Selective attention in a synchronising bushcricket: physiology

Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.

Selective attention in a synchronising bushcricket: physiology, behaviour and ecology

Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.

Pollinator limitation and the effect of breeding systems on plant reproduction in forest fragments

Reproduction of plants in fragmented habitats may be limited because of lower diversity or abundance of pollinators, and/or variation in local plant density. We assessed natural fruit set and pollinator limitation in ten species of woody plants in natural and restored fragments in the Pondicherry region of southern India, to see whether breeding system of plants (self-compatible and self-incompatible) affected fruit set. We tested whether the number of flowering individuals in the fragments affected the fruit set and further examined the adult and sapling densities of self-compatible (SC) and self-incompatible (SI) species. We measured the natural level of fruit set and pollinator limitation (calculated as the difference in fruit set between hand cross-pollinated and naturally pollinated flowers). Our results demonstrate that there was a higher level of pollinator limitation and hence lower levels of natural fruit set in self-incompatible species as compared to self-compatible species. However, the hand cross-pollinated flowers in SC and SI species produced similar levels of fruit set,further indicating that lower fruit set was due to pollinator limitation and not due to lack of cross-compatible individuals in the fragments. There was no significant relation between number of flowering individuals and the levels of natural fruit set, except for two species Derris ovalifolia, Ixora pavetta. In these species the natural fruit set decreased with increasing population size, again indicating pollinator limitation. The adult and sapling densities in self-compatible species were significantly higher than inself-incompatible species. These findings indicate that the low reproductive output in self-incompatible species may eventually lead to lower population sizes. Restoration of pollinator services along with plant species in fragmented habitats is important for the long-term conservation of biodiversity. (C) 2009 Elsevier Masson SAS. All rights reserved.

The complete mitochondrial genome of the tarnished plant bug, Lygus lineolaris (Heteroptera: Miridae)

The complete mitochondrial genome of the tarnished plant bug, Lygus lineolaris, comprised 17,027 bp. The genome contained 13 protein coding regions, 22 tRNA genes and 2 ribosomal RNA genes. The gene arrangement corresponded to the common order found among insect mtDNAs which was considered to be the ancestral arrangement. The protein coding genes started with ATN and stopped with TAA or TAG. The nucleotide distribution was 76.0% A + T. The control region contained two repeat regions, one was 24 bp and the other was 161 bp. The Genbank accession for the complete L. lineolaris mt genome is EU401991.

A generic individual-based spatially explicit model as a novel tool for investigating insect-plant interactions: A case study of the behavioural ecology of frugivorous Tephritidae

Computational modelling of mechanisms underlying processes in the real world can be of great value in understanding complex biological behaviours. Uptake in general biology and ecology has been rapid. However, it often requires specific data sets that are overly costly in time and resources to collect. The aim of the current study was to test whether a generic behavioural ecology model constructed using published data could give realistic outputs for individual species. An individual-based model was developed using the Pattern-Oriented Modelling (POM) strategy and protocol, based on behavioural rules associated with insect movement choices. Frugivorous Tephritidae (fruit flies) were chosen because of economic significance in global agriculture and the multiple published data sets available for a range of species. The Queensland fruit fly (Qfly), Bactrocera tryoni, was identified as a suitable individual species for testing. Plant canopies with modified architecture were used to run predictive simulations. A field study was then conducted to validate our model predictions on how plant architecture affects fruit flies’ behaviours. Characteristics of plant architecture such as different shapes, e.g., closed-canopy and vase-shaped, affected fly movement patterns and time spent on host fruit. The number of visits to host fruit also differed between the edge and centre in closed-canopy plants. Compared to plant architecture, host fruit has less contribution to effects on flies’ movement patterns. The results from this model, combined with our field study and published empirical data suggest that placing fly traps in the upper canopy at the edge should work best. Such a modelling approach allows rapid testing of ideas about organismal interactions with environmental substrates in silico rather than in vivo, to generate new perspectives. Using published data provides a saving in time and resources. Adjustments for specific questions can be achieved by refinement of parameters based on targeted experiments.

Selective attention in a synchronising bushcricket: physiology, behaviour and ecology

Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.

Unusual RNA plant virus integration in the soybean genome leads to the production of small RNAs

Horizontal gene transfer (HGT) is known to be a major force in genome evolution. The acquisition of genes from viruses by eukaryotic genomes is a well-studied example of HGT, including rare cases of non-retroviral RNA virus integration. The present study describes the integration of cucumber mosaic virus RNA-1 into soybean genome. After an initial metatranscriptomic analysis of small RNAs derived from soybean, the de novo assembly resulted a 3029-nt contig homologous to RNA-1. The integration of this sequence in the soybean genome was confirmed by DNA deep sequencing. The locus where the integration occurred harbors the full RNA-1 sequence followed by the partial sequence of an endogenous mRNA and another sequence of RNA-1 as an inverted repeat and allowing the formation of a hairpin structure. This region recombined into a retrotransposon located inside an exon of a soybean gene. The nucleotide similarity of the integrated sequence compared to other Cucumber mosaic virus sequences indicates that the integration event occurred recently. We described a rare event of non-retroviral RNA virus integration in soybean that leads to the production of a double-stranded RNA in a similar fashion to virus resistance RNAi plants.

Missing pieces in the puzzle of plant microRNAs

Plant microRNAs (miRNAs) are important regulatory switches. Recent advances have revealed many regulatory layers between the two essential processes, miRNA biogenesis and function. However, how these multilayered regulatory processes ultimately control miRNA gene regulation and connects miRNAs and plant responses with the surrounding environment is still largely unknown. In this opinion article, we propose that the miRNA pathway is highly dynamic and plastic. The apparent flexibility of the miRNA pathway in plants appears to be controlled by a number recently identified proteins and poorly characterized signaling cascades. We further propose that altered miRNA accumulation can be a direct consequence of the rewiring of interactions between proteins that function in the miRNA pathway, an avenue that remains largely unexplored.

