Department of Mathematics and Statistics, University of Turku, FI-20014 Turku, Finland;
Evolution and Ecology Program, International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria.
Proc Natl Acad Sci U S A. 2020 Mar 31;117(13):7290-7295. doi: 10.1073/pnas.1915881117. Epub 2020 Mar 18.
Dispersal is one of the fundamental life-history strategies of organisms, so understanding the selective forces shaping the dispersal traits is important. In the Wright's island model, dispersal evolves due to kin competition even when dispersal is costly, and it has traditionally been assumed that the living conditions are the same everywhere. To study the effect of spatial heterogeneity, we extend the model so that patches may receive different amounts of immigrants, foster different numbers of individuals, and give different reproduction efficiency to individuals therein. We obtain an analytical expression for the fitness gradient, which shows that directional selection consists of three components: As in the homogeneous case, the direct cost of dispersal selects against dispersal and kin competition promotes dispersal. The additional component, spatial heterogeneity, more precisely the variance of so-called relative reproductive potential, tends to select against dispersal. We also obtain an expression for the second derivative of fitness, which can be used to determine whether there is disruptive selection: Unlike the homogeneous case, we found that divergence of traits through evolutionary branching is possible in the heterogeneous case. Our numerical explorations suggest that evolutionary branching is promoted more by differences in patch size than by reproduction efficiency. Our results show the importance of the existing spatial heterogeneity in the real world as a key determinant in dispersal evolution.
扩散是生物基本生活史策略之一，因此理解塑造扩散特征的选择压力非常重要。在 Wright 的岛屿模型中，即使扩散是有代价的，扩散也会由于亲缘竞争而进化，并且传统上假设所有地方的生活条件都是相同的。为了研究空间异质性的影响，我们扩展了该模型，使得斑块可能接收不同数量的移民，养育不同数量的个体，并为其中的个体提供不同的繁殖效率。我们得到了适合度梯度的解析表达式，该表达式表明，定向选择由三个组成部分组成：与均匀情况下一样，扩散的直接代价选择不利于扩散，而亲缘竞争则促进扩散。额外的组成部分，即空间异质性，更准确地说是所谓的相对繁殖潜力的方差，往往不利于扩散。我们还得到了适合度二阶导数的表达式，可用于确定是否存在破坏性选择：与均匀情况不同，我们发现，在异质情况下，通过进化分支的特征分歧是可能的。我们的数值探索表明，斑块大小的差异比繁殖效率更能促进进化分支。我们的研究结果表明，在现实世界中，现有的空间异质性作为扩散进化的关键决定因素具有重要意义。
