Killing me slowly: Harsh environment extends plant maximum life span

Life span (the age of death for individuals that survived the establishment phase) is a key trait in plant life history. Despite its importance for understanding plant–environment relationships, there are still numerous substantial knowledge gaps about variation in plant maximum life spans and the ecological processes underlying these patterns.Based on plant age data obtained by means of herbochronology, we analysed patterns of intraspecific plant maximum life span variation in three perennial species (Campanula scheuchzeri, Helianthemun nummularium and Lotus corniculatus) along environmental gradients of mean annual temperature, soil depth and soil nutrients. This variation was compared with predictions from the ‘death-by-starvation hypothesis’ proposed by Hans Molisch in 1938, an unjustly forgotten ‘extrinsic’ theory on plant life span variation.Our study suggests that plant age variation within populations responds sensitively to growing conditions. The most important finding is that mean annual temperature or environmental conditions related to it seems to be a driving factor for intraspecific variation in plant maximum life span in all species studied. Despite large within-population variation, individuals of C. scheuchzeri, L. corniculatus and H. nummularium generally had a longer life span under colder climates (uplands in our case). In addition, soil depth (as a proxy for habitat susceptibility to drought) was found to have a significant positive effect on the age values in the case of C. scheuchzeri.These findings, therefore, are in line with Molisch’s “death-by-starvation hypothesis”: extended maximum life span results from reduced production of sink tissues and slow vegetative growth. We conclude that the analysis of plant life span adjustments along gradients of environmental factors can considerably contribute to our understanding of how plants may cope with changing environmental conditions, e.g., due to global change.     

Genetic structure and diversity of the Diachasmimorpha longicaudata species complex in Thailand: SSCP analysis of mitochondrial 16S rDNA and COI DNA sequences

Genetic variation among 20 populations of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in Thailand was investigated using single strand conformation polymorphism (SSCP) analysis of mitochondrial DNA sequences. From a total 641 individual parasitoids, seven distinct haplotypes containing a total of 32 polymorphic sites were observed from cytochrome oxidase subunit I (COI) sequences along with five distinct haplotypes containing a total 16 polymorphic sites from 16S rDNA sequences. Values obtained through pairwise F_ST comparisons and analysis of molecular variance (AMOVA) indicated significant genetic differentiation among D. longicaudata populations in Thailand. Congruent relationships showing separation of these populations into three groups were obtained from Neighbor joining and Bayesian phylogenetic tree analyses along with the use of haplotype networks. This SSCP analysis of populations of the D. longicaudata species complex is the first report using molecular population genetic methods to analyze the structure of this parasitoid species in Thailand. This may provide useful information for release of parasitoid strains to maximize their benefit in biological control programs.     

Simultaneous achievement of accurate CT number and image quality improvement for myocardial perfusion CT at 320-MDCT volume scanning

PurposeTo investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study.MethodsUsing a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise.ResultsThe image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction.ConclusionMyocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation.     

Degradation, Recycling, and Shedding of Trypanosoma brucei Variant Surface Glycoprotein

ABSTRACT. Trypanosoma brucei bloodstream forms express a densely packed surface coat consisting of identical variant surface glycoprotein (VSG) molecules. This surface coat is subject to antigenic variation by sequential expression of different VSG genes and thus enables the cells to escape the mammalian host's specific immune response. VSG turnover was investigated and compared with the antigen switching rate. Living cells were radiochemically labeled with either ¹²⁵I-Bolton-Hunter reagent or ³⁵S-methionine, and immunogold-surface labeled for electron microscopy studies. The fate of labeled VSG was studied during subsequent incubation or cultivation of labeled trypanosomes. Our data show that living cells slowly released VSG into the medium with a shedding rate of 2.2 ± 0.6% h⁻¹ (t_1/2= 33 ± 9 h). In contrast, VSG degradation accounted for only 0.3 ± 0.06% h⁻¹ (t_1/2= 237 ± 45 h) and followed the classical lysosomal pathway as judged by electron microscopy. Since VSG uptake by endocytosis was rather high, our data suggest that most of the endocytosed VSG was recycled to the surface membrane. These results indicate that shedding of VSG at a regular turnover rate is sufficient to remove the old VSG coat within one week, and no increase of the VSG turnover rate seems to be necessary during antigenic variation.     

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.     

