Metal accumulation and its effect on leaf herbivory in an allopolyploid species Arabidopsis kamchatica inherited from a diploid hyperaccumulator A. halleri

Excessive amounts of metal ions in soil are toxic for most plant species, yet metal can also facilitate plant survival by elemental defense against herbivores and pathogens. Zinc and cadmium hyperaccumulation in Arabidopsis halleri is known to be effective for the defense against natural enemies. The allotetraploid species A. kamchatica, derived from A. halleri and a non-hyperaccumulator A. lyrata, has a lower hyperaccumulation level of zinc than A. halleri, but its significance for elemental defense remains unknown. In this study, we evaluated the accumulation levels of zinc and cadmium in the allotetraploid compared with its diploid progenitors, and evaluated the contribution of metal treatments to anti-herbivore resistance under field conditions. The accumulation level of zinc in A. kamchatica was intermediate between the progenitors, but that of cadmium was lower than in both diploid progenitors. The elemental defense of A. kamchatica and A. halleri was supported by a field experiment comparing the herbivory level between a control group and metal-supplemented plants. Moreover, the effect of elemental defense was lower in A. kamchatica than in the hyperaccumulator progenitor A. halleri, which is consistent with the metal accumulation level. This result reveals that the allotetraploid plant inherited its hyperaccumulating ability from one progenitor as an advantageous trait but at an intermediate level.     

The three criteria for resistance by plant carrion‐provisioning: insect entrapment and predator enrichment on Mimulus bolanderi

1. Many sticky plants provision mutualistic scavenging arthropod predators with carrion, which in turn protect the plant from insect herbivores. While insect entrapment is a common trait across plants, which plants attract these predators and may derive protection is still largely unknown. 2. Three conditions were proposed that must be satisfied for observational data to suggest this defensive strategy: (i) the consistent presence of scavenging predators, (ii) positive correlation between predator numbers and carrion, and (iii) suitability of these predators for controlling known herbivores. 3. As a case study, we examined the fire‐following annual, Mimulus [Diplacus] bolanderi (Phyrmaceae), which is part of a well‐studied radiation of California monkeyflowers. Many monkeyflowers entrap insects, though attraction to predators has not been quantified in this genus. 4. A guild of scavenging arthropod predators on M. bolanderi (condition #1) was found, which correlated positively with carrion abundance (#2) and could consume the primary herbivore (#3), suggesting a carrion‐mediated defensive strategy. Lastly, as M. bolanderi is variable in time and space, these interactions are facultative, and these predators are quick to adopt ephemeral carrion resources on novel host plants.     

Preference–performance relationship in the gall midge Rabdophaga rosaria: insights from a common‐garden experiment with nine willow clones

1. Oviposition preferences of herbivorous insects are predicted to match offspring performance on different host taxa or on conspecific host genotypes. In gall‐inducing insects, host‐plant properties such as growth rate and gall size, which are determined by plant genotype and growing conditions, may have a significant impact on offspring performance and, hence, should influence oviposition site selection. 2. The present study investigated host preference of the European rosette willow gall midge Rabdophaga rosaria (Loew) in relation to offspring success on seven clones of Salix myrsinifolia Salisb. and two naturally hybridised S. myrsinifolia × phylicifolia L. clones growing in a replicated design in an experimental field under two fertilisation regimes. For each clone, the average growth rate, number of shoot tips, and leaf and gall size were determined, and their effects on midge preference and larval survival were examined. 3. Main shoot height, number of shoot tips, and gall size were significantly affected by clone. The midges clearly preferred certain clones over the others, but preferences were not related to willow growth traits or to gall size. Survival probability was higher in large than in small galls, but females did not prefer large‐leaved clones that produced the biggest rosette galls. Midge oviposition was also uncorrelated with prior rates of leaf‐rust infection and with feeding preferences of voles and folivorous insects. 4. The weak preference–performance relationship of R. rosaria within S. myrsinifolia is probably explained by evolutionary constraints that prevent generalist insects from achieving an ability to discriminate among conspecific hosts of variable quality.     

Consequences of elevated temperature and pCO2 on insect folivory at the ecosystem level: perspectives from the fossil record

Paleoecological studies document the net effects of atmospheric and climate change in a natural laboratory over timescales not accessible to laboratory or ecological studies. Insect feeding damage is visible on well‐preserved fossil leaves, and changes in leaf damage through time can be compared to environmental changes. We measured percent leaf area damaged on four fossil leaf assemblages from the Bighorn Basin, Wyoming, that range in age from 56.1 to 52.65 million years (Ma). We also include similar published data from three US sites 49.4 to ~45 Ma in our analyses. Regional climate was subtropical or warmer throughout this period, and the second oldest assemblage (56 Ma) was deposited during the Paleocene–Eocene Thermal Maximum (PETM), a geologically abrupt global warming event caused by massive release of carbon into the atmosphere. Total and leaf‐chewing damage are highest during the PETM, whether considering percent area damaged on the bulk flora, the average of individual host plants, or a single plant host that occurs at multiple sites. Another fossil assemblage in our study, the 52.65 Ma Fifteenmile Creek paleoflora, also lived during a period of globally high temperature and pCO₂, but does not have elevated herbivory. Comparison of these two sites, as well as regression analyses conducted on the entire dataset, demonstrates that, over long timescales, temperature and pCO₂ are uncorrelated with total insect consumption at the ecosystem level. Rather, the most important factor affecting herbivory is the relative abundance of plants with nitrogen‐fixing symbionts. Legumes dominate the PETM site; their prevalence would have decreased nitrogen limitation across the ecosystem, buffering generalist herbivore populations against decreased leaf nutritional quality that commonly occurs at high pCO₂. We hypothesize that nitrogen concentration regulates the opposing effects of elevated temperature and CO₂ on insect abundance and thereby total insect consumption, which has important implications for agricultural practices in today's world of steadily increasing pCO₂.