Increased insect herbivore performance under elevated CO2 is associated with lower plant defence signalling and minimal declines in nutritional quality

Changes in insect herbivore performance under elevated atmosphere carbon dioxide concentrations e[CO2] are often driven by changes in the nutritional and defensive chemistry of their host plants. Studies addressing how the prolific pest cotton bollworm (Helicoverpa armigera) responds to e[CO2] show that performance usually declines, often associated with lower nutritional (e.g. nitrogen (N) concentrations) quality of host plants under e[CO2]. We investigated the impacts of e[CO2] on nutritional quality and anti-herbivore (jasmonate) defensive signalling in lucerne (Medicago sativa) when challenged by H. armigera. While foliar N decreased under e[CO2], other aspects of nutritional quality (soluble protein, amino acids, foliar C:N) were largely unaffected, potentially due to increased root nodulation under e[CO2]. In contrast, e[CO2] greatly reduced jasmonate signalling in M. sativa following H. armigera attack; jasmonic acid concentrations were ca. 56% lower in attacked plants grown under e[CO2]. Concurrent with this, relative growth rates of H. armigera were ca. 66% higher when feeding on e[CO2]-grown plants. In contrast with previous reports, which we meta-analytically summarise, we provide the first evidence that H. armigera performance can increase under e[CO2]. This may occur in plants, such as M. sativa, where e[CO2] has limited impacts on nutritional quality yet reduces jasmonate defence signalling. Note: An Author Correction to this article was published on 07 December 2020. The PDF available here includes the correction appended to the original

Aphid feeding induces phytohormonal cross-talk without affecting silicon defense against subsequent chewing herbivores

Prior feeding by insect herbivores frequently affects plant quality for herbivores that subsequently feed on the plant. Facilitation occurs when one herbivore improves plant quality for other herbivores, including when the former compromises plant defenses. Silicon (Si) is an important defense in grasses that increases following activation of the jasmonic acid (JA) pathway. Given that aphids often stimulate the salicylic acid (SA) pathway, we hypothesized that this could reduce Si defense because of the well documented antagonistic cross-talk between SA and JA. We tested this in the model grass Brachypodium distachyon with and without Si (+Si and −Si, respectively); half of the plants were exposed to aphids (Rhopalosiphum padi) and half remained aphid-free. Aphid-free and aphid-exposed plants were then fed to chewing herbivores (Helicoverpa armigera). Aphids triggered higher SA concentrations which suppressed JA concentrations but this did not affect foliar Si. Chewing herbivores triggered higher JA concentrations and induced Si uptake, regardless of previous feeding by aphids. Chewer growth rates were not impacted by prior aphid herbivory but were reduced by 75% when feeding on +Si plants. We concluded that aphids caused phytohormonal cross-talk but this was overridden by chewing herbivory that also induced Si uptake

Silicon alters leaf surface morphology and suppresses insect herbivory in a model grass species

Grasses accumulate large amounts of silicon (Si) which is deposited in trichomes, specialised silica cells and cell walls. This may increase leaf toughness and reduce cell rupture, palatability and digestion. Few studies have measured leaf mechanical traits in response to Si, thus the effect of Si on herbivores can be difficult to disentangle from Si-induced changes in leaf surface morphology. We assessed the effects of Si on Brachypodium distachyon mechanical traits (specific leaf area (SLA), thickness, leaf dry matter content (LDMC), relative electrolyte leakage (REL)) and leaf surface morphology (macrohairs, prickle, silica and epidermal cells) and determined the effects of Si on the growth of two generalist insect herbivores (Helicoverpa armigera and Acheta domesticus). Si had no effect on leaf mechanical traits; however, Si changed leaf surface morphology: silica and prickle cells were on average 127% and 36% larger in Si supplemented plants, respectively. Prickle cell density was significantly reduced by Si, while macrohair density remained unchanged. Caterpillars were more negatively affected by Si compared to crickets, possibly due to the latter having a thicker and thus more protective gut lining. Our data show that Si acts as a direct defence against leaf-chewing insects by changing the morphology of specialised defence structures without altering leaf mechanical traits

