reproductive isolation and the architecture of genomic landscapes remains elusive. For example, introgression between certain species might contribute to increased divergence and reproductive isolation between those species and other related species. In the end, a multispecies perspective on hybridization in combination with network approaches will lead to important insights into the history of life on this planet.

中文翻译：

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鸟类中的多物种杂交

杂交并不总是局限于两个物种。通常有多种物种在杂交。在鸟类中，有许多与多种其他物种杂交的物种。基因组数据的出现为研究多物种杂交的生态和进化后果提供了机会。几个杂交物种之间的相互作用可以描述为一个网络，其中相互作用的物种通过边缘连接。这样的混合网络可用于识别与多个其他物种杂交的“轮毂物种”。这种“枢纽物种”的禽类例子有野鸡（Phasianus colchicus），野鸭（Anas platyrhynchos）和欧洲鲱鸥（Larus argentatus）。这些网络可能导致假设的表述，例如哪些连接最有可能有助于种间基因流动（即基因渗入）。杂交不一定导致基因渗入。有许多统计测试可用于根据遗传数据推断种间基因流，这些测试中的大多数可用于多物种环境。具体而言，基于模型的方法和系统发育网络在多物种渗入的检测和表征中很有前途。有待确定的是鸟类中常见的多种物种渗入以及该过程多长时间促进适应性变化。而且，多物种杂交对生殖隔离的建立和基因组景观结构的影响仍然难以捉摸。例如，某些物种之间的基因渗入可能会导致这些物种与其他相关物种之间的分歧和生殖隔离加剧。最后，结合网络方法对杂交的多物种观点将导致对这个星球上生命史的重要见解。