Role of plant sensory perception in plant-animal interactions

Plants actively gather information about their environments via a range of sensory modalities and respond in ways that profoundly influence their interactions with other organism

Olfactory Cues from Plants Infected by Powdery Mildew Guide Foraging by a Mycophagous Ladybird Beetle

Powdery mildews (Erysiphales) are economically important plant pathogens that attack many agricultural crops. Conventional management strategies involving fungicide application face challenges, including the evolution of resistance and concerns over impacts on non-target organisms, that call for investigation of more sustainable alternatives. Mycophagous ladybird beetles (Coleoptera: Coccinellidae) feed on powdery mildew and have considerable potential as biological control agents; however, the foraging ecology and behavior of these beetles is not well understood. Here we document the olfactory cues presented by squash plants (Cucurbita moschata) infected by powdery mildew (Podosphaera sp.) and the behavioral responses of twenty-spotted ladybird beetles (Psyllobora vigintimaculata) to these cues. Volatile analyses through gas chromatography revealed a number of volatile compounds characteristic of infected plants, including 3-octanol and its analogues 1-octen-3-ol and 3-octanone. These compounds are typical “moldy” odorants previously reported in volatiles collected from other fungi. In addition, infected plants exhibited elevated emissions of several compounds also observed in collections from healthy leaves, including linalool and benzyl alcohol, which are reported to have anti-fungal properties. In Y-tube choice assays, P. vigintimaculata beetles displayed a significant preference for the odors of infected plants compared to those of healthy plants. Moreover, beetles exhibited strong attraction to one individual compound, 1-octen-3-ol, which was the most abundant of the characteristic fungal compounds identified. These results enhance our understanding of the olfactory cues that guide foraging by mycophagous insects and may facilitate the development of integrated disease-management strategies informed by an understanding of underlying ecological mechanisms

Distribution of the Two Social Forms of the Fire Ant Solenopsis invicta (Hymenoptera: Formicidae) in the Native South American Range

Polygyne (multiple queen) colony social organization in the fire ant Solenopsis invicta Buren is always associated with the presence of a particular class of alleles at the gene Gp-9. We used diagnostic polymerase chain reaction assays capable of distinguishing these alleles to determine the location of polygyne populations in the native South American range of this species. We found that polygyny occurs in a mosaic pattern with respect to the more common monogyne (single queen) social form, a pattern superficially similar to that seen in the introduced range in the United States. However, polygyny appears to be relatively restricted in its geographical prevalence in the native range compared with the introduced range. This difference may stem from higher dispersal rates in the introduced range, which are associated with greater opportunities for human-mediated transport of mated queens or colony fragments. On the basis of our distributional data and results from other studies, the southern part of the native range of S. invicta, particularly northeastern Argentina, is emerging as the most likely geographic source of the founders of the U.S. populatio

Habitat protection and removal of encroaching shrubs support the recovery of biodiversity and ecosystem functioning

Livestock overgrazing causes environmental degradation, species invasion, biodiversity loss, and productivity decline, with profound consequences for ecological sustainability and human livelihoods. Habitat protection can mitigate such impacts, but we know little about how the long-term recovery of plant communities from livestock overgrazing depends on the presence of encroaching shrubs. Here, we explored how shrub encroachment mediates the effects of habitat protection (i.e., livestock exclusion and creation of UNESCO protected areas) on biodiversity recovery and ecosystem functioning (i.e., biomass productivity). We leveraged a long-term (15–25 years) experiment of livestock exclusion and complemented it with the removal of an encroaching shrub species in pasture areas and protected areas. We reveal that habitat protection has positive effects on patterns of recovery. Yet, the effects of habitat protection are mediated by shrub encroachment. Encroaching shrubs have net positive effects on plant diversity in pasture areas but inhibit biodiversity recovery in protected areas. The combination of habitat protection and the removal of encroaching shrubs best enhances the recovery of plant diversity and biomass productivity. A potential underlying mechanism is the shift in plant interactions from facilitation for recruitment and associated resistance to competition for water. Understanding species interactions is key to guiding conservation and restoration actions which can turn degraded ecosystems back into functional, species-rich communities

