More Like this

1. Top‐down effects from parasitoids may mediate plant defence and plant fitness

   https://doi.org/10.1111/1365-2435.13617  

   Tan, Ching‐Wen ; Peiffer, Michelle L. ; Ali, Jared G. ; Luthe, Dawn S. ; Felton, Gary W. ; Biere, ed., Arjen ( July 2020 , Functional Ecology)

   Plants face many environmental stresses that can impact their survival, development and fitness. Insects are the most diverse, abundant and threatening herbivores in nature. As a consequence, plants produce direct chemical and physical defences to reduce herbivory. They also release volatiles to recruit natural enemies that indirectly protect them from herbivory. The recruitment of parasitic wasps can benefit plant fitness because they ultimately kill their insect hosts.

   Recently, studies showed that parasitoids can indirectly mediate plant defences by modulating herbivore oral secretions. In addition to the direct benefits of parasitoids in terms of reducing herbivore survival, we tested if the reduction in induced defences by parasitized caterpillars compared to non‐parasitized caterpillars may reduce the costs associated with defence expression.

   We provide evidence that tomato plants treated with saliva from parasitized caterpillars have significantly higher fitness parameters including increased flower numbers (16.3%) and heavier fruit weight (13.5%), compared to plants treated with saliva from non‐parasitized caterpillars. Since plants were grown without actual herbivores, the higher values for these fitness parameters were due to lower costs of induced defences and not due to reduced herbivory by parasitized caterpillars. Furthermore, the resulting seed germination time was shorter and the germination rate was higher when the maternal plants were previously exposed to parasitized herbivore treatment compared to control (non‐treated) plants.

   Overall, application of saliva did not result in transgenerational priming of offspring defence responses. However, offspring of parents exposed to caterpillar saliva had lower constitutive levels and higher induced levels of trypsin inhibitor than offspring from unexposed parents.

   This study shows that the saliva of parasitized caterpillars can modulate plant defences and further demonstrates that the lower induction of plant defences is associated with elevated plant fitness in the absence of herbivore feeding, suggesting that induced plant defences are costly.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

   more » « less
2. Beneficial microbes ameliorate abiotic and biotic sources of stress on plants

   https://doi.org/10.1111/1365-2435.13499  

   Porter, Stephanie S. ; Bantay, Roxanne ; Friel, Colleen A. ; Garoutte, Aaron ; Gdanetz, Kristi ; Ibarreta, Kathleen ; Moore, Bethany M. ; Shetty, Prateek ; Siler, Eleanor ; Friesen, Maren L. ; et al ( January 2020 , Functional Ecology)

   Global climate change and shifting land‐use are increasing plant stress due to abiotic factors such as drought, heat, salinity and cold, as well as via the intensification of biotic stressors such as herbivores and pathogens. The ability of plants to tolerate such stresses is modulated by the bacteria and fungi that live on or inside of plant tissues and comprise the plant microbiome. However, the impacts of diverse classes of beneficial members of the microbiome and the contrasting stresses that impact plants are most commonly studied independently of each other.

   Our meta‐analysis of 288 experiments across 89 studies moves beyond previous studies in that we simultaneously compare the roles of bacterial versus fungal microbiome members that live within plant tissues and colonize plant surfaces in ameliorating biotic versus abiotic sources of plant stress.

   The magnitude of microbial stress amelioration can be measured as the greater proportional impact of beneficial microbes on plant performance in more stressful environments. In the plant experiments we examine, the magnitude of microbial stress amelioration is substantial: it is 23% of the effect size of the typical impact of stress and 56% of the effect size of beneficial microbiome members in the absence of stress.

   The amount of benefit microbiome members confer to plants differs among classes of microbes, depending on whether plants are grown in stressful or non‐stressful environments. In the absence of stress, beneficial bacteria tend to confer greater plant benefits than do fungi. However, symbiotic fungi, especially arbuscular mycorrhizal fungi, more strongly ameliorate plant stress than do bacteria. In particular, beneficial microbes ameliorate salinity, foliar herbivory and fungal pathogen stress.

   These results highlight the fact that the impacts of beneficial and antagonistic components of the microbiome on plant performance depend on biotic and abiotic environmental contexts. Furthermore, beneficial microbes are especially critical for plant health in stressful environments and thus present opportunities to mitigate negative consequences of global change.

   A freeplain language summarycan be found within the Supporting Information of this article.

    

   more » « less
3. The interactive effects of heat stress, parasitism and host plant quality in a host–parasitoid system

   https://doi.org/10.1111/1365-2435.14498  

   Parker, Anna L. ; Kingsolver, Joel G. ( January 2024 , Functional Ecology)

   Species interactions are expected to change in myriad ways as the frequency and magnitude of extreme temperature events increase with anthropogenic climate change.

   The relationships between endosymbionts, parasites and their hosts are particularly sensitive to thermal stress, which can have cascading effects on other trophic levels.

