Functional groups of Sahelian trees in a semiarid agroforestry system of Senegal

Aims Addressing plant responses to water stress is critical to understand the structure of plant communities in water-limited environments and to forecast their resilience to future changes in climate. In a semiarid agroforestry system in the Sahelian savannah of Leona (Senegal), we selected nine common tree species and explored their stress-resistance mechanisms. These species represent a variety of life forms and are of high regional socio-economic importance. We hypothesized that different species would show different suites of traits to cope with water stress and expected to identify functional groups differing in strategies to withstand water shortage.Methods Along a dry and a wet season, we monitored four traits reflecting above- and below-ground strategies of resource acquisition such as predawn leaf water potential (ψ pd), specific leaf area (SLA), leaf thickness and leaf area index (LAI). We also measured two morphological traits: trunk diameter and tree height. LAI and ψ pd were measured six times during the dry and rainy seasons, and the other traits were measured once.Important findings We identified two functional classes subdivided into two functional groups of each class. The first class included deciduous and semi-deciduous species that generally had large SLA, low leaf thickness and small-to-intermediate inter-seasonal variations in ψ pd. The second class included evergreen species of two functional groups that differ in SLA, leaf thickness and the magnitude of inter-seasonal variations of ψ pd throughout the year. The four functional groups identified in this study represent plant strategies differing in their response to changing environmental conditions.     

Tick-borne relapsing fever Borreliosis,a major public health problem overlooked in Senegal

BackgroundTick-borne relapsing fever (TBRF) is the most common vector-borne bacterial disease in humans in West Africa. It is frequently clinically confused with malaria. Our study aims to determine, on a micro-geographic scale, the conditions for the maintenance and spread of TBRF in the Niakhar district of Senegal.Methodology/Principal findingsWe conducted clinical, entomological and animal reservoir investigations. Field surveys were carried out in order to investigate the presence of Ornithodoros sonrai vector ticks and to detect Borrelia spp. by qPCR using the 16S rRNA and glpQ genes, respectively. Micromammal trapping series were carried out inside homes and Borrelia infection was detected using brain tissue qPCR. Capillary blood samples from febrile patients were also tested for Borrelia using qPCR. More than 97% (40/41) of the villages surveyed were infested with O. sonrai ticks. The prevalence of Borrelia spp. infections in ticks was 13% (116/910), and over 73% (85/116) were positively confirmed as being Borrelia crocidurae. Borreliosis cases accounted for 12% (94/800) of episodes of fever and all age groups were infected, with children and young people between the ages of 8–14 and 22–28 being the most infected by the disease (16% and 18.4%). TBRF cases occurred in all seasons, with a peak in August. In two species of small rodents that were found to be infected (Arvicanthis niloticus, Mus musculus), the proportion of Borrelia infection was 17.5% (10/57), and the highest prevalence of infection (40.9%, 9/22) was observed in A. niloticus.Conclusion/SignificanceOur study indicates that TBRF is an endemic disease in the Niakhar district, where children and young people are the most infected. Arvicanthis niloticus and O. sonrai ticks are massively present and appear to be the main epidemiological reservoirs causing its extensive spread to humans.     

Evaluation of anti-Plasmodium falciparum antibodies in Senegalese adults using different types of crude extracts from various strains of parasite

To date, no consensus exists on the type of crude Plasmodium falciparum Ags to be used in a standard assay for the evaluation of the overall anti-blood-stage immune response in humans. Comparison of the dose-dependent reactivity of using a pool of hyper-immune Senegalese sera to saponin and water schizont extracts of the Senegalese 07/03 isolate indicated similar reactivity on both types of antigen preparations. Water schizont extracts from three different strains of P. falciparum adapted to in vitro culture probed with a panel of specific mouse antisera and monoclonal antibodies reacting with conserved antigens showed similar antigenic content. Seroreactivity of immune individuals living in three different areas of endemicity was assessed in parallel on water crude extracts. The individual IgG, IgM and IgG subclass antibody responses to the various schizont preparations correlated positively. The specific IgM response was higher on the Senegalese schizont extract than on the FCR3 extract and was highest in Dielmo villagers. The IgG response was similar in all three locations and was strain independent. These results indicate that monitoring IgG antibody levels to the widely distributed FCR3 strain using an easily prepared crude lysate might represent a valuable reference ELISA allowing homogenisation and comparison of data from different laboratories.     

Species delimitation and phylogeny in the genus Nasutitermes (Termitidae: Nasutitermitinae) in French Guiana

Species delimitation and identification can be arduous for taxa whose morphologic characters are easily confused, which can hamper global biodiversity assessments and pest species management. Exploratory methods of species delimitation that use DNA sequence as their primary information source to establish group membership and estimate putative species boundaries are useful approaches, complementary to traditional taxonomy. Termites of the genus Nasutitermes make interesting models for the application of such methods. They are dominant in Neotropical primary forests but also represent major agricultural and structural pests. Despite the prevalence, pivotal ecological role and economical impact of this group, the taxonomy of Nasutitermes species mainly depends on unreliable characters of soldier external morphology. Here, we generated robust species hypotheses for 79 Nasutitermes colonies sampled throughout French Guiana without any a priori knowledge of species affiliation. Sequence analysis of the mitochondrial cytochrome oxidase II gene was coupled with exploratory species‐delimitation tools, using the automatic barcode gap discovery method (ABGD) and a generalized mixed Yule‐coalescent model (GMYC) to propose primary species hypotheses (PSHs). PSHs were revaluated using phylogenetic analyses of two more loci (mitochondrial 16S rDNA and nuclear internal transcribed spacer 2) leading to 16 retained secondary species hypotheses (RSSH). Seven RSSHs, represented by 44/79 of the sampled colonies, were morphologically affiliated to species recognized as pests in the Neotropics, where they represent a real invasive pest potential in the context of growing ecosystem anthropization. Multigenic phylogenies based on combined alignments (1426–1784 bp) were also reconstructed to identify ancestral ecological niches and major‐pest lineages, revealing that Guyanese pest species do not form monophyletic groups.     

