Climate-induced phenological shift of apple trees has diverse effects on pollinators, herbivores and natural enemies

Climate change is altering the phenology of trophically linked organisms, leading to increased asynchrony between species with unknown consequences for ecosystem services. Although phenological mismatches are reported from several ecosystems, experimental evidence for altering multiple ecosystem services is hardly available. We examined how the phenological shift of apple trees affected the abundance and diversity of pollinators, generalist and specialist herbivores and predatory arthropods. We stored potted apple trees in the greenhouse or cold store in early spring before transferring them into orchards to cause mismatches and sampled arthropods on the trees repeatedly. Assemblages of pollinators on the manipulated and control trees differed markedly, but their overall abundance was similar indicating a potential insurance effect of wild bee diversity to ensure fruit set in flower-pollinator mismatch conditions. Specialized herbivores were almost absent from manipulated trees, while less-specialized ones showed diverse responses, confirming the expectation that more specialized interactions are more vulnerable to phenological mismatch. Natural enemies also responded to shifted apple tree phenology and the abundance of their prey. While arthropod abundances either declined or increased, species diversity tended to be lower on apple trees with shifted phenology. Our study indicates novel results on the role of biodiversity and specialization in plant-insect mismatch situations.

Cumulative effects of transgenerational induction on plant palatability to generalist and specialist herbivores

Herbivore damage can induce anti-herbivore traits in plants. However, there is little data regarding how these induced traits affect a plant's palatability (an important factor in determining the likelihood and magnitude of herbivore damage) across multiple generations post-induction, or whether the effect of transgenerational induction differs between generalist and specialist herbivores. Here we used palatability as a measure of the effects of transgenerational defensive induction in wild radish plants. We conducted a greenhouse experiment to determine whether generalist (slugs) and specialist (caterpillars of the white cabbage butterfly) herbivores' preference for wild radish differed depending on the number of previous generations that experienced herbivory. We found lowered palatability in plants with two or three inductions in their past in the case of generalist slugs, while palatability to a specialist herbivore was not affected by transgenerational induction. We conclude that the history of herbivory experienced by a plant's ancestors over multiple generations may play an important role in its ability to defend itself against generalist herbivores, but not against the specialists with whom they have co-evolved. Our findings suggest that the effects that multiple past inductions may have on palatability down the family line can be expected to have ecological and evolutionary implications.

Variation of pyrrolizidine alkaloids in Senecio vulgaris plants from native and invasive ranges

Pyrrolizidine alkaloids (PAs), a typical kind of secondary metabolites in plants, have important roles on defense against herbivores and pathogens; however, specialist herbivores adapted to PAs can use them as cues for oviposition and feeding. Thus, in the native ranges, PA diversity and concentration in plants were selected by the balance between pressure from generalist and specialist herbivores. In introduced ranges, where the specialist herbivores are absent, the introduced plants could increase concentration and diversity of PAs. This predication is deduced from the Shift Defense Hypothesis (SDH). In this research, we investigated whether there were any differences between native and invasive Senecio vulgaris plants (from Europe and China, respectively) with regards to the PA composition and concentration. We grew the native and invasive S. vulgaris plants in an identical condition and harvested them when they started to bloom. Their roots and shoots were separately harvested and dried. PA composition and concentration from powder of the shoots and roots were detected by using liquid chromatography – tanderm mass spectrometry (LC-MS/MS). We identified 14 PAs which belongs to the structural group senecionine – like PAs. Most of them occurred in both the native and invasive S. vulgaris plants, except the usaramine N – oxide that was only found in the native ones. From the 14 PAs identified, only riddelliine N – oxide had significantly higher present frequency in the invasive plants than in the native plants. The invasive S. vulgaris plants had significantly lower concentration of 3 individual PAs (seneciphylline N – oxide, spartioidine and spartioidine N – oxide) than the native ones. These results demonstrated that PA diversity and concentration of some individual PAs tended to reduce in the invasive range of S. vulgaris. This is contrary to the predictions of the SDH that the invasive plants would produce more qualitative defense than the native ones, and it is probably an evidence that a little trade – off between defense and growth happened to the S. vulgaris in China.

Variation of pyrrolizidine alkaloids in Senecio vulgaris plants from native and invasive ranges

Pyrrolizidine alkaloids (PAs), a typical kind of secondary metabolites in plants, have important roles on defense against herbivores and pathogens; however, specialist herbivores adapted to PAs can use them as cues for oviposition and feeding. Thus, in the native ranges, PA diversity and concentration in plants were selected by the balance between pressure from generalist and specialist herbivores. In introduced ranges, where the specialist herbivores are absent, the introduced plants could increase concentration and diversity of PAs. This predication is deduced from the Shift Defense Hypothesis (SDH). In this research, we investigated whether there were any differences between native and invasive Senecio vulgaris plants (from Europe and China, respectively) with regards to the PA composition and concentration. We grew the native and invasive S. vulgaris plants in an identical condition and harvested them when they started to bloom. Their roots and shoots were separately harvested and dried. PA composition and concentration from powder of the shoots and roots were detected by using liquid chromatography – tanderm mass spectrometry (LC-MS/MS). We identified 14 PAs which belongs to the structural group senecionine – like PAs. Most of them occurred in both the native and invasive S. vulgaris plants, except the usaramine N – oxide that was only found in the native ones. From the 14 PAs identified, only riddelliine N – oxide had significantly higher present frequency in the invasive plants than in the native plants. The invasive S. vulgaris plants had significantly lower concentration of 3 individual PAs (seneciphylline N – oxide, spartioidine and spartioidine N – oxide) than the native ones. These results demonstrated that PA diversity and concentration of some individual PAs tended to reduce in the invasive range of S. vulgaris. This is contrary to the predictions of the SDH that the invasive plants would produce more qualitative defense than the native ones, and it is probably an evidence that a little trade – off between defense and growth happened to the S. vulgaris in China.