Data from: Differential adaptation to a harsh granite outcrop habitat between sympatric Mimulus species

Understanding which environmental variables and traits underlie adaptation to harsh environments is difficult since many traits evolve simultaneously as populations or species diverge. Here we investigate the ecological variables and traits that underlie Mimulus laciniatus’ adaptation to granite outcrops compared to its sympatric, mesic-adapted progenitor M. guttatus. We use fine scale measurements of soil moisture and herbivory to examine differences in selective forces between the species’ habitats, and measure selection on flowering time, flower size, plant height, and leaf shape in a reciprocal transplant using M. laciniatus x M. guttatus F4 hybrids. We find that differences in drought & herbivory drive survival differences between habitats, that M. laciniatus and M. guttatus are each better adapted to their native habitat, and differential habitat selection on flowering time, plant stature, and leaf shape. While early flowering time, small stature, and lobed leaf shape underlie plant fitness in M. laciniatus’ seasonally dry environment, increased plant size is advantageous in a competitive mesic environment replete with herbivores like M. guttatus’. Given that we observed divergent selection between habitats in the direction of species differences, we conclude that adaptation to different microhabitats is an important component of reproductive isolation in this sympatric species pair.

明确哪些环境变量与性状构成极端环境适应的基础颇具挑战，因为种群或物种分化过程中诸多性状会同步演化。本研究以同域分布、适生于湿润生境的祖先种斑点沟酸浆（M. guttatus）为对照，探讨裂叶沟酸浆（Mimulus laciniatus）适应花岗岩露头生境背后的生态变量与性状机制。我们通过土壤湿度与植食作用的精细尺度测量，分析两个物种种群间生境选择压力的差异，并利用裂叶沟酸浆与斑点沟酸浆的F4代杂交群体开展互作移植实验，检测开花时间、花大小、株高以及叶形所受的选择作用。研究发现，干旱与植食作用的差异驱动了两个物种种群间的存活率分化；裂叶沟酸浆与斑点沟酸浆各自更适应其原生生境；且两个生境对开花时间、株高以及叶形的选择作用存在分化。在裂叶沟酸浆所处的季节性干旱生境中，早开花、矮株高与具裂片叶形是提升植株适合度的核心性状；而在斑点沟酸浆所处的充满植食者且竞争激烈的湿润生境中，更大的植株尺寸则具有适应性优势。鉴于本研究观测到两个生境间的分化选择方向与物种间的性状差异相契合，我们认为，对不同微生境的适应是该同域物种对生殖隔离的重要组成部分。