Leaf trichomes affect caterpillar feeding in an instar-specific manner

Leaf trichomes play well-established roles in defense against insect herbivores, both as a physical barrier that impedes herbivore movement and by mediating chemical defenses. However, little work has examined how different trichome types influence herbivory by herbivores at different stages of development. We examined whether caterpillar instar and trichome type (glandular or non-glandular) affected the ability of the specialist herbivore caterpillar Manduca sexta to initiate feeding on 11 Solanaceous species exhibiting variation in the density and type of leaf trichomes. Our results suggest that non-glandular trichomes are far more effective than glandular trichomes in deterring the initiation of feeding by first- and second-instar caterpillars. Meanwhile, neither glandular nor non-glandular trichomes significantly affected the ability of third-instar caterpillars to commence feeding. These findings suggest that while non-glandular trichomes deter feeding initiation by early instar caterpillars, the contribution of both trichomes on later instars may depend on effects after feeding initiation

Herbivory and inbreeding affect growth, reproduction, and resistance in the rhizomatous offshoots of Solanum carolinense (Solanaceae)

Resource sharing within clonal plant networks can occur via the translocation of water, nutrients, and photoassimilates through rhizomes and stolons. Similar mechanisms may mediate the sharing of information (e.g., about herbivory or other environmental stressors) among ramets via molecular or biochemical signals. The storage of such information in belowground structures could facilitate the transmission of appropriate phenotypic responses across growing seasons in perennial species. However, few previous studies have explored the potential transfer of ecologically relevant information within such networks. This study addresses the effects of foliar herbivory and belowground overwintering on the growth and flowering, physical defenses, and herbivore resistance in the clonally spreading species Solanum carolinense L. (Solanaceae). We used rhizomes from inbred and outbred plants that were repeatedly exposed to feeding damage by Manduca sexta L. (Sphingidae) caterpillars and rhizomes from undamaged control plants. These rhizomes were either planted immediately or exposed to overwintering conditions and allowed to produce new ramets (rhizomatous offshoots). We then assessed offshoot emergence, flowering, physical defense traits, and herbivore performance. Relative to controls, offshoots of herbivore-damaged plants exhibited greater spine and trichome densities, and reduced performance of M. sexta larvae. However, they also emerged and flowered significantly later, and produced fewer flowers than offshoots of undamaged plants. Inbreeding also negatively affected offshoot emergence, flowering, trichome production, and herbivore resistance. These effects of parental herbivory were more pronounced in outbred offshoots, indicating that inbreeding may compromise the trans-seasonal induction of plant defenses. Finally, exposure to overwintering conditions increased trichome production and reduced caterpillar performance on offshoots. Together, these results show that induced defenses can be transmitted through rhizomes and affect offshoot growth, flowering, defensive traits, and herbivore resistance. They also document fitness-related costs associated with defense induction in offshoots and suggest that the transfer of defenses across seasons can be compromised by inbreeding

