Data from: Lack of evolution in a leaf beetle that lives on two contrasting host plants

The interactions between plant-eating insects and their hosts have shaped both the insects and the plants, driving evolution of plant defenses and insect specialization. The leaf beetle Trirhabda eriodictyonis (Chrysomelidae) lives on two shrubs with differing defenses: Eriodictyon crassifolium has hairy leaves, whereas E. trichocalyx has resinous leaves. We tested whether these beetles have differentiated onto the two host plants, and if not, whether the beetles prefer the better host plant and prefer mates who are from that host plant. In feeding tests, adult beetles strongly preferred eating E. trichocalyx regardless of which host they came from. In addition, females laid more eggs if they ate E. trichocalyx than E. crassifolium. So, E. trichocalyx is generally the better host. However, beetle mate preference was not in line with food choice. Males did not prefer to mate with females from E. trichocalyx. Females from E. crassifolium did prefer males from E. trichocalyx over males from E. crassifolium, but did not lay more eggs as a result of these matings. We conclude that the beetle populations we studied have not differentiated based on their host plants and may not have even adapted to the better host. Although to humans these host plant defenses differ dramatically, signs that they have caused evolution in the beetles are lacking. The case of T. eriodictyonis stands counter to many other studies that have seen the differentiation of ecotypes and/or adaptive coordination of an herbivore's life cycle based on host plant differences.植食性昆虫（plant-eating insects）与其宿主植物之间的相互作用，对昆虫与植物双方均产生了塑造作用，推动了植物防御机制（plant defenses）与昆虫特化（insect specialization）的演化。叶甲科（Chrysomelidae）的*Trirhabda eriodictyonis*，其宿主为两种防御特征迥异的灌木：*Eriodictyon crassifolium*的叶片密被绒毛，而*E. trichocalyx*的叶片则具树脂性。本研究旨在探究该叶甲是否已因宿主植物的差异产生种群分化；若未分化，则叶甲是否更偏好取食更优质的宿主植物，以及是否更倾向于选择来自该优质宿主的配偶。取食试验（feeding tests）结果显示，无论成虫原本的宿主植物为何，均显著偏好取食*E. trichocalyx*。此外，取食*E. trichocalyx*的雌虫产卵量显著高于取食*E. crassifolium*的个体。由此可见，*E. trichocalyx*整体为更优质的宿主植物。但叶甲的配偶偏好与取食偏好并不一致：雄虫并未表现出对来自*E. trichocalyx*的雌虫的交配偏好。而来自*E. crassifolium*的雌虫，虽相较于同宿主的雄虫，更偏好与来自*E. trichocalyx*的雄虫交配，但此类交配并未使其产卵量提升。本研究结论表明，所研究的叶甲种群并未因宿主植物的差异产生种群分化，甚至可能尚未对更优质的宿主产生适应性演化。尽管在人类视角中，这两种宿主植物的防御机制差异显著，但目前尚无证据表明其驱动了叶甲的演化。*T. eriodictyonis*的这一研究案例，与诸多已报道的研究结果相悖——后者均发现植食性昆虫会因宿主植物的差异产生生态型（ecotypes）分化，或其生活史与宿主植物形成适应性协同演化。