Data from: Antiherbivore defenses alter natural selection on plant reproductive traits

While many studies demonstrate that herbivores alter selection on plant reproductive traits, little is known about whether antiherbivore defenses affect selection on these traits. We hypothesized that antiherbivore defenses could alter selection on reproductive traits by altering trait expression through allocation trade-offs, or by altering interactions with mutualists and/or antagonists. To test our hypothesis, we used white clover, Trifolium repens, which has a Mendelian polymorphism for the production of hydrogen cyanide—a potent antiherbivore defense. We conducted a common garden experiment with 185 clonal families of T. repens that included cyanogenic and acyanogenic genotypes. We quantified resistance to herbivores, and selection on 6 floral traits and phenology via male and female fitness. Cyanogenesis reduced herbivory but did not alter the expression of reproductive traits through allocation trade-offs. However, the presence of cyanogenic defenses altered natural selection on petal morphology and the number of flowers within inflorescences via female fitness. Herbivory influenced selection on flowers and phenology via female fitness independently of cyanogenesis. Our results demonstrate that both herbivory and antiherbivore defenses alter natural selection on plant reproductive traits. We discuss the significance of these results for understanding how antiherbivore defenses interact with herbivores and pollinators to shape floral evolution.

尽管诸多研究已证实植食动物会对植物繁殖性状施加自然选择，但目前学界对抗植食防御（antiherbivore defenses）是否会对这类性状施加选择仍不甚明晰。我们提出假说：抗植食防御可通过资源分配权衡改变性状表达，或通过调控与互利生物及/或拮抗生物的互作关系，来改变繁殖性状所受的自然选择压力。为验证该假说，我们选取了存在孟德尔多态性（Mendelian polymorphism）、可产氢氰酸（hydrogen cyanide，一种强效抗植食防御物质）的白三叶（Trifolium repens）作为实验材料。我们开展了同质园实验（common garden experiment），共纳入185个白三叶无性系家系，涵盖产氰型与非产氰型两种基因型。我们量化了植株的植食抗性，并通过雄性适合度与雌性适合度，对6个花部性状及物候进行了选择分析。结果显示，产氰作用降低了植株受植食的程度，但并未通过资源分配权衡改变繁殖性状的表达。然而，产氰型防御的存在会通过雌性适合度，改变花瓣形态与花序内花数所受的自然选择。植食作用会独立于产氰作用，通过雌性适合度影响花部性状及物候所受的自然选择。本研究结果表明，植食作用与抗植食防御均会改变植物繁殖性状所受的自然选择。我们还讨论了本研究结果对于理解抗植食防御如何与植食动物、传粉者互作，进而塑造花部演化的重要意义。