Housman David C, Price Mary V, Redak Richard A
Department of Biology, University of California, Riverside, California 92521 USA;
Am J Bot. 2002 Aug;89(8):1303-10. doi: 10.3732/ajb.89.8.1303.
The shrub Encelia farinosa (Asteraceae) exhibits geographic variation in aboveground architecture and leaf traits in parallel with environmental variation in temperature and moisture. Measurements of plants occurring across a natural gradient demonstrated that plants in desert populations produce smaller, more pubescent leaves and are more compact and branched than plants in more mesic coastal environments. This phenotypic variation is interpreted in part as adaptive genetic differentiation; small size and pubescence reduce leaf temperature and thus increase water-use efficiency but at the cost of lower photosynthetic rate, which results in slower growth and more compact growth form. We explored the basis of phenotypic variation by planting seed offspring from coastal and desert populations in common gardens in both environments. Phenotypic differences among populations persisted in both common gardens, suggesting a genetic basis for trait variation. Desert offspring outperformed coastal offspring in the desert garden, suggesting superior adaptation to hot, dry conditions. Herbivore damage was greater for all offspring in the coastal garden. Phenotypic characters also showed plastic responses; all offspring had smaller, more pubescent leaves and more compact growth form in the desert garden. Our results confirm that leaf size and pubescence are heritable characters associated with pronounced variation in plant architecture.
灌木粉苞菊（菊科）地上部分的结构和叶片性状呈现出地理变异，这与温度和湿度的环境变异是平行的。对沿自然梯度分布的植株进行测量表明，与生长在湿度较高的沿海环境中的植株相比，沙漠种群中的植株叶片更小、毛被更密，且植株更为紧凑、分枝更多。这种表型变异部分被解释为适应性遗传分化；叶片较小和具毛被可降低叶片温度，从而提高水分利用效率，但代价是光合速率较低，这导致生长较慢且生长形态更为紧凑。我们通过在两种环境的共同园地里种植来自沿海和沙漠种群的种子后代，探究了表型变异的基础。在两个共同园地里，种群间的表型差异都持续存在，这表明性状变异具有遗传基础。在沙漠园地里，沙漠后代的表现优于沿海后代，这表明其对炎热干燥条件具有更强的适应性。在沿海园地里，所有后代遭受的食草动物损害都更大。表型特征也表现出可塑性反应；在沙漠园地里，所有后代的叶片都更小、毛被更密，且生长形态更为紧凑。我们的结果证实，叶片大小和毛被是与植株结构显著变异相关的可遗传性状。
