When divergent populations form hybrids, hybrid fitness can vary with genome composition, current environmental conditions, and the divergence history of the populations. We develop analytical predictions for hybrid fitness, which incorporate all three factors. The predictions are based on Fisher's geometric model, and apply to a wide range of population genetic parameter regimes and divergence conditions, including allopatry and parapatry, local adaptation, and drift. Results show that hybrid fitness can be decomposed into intrinsic effects of admixture and heterozygosity, and extrinsic effects of the (local) adaptedness of the parental lines. Effect sizes are determined by a handful of geometric distances, which have a simple biological interpretation. These distances also reflect the mode and amount of divergence, such that there is convergence toward a characteristic pattern of intrinsic isolation. We next connect our results to the quantitative genetics of line crosses in variable or patchy environments. This means that the geometrical distances can be estimated from cross data, and provides a simple interpretation of the “composite effects.” Finally, we develop extensions to the model, involving selectively induced disequilibria, and variable phenotypic dominance. The geometry of fitness landscapes provides a unifying framework for understanding speciation, and wider patterns of hybrid fitness.

中文翻译：

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杂交的几何学和遗传学


当不同的种群形成杂交体时，杂交适应度可能会随着基因组组成、当前环境条件和种群的分化历史而变化。我们开发了混合健身的分析预测，其中包含了所有三个因素。这些预测基于费舍尔的几何模型，适用于广泛的种群遗传参数体系和分歧条件，包括异域和共域、局部适应和漂移。结果表明，杂种适应度可以分解为混合和杂合性的内在效应，以及亲本系（局部）适应性的外在效应。效应大小由几个几何距离决定，这些几何距离具有简单的生物学解释。这些距离还反映了发散的模式和数量，从而趋向于内在隔离的特征模式。接下来，我们将我们的结果与可变或不完整环境中系杂交的定量遗传学联系起来。这意味着可以根据交叉数据估计几何距离，并提供对“复合效应”的简单解释。最后，我们开发了模型的扩展，涉及选择性诱导的不平衡和可变表型优势。适应度景观的几何形状为理解物种形成和更广泛的混合适应度模式提供了一个统一的框架。