Data from: Maladaptive plasticity masks the effects of natural selection in the red-shouldered soapberry bug

Natural selection can produce local adaptation, but local adaptation can be masked by maladaptive plasticity. Maladaptive plasticity may arise as a result of gene flow producing novel gene combinations that have not been exposed to selection. In the 1980s, populations of the red-shouldered soapberry bug (Jadera haematoloma) were locally adapted to feed on the seeds of a native host plant and an introduced host plant; by 2014, local differentiation in beak length had been lost, likely as a consequence of increased gene flow. In this study, I assess the relative contributions of natural selection and plasticity to beak length on these two hosts. I confirm the earlier hypothesis that the host plant seedpod drives divergent natural selection on beak length. I then demonstrate that the proximate cause of the loss of observable differentiation in beak length is maladaptive plasticity, which masks persistent genetic differences between host-associated populations. Maladaptive plasticity is highest in areas where the two plants co-occur; in combination with historical measures of plasticity in hybrids, this indicates that maladaptive plasticity may be a consequence of ongoing gene flow. Although natural selection produced locally adapted genotypes in soapberry bugs, maladaptive plasticity is masking phenotypic differences between populations in nature.

自然选择可引发局部适应（local adaptation），但局部适应常会被适应不良的表型可塑性（maladaptive plasticity）所掩盖。适应不良的表型可塑性可能因基因流（gene flow）产生未经历过选择的全新基因组合而出现。20世纪80年代，红肩皂荚蝽（*Jadera haematoloma*）的种群已分别适应取食本土宿主植物（host plant）与外来宿主植物的种子；至2014年，其喙长（beak length）的种群间分化已消失，这一现象大概率由基因流增强所致。本研究评估了自然选择与表型可塑性对两种宿主上喙长的相对贡献，证实了此前提出的假说：宿主植物的种子荚驱动了喙长的分化性自然选择（divergent natural selection）。随后本研究证明，可观测到的喙长分化消失的直接原因是适应不良的表型可塑性——该现象掩盖了宿主关联种群间持续存在的遗传差异（genetic differences）。适应不良的表型可塑性在两种植物共生的区域最为显著；结合此前对杂交种群可塑性的测定结果，这表明适应不良的表型可塑性可能是持续基因流的产物。尽管自然选择使皂荚蝽形成了局部适应的基因型，但适应不良的表型可塑性掩盖了自然种群中不同种群间的表型差异（phenotypic differences）。