   We investigate the interactive effects of heat stress and parasitism on a terrestrial tritrophic system consisting of two host plants (one common, high‐quality plant and one novel, low‐quality plant), a caterpillar herbivore and a specialist parasitoid wasp.

   We used a fully factorial experiment to determine the bottom‐up effects of the novel host plant on both the caterpillars' life history traits and the wasps' survival, and the top‐down effects of parasitism and heat shock on caterpillar developmental outcomes and herbivory levels.

   Host plant identity interacted with thermal stress to affect wasp success, with wasps performing better on the low‐quality host plant under constant temperatures but worse under heat‐shock conditions.

   Surprisingly, caterpillars consumed less leaf material from the low‐quality host plant to reach the same final mass across developmental outcomes.

   In parasitized caterpillars, heat shock reduced parasitoid survival and increased both caterpillar final mass and development time on both host plants.

   These findings highlight the importance of studying community‐level responses to climate change from a holistic and integrative perspective and provide insight into potential substantial interactions between thermal stress and diet quality in plant–insect systems.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

   more » « less
4. Biogeographic variation of distance‐dependent effects in an invasive tree species

   https://doi.org/10.1111/1365-2435.13306  

   Yang, Qiang ; Ding, Jianqing ; Siemann, Evan ; Godoy, ed., Oscar ( March 2019 , Functional Ecology)

   Plant pathogens and herbivores can maintain forest diversity by reducing survival of tree seedlings close to conspecifics. However, how biogeographic variation in these natural enemies affects such distance‐dependent processes is unknown. Because invasive plants escape ecologically important enemies when introduced to a new range, distance‐dependent mortality may differ between their native and introduced ranges.

   Here, we test whether the invasive treeTriadica sebiferaescaped distance‐dependent mortality when introduced to the United States from China, and examine the roles of natural enemies in native and introduced ranges. In both the United States and China, we performed field surveys along with field and greenhouse experiments with field‐collected soils and soil sterilization treatments.

   In field surveys and the field experiment, insect damage onT. sebiferaseedlings decreased with distance to conspecific trees in the native range (China), but damage was low at all distances in the introduced range (United States). In the greenhouse experiment testing the effects of soil pathogens,T. sebiferaseedling mortality decreased with soil distance from conspecific trees in both ranges but distance‐independent mortality was higher in native range soils.

   Our findings indicate that both insect herbivores and the soil biota contribute to distance‐dependent effects onT. sebiferain its native range. They suggest, however, that plants may more readily escape herbivore than soil biota distance‐dependent effects when introduced to a new range and so herbivores, rather than soil pathogens, contribute more strongly to biogeographic variation in distance‐dependent effects. These results highlight the importance of considering species biogeographic variation in distance‐dependent effects and teasing apart the roles that different natural enemies play when studying species coexistence, community diversity and biological invasions.

    

   more » « less
5. Independent and interactive effects of plant genotype and environment on plant traits and insect herbivore performance: A meta‐analysis with Salicaceae

   https://doi.org/10.1111/1365-2435.13249  

   Barker, Hilary L. ; Holeski, Liza M. ; Lindroth, Richard L. ; Koricheva, ed., Julia ( December 2018 , Functional Ecology)

   Ecological research has increasingly highlighted the importance of intraspecific variation in shaping the structure and function of communities and ecosystems. Indeed, the effects of intraspecific variation can match or exceed those of interspecific variation. Previous reviews of intraspecific variation in plant traits across heterogeneous environments have focused primarily onmeanphenotypic effects. We propose that a richer and fuller understanding of the ecological causes and consequences of intraspecific variation would be provided by partitioning traitvarianceinto its subcomponents (genetic, environment, genotype by environment interaction).

   We used a meta‐analysis of 352 sets of genetic, environment and genotype by environment (G×E) variation estimates from 72 studies of Salicaceae to compare these sources of variation across plant traits (growth, foliar nitrogen, defence compounds), insect herbivore performance metrics (e.g., survival, growth, fecundity) and environmental conditions (e.g., soil nutrients, water, defoliation).

   Our findings revealed that variation in levels of defence compounds (both condensed tannins and salicinoids) and insect herbivore performance were primarily genetically determined, while variation in plant growth and foliar nitrogen was more environmentally determined.

   Plasticity in plant growth, foliar nitrogen levels and insect herbivore performance varied substantially across different sites (year × location), and nutrient, water and carbon dioxide environments. Plasticity was lowest for chemical defence traits and all traits in contrasting ozone and defoliation environments.

   Our quantitative review also revealed several gaps in the literature, including a need for surveying more mature plants, a wider variety of insect herbivore species (e.g., leaf‐galling insects, specialist insects) and underrepresented environmental treatments (e.g., competition, defoliation, disease, light and water availability).

   Findings from this analysis highlight the importance of, and patterns within, intraspecific variation with respect to shaping the evolvability and plasticity of traits and governing the interactions of plants and insects.

   Aplain language summaryis available for this article.

    

   more » « less