LoPresti Eric F, Karban Richard
Ecology. 2016 Apr;97(4):826-33. doi: 10.1890/15-1696.1.
Sand entrapment on plant surfaces, termed psammophory or sand armor, is a phylogenetically and geographically widespread trait. The functional significance of this phenomenon has been poorly investigated. Sand and soil are nonnutritive and difficult for herbivores to process, as well as visually identical to the background. We experimentally investigated whether this sand coating physically protected the plant from herbivores or increased crypsis (e.g., decreased apparency to herbivores). We tested the former hypothesis by removing entrapped sand from stems, petioles, and leaves of the sand verbena Abronia latifolia and by supplementing natural sand levels in the honeyscented pincushion plant Navarretia mellita. Consistent with a physical defensive function, leaves with sand present or supplemented suffered less chewing herbivory than those with sand removed or left as is. To test a possible crypsis effect, we coated some sand verbena stems with green sand, matching the stem color, as well as others with brown sand to match the background color. Both suffered less chewing herbivory than controls with no sand and herbivory did not significantly differ between the colors, suggesting crypsis was not the driving resistance mechanism. Strong tests of plant apparency are rare; this experimental approach may be possible in other systems and represents one of few manipulative tests of this long-standing hypothesis.
植物表面的沙粒附着现象，即所谓的沙粒附着或沙甲，是一种在系统发育和地理分布上广泛存在的特征。这一现象的功能意义尚未得到充分研究。沙子和土壤没有营养，食草动物难以处理，而且在视觉上与背景相同。我们通过实验研究了这种沙质覆盖层是否能在物理上保护植物免受食草动物侵害，或者是否能增加植物的隐蔽性（例如，降低被食草动物发现的可能性）。我们通过去除宽叶砂马鞭草（Abronia latifolia）茎、叶柄和叶片上附着的沙子，以及增加蜜香针垫花（Navarretia mellita）的自然沙量，来检验前一个假设。与物理防御功能一致，有沙子附着或添加了沙子的叶片比去除了沙子或未处理的叶片遭受的咀嚼式食草动物侵害更少。为了测试可能的隐蔽效果，我们用与茎颜色匹配的绿色沙子以及与背景颜色匹配的棕色沙子覆盖了一些砂马鞭草的茎。两者遭受的咀嚼式食草动物侵害都比没有沙子的对照组少，而且两种颜色之间的食草动物侵害没有显著差异，这表明隐蔽性不是主要的抗性机制。对植物明显度的有力测试很少见；这种实验方法在其他系统中可能可行，并且是对这一长期假设的少数操纵性测试之一。
