Analytic partitioning of honeybee (Apis mellifera L.) flight activity at nest entrance: adaptation and behavioural inertia in a changing environment

Ecology of bees (Hymenoptera, Apiformes) is entirely constrained by the centralized exchange between the nest and its environment. Herein, we investigate the ecological meaning of the flight activity of honeybees (Apis mellifera L.) at the entrance of the nest, and assessed whether this simple metric can be used as a proxy to infer on the colony state (population size and foraging activity). Theory predicts that flight activity of a colony should increase (1) with population size (density-dependence hypothesis), (2) with floral resource availability (optimal foraging hypothesis), and (3) with the flight activity during previous hours or days, due to a temporal autocorrelation (behavioural inertia hypothesis). We built and compared series of explanatory models for the flight activity measured at the entrance of hives, and its two visible components, namely bees with and without pollen loads. Data were collected on 26 honeybee colonies, both before and after a translocation into a new environment with controlled floral resource availability in order to distinguish among the respective contributions of explanatory factors. Current flight activity was consistently and positively influenced by previous flight activity as well as by the current resource availability. To our knowledge, this represents the first characterization of behavioural inertia in the context of a collective behaviour. Population size only influenced flight activity of bees without pollen loads. We discuss the limits of using simple counts of flying bees at the hive entrance to infer the colony state.     

Next generation modeling in GWAS: comparing different genetic architectures

The continuous advancement in genotyping technology has not been accompanied by the application of innovative statistical methods, such as multi-marker methods (MMM), to unravel genetic associations with complex traits. Although the performance of MMM has been widely explored in a prediction context, little is known on their behavior in the quantitative trait loci (QTL) detection under complex genetic architectures. We shed light on this still open question by applying Bayes A (BA) and Bayesian LASSO (BL) to simulated and real data. Both methods were compared to the single marker regression (SMR). Simulated data were generated in the context of six scenarios differing on effect size, minor allele frequency (MAF) and linkage disequilibrium (LD) between QTLs. These were based on real SNP genotypes in chromosome 21 from the Spanish Bladder Cancer Study. We show how the genetic architecture dramatically affects the behavior of the methods in terms of power, type I error and accuracy of estimates. Markers with high MAF are easier to detect by all methods, especially if they have a large effect on the phenotypic trait. A high LD between QTLs with either large or small effects differently affects the power of the methods: it impairs QTL detection with BA, irrespectively of the effect size, although boosts that of small effects with BL and SMR. We demonstrate the convenience of applying MMM rather than SMR because of their larger power and smaller type I error. Results from real data when applying MMM suggest novel associations not detected by SMR.     

Hennekam syndrome can be caused by FAT4 mutations and be allelic to Van Maldergem syndrome

The Hennekam lymphangiectasia–lymphedema syndrome is a genetically heterogeneous disorder. It can be caused by mutations in CCBE1 which are found in approximately 25 % of cases. We used homozygosity mapping and whole-exome sequencing in the original HS family with multiple affected individuals in whom no CCBE1 mutation had been detected, and identified a homozygous mutation in the FAT4 gene. Subsequent targeted mutation analysis of FAT4 in a cohort of 24 CCBE1 mutation-negative Hennekam syndrome patients identified homozygous or compound heterozygous mutations in four additional families. Mutations in FAT4 have been previously associated with Van Maldergem syndrome. Detailed clinical comparison between van Maldergem syndrome and Hennekam syndrome patients shows that there is a substantial overlap in phenotype, especially in facial appearance. We conclude that Hennekam syndrome can be caused by mutations in FAT4 and be allelic to Van Maldergem syndrome.     

