Section of Ecology, Department of Biology, University of Turku, Turku, Finland.
Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Alnarp, Sweden.
PLoS One. 2018 Jun 12;13(6):e0198869. doi: 10.1371/journal.pone.0198869. eCollection 2018.
Host specialization is considered a primary driver of the enormous diversity of herbivorous insects. Trade-offs in host use are hypothesized to promote this specialization, but they have mostly been studied in generalist herbivores. We conducted a multi-generation selection experiment to examine the adaptation of the specialist seed-feeding bug, Lygaeus equestris, to three novel host plants (Helianthus annuus, Verbascum thapsus and Centaurea phrygia) and to test whether trade-offs promote specialization. During the selection experiment, body size of L. equestris increased more on the novel host plant H. annuus compared to the primary host plant, Vincetoxicum hirundinaria, but this effect was not observed in other fitness related traits. In addition to selection, genetic drift caused variation among the experimental herbivore populations in their ability to exploit the host plants. Microsatellite data indicated that the level of within-population genetic variation decreased and population differentiation increased more in the selection line feeding on H. annuus compared to V. hirundinaria. We found a negative correlation between genetic differentiation and heterozygosity at the end of the experiment, suggesting that differentiation was significantly affected by genetic drift. We did not find fitness trade-offs between L. equestris feeding on the four hosts. Thus, trade-offs do not seem to promote specialization in L. equestris. Our results suggest that this insect herbivore is not likely to adapt to a novel host species in a time-scale of 20 generations despite sufficient genetic variation and that genetic drift disrupted the response to selection.
宿主专化被认为是食草昆虫巨大多样性的主要驱动因素。人们假设在宿主利用方面的权衡促进了这种专化，但这些权衡大多在一般性食草动物中进行了研究。我们进行了多代选择实验，以研究专门以种子为食的盲蝽 Lygaeus equestris 对三种新宿主植物（向日葵、婆婆纳和矢车菊）的适应能力，并测试权衡是否促进了专化。在选择实验中，与主要宿主植物 Vincetoxicum hirundinaria 相比，L. equestris 在新型宿主植物向日葵上的体型增大更多，但在其他与适应性相关的特征中没有观察到这种效果。除了选择之外，遗传漂变导致实验食草动物种群在利用宿主植物方面的能力存在差异。微卫星数据表明，与在 V. hirundinaria 上觅食的种群相比，在 H. annuus 上觅食的选择系中的种群内遗传变异水平降低，种群分化增加更多。我们在实验结束时发现遗传分化和杂合度之间存在负相关，这表明遗传漂变显著影响了分化。我们没有发现 L. equestris 在四种宿主上的适应性权衡。因此，权衡似乎并没有促进 L. equestris 的专化。我们的研究结果表明，尽管有足够的遗传变异，但这种昆虫食草动物不太可能在 20 代的时间内适应新的宿主物种，而且遗传漂变破坏了对选择的反应。
