Data from: Additive genetic variation in resistance traits of an exotic pine species: little evidence for constraints on evolution of resistance against native herbivores

The apparent failure of invasions by alien pines in Europe has been explained by the co-occurrence of native pine congeners supporting herbivores that might easily recognize the new plants as hosts. Previous studies have reported that exotic pines show reduced tolerance and capacity to induce resistance to those native herbivores. We hypothesize that limited genetic variation in resistance to native herbivores and the existence of evolutionary trade-offs between growth and resistance could represent additional potential constraints on the evolution of invasiveness of exotic pines outside their natural range. In this paper, we examined genetic variation for constitutive and induced chemical defences (measured as non-volatile resin in the stem and total phenolics in the needles) and resistance to two major native generalist herbivores of pines in cafeteria bioassays (the phloem-feeder Hylobius abietis and the defoliator Thaumetopoea pityocampa) using half-sib families drawn from a sample of the population of Pinus radiata introduced to Spain in the mid-19th century. We found (i) significant genetic variation, with moderate-to-high narrow-sense heritabilities for both the production of constitutive non-volatile resin and induced total phenolics, and for constitutive resistance against T. pityocampa in bioassays, (ii) no evolutionary trade-offs between plant resistance and growth traits or between the production of different quantitative chemical defences and (iii) a positive genetic correlation between constitutive resistance to the two studied herbivores. Overall, results of our study indicate that the exotic pine P. radiata has limited genetic constraints on the evolution of resistance against herbivores in its introduced range, suggesting that, at least in terms of interactions with these enemies, this pine species has potential to become invasive in the future.

欧洲外来松树入侵看似失败的现象，此前被解释为本土松树近缘种的共存所致：这类本土近缘松会供养一类可轻易将新引入松树识别为寄主的植食性动物。既往研究表明，外来松树对这类本土植食性动物的耐受能力以及诱导产生抗性的能力均有所下降。
我们提出如下假说：对外来松树而言，在其天然分布范围之外，针对本土植食性动物的抗性遗传变异有限，且生长与抗性之间存在进化权衡（evolutionary trade-off），这二者可能构成其入侵性演化的额外潜在限制因素。
本研究以19世纪中期引入西班牙的辐射松（Pinus radiata）种群的半同胞家系为材料，通过取食选择生物测定（cafeteria bioassay），检测组成型与诱导型化学防御（分别以茎部非挥发性树脂（non-volatile resin）和针叶总酚类（total phenolics）含量为衡量指标）的遗传变异，以及对两种主要本土松树广食性植食性动物的抗性。两种受试植食性动物分别为取食韧皮部的欧洲松黑象甲（Hylobius abietis）和食叶昆虫松异舟蛾（Thaumetopoea pityocampa）。
本研究结果显示：(1) 组成型非挥发性树脂合成、诱导型总酚类合成，以及生物测定中针对松异舟蛾（T. pityocampa）的组成型抗性均存在显著遗传变异，且其狭义遗传力（narrow-sense heritability）为中等至高水平；(2) 植物抗性与生长性状之间，以及不同定量化学防御物质的合成之间均未发现进化权衡；(3) 针对两种受试植食性动物的组成型抗性之间存在显著正遗传相关。
综合来看，本研究结果表明，外来树种辐射松（Pinus radiata）在其引入分布区内，针对植食性动物的抗性演化所受遗传限制有限，这意味着至少在与这类天敌的互作层面，该松树物种未来具备入侵潜力。