Impacts of a native parasitic plant on an introduced and a native host species: implications for the control of an invasive weed

Background and Aims: While invasive species may escape from natural enemies in thenew range, the establishment of novel biotic interactions withspecies native to the invaded range can determine their success.Biological control of plant populations can be achieved by manipulationof a species' enemies in the invaded range. Interactions weretherefore investigated between a native parasitic plant andan invasive legume in Mediterranean-type woodlands of SouthAustralia. Methods: The effects of the native stem parasite, Cassytha pubescens,on the introduced host, Cytisus scoparius, and a co-occurringnative host, Leptospermum myrsinoides, were compared. The hypothesisthat the parasitic plant would have a greater impact on theintroduced host than the native host was tested. In a fieldstudy, photosynthesis, growth and survival of hosts and parasitewere examined. Key Results: As predicted, Cassytha had greater impacts on the introducedhost than the native host. Dead Cytisus were associated withdense Cassytha infections but mortality of Leptospermum wasnot correlated with parasite infection. Cassytha infection reducedthe photosynthetic rates of both hosts. Infected Cytisus showedslower recovery of photosystem II efficiency, lower transpirationrates and reduced photosynthetic biomass in comparison withuninfected plants. Parasite photosynthetic rates and growthrates were higher when growing on the introduced host Cytisus,than on Leptospermum. Conclusions: Infection by a native parasitic plant had strong negative effectson the physiology and above-ground biomass allocation of anintroduced species and was correlated with increased plant mortality.The greater impact of the parasite on the introduced host maybe due to either the greater resources that this host providesor increased resistance to infection by the native host. Thisdisparity of effects between introduced host and native hostindicates the potential for Cassytha to be exploited as a controltool.     

The Importance of Hydrodynamics for Protected and Endangered Biodiversity of Lowland Rivers

This paper examines the relationship between protected and endangered riverine species (target species) and hydrodynamics in river-floodplain ecosystems, combining ecological and policy-legal aspects of biodiversity conservation in river management. The importance of different hydrodynamic conditions along a lateral gradient was quantified for various taxonomic groups. Our results show that (i) target species require ecotopes along the entire hydrodynamic gradient; (ii) different parts of the hydrodynamic gradient are important to different species, belonging to different taxonomic groups; (iii) in particular low-dynamic parts are important for many species and (iv) species differ in their specificity for hydrodynamic conditions. Many species of higher plants, fish and butterflies have a narrow range for hydrodynamics and many species of birds and mammals use ecotopes along the entire gradient. Even when focussing only on target species, the entire natural hydrodynamic gradient is important. This means that the riverine species assemblage as a whole can benefit from measures focussing on target species only. River reconstruction and management should aim at re-establishing the entire hydrodynamic gradient, increasing the spatial heterogeneity of hydrodynamic conditions.     

EXPERIMENTAL EVOLUTION OF RESISTANCE IN BRASSICA RAPA: CORRELATED RESPONSE OF TOLERANCE IN LINES SELECTED FOR GLUCOSINOLATE CONTENT

The evolutionary response of plant populations to selection for increased defense may be constrained by costs of defense. The purpose of this study was to investigate such constraints on the evolution of defense due to a cost of defense manifested as a trade-off between defense and tolerance. Variation in the response to artificial damage (tolerance) among lines of Brassica rapa that had been artificially selected for foliar glucosinolate content (defense) was examined. Leaf area was removed from replicates of three selection lines (high glucosinolates, control, and low glucosinolates) at three damage levels (0%, 20%, and 60% damage). An external cost of defense would result in a statistically significant selection line by damage treatment interaction, with those selected for high defense expressing less tolerance than those selected for low defense. Damage treatment had a significant overall effect on estimated total fitness, with fitness declining with increasing damage level. Further, selection line also had a significant overall effect on estimated total fitness, with low-defense selection lines having higher fitness compared to both control and high-defense selection lines. More importantly, a cost of defense in terms of tolerance was demonstrated by a significant selection line-by-damage treatment interaction. This interaction was in the direction to demonstrate a genetic trade-off between defense and tolerance, with low-defense selection lines decreasing estimated total fitness in response to damage less than both control and high-defense selection lines. Variation in tolerance among selection lines was due to the greater ability of low-defense lines to maintain fruit and seed production despite the presence of damage. In terms of tolerance, this cost of glucosinolate production in B. rapa could constrain the evolution of increased defense and, in so doing, maintain individuals within the population that are poorly defended yet tolerant.     

Alcohol consumption by youth: Peers,parents, or prices?

