Ding Jianqing, Blossey Bernd
Department of Natural Resources, Cornell University, Ithaca, NY 14850, USA.
Environ Entomol. 2009 Dec;38(6):1653-60. doi: 10.1603/022.038.0618.
Plant invasions represent ecological opportunities for herbivorous insects able to exploit novel host plants. The availability of new hosts and rapid adaptations may lead to host race formation and ultimately speciation. We studied potential host race formation in the water lily leaf beetle, Galerucella nymphaeae, in response to invasion by water chestnut, Trapa natans, in eastern North America. This leaf beetle is well suited for such studies because previous work showed that different herbivore populations follow different "evolutionary pathways" and specialize locally in response to differences in habitat preferences and host plant availability. We compared host preference and performance of G. nymphaeae offspring originating from T. natans and offspring of individuals originating from an ancestral host Nuphar lutea, yellow water lily, on T. natans and three native hosts (N. lutea, Nympheae odorata, and Brasenia schreberi). Regardless of origin (Trapa or Nuphar), adults strongly preferred their native host, N. lutea, over T. natans. Although laboratory survival rates (larva to pupa) were extremely high (80%) regardless of origin or host offered, survival rates in a common garden were greatly reduced, particularly for T. natans (24%) and to a lesser extent on N. lutea (54%), regardless of beetle origin. Larval drowning during more frequent leaf changes when developing on small Trapa leaves seems to be responsible for this difference. Preference of females for N. lutea is beneficial considering the much higher larval survival on the ancestral host. Abundant T. natans where the plant is invasive provides an alternative food source that beetles can use after egg/larval loads on their preferred host reach carrying capacity, but this utilization comes at a cost of high larval mortality.
植物入侵为能够利用新宿主植物的食草昆虫带来了生态机遇。新宿主的出现以及快速适应可能导致宿主种族的形成，并最终引发物种形成。我们研究了北美东部菱角（Trapa natans）入侵后，睡莲叶甲（Galerucella nymphaeae）潜在的宿主种族形成情况。这种叶甲非常适合此类研究，因为先前的研究表明，不同的食草动物种群遵循不同的“进化路径”，并根据栖息地偏好和宿主植物可利用性的差异在当地实现特化。我们比较了源自菱角的睡莲叶甲后代以及源自祖先宿主黄水莲（Nuphar lutea）的个体后代，在菱角和三种本地宿主（黄水莲、香睡莲和芡实）上的宿主偏好和表现。无论来源如何（菱角或黄水莲），成虫都强烈偏好其本地宿主黄水莲，而非菱角。尽管无论来源或提供的宿主如何，实验室中的存活率（幼虫到蛹）都极高（80%），但在共同花园中的存活率却大幅降低，尤其是在菱角上（24%），在黄水莲上的存活率降低程度较小（54%），且与甲虫来源无关。在小菱角叶上发育时，由于叶片更换更频繁导致幼虫溺水，这似乎是造成这种差异的原因。考虑到在祖先宿主上幼虫存活率要高得多，雌性对黄水莲的偏好是有益的。在菱角入侵的地方，大量的菱角提供了一种替代食物来源，当甲虫在其偏好宿主上的卵/幼虫数量达到承载能力后，它们可以利用这种食物来源，但这种利用是以幼虫高死亡率为代价的。
