Data_Sheet_1_Higher Elevations Tend to Have Higher Proportion of Plant Species With Glandular Trichomes.docx

Glandular trichomes are well known to participate in plant chemical and physical defenses against herbivores, especially herbivorous insects. However, little is known about large-scale geographical patterns in glandular trichome occurrence. Herbivory pressure is thought to be higher at low elevations because of warmer and more stable climates. We therefore predicted a higher proportion of species with glandular trichomes at low elevations than at higher elevations. We compiled glandular trichome data (presence/absence) for 6,262 angiosperm species from the Hengduan Mountains (a global biodiversity hotspot in southwest China). We tested the elevational gradient (800–5,000 m a.s.l.) in the occurrence of plant species with glandular trichomes, and its correlations with biotic (occurrence of herbivorous insects) and abiotic factors, potentially shaping the elevational gradient in the occurrence of glandular trichomes. We found a significantly positive relationship between elevation and the occurrence of glandular trichomes, with the proportion of species having glandular trichomes increasing from 11.89% at 800 m a.s.l. to 17.92% at above 4,700 m. This cross-species relationship remained significant after accounting for phylogenetic relationships between species. Herbivorous insect richness peaked at mid-elevations and its association with the incidence of glandular trichomes was weak. Mean annual temperature was the most important factor associated negatively with glandular trichomes. Our results do not support the hypothesis that plant defenses decrease with increasing elevation. In contrast, a higher proportion of plant species with glandular trichome toward higher elevations is observed. Our results also highlight the importance of considering the simultaneous influences of biotic and abiotic factors in testing geographical variation in multifunctional plant defenses.

腺毛（glandular trichome）众所周知可参与植物的化学与物理防御，抵御植食性生物，尤其是植食性昆虫。然而，学界对腺毛发生的大规模地理格局仍知之甚少。由于低海拔地区气候更温暖且更稳定，植食压力被认为在低海拔处更高。因此我们预测，低海拔地区拥有腺毛的物种比例应高于高海拔地区。我们从中国西南的全球生物多样性热点区域——横断山区收集了6262种被子植物的腺毛数据（存在/缺失）。我们检验了腺毛植物物种在海拔梯度（800~5000米，相对于海平面）上的分布格局，及其与可能调控腺毛海拔分布格局的生物因子（植食性昆虫分布）和非生物因子的相关性。我们发现海拔与腺毛发生呈显著正相关：拥有腺毛的物种比例从海拔800米处的11.89%升至4700米以上的17.92%。在校正物种间系统发育关系后，这一跨物种关联仍显著。植食性昆虫丰富度在中海拔达到峰值，其与腺毛发生率的关联较弱。年平均温度是与腺毛发生呈显著负相关的最关键因子。我们的结果不支持“植物防御随海拔升高而降低”的假说。相反，我们观测到高海拔地区拥有腺毛的植物物种比例更高。本研究同时强调，在检验多功能植物防御的地理变异时，需同时考虑生物与非生物因子的共同影响。