Phytoplasma Infection of Cranberries Benefits Non-vector Phytophagous Insects

Despite increasing knowledge about the impacts of pathogens on the interactions between plants and insect vectors, relatively little is known about their effects on other, non-vector, organisms. In cranberries, phytoplasma infection causes false blossom disease, which is transmitted by leafhoppers. We hypothesized that changes in plant chemistry induced by phytoplasma infection might affect the performance and feeding behavior not only of vectors but also of other phytophagous insects. To test this, we measured growth, survival, and the number of leaves damaged by larvae of three common non-vector herbivores: spotted fireworm (Choristoneura parallela Robinson), Sparganothis fruitworm (Sparganothis sulfureana Clemens), and gypsy moth (Lymantria dispar L.) on phytoplasma-infected and uninfected cranberries (Vaccinium macrocarpon Ait.). We also assessed the effects of phytoplasma infection on nutrients and phytochemistry related to defenses. In general, larvae of all three herbivore species grew 2–3 times bigger, and damaged 1.5–3.5 times more leaves, while feeding on infected vs. uninfected plants. Survival of Sparganothis fruitworm larvae was also ~1.5 times higher on infected plants, while spotted fireworm and gypsy moth larval survival was not affected. In a long-term (5-week) assay, gypsy moth larval survival and mass were enhanced when feeding on phytoplasma-infected leaves. Levels of important plant nutrients (e.g., N, P, K, Ca, S, Mn, Fe, B, Al, and Na) were higher in infected plants, while levels of defensive proanthocyanidins were reduced by 20–40% compared to uninfected plants. In contrast, levels of Mg were lower in infected plants, while concentrations of Cu, Zn, and defensive flavonols were not affected. Taken together, these findings suggest that phytoplasma infection enhances plant nutritional quality, while reducing plant defenses in cranberries. These effects, in turn, may explain the observed enhancement of non-vector herbivore performance, as well as the higher number of damaged leaves, on infected plants. Improved understanding of the ecology of pathogen-plant-herbivore interactions could aid efforts to enhance plant resistance and suppress disease transmission in agricultural settings

Horizontal Gene Acquisitions, Mobile Element Proliferation, and Genome Decay in the Host-Restricted Plant Pathogen \u3ci\u3eErwinia Tracheiphila\u3c/i\u3e

Modern industrial agriculture depends on high-density cultivation of genetically similar crop plants, creating favorable conditions for the emergence of novel pathogens with increased fitness in managed compared with ecologically intact settings. Here, we present the genome sequence of six strains of the cucurbit bacterial wilt pathogen Erwinia tracheiphila (Enterobacteriaceae) isolated from infected squash plants in New York, Pennsylvania, Kentucky, and Michigan. These genomes exhibit a high proportion of recent horizontal gene acquisitions, invasion and remarkable amplification of mobile genetic elements, and pseudogenization of approximately 20% of the coding sequences. These genome attributes indicate that E. tracheiphila recently emerged as a host-restricted pathogen. Furthermore, chromosomal rearrangements associated with phage and transposable element proliferation contribute to substantial differences in gene content and genetic architecture between the six E. tracheiphila strains and other Erwinia species. Together, these data lead us to hypothesize that E. tracheiphila has undergone recent evolution through both genome decay (pseudogenization) and genome expansion (horizontal gene transfer and mobile element amplification). Despite evidence of dramatic genomic changes, the six strains are genetically monomorphic, suggesting a recent population bottleneck and emergence into E. tracheiphila’s current ecological niche

Integration of attractive and defensive phytochemicals is unlikely to constrain chemical diversification in a perennial herb

Diversification of plant chemical phenotypes is typically associated with spatially and temporally variable plant–insect interactions. Floral scent is often assumed to be the target of pollinator-mediated selection, whereas foliar compounds are considered targets of antagonist-mediated selection. However, floral and vegetative phytochemicals can be biosynthetically linked and may thus evolve as integrated phenotypes. Utilizing a common garden of 28 populations of the perennial herb Arabis alpina (Brassicaceae), we investigated integration within and among floral scent compounds and foliar defense compounds (both volatile compounds and tissue-bound glucosinolates). Within floral scent volatiles, foliar volatile compounds, and glucosinolates, phytochemicals were often positively correlated, and correlations were stronger within these groups than between them. Thus, we found no evidence of integration between compound groups indicating that these are free to evolve independently. Relative to self-compatible populations, self-incompatible populations experienced stronger correlations between floral scent compounds, and a trend toward lower integration between floral scent and foliar volatiles. Our study serves as a rare test of integration of multiple, physiologically related plant traits that each are potential targets of insect-mediated selection. Our results suggest that independent evolutionary forces are likely to diversify different axes of plant chemistry without major constraints