Data from: Do mites evolving in alternating host plants adapt to host switch?

A fluctuating environment may be perceived as a composition of different environments, or as an environment per se, in which it is the fluctuation itself that poses a selection pressure. If so, then organisms may adapt to this alternation. We tested this using experimental populations of spider mites that have been evolving for 45 generations in a homogeneous environment (pepper or tomato plants), or in a heterogeneous environment composed of an alternation of these two plants approximately at each generation. The performance (daily oviposition rate and juvenile survival) of individuals from these populations was tested in each of the homogeneous environments, and in two alternating environments, one every three days and the other between generations. To discriminate between potential genetic interactions between alleles conferring adaptation to each host plant and environmental effects of evolving in a fluctuating environment, we compared the performance of all lines with that of a cross between tomato and pepper lines. As a control, two lines within each selection regime were also crossed. We found that crosses between alternating lines and between pepper and tomato lines performed worse than crosses between lines evolving in homogeneous environments when tested in that environment. In contrast, alternating lines performed either better or similarly to lines evolving in homogeneous environments when tested in a fluctuating environment. Our results suggest that fluctuating environments are more than the juxtaposition of two environments. Hence, tests for adaptation of organisms evolving in such environments should be done in fluctuating conditions.

波动环境既可被视作不同环境的组合体，亦可被视为独立的环境实体——此时正是波动本身构成了选择压力。若该假设成立，则生物可适应这种环境交替过程。本研究以叶螨（spider mites）实验种群验证该假设：这些种群分别在同质环境（homogeneous environment，辣椒或番茄植株）中演化了45个世代，或在由两种植株交替构成的异质环境（heterogeneous environment）中演化，且大致每一世代更换一次寄主。我们在两种同质环境与两种交替环境中，测试了各实验种群个体的适合度表现：两种交替环境分别为每3天更换一次寄主，以及按世代交替寄主；测试指标包括日均产卵率（daily oviposition rate）与幼体存活率（juvenile survival）。为区分赋予不同寄主适应性的等位基因（allele）间潜在的遗传互作，与在波动环境中演化所产生的环境效应，我们将所有实验品系的适合度表现，与番茄品系和辣椒品系的杂交后代的表现进行了对比。作为对照，我们还对每种选择处理（selection regime）下的2个品系开展了杂交实验。研究发现，在同质环境中开展测试时，交替环境演化品系间的杂交后代，以及番茄与辣椒品系间的杂交后代，其适合度表现均劣于同质环境演化品系间的杂交后代。与之相反，在波动环境中开展测试时，交替环境演化品系的适合度表现要么优于同质环境演化品系，要么与其无显著差异。本研究结果表明，波动环境绝非两种环境的简单并置。因此，针对在这类环境中演化的生物的适应性测试，应在波动环境条件下开展。