Xenopus exhibits seasonal variation in retinotectal latency but not tecto-isthmo-tectal latency

1. The tectum of Xenopus receives visuotopic input from both eyes. The contralateral eye's projection reaches the tectum directly, via the optic nerve. The ipsilateral eye's projection reaches the tectum indirectly, via the nucleus isthmi and isthmo-tectal projection. 2. Because of the multi-synaptic nature of the ipsilateral pathway, there is an inherent delay between the time that information from the contralateral eye reaches the tectum and the time that information from the ipsilateral eye arrives at the tectum. The length of the intertectal delay is a function of the latencies of the contralateral and ipsilateral pathways. 3. The length of this intertectal delay has functional, as well as developmental, implications with regard to the role of N-methyl-D-aspartate receptors in tectal cell activity and development of orderly synaptic connections. 4. We have found that the latencies of the contralateral and ipsilateral pathways exhibit a seasonal variation, increasing during the winter months. The increases of both latencies during the winter were of similar magnitude, indicating that there were no significant changes in intertectal delay. The seasonal alteration in contralateral latency was not affected by dark-rearing and was affected to only a minor extent by a week-long alteration of ambient temperature.     

The Influence of Changes in Magnetic Variations and Light–Dark Cycle on Life-History Traits of Daphnia magna

Day–night cycle is the main zeitgeber (time giver) for biological circadian rhythms. Recently, it was suggested that natural diurnal geomagnetic variation may also be utilized by organisms for the synchronization of these rhythms. In this study, life-history traits in Daphnia magna were evaluated after short-term and multigenerational exposure to 16 h day/8 h night cycle, 32 h day/16 h night cycle, diurnal geomagnetic variation of 24 h, simulated magnetic variation of 48 h, and combinations of these conditions. With short-term exposure, the lighting mode substantially influenced the brood to brood period and the lifespan in daphnids. The brood to brood period, brood size, and body length of crustaceans similarly depended on the lighting mode during the multigenerational exposure. At the same time, an interaction of lighting mode and magnetic variations affected to a lesser extent brood to brood period, brood size, and newborn's body length. The influence of simulated diurnal variation on life-history traits in daphnids appeared distinctly as effects of synchronization between periods of lighting mode and magnetic variations during the multigenerational exposure. Newborn's body length significantly depended on the lighting regime when the periods of both studied zeitgebers were unsynchronized, or on the interaction of light regime with magnetic variations when the periods were synchronized. These results confirm the hypothesis that diurnal geomagnetic variation is an additional zeitgeber for biological circadian rhythms. Possible mechanisms for these observed effects are discussed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society     

The persistence of short‐term cold acclimation in Drosophila melanogaster (Diptera: Drosophilidae)

Daily and seasonal fluctuations in temperature present significant challenges for the survival of many ectothermic species that can be tempered via thermal acclimation. In the present study, we use multiple naturally derived genotypes of Drosophila melanogaster to determine the persistence of beneficial short‐term thermal acclimation on subsequent survival after cold shock. We found that the benefit of short‐term acclimation persisted for 2 h in most genotypes after a rapid cold hardening treatment. Genotype did not directly influence the persistence of short‐term acclimation benefits, indicating that environmental variation may be more important for the persistence of acclimation benefits rather than genetic capacity for acclimation. The present study extends the current understanding of the limits and importance of short‐term acclimation events, providing greater detail on the timing of the loss of short‐term acclimation benefits in a genetically variable natural population.     

Identification of a 13-kDa protein associated with the polyhydroxyalkanoic acid granules from Acinetobacter spp.

Abstract Transferrin-binding proteins from Neisseria meningitidis vary among different isolates. We have identified and studied a hypervariable region adjacent to the carboxyl-end of the transferrin-binding domain of the Tbp2 molecule. The tbp2 genes from six strains of N. meningitidis were cloned and sequenced in this particular region. Sequence analysis of these regions along with five other sequences available from pathogenic Neisseria showed a common organisation of seven highly variable nucleotide stretches interspersed with six conserved nucleotide stretches. The variable regions correlated with the location of immunoreactive epitopes in polyclonal antisera raised to transferrin-binding proteins identified by peptide pin technology. Sequence analysis suggested a mosaic-like organisation of the tbp2 genes. Taken together, these data suggest that the antigenic variation in this part of the protein may result from a strong host immune pressure.