School of Environmental and Forest Sciences, University of Washington, Box 354115, Seattle, Washington, 98195, USA.
Ecology and Evolutionary Biology and Museum of Natural History, University of Colorado at Boulder, UCB 334, Boulder, Colorado, 80309, USA.
Ecology. 2018 Feb;99(2):399-410. doi: 10.1002/ecy.2087. Epub 2017 Dec 27.
Parasitic plants can serve as critical intermediaries between their hosts and other organisms; however these relationships are not well understood. To investigate the relative importance of plant traits in such interactions, we studied the role of the root hemiparasite, Castilleja levisecta (Orobanchaceae), as a mediator of interactions between the host plants it parasitizes and the lepidopteran herbivore Euphydryas editha (Nymphalidae), whose caterpillars feed on Castilleja and sequester iridoid glycosides from it. We tested whether the hemiparasite's size, leaf N concentration, and iridoid glycoside concentrations were influenced by the identity of its host plant, and then whether these traits influenced outcomes for the herbivore. We found that the hemiparasite's size and leaf N depended on the host it parasitized, and these traits in turn affected outcomes for E. editha. Specifically, Euphydryas editha survival increased with hemiparasite size and caterpillar mass increased with leaf N; caterpillars with greater mass were more likely to survive during diapause. We also found preliminary evidence that host identity influenced iridoid glycoside sequestration by the herbivore. Mean iridoid glycoside concentrations in caterpillars ranged from 1-12% depending on the host being parasitized by Castilleja. This study demonstrates that root parasitism can result in strong indirect effects on higher trophic levels, influencing organisms' survival, growth, and chemical interactions.
寄生植物可以作为其宿主和其他生物之间的关键中介；然而，这些关系还没有得到很好的理解。为了研究植物特征在这些相互作用中的相对重要性，我们研究了根半寄生植物 Castilleja levisecta（玄参科）在寄生植物与其所寄生的鳞翅目食草动物 Euphydryas editha（蛱蝶科）之间的相互作用中所起的作用，其幼虫以 Castilleja 为食，并从中摄取环烯醚萜糖苷。我们测试了半寄生植物的大小、叶片氮浓度和环烯醚萜糖苷浓度是否受其宿主植物的影响，然后这些特征是否影响食草动物的结果。我们发现，半寄生植物的大小和叶片氮取决于它所寄生的宿主，而这些特征又反过来影响了 E. editha 的结果。具体来说，Euphydryas editha 的存活率随着半寄生植物的大小而增加，而毛毛虫的质量随着叶片氮的增加而增加；质量较大的毛毛虫在滞育期间更有可能存活。我们还发现了初步证据表明，宿主身份影响了食草动物对环烯醚萜糖苷的摄取。取决于 Castilleja 所寄生的宿主，毛毛虫中环烯醚萜糖苷的浓度范围从 1-12%不等。这项研究表明，根寄生可以对更高营养级别的生物产生强烈的间接影响，影响生物体的存活、生长和化学相互作用。