Functional analysis of pyochelin-/enantiopyochelin-related genes from a pathogenicity island of Pseudomonas aeruginosa strain PA14

Genomic islands are foreign DNA blocks inserted in so-called regions of genomic plasticity (RGP). Depending on their gene content, they are classified as pathogenicity, symbiosis, metabolic, fitness or resistance islands, although a detailed functional analysis is often lacking. Here we focused on a 34-kb pathogenicity island of Pseudomonas aeruginosa PA14 (PA14GI-6), which is inserted at RGP5 and carries genes related to those for pyochelin/enantiopyochelin biosynthesis. These enantiomeric siderophores of P. aeruginosa and certain strains of Pseudomonas protegens are assembled by a thiotemplate mechanism from salicylate and two molecules of cysteine. The biochemical function of several proteins encoded by PA14GI-6 was investigated by a series of complementation analyses using mutants affected in potential homologs. We found that PA14_54940 codes for a bifunctional salicylate synthase/salicyl-AMP ligase (for generation and activation of salicylate), that PA14_54930 specifies a dihydroaeruginoic acid (Dha) synthetase (for coupling salicylate with a cysteine-derived thiazoline ring), that PA14_54910 produces a type II thioesterase (for quality control), and that PA14_54880 encodes a serine O-acetyltransferase (for increased cysteine availability). The structure of the PA14GI-6-specified metabolite was determined by mass spectrometry, thin-layer chromatography, and HPLC as (R)-Dha, an iron chelator with antibacterial, antifungal and antitumor activity. The conservation of this genomic island in many clinical and environmental P. aeruginosa isolates of different geographical origin suggests that the ability for Dha production may confer a selective advantage to its host.     

Genetic diversity,spatial genetic structure and realised seed and pollen dispersal of Himatanthus drasticus (Apocynaceae) in the Brazilian savanna

We assessed the pollen and seed dispersal patterns, genetic diversity, inbreeding and spatial genetic structure of Himatanthus drasticus (Apocynaceae), a tree native to the Brazilian Savanna (Cerrado) that is heavily exploited for its medicinal latex. The study was conducted in the Araripe National Forest, Ceará State, Brazil. Within a one-hectare plot, samples were collected from all adult trees, adult trees located in the immediate vicinity of the plot, and seedlings. All sampled individuals were mapped and genotyped using microsatellite markers. High levels of polymorphism and significant levels of inbreeding were found, which indicates that self-fertilisation and mating among relatives occur in this population. Both the adults and seedlings had significant spatial genetic structure up to ~40 m and our results confirmed the occurrence of isolation by distance. Pollen and seeds were dispersed over short distances and immigration of pollen and seeds into the plot was estimated at 13 and 9 %, respectively. Taking into consideration the degree of inbreeding, relatedness, intrapopulation spatial genetic structure and pollen dispersal distance, we recommend collecting seeds from a large number of trees spaced at least 150 m apart to avoid collecting seeds from related individuals and an overlap of pollen pools among seed trees.     

Habitat-Specific Effects of Fishing Disturbance on Benthic Species Richness in Marine Soft Sediments

Around the globe, marine soft sediments on continental shelves are affected by bottom trawl fisheries. In this study, we explore the effect of this widespread anthropogenic disturbance on the species richness of a benthic ecosystem, along a gradient of bottom trawling intensities. We use data from 80 annually sampled benthic stations in the Dutch part of the North Sea, over a period of 6 years. Trawl disturbance intensity at each sampled location was reconstructed from satellite tracking of fishing vessels. Using a structural equation model, we studied how trawl disturbance intensity relates to benthic species richness, and how the relationship is mediated by total benthic biomass, primary productivity, water depth, and median sediment grain size. Our results show a negative relationship between trawling intensity and species richness. Richness is also negatively related to sediment grain size and primary productivity, and positively related to biomass. Further analysis of our data shows that the negative effects of trawling on richness are limited to relatively species-rich, deep areas with fine sediments. We find no effect of bottom trawling on species richness in shallow areas with coarse bottoms. These condition-dependent effects of trawling suggest that protection of benthic richness might best be achieved by reducing trawling intensity in a strategically chosen fraction of space.     

