Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, NY 14853-2701, USA.
Ecol Lett. 2011 May;14(5):476-83. doi: 10.1111/j.1461-0248.2011.01609.x. Epub 2011 Mar 3.
Attempts over the past 50 years to explain variation in the abundance, distribution and diversity of plant secondary compounds gave rise to theories of plant defense. Remarkably, few phylogenetically robust tests of these long-standing theories have been conducted. Using >50 species of milkweed (Asclepias spp.), we show that variation among plant species in the induction of toxic cardenolides is explained by latitude, with higher inducibility evolving more frequently at lower latitudes. We also found that: (1) the production of cardenolides showed positive-correlated evolution with the diversity of cardenolides, (2) greater cardenolide investment by a species is accompanied by an increase in an estimate of toxicity (measured as chemical polarity) and (3) instead of trading off, constitutive and induced cardenolides were positively correlated. Analyses of root and shoot cardenolides showed concordant patterns. Thus, milkweed species from lower latitudes are better defended with higher inducibility, greater diversity and added toxicity of cardenolides.
过去 50 年来，人们试图解释植物次生化合物的丰度、分布和多样性的变化，这促成了植物防御理论的发展。值得注意的是，这些长期存在的理论很少经过系统发育稳健的检验。利用超过 50 种马利筋属植物（Asclepias spp.），我们表明，植物物种之间诱导毒性的强心苷的变化可以用纬度来解释，在较低的纬度，更高的诱导能力进化得更为频繁。我们还发现：（1）强心苷的产生与强心苷的多样性呈正相关进化；（2）一个物种对强心苷的投资越大，其毒性（以化学极性衡量）就越高；（3）组成型和诱导型强心苷呈正相关，而不是相互排斥。根和茎强心苷的分析显示出一致的模式。因此，来自较低纬度的马利筋属植物具有更高的诱导能力、更强的多样性和更高的毒性，防御能力也更强。