Profiling the Succession of Bacterial Communities throughout the Life Stages of a Higher Termite Nasutitermes arborum (Termitidae,Nasutitermitinae) Using 16S rRNA Gene Pyrosequencing

Previous surveys of the gut microbiota of termites have been limited to the worker caste. Termite gut microbiota has been well documented over the last decades and consists mainly of lineages specific to the gut microbiome which are maintained across generations. Despite this intimate relationship, little is known of how symbionts are transmitted to each generation of the host, especially in higher termites where proctodeal feeding has never been reported. The bacterial succession across life stages of the wood-feeding higher termite Nasutitermes arborum was characterized by 16S rRNA gene deep sequencing. The microbial community in the eggs, mainly affiliated to Proteobacteria and Actinobacteria, was markedly different from the communities in the following developmental stages. In the first instar and last instar larvae and worker caste termites, Proteobacteria and Actinobacteria were less abundant than Firmicutes, Bacteroidetes, Spirochaetes, Fibrobacteres and the candidate phylum TG3 from the last instar larvae. Most of the representatives of these phyla (except Firmicutes) were identified as termite-gut specific lineages, although their relative abundances differed. The most salient difference between last instar larvae and worker caste termites was the very high proportion of Spirochaetes, most of which were affiliated to the Treponema Ic, Ia and If subclusters, in workers. The results suggest that termite symbionts are not transmitted from mother to offspring but become established by a gradual process allowing the offspring to have access to the bulk of the microbiota prior to the emergence of workers, and, therefore, presumably through social exchanges with nursing workers.     

Study of NAT2 genetic polymorphism in West African subjects: example of an healthy non-smoker Senegalese population

The NAT2 genetic polymorphism determines the individual acetylator status and, consequently, the capacity to metabolize, or not, drugs and xenobiotics which are substrates of NAT2. As the nature and frequency of the NAT2 polymorphisms vary remarkably between populations of different ethnic origins, genotyping strategies used to predict the acetylation phenotype need to be adapted for each particular population regarding their genetic backgrounds at this locus. As few data on the genetic polymorphism of NAT2 are available in the Senegalese population, we performed an extensive identification of NAT2 variants in 105 healthy non-smoker Senegalese subjects by direct PCR sequencing of the coding region. Eleven previously described SNPs were identified in this Senegalese population. Upon allele analysis, the four most frequent alleles were of the NAT2*5- (35.7?%), NAT2*6- (21.0?%), NAT2*12- (16.7?%) and NAT2*14- (10.0?%) type, the remaining alleles, including the wild-type NAT2*4, having each a frequency lower than 10?%. According to the observed genotypes, 51 and 50 subjects were predicted to be of the rapid (48.6?%) and slow (47.6?%) acetylator phenotype, respectively, while four individuals (3.8?%) were considered of unknown phenotype as they carry at least one allele with a yet unknown functional effect. These baseline data would be of particular interest to set up an efficient genotyping strategy to predict the acetylation status of Senegalese patients with tuberculosis and, thus, to optimize their isoniazid treatment.     

Size-selection of cDNA libraries for the cloning of cDNAs after suppression subtractive hybridization

Here we describe the establishment of size-selected cDNA libraries for the cloning of full-length cDNAs that were initially identified by suppression subtractive hybridization (SSH) technology as being differentially expressed. First, the SSH-cDNA fragments were used as 32P-probes to verify their level and differential pattern of expression by virtual Northern and to establish their corresponding full-length cDNA size. Second, cDNAs were separated by size on agarose gels and used to construct size-selected cDNA plasmid libraries, which were then screened by colony hybridization with the SSH-cDNA fragments. We conclude that the described approach complements SSH technology by allowing efficient cloning and characterization of the corresponding full-length cDNA from any desired cell type or species. This approach will give researchers the ability to specifically target and study differentially expressed genes in an efficient manner for functional genomic studies.     

Does geographic origin dictate ecological strategies in Acacia senegal (L.) Willd.? Evidence from carbon and nitrogen stable isotopes

Background and aims

Acacia senegal, a leguminous dryland tree, is economically and ecologically important to sub-Saharan Africa. Water-use efficiency (WUE) and biological nitrogen fixation (BNF) are fundamental to plant productivity and survival. We quantify provenance differences in WUE, BNF, photosynthesis, biomass and gum arabic production from A. senegal assessing genetic improvement potential.

Methods

Using stable isotope ratios, we determined WUE (δ¹³C) and BNF (δ¹⁵N) from provenances of mature A. senegal in field-trials (Senegal), sampling leaves at the beginning (wet) and end (dry) of the rainy season. Seedling provenance trials (UK) determined photosynthesis, and biomass and δ¹³C in relation to water table. Environmental data were characterised for all provenances at their sites of origin.

Results

Provenances differed in both δ¹³C and δ¹⁵N. Gum yield declined with increasing WUE. Virtually no BNF was detected during the dry season and seedlings and mature trees may have different WUE strategies. Wind speed and soil characteristics at provenance origin were correlated with isotope composition and gum production.

Conclusion

Provenance differences suggest that selection for desirable traits, e.g., increased gum production, may be possible. As ecological strategies relate to native locality, the environmental conditions at plantation site and provenance origin are important in assessing selection criteria.