Humphrey P T, Gloss A D, Frazier J, Nelson-Dittrich A C, Faries S, Whiteman N K
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA.
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.
Oecologia. 2018 Jun;187(2):427-445. doi: 10.1007/s00442-018-4116-4. Epub 2018 Mar 30.
Organismal phenotypes often co-vary with environmental variables across broad geographic ranges. Less is known about the extent to which phenotypes match local conditions when multiple biotic and abiotic stressors vary at fine spatial scales. Bittercress (Brassicaceae: Cardamine cordifolia), a perennial forb, grows across a microgeographic mosaic of two contrasting herbivory regimes: high herbivory in meadows (sun habitats) and low herbivory in deeply shaded forest understories (shade habitats). We tested for local phenotypic differentiation in plant size, leaf morphology, and anti-herbivore defense (realized resistance and defensive chemicals, i.e., glucosinolates) across this habitat mosaic through reciprocal transplant-common garden experiments with clonally propagated rhizomes. We found habitat-specific divergence in morphological and defensive phenotypes that manifested as contrasting responses to growth in shade common gardens: weak petiole elongation and attenuated defenses in populations from shade habitats, and strong petiole elongation and elevated defenses in populations from sun habitats. These divergent phenotypes are generally consistent with reciprocal local adaptation: plants from shade habitats that naturally experience low herbivory show reduced investment in defense and an attenuated shade avoidance response, owing to its ineffectiveness within forest understories. By contrast, plants from sun habitats with high herbivory show shade-induced elongation, but no evidence of attenuated defenses canonically associated with elongation in shade-intolerant plant species. Finally, we observed differences in flowering phenology between habitat types that could potentially contribute to inter-habitat divergence by reducing gene flow. This study illuminates how clonally heritable plant phenotypes track a fine-grained mosaic of herbivore pressure and light availability in a native plant.
在广阔的地理范围内，生物体表型通常会随环境变量共同变化。当多种生物和非生物胁迫因子在精细空间尺度上变化时，表型与当地环境条件的匹配程度则鲜为人知。碎米荠（十字花科：心叶碎米荠）是一种多年生草本植物，生长在两种截然不同的食草动物活动模式的微观地理镶嵌区域：草地（阳光充足的栖息地）食草动物活动频繁，而在深度遮荫的森林下层（荫蔽栖息地）食草动物活动较少。我们通过对克隆繁殖的根状茎进行相互移栽-共同园实验，测试了在这个栖息地镶嵌区域内，植物大小、叶片形态和抗食草动物防御（实际抗性和防御性化学物质，即芥子油苷）方面的局域表型分化。我们发现形态和防御表型存在栖息地特异性差异，表现为对荫蔽共同园生长的不同反应：来自荫蔽栖息地的种群叶柄伸长较弱且防御减弱，而来自阳光充足栖息地的种群叶柄伸长较强且防御增强。这些不同的表型通常与相互的局部适应一致：来自荫蔽栖息地的植物自然经历低食草动物压力，由于在森林下层这种反应无效，所以对防御的投资减少且荫蔽回避反应减弱。相比之下，来自食草动物活动频繁的阳光充足栖息地的植物表现出荫蔽诱导的伸长，但没有证据表明不耐荫植物物种中与伸长相关的防御减弱。最后，我们观察到栖息地类型之间开花物候的差异，这可能通过减少基因流动对栖息地间的分化产生潜在影响。这项研究阐明了克隆遗传的植物表型如何追踪本地植物中食草动物压力和光照可用性的精细镶嵌区域。