Trophic overlap between sexes in the dimorphic African black oystercatcher foraging on an alien mussel

Sex‐specific feeding segregation related to sexual bill dimorphism has been described in several oystercatcher species, including the African black oystercatcher. For the latter, studies concerned only a small number of breeding pairs and were done prior the invasion of the South African rocky shores by the Mediterranean mussel, which is believed to have benefited oystercatchers by increasing overall biomass. Here, we investigated geographic variability in the segregation of diet, biometrics and body condition between sexes in the African species, in relation to changes in foraging habitats along the South African coastline, using stable isotope analyses. Males and females and their potential prey (mussels, limpets, polychaetes and ascidians) were sampled on the southern African west, south‐west and south‐east coasts for stable isotope analyses and biometrics and body conditions of birds were measured. Bill dimorphism occurred throughout the study area and south‐west males had lower body conditions than other males and females in general. Sexes displayed little differences in their δ¹³C ratios and in the relative consumption of the different prey throughout the study area, except on the south‐east coast where males were slightly depleted in ¹³C relative to females and the most abundant prey elsewhere (the Mediterranean mussel) is rare. Females were slightly but significantly enriched in ¹⁵N by 0.3‰ compared to their breeding partners and this did not link clearly to differences in diet. We argue that the combined effect of biogeographic variations in rocky shores diversity and biomass, heterogeneous invasion by the Mediterranean mussel on the South African coastline and bill dimorphism may have altered the sex‐specific feeding behaviour of oystercatchers differently between coastal regions and possibly had an additional cost for male oystercatchers faced with lower prey biomass and diversity on the south‐west coast.     

Invasion of insect cells by Spiroplasma citri involves spiralin relocalization and lectin/glycoconjugate‐type interactions

Spiroplamas are helical, cell wall‐less bacteria belonging to the Class Mollicutes, a group of microorganisms phylogenetically related to low G+C, Gram‐positive bacteria. Spiroplasma species are all found associated with arthropods and a few, including Spiroplasma citri are pathogenic to plant. Thus S. citri has the ability to colonize cells of two very distinct hosts, the plant and the insect vector. While spiroplasmal factors involved in transmission by the leafhopper Circulifer haematoceps have been identified, their specific contribution to invasion of insect cells is poorly understood. In this study we provide evidence that the lipoprotein spiralin plays a major role in the very early step of cell invasion. Confocal laser scanning immunomicroscopy revealed a relocalization of spiralin at the contact zone of adhering spiroplasmas. The implication of a role for spiralin in adhesion to insect cells was further supported by adhesion assays showing that a spiralin‐less mutant was impaired in adhesion and that recombinant spiralin triggered adhesion of latex beads. We also showed that cytochalasin D induced changes in the surface‐exposed glycoconjugates, as inferred from the lectin binding patterns, and specifically improved adhesion of S. citri wild‐type but not of the spiralin‐less mutant. These results indicate that cytochalasin D exposes insect cell receptors of spiralin that are masked in untreated cells. In addition, competitive adhesion assays with lectins strongly suggest spiralin to exhibit glycoconjugate binding properties similar to that of the Vicia villosa agglutinin (VVA) lectin.     

The biofilm mode of life boosts the anti‐inflammatory properties of Lactobacillus

The predominant form of life for microorganisms in their natural habitats is the biofilm mode of growth. The adherence and colonization of probiotic bacteria are considered as essential factors for their immunoregulatory function in the host. Here, we show that Lactobacillus casei ATCC334 adheres to and colonizes the gut of zebrafish larvae. The abundance of pro‐inflammatory cytokines and the recruitment of macrophages were low when inflammation was induced in probiotic‐fed animals, suggesting that these bacteria have anti‐inflammatory properties. We treated human macrophage‐differentiated monocytic THP‐1 cells with supernatants of L. casei ATCC334 grown in either biofilm or planktonic cultures. TNF‐α production was suppressed and the NF‐κB pathway was inhibited only in the presence of supernatants from biofilms. We identified GroEL as the biofilm supernatant compound responsible, at least partially, for this anti‐inflammatory effect. Gradual immunodepletion of GroEL demonstrated that the abundance of GroEL and TNF‐α were inversely correlated. We confirmed that biofilm development in other Lactobacillus species affects the immune response. The biofilms supernatants of these species also contained large amounts of GroEL. Thus, our results demonstrate that the biofilm enhances the immunomodulatory effects of Lactobacillus sp. and that secreted GroEL is involved in this beneficial effect.