Geraldine D. Ryan

A meta‐analytical review of the effects of elevated CO2 on plant–arthropod interactions highlights the importance of interacting environmental and biological variables

We conducted the most extensive meta-analysis of plant and animal responses to elevated CO(2) to date. We analysed > 5000 data points extracted from 270 papers published between 1979 and 2009. We examined the changes in 19 animal response variables to the main effect of elevated CO(2). We found strong evidence for significant variation among arthropod orders and feeding guilds, including interactions in the direction of response. We also examined the main effects of elevated CO(2) on: six plant growth and allocation responses, seven primary metabolite responses, eight secondary metabolite responses, and four physical defence responses. We examined these response variable changes under two-way and three-way interactions between CO(2) and: soil nitrogen, ambient temperature, drought, light availability, photosynthetic pathway, reproductive system, plant growth rate, plant growth form, tissue type, and nitrogen fixation. In general we found smaller effect sizes for many response variables than have been previously reported. We also found that many of the oft-reported main effects of CO(2) obscure the presence of significant two- and three-way interactions, which may help better explain the relationships between the response variables and elevated CO(2).

Leatherback turtles: The menace of plastic

The leatherback, Dermochelyscoriacea, is a large sea turtle that feeds primarily on jellyfish. Floating plastic garbage could be mistaken for such prey. Autopsy records of 408 leatherback turtles, spanning 123 years (1885-2007), were studied for the presence or absence of plastic in the GI tract. Plastic was reported in 34% of these cases. If only cases from our first report (1968) of plastic were considered, the figure was 37%. Blockage of the gut by plastic was mentioned in some accounts. These findings are discussed in the context of removal of top predators from poorly understood food chains.

Development, Reproductive Output and Population Growth of the Fruit Fly Pest Drosophila suzukii (Diptera: Drosophilidae) on Artificial Diet

ABSTRACT Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a fruit pest of Asian origin that invaded North America in 2008. Despite the widespread economic impact of this species, much of the biology and general life history of this pest remains largely unknown. Under optimal laboratory conditions (22°C, ≈25% relative humidity),wemeasured development, survival, fecundity, hatch rate, and sex ratio of a North American ecotype of D. suzukii. Life history traits were used to construct a life table and reproductive schedule, and to calculate the intrinsic rate of population increase. The mean (±SE) total lifespan (egg to adult mortality) was 86.1 ± 4.25 d, with a maximum value of 153.7 d. On average, females produced 5.7 ± 0.24 eggs per day, with a mean total lifetime production of 635.6 eggs. The gross reproductive rate was 317.8 daughter eggs per female and the net reproductive rate was 240.4 daughter eggs per female. The intrinsic rate of natural increase was 0.179. The stable age distribution (cx ) was comprised of 51% larvae, 25% eggs, 16% pupae, and 8% adults. The sex ratio over time was≈1:1.Weconclude with a comparison of our data with previous work on D. suzukii and other Drosophila, and discuss the implications for control and monitoring of this pest.

Thermal Tolerances of the Spotted-Wing Drosophila Drosophila suzukii (Diptera: Drosophilidae)

Abstract The spotted-wing drosophila (Drosophila suzukii Matsumura) is an invasive species of Asian origin that is now widely distributed in North America and Europe. Because of the females serrated ovipositor, eggs are laid in preharvest fruit, causing large economic losses in cultivated berries and stone fruit. Modeling D. suzukii population dynamics and potential distribution will require information on its thermal tolerance. Large summer populations have been found in regions with severe winter conditions, though little is known about responses to prolonged low-temperature exposure. We used controlled chambers to examine D. suzukii fecundity, development rate, and mortality across a range of temperatures encompassing the upper and lower thresholds (5–35°C). Optimal temperatures (T opt) were found to be 28.2°C for the development of the egg-to-adult stage, and 22.9°C for reproductive output. No adult eclosion occurred below 8.1°C (T lower) or above 30.9°C (T upper). We also investigated survival outcomes following prolonged (42-d) low-temperature exposure to a simulated cold winter (−5, −3, −1, 1, 3, and 5°C). Adult survival was dependent on temperature, with a mean LT50 of 4.9°C. There were no effects of sex, mating status, geographic strain, and photoperiod preexposure on overwintering survival. Thirty-eight percent of females that were mated prior, but not after, prolonged low-temperature exposure produced viable offspring, suggesting that this species may undergo sperm storage. This study provides data on the thermal tolerances of D. suzukii, which can be used for models of D. suzukii population dynamics, degree-day, and distribution models.