Climatic drivers of silicon accumulation in a model grass operate in low- but not high-silicon soils

Grasses are hyper-accumulators of silicon (Si), which is known to alleviate diverse environmental stresses, prompting speculation that Si accumulation evolved in response to unfavourable climatic conditions, including seasonally arid environments. We conducted a common garden experiment using 57 accessions of the model grass Brachypodium distachyon, sourced from different Mediterranean locations, to test relationships between Si accumulation and 19 bioclimatic variables. Plants were grown in soil with either low or high (Si supplemented) levels of bioavailable Si. Si accumulation was negatively correlated with temperature variables (annual mean diurnal temperature range, temperature seasonality, annual temperature range) and precipitation seasonality. Si accumulation was positively correlated with precipitation variables (annual precipitation, precipitation of the driest month and quarter, and precipitation of the warmest quarter). These relationships, however, were only observed in low-Si soils and not in Si-supplemented soils. Our hypothesis that accessions of B. distachyon from seasonally arid conditions have higher Si accumulation was not supported. On the contrary, higher temperatures and lower precipitation regimes were associated with lower Si accumulation. These relationships were decoupled in high-Si soils. These exploratory results suggest that geographical origin and prevailing climatic conditions may play a role in predicting patterns of Si accumulation in grasses

Factors Related to Accelerometer-determined Patterns of Physical Activity in Adults: The Houston TRAIN Study

Meeting U.S. Physical Activity (PA) Guidelines has health benefits. Yet, little is known about the factors related to changes in PA over time, particularly among minority populations. PURPOSE: To examine sociodemographic, PA preferences, and health factors related to accelerometer-derived patterns of 1-year PA change in the Houston Travel Related Activity in Neighborhoods (TRAIN) Study, a majority-minority cohort. METHODS: Participants wore an ActiGraph wGT3X-BT monitor and completed self-report surveys at baseline and follow-up. Valid wear time was defined as ≥ 4 days, ≥ 10 hrs/day. PA was stratified by meeting Guidelines using total MVPA, defined by Freedson. Four PA patterns were defined: (i) ‘maintain high’ activity above Guidelines, (ii) ‘increased’ to meet Guidelines, (iii) ‘decreased’ from meet to not meet Guidelines, and (iv) ‘maintained low’ activity. Multinomial logistic regression was used to examine associations between studied factors and each PA pattern, with the ‘maintain high’ group as referent. RESULTS: Complete data were available for 153 adults (19% maintained high activity, 8.5% increased, 13% decreased, 59.5% maintained low activity). Controlling for all variables, males (OR = 0.3, 95% CI = 0.1, 0.9) had lower odds of being in the ‘maintain low’ group. Blacks (vs. whites, OR = 18.8, 95% CI = 2.6, 275.0), those liking biking (vs. strongly liking, OR = 4.6, 95% CI = 1.3, 15.6), and older participants (vs. younger, on continuous scale, OR = 1.1, 95% CI = 1.0, 1.1) had higher odds of being in the ‘maintain low’ group. Factors directly associated with being in the ‘increased’ group were being black (vs. white, OR = 17.9, 95% CI = 1.3, 120.9), strong dislike for biking (vs. strongly liking OR = 25.2, 95% CI = 1.6, 401.3), and having more chronic diseases (vs. less, on continuous scale, 95% CI = 1.5, 11.7). Having low educational attainment (vs. high, OR = 0.04, 95% CI = 0.0, 0.9) was inversely associated with being in the ‘increased’ group. No studied factors were significantly associated with being in the ‘decreased’ group. CONCLUSION: PA patterns are dynamic and suggest that sociodemographic, PA preferences, and health factors relate to change patterns over time. Future studies should examine the role of these factors over longer follow-up periods, and consider these factors when designing interventions

