Alzate A, Bisschop K, Etienne R S, Bonte D
Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, The Netherlands.
Terrestrial Ecology Unit, Ghent University, Ghent, Belgium.
J Evol Biol. 2017 Nov;30(11):1966-1977. doi: 10.1111/jeb.13123. Epub 2017 Jun 23.
Dispersal and competition have both been suggested to drive variation in adaptability to a new environment, either positively or negatively. A simultaneous experimental test of both mechanisms is however lacking. Here, we experimentally investigate how population dynamics and local adaptation to a new host plant in a model species, the two-spotted spider mite (Tetranychus urticae), are affected by dispersal from a stock population (no-adapted) and competition with an already adapted spider mite species (Tetranychus evansi). For the population dynamics, we find that competition generally reduces population size and increases the risk of population extinction. However, these negative effects are counteracted by dispersal. For local adaptation, the roles of competition and dispersal are reversed. Without competition, dispersal exerts a negative effect on adaptation (measured as fecundity) to a novel host and females receiving the highest number of immigrants performed similarly to the stock population females. By contrast, with competition, adding more immigrants did not result in a lower fecundity. Females from populations with competition receiving the highest number of immigrants had a significantly higher fecundity than females from populations without competition (same dispersal treatment) and than the stock population females. We suggest that by exerting a stronger selection on the adapting populations, competition can counteract the migration load effect of dispersal. Interestingly, adaptation to the new host does not significantly reduce performance on the ancestral host, regardless of dispersal rate or competition. Our results highlight that assessments of how species can adapt to changing conditions need to jointly consider connectivity and the community context.
扩散和竞争都被认为会对适应新环境的能力产生影响，这种影响可能是积极的，也可能是消极的。然而，目前缺乏对这两种机制的同步实验测试。在这里，我们通过实验研究了在一个模式物种——二斑叶螨（Tetranychus urticae）中，来自原种种群（未适应）的扩散以及与已经适应的叶螨物种（Tetranychus evansi）的竞争如何影响种群动态和对新宿主植物的局部适应。对于种群动态，我们发现竞争通常会减少种群规模并增加种群灭绝的风险。然而，这些负面影响会被扩散抵消。对于局部适应，竞争和扩散的作用则相反。在没有竞争的情况下，扩散对适应新宿主（以繁殖力衡量）产生负面影响，接收移民数量最多的雌性与原种种群的雌性表现相似。相比之下，在有竞争的情况下，增加更多移民并不会导致繁殖力降低。来自有竞争种群且接收移民数量最多的雌性比来自无竞争种群（相同扩散处理）的雌性以及原种种群的雌性具有显著更高的繁殖力。我们认为，通过对适应种群施加更强的选择，竞争可以抵消扩散的迁移负荷效应。有趣的是，无论扩散率或竞争情况如何，对新宿主的适应并不会显著降低在原始宿主上的表现。我们的结果强调，对物种如何适应变化条件的评估需要同时考虑连通性和群落背景。
