Hoan Ryan P, Ormond Rhys A, Barton Kasey E
Department of Botany, University of Hawai'i at Mānoa, Honolulu, Hawai'i, United States of America.
Biology Department, Willamette University, Salem, Oregon, United States of America.
PLoS One. 2014 May 6;9(5):e96796. doi: 10.1371/journal.pone.0096796. eCollection 2014.
Plant ontogeny is a common source of variation in defense and herbivory. Yet, few studies have investigated how the induction of physical defense traits changes across plant ontogeny. Physical defense traits are costly to produce, and thus, it was predicted that induction as a cost-saving strategy would be particularly favorable for seedlings, leading to ontogenetic declines in the inducibility of these traits. We tested for induction of three different physical defense traits (prickles, latex and leaf toughness) in response to mechanical defoliation and jasmonic acid application using prickly poppies (Argemone glauca and A. mexicana, Papaveraceae) as a model system. Genetic variation in the induction of physical defenses was tested using maternal sib-ships sampled from multiple populations. Both species induced higher densities of laminar prickles, although the magnitude of induction was much higher in the endemic Hawaiian prickly poppy, A. glauca, than in the cosmopolitan A. mexicana. The magnitude of prickle induction was also higher in young compared to older juvenile plant stages in A. glauca, demonstrating a strong role of ontogeny. Neither latex exudation nor leaf toughness was induced in either species. Although significant genetic variation was detected within and among populations for constitutive expression of physical defense traits in Argemone, there was no evidence for genetic variation in the induction of these traits. This study provides the first evidence for the induction of physical defenses in prickly poppies, emphasizing how an ontogenetically explicit framework can reveal new insights into plant defense. Moreover, this study illustrates how sister species comparisons between island vs. continental plants can provide new insights into plant functional and evolutionary ecology, highlighting a fruitful area for future research on more species pairs.
植物个体发育是防御和食草作用变异的常见来源。然而，很少有研究调查物理防御性状的诱导如何随植物个体发育而变化。产生物理防御性状成本高昂，因此，有人预测，作为一种节省成本的策略，诱导对幼苗特别有利，导致这些性状的诱导性在个体发育过程中下降。我们以多刺罂粟（Argemone glauca和A. mexicana，罂粟科）为模型系统，测试了三种不同物理防御性状（刺、乳汁和叶片韧性）对机械去叶和茉莉酸处理的诱导反应。利用从多个种群中采样的母系同胞关系，测试了物理防御诱导的遗传变异。两个物种都诱导出更高密度的叶片刺，尽管在夏威夷特有多刺罂粟A. glauca中诱导的幅度比在世界性的A. mexicana中高得多。在A. glauca中，与较老的幼年植物阶段相比，刺的诱导幅度在较年轻阶段也更高，这表明个体发育起了重要作用。在这两个物种中，乳汁分泌和叶片韧性均未被诱导。虽然在种群内部和种群之间检测到了多刺罂粟物理防御性状组成型表达的显著遗传变异，但没有证据表明这些性状的诱导存在遗传变异。本研究首次提供了多刺罂粟物理防御诱导的证据，强调了一个个体发育明确的框架如何能够揭示植物防御的新见解。此外，本研究说明了岛屿植物与大陆植物之间的姊妹种比较如何能够为植物功能和进化生态学提供新见解，突出了未来对更多物种对进行研究的一个富有成果的领域。