Metabolite analysis of the effects of elevated CO2 and nitrogen fertilization on the association between tall fescue (Schedonorus arundinaceus) and its fungal symbiont Neotyphodium coenophialum

Atmospheric CO2 is expected to increase to between 550 ppm and 1000 ppm in the next century. CO2-induced changes in plant physiology can have ecosystem-wide implications and may alter plant-plant, plant-herbivore and plant-symbiont interactions. We examined the effects of three concentrations of CO2 (390, 800 and 1000 ppm) and two concentrations of nitrogen fertilizer (0.004 g N/week versus 0.2 g N/week) on the physiological response of Neotyphodium fungal endophyte-infected and uninfected tall fescue plants. We used quantitative PCR to estimate the concentration of endophyte under altered CO2 and N conditions. We found that elevated CO2 increased the concentration of water-soluble carbohydrates and decreased the concentration of plant total amino acids in plants. Fungal-derived alkaloids decreased in response to elevated CO2 and increased in response to nitrogen fertilization. Endophyte concentration (expressed as the number of copies of an endophyte-specific gene per total genomic DNA) increased under elevated CO2 and nitrogen fertilization. The correlation between endophyte concentration and alkaloid production observed at ambient conditions was not observed under elevated CO2. These results suggest that nutrient exchange dynamics important for maintaining the symbiotic relationship between fungal endophytes and their grass hosts may be altered by changes in environmental variables such as CO2 and nitrogen fertilization.

Global Atmospheric Change and Trophic Interactions: Are There Any General Responses?

Increasing atmospheric CO2 is hypothesized to alter plant physiology and metabolism, which may have important implications for species interactions. In this chapter, we review published studies on the effects of elevated atmospheric CO2 on plant-derived allelochemicals and the possible effects of CO2-mediated changes on higher trophic levels such as herbivores, parasitoids, and predators. We provide a critical assessment of conventional ecological theories used to predict phytochemical responses to CO2 and we make some suggestions as to how this field may be expanded and improved.

Towards an understanding of how phloem amino acid composition shapes elevated CO2‐induced changes in aphid population dynamics

1. The performance of foliage feeders tends to decrease under elevated CO2, but the responses of phloem‐feeding insects have been much more equivocal. As phloem tissues are less accessible than whole‐plant tissues, much less is known about how phloem composition is altered under elevated CO2 and the mechanisms driving changes in aphid performance.

Phloem phytochemistry and aphid responses to elevated CO2, nitrogen fertilization and endophyte infection

Rising atmospheric CO2 has been shown to alter plant nitrogen metabolism, growth and secondary chemistry. We hypothesized that altered aphid performance under elevated CO2 is linked to phloem nitrogen chemistry. Rhopalosiphum padi performance on endophyte‐infected or uninfected tall fescue was examined under three levels of CO2 (ambient, 800 and 1000 p.p.m.) and high and low nitrogen fertilization. Ethylenediaminetetracetic acid‐facilitated exudation was used to sample phloem sap, followed by quantification of relative amino acid concentrations using reverse‐phase high‐performance liquid chromatography. Aphid abundance was reduced at 800 p.p.m. relative to ambient CO2 but returned to baseline at 1000 p.p.m. The density of aphids was reduced in both the elevated CO2 treatments. Aphids were unsuccessful at colonizing endophyte‐infected plants, possibly as a result of the presence of loline alkaloids. Multivariate analysis showed that certain groups of phloem amino acids were altered by nitrogen fertilization and CO2. We found that four amino acids (valine, arginine, glutamine and aspartate) were correlated with aphid performance. These findings partially explained the effect of plant nitrogen fertilization and elevated CO2 on aphids. The present study represents a first step toward providing a mechanistic explanation of the aphid performance changes that may result from rising atmospheric CO2.

Aphid and host-plant genotype × genotype interactions under elevated CO2

1. Elevated CO2 can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO2 and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation.

Epichloë Fungal Endophytes for Grassland Ecosystems

The Epichloe fungal endophytes that inhabit grasses have potentially large-scale consequences for macro- and micro-organisms and food chains in agriculture. Over 40 years of study on the benefits of symbiotic Epichloe fungal endophytes for host grasses, investigations have focused on the major agricultural species, tall fescue and perennial ryegrass. However, many other grass species remain to be evaluated for the effects of Epichloe endophytes. Animal toxicity due to accumulation of nitrogenous compounds, e.g. endophyte-dervived alkaloids, particularly in areas and periods under abiotic stress, still prevent widespread application of endophyte-infected grasses in agroecosystems.