Department of Ecology and Evolutionary Biology, UC Irvine, Irvine, CA 92612, USA.
Evolution. 2012 Apr;66(4):1091-113. doi: 10.1111/j.1558-5646.2011.01500.x. Epub 2011 Nov 27.
We model direct fitness benefits of genetic mosaicism for a long-lived tree in coevolution with a short-lived herbivore to test four hypotheses: that mosaicism reduces selection on the herbivore for resistance to plant defenses; that module-level selection allows the individual tree to adapt to its herbivore; and that this benefits the tree population, increasing average tree fitness and reducing local adaptation of the herbivore. We show that: mosaicism does not sufficiently reduce selection for resistance in the herbivore to benefit the tree; that individual trees do benefit from module-level selection when somatic mutation introduces new defenses; and that mosaicism does reduce local adaptation in the herbivore, which increases average tree fitness. These results are robust to varying genetic assumptions of dominance and the somatic mutation rate, but only hold for sufficiently long-lived trees with relatively strong selection. We also show that a mixed reproductive strategy of primarily asexual reproduction interspersed with occasional sexual reproduction is effective in coevolving with the herbivore, as it maintains beneficial allele combinations. Finally, we argue that intraorganismal genetic heterogeneity need not threaten the integrity of the individual and may be adaptive when selection acts concordantly between levels.
我们构建了一个数学模型，以研究一个与短期生活史的草食性昆虫协同进化的长寿树种的遗传镶嵌体的直接适合度优势，以检验四个假说：即镶嵌性降低了草食性昆虫对植物防御的抗性选择；模块水平选择使个体树木适应其草食性昆虫；并且这有利于树木种群，提高平均树木的适合度并降低草食性昆虫的局部适应。结果表明：镶嵌性并没有充分降低草食性昆虫的抗性选择，从而使树木受益；当体细胞突变引入新的防御机制时，个体树木确实可以从模块水平选择中受益；并且镶嵌性确实降低了草食性昆虫的局部适应，从而提高了平均树木的适合度。这些结果对于显性和体细胞突变率的不同遗传假设具有稳健性，但仅适用于具有相对较强选择的足够长寿的树木。我们还表明，在与草食性昆虫协同进化中，主要通过无性繁殖与偶尔的有性繁殖相结合的混合繁殖策略是有效的，因为它可以维持有益的等位基因组合。最后，我们认为，当水平之间的选择一致时，个体内部的遗传异质性不一定会威胁到个体的完整性，并且可能是适应性的。