Microcalorimetric indications for ligand binding as a function of the protein for galactoside-specific plant and avian lectins

The process cascade leading to the final accommodation of the carbohydrate ligand in the lectin’s binding site comprises enthalpic and entropic contributions of the binding partners and solvent molecules. With emphasis on lactose, N-acetyllactosamine, and thiodigalactoside as potent inhibitors of binding of galactoside-specific lectins, the question was addressed to what extent these parameters are affected as a function of the protein. The microcalorimetric study of carbohydrate association to the galectin from chicken liver (CG-16) and the agglutinin from Viscum album (VAA) revealed enthalpy–entropy compensation with evident protein type-dependent changes for N-acetyllactosamine. Reduction of the entropic penalty by differential flexibility of loops or side chains and/or solvation properties of the protein will have to be reckoned with to assign a molecular cause to protein type-dependent changes in thermodynamic parameters for lectins sharing the same monosaccharide specificity.

Interrelations of soil micro-orgamisms and mulberry I.Phytohormone production by soil and rhizosphere bacteria and their effect on plant growth

Bacteria isolated from the rhizosphere of mulberry (Morus indica) as well as from control soil were tested for their effects on the growth of mulberry seedlings and for phytohormone production. About 12.8 per cent of the rhizosphere and 9.7 per cent of the soil isolates produced phytohormones in cultures. Rhizosphere isolates were more active in hormone synthesis than their soil counterparts. Soaking mulberry stem cuttings in culture filtrates of phytohormone synthesisers hastened their rooting. Culture filtrates of many isolates — hormone producers or not — stimulated or inhibited the growth of shoot and/or root of plants. Many cultures could also inhibit the germination of mulberry seeds.

Transposable elements in a marginal plant population

Background
How new forms arise in nature has engaged evolutionary biologists since Darwin's seminal treatise on the origin of species. Transposable elements (TEs) may be among the most important internal sources for intraspecific variability. Thus, we aimed to explore the temporal dynamics of several TEs in individual genotypes from a small, marginal population of Aegilops speltoides. A diploid cross-pollinated grass species, it is a wild relative of the various wheat species known for their large genome sizes contributed by an extraordinary number of TEs, particularly long terminal repeat (LTR) retrotransposons. The population is characterized by high heteromorphy and possesses a wide spectrum of chromosomal abnormalities including supernumerary chromosomes, heterozygosity for translocations, and variability in the chromosomal position or number of 45S and 5S ribosomal DNA (rDNA) sites. We propose that variability on the morphological and chromosomal levels may be linked to variability at the molecular level and particularly in TE proliferation.

Results
Significant temporal fluctuation in the copy number of TEs was detected when processes that take place in small, marginal populations were simulated. It is known that under critical external conditions, outcrossing plants very often transit to self-pollination. Thus, three morphologically different genotypes with chromosomal aberrations were taken from a wild population of Ae. speltoides, and the dynamics of the TE complex traced through three rounds of selfing. It was discovered that: (i) various families of TEs vary tremendously in copy number between individuals from the same population and the selfed progenies; (ii) the fluctuations in copy number are TE-family specific; (iii) there is a great difference in TE copy number expansion or contraction between gametophytes and sporophytes; and (iv) a small percentage of TEs that increase in copy number can actually insert at novel locations and could serve as a bona fide mutagen.

Conclusions
We hypothesize that TE dynamics could promote or intensify morphological and karyotypical changes, some of which may be potentially important for the process of microevolution, and allow species with plastic genomes to survive as new forms or even species in times of rapid climatic change.

Defoliation and patchy nutrient return drive grazing effects on plant and soil properties in a dairy cow pasture

Large herbivores can influence plant and soil properties in grassland ecosystems, but especially for belowground biota and processes, the mechanisms that explain these effects are not fully understood. Here, we examine the capability of three grazing mechanisms-plant defoliation, dung and urine return, and physical presence of animals (causing trampling and excreta return in patches)-to explain grazing effects in Phleum pratense-Festuca pratensis dairy cow pasture in Finland. Comparison of control plots and plots grazed by cows showed that grazing maintained original plant-community structure, decreased shoot mass and root N and P concentrations, increased shoot N and P concentrations, and had an inconsistent effect on root mass. Among soil fauna, grazing increased the abundance of fungivorous nematodes and Aporrectodea earthworms and decreased the abundance of detritivorous enchytraeids and Lumbricus earthworms. Grazing also increased soil density and pH but did not affect average soil inorganic-N concentration. To reveal the mechanisms behind these effects, we analyzed results from mowed plots and plots that were both mowed and treated with a dung and urine mixture. This comparison revealed that grazing effects on plant attributes were almost entirely explained by defoliation, with only one partly explained by excreta return. Among belowground attributes, however, the mechanisms were more mixed, with effects explained by defoliation, patchy excreta return, and cow trampling. Average soil inorganic-N concentration was not affected by grazing because it was simultaneously decreased by defoliation and increased by cow presence. Presence of cows created great spatial heterogeneity in soil N availability and abundance of fungivorous nematodes. A greenhouse trial revealed a grazing-induced soil feedback on plant growth, which was explained by patchiness in N availability rather than changes in soil biota. Our results show that grazing effects on plant attributes can be satisfactorily predicted using the effects of defoliation, whereas those on soil fauna and soil N availability need understanding of other mechanisms as well. The results indicate that defoliation-induced changes in plant ecophysiology and the great spatial variation in N availability created by grazers are the two key mechanisms through which large herbivores can control grassland ecosystems.

Structure-function relationships of icosahedral plant

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary organization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.