In tropical forests, insect herbivores exert significant pressure on plant populations. Adaptation to such pressure is hypothesized to be a driver of high tropical diversity, but direct evidence for local adaptation to herbivory in tropical forests is sparse. At the same time, herbivore pressure has been hypothesized to increase with rainfall in the tropics, which could lead to differences among sites in the degree of local adaptation. To assess the presence of local adaptation and its interaction with rainfall, we compared herbivore damage on seedlings of local vs non-local populations at sites differing in moisture availability in a reciprocal transplant experiment spanning a rainfall gradient in Panama. For 13 native tree species, seeds collected from multiple populations along the rainfall gradient were germinated in a shadehouse and then transplanted to experimental sites within the species range. We tracked the proportion of seedlings attacked over 1.5 years and quantified the percentage of leaf area damaged at the end of the study. Seedlings originating from local populations were less likely to be attacked and experienced lower amounts of herbivore damage than those from non-local populations, but only on the wetter end of the rainfall gradient. However, overall herbivore damage was higher at the drier site compared to wetter sites, contrary to expectation. Taken together, these findings support the idea that herbivory can result in local adaptation within tropical tree species; however, the likelihood of local adaptation varies among sites due to environmentally-driven differences in investment in defense or herbivore specialization or both.

中文翻译：

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沿降雨梯度对热带树种内食草的局部适应

在热带森林中，昆虫食草动物对植物种群施加巨大压力。对这种压力的适应被假设是高度热带多样性的驱动因素，但当地适应热带森林食草动物的直接证据很少。同时，假设热带地区的降雨量会增加食草动物的压力，这可能导致不同地点的当地适应程度存在差异。为了评估局部适应的存在及其与降雨的相互作用，我们在巴拿马降雨梯度的互惠移植实验中，比较了草食动物对当地和非当地种群在水分可用性不同的地点的幼苗的损害。对于 13 种本地树种，沿着降雨梯度从多个种群中收集的种子在阴凉处发芽，然后移植到物种范围内的实验地点。我们跟踪了 1.5 年间受到攻击的幼苗的比例，并量化了研究结束时受损叶面积的百分比。与来自非本地种群的幼苗相比，来自本地种群的幼苗受到攻击的可能性更小，遭受的食草动物伤害也更低，但仅限于降雨梯度的较湿端。然而，与预期相反，与较湿润的地点相比，较干燥地点的总体食草动物损害更高。综上所述，这些发现支持食草可以导致热带树种内的局部适应的观点；然而，