A blend of microencapsulated organic acids and botanicals reduces necrotic enteritis via specific signaling pathways in broilers

Necrotic enteritis (NE) is a devastating disease that has seen a resurgence of cases following the removal of antibiotics from feed resulting in financial loss and significant animal health concerns across the poultry industry. The objective was to evaluate the efficacy of a microencapsulated blend of organic (25 % citric and 16.7% sorbic) acids and botanicals (1.7% thymol and 1% vanillin [AviPlus®P]) to reduce clinical NE and determine the signaling pathways associated with any changes. Day-of-hatch by-product broiler breeder chicks were randomly assigned to a control (0) or supplemented (500 g/MT) diet (n=23-26) and evaluated in a NE challenge model (n=3). Birds were administered 2X cocci vaccine on d14 and challenged with a cocktail of Clostridium perfringens strains (107) on d17-19. On d20-21 birds were weighed, euthanized, and scored for NE lesions. Jejunal tissue was collected for kinome analysis using an immuno-metabolism peptide array (n=5; 15/treatment) to compare tissue from supplement-fed birds to controls. Mortality and weight were analyzed using Student's t-test and lesion scores analyzed using F-test two-sample for variances (P<0.05). The kinome data was analyzed using PIIKA2 peptide array analysis software and fold-change between control and treated groups determined. Mortality in the supplemented group was 47.4% and 70.7% in controls (P=0.004). Lesions scores were lower (P=0.006) in supplemented birds (2.47) compared to controls (3.3). Supplement-fed birds tended (P=0.19) to be heavier (848.6g) than controls (796.2g). Kinome analysis showed T cell receptor, TNF and NF-kB signaling pathways contributed to the improvements seen in the supplement-fed birds. The following peptides were significant (P<0.05) in all three pathways: CHUK, MAP3K14, MAP3K7, and NFKB1 indicating their importance. Additionally, there were changes to IL6, IL10, and IFN- γ mRNA expression in tissue between control- and supplement-fed chickens. In conclusion, the addition of a microencapsulated blend of organic acids and botanicals to a broiler diet reduced the clinical signs of NE that was mediated by specific immune-related pathways

Selection of ULIRGs in Infrared and Submm Surveys

We examine the selection characteristics of infrared and sub-mm surveys with IRAS, Spitzer, BLAST, Herschel and SCUBA and identify the range of dust temperatures these surveys are sensitive to, for galaxies in the ULIRG luminosity range (12<log(LIR)<13), between z=0 and z=4. We find that the extent of the redshift range over which surveys are unbiased is a function of the wavelength of selection, flux density limit and ULIRG luminosity. Short wavelength (<200{\mu}m) surveys with IRAS, Spitzer/MIPS and Herschel/PACS are sensitive to all SED types in a large temperature interval (17-87K), over a substantial fraction of their accessible redshift range. On the other hand, long wavelength (>200{\mu}m) surveys with BLAST, Herschel/ SPIRE and SCUBA are significantly more sensitive to cold ULIRGs, disfavouring warmer SEDs even at low redshifts. We evaluate observations in the context of survey selection effects, finding that the lack of cold ULIRGs in the local (z<0.1) Universe is not a consequence of selection and that the range of ULIRG temperatures seen locally is only a subset of a much larger range which exists at high redshift. We demonstrate that the local luminosity-temperature (L-T) relation, which indicates that more luminous sources are also hotter, is not applicable in the distant Universe when extrapolated to the ULIRG regime, because the scatter in observed temperatures is too large. Finally, we show that the difference between the ULIRG temperature distributions locally and at high redshift is not the result of galaxies becoming colder due to an L-T relation which evolves as a function of redshift. Instead, they are consistent with a picture where the evolution of the infrared luminosity function is temperature dependent, i.e. cold galaxies evolve at a faster rate than their warm counterparts.Comment: 11 pages, 6 figures, accepted for publication in MNRA