Using data from the National Longitudinal Survey of Adolescent to Adult Health, we estimate the effect of peers’ alcohol consumption and alcohol prices on the drinking habits of high-school-age youth. We use the two-stage residual inclusion method to account for the endogeneity of peer drinking in nonlinear models. For our sample of high school students, we find that peer effects are statistically and economically significant regarding the choice to participate in drinking but are not significant for the frequency of drinking, including binge drinking. Regarding alcohol prices, even though we have good price variation in our sample, alcohol prices are not found to be significant. The results are important for policymakers who are considering policies to reduce underage drinking, as we conclude that no significant impact on underage drinking will result from low-tax states’ increasing excise taxes on alcohol so they are similar to those of high-tax states. Policymakers may choose to focus instead on the influence of peers and changing the social norm behavior.     

Intraspecific variation in host plant traits mediates taxonomic and functional composition of local insect herbivore communities

1. Host plant phenotypic traits affect the structure of the associated consumer community and mediate species interactions. Intraspecific variation in host traits is well documented, although a functional understanding of variable traits that drive herbivore community response is lacking. We address this gap by modelling the trait-environment relationship using insect traits and host plant traits in a multilevel model. 2. We compare herbivore assemblages from the canopy of the phenotypically variable tree Metrosideros polymorpha on Hawai‘i Island. Multiple distinct varieties of M. polymorpha frequently co-occur, with variation in morphological traits. Using this system, we identify host and insect traits that underlie patterns of herbivore abundance and quantify the strength of host-insect trait interactions. 3. This work examines plant-insect interactions at a community scale, across 36 herbivore species in three orders. We find that co-occurring trees of varying phenotype support distinct communities. Leaf traits, including specific leaf area, trichome presence, and leaf nutrients, explain 46% of variation in insect communities. We find that feeding guild and nymphal life history are correlated with host plant traits, and we show that model predictions are improved by including the host and insect trait interaction. 4. This study demonstrates how insect herbivores traits influence community response to morphologically variable hosts. Environmental heterogeneity indirectly affected herbivore community structure via intraspecific variation in host plants, providing an important source of variation for maintaining diversity in the broader community.     

CRISPR-based peptide library display and programmable microarray self-assembly for rapid quantitative protein binding assays

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Short-chain fatty acids and polyamines in the pathogenesis of necrotizing enterocolitis: Kinetics aspects in gnotobiotic quails

Despite years of investigation, pathogenesis of necrotizing enterocolitis (NEC) remains elusive. Bacterial metabolites were implicated by several authors but their roles remain controversial. The aim of our study was to investigate the role of SCFAs and polyamines through a kinetic study of histological and macroscopical digestive lesions in monobiotic quails. Germ-free quails, inoculated with a Clostridium butyricum strain involved in a NEC case, were fed or not with a diet including lactose (7%). Quails were sacrificed at various times between D7 and D24 after bacterial inoculation. NEC-like lesions, i.e. thickening, pneumatosis, and hemorrhages, occurred only in lactose-fed quails and increased with time. The main histological characteristics were infiltrates of mononuclear cells, then heterophilic cells, then gas cyst and necrosis. The first event observed, before histological and macroscopical lesions, is a high production of butyric acid, which precedes an increase of iNOS gene expression. No difference in polyamines contents depending on the diet was observed. These results show the major role of butyric acid produced by commensal bacteria in the onset of the digestive lesions.     

Use of flavin photochemistry to probe intraprotein and interprotein electron transfer mechanisms

Photoexcitation of flavin analogs generates the lowest triplet state (via intersystem crossing from the first excited singlet state) in the nanosecond time domain and with high quantum efficiency. The triplet, being a strong oxidant, can abstract a hydrogen atom (or an electron) from a reduced donor in a diffusion-controlled reaction. If the donor is a redox protein, the oxidation process can be used to initiate an electron transfer sequence involving either intramolecular or intermolecular reactions. If the donor is an organic compound such as EDTA, the neutral flavin semiquinone will be produced by H atom abstraction; this is a strong reductant and can subsequently transfer a hydrogen atom (or an electron) to an oxidized redox protein, thereby again initiating a sequence of intramolecular or intermolecular processes. If flavin photoexcitation is accomplished using a pulsed laser light source, the initiation of these protein electron transfer reactions can be made to occur in the nanosecond to microsecond time domain, and the sequence of events can be followed by time-resolved spectrophotometry to obtain rate constants and thus mechanistic information. The present paper describes this technology, and selected examples of its use in the investigation of redox protein mechanisms are given.