Spatial Analysis of Anthropogenic Landscape Disturbance and Buruli Ulcer Disease in Benin

Background

Land use and land cover (LULC) change is one anthropogenic disturbance linked to infectious disease emergence. Current research has focused largely on wildlife and vector-borne zoonotic diseases, neglecting to investigate landscape disturbance and environmental bacterial infections. One example is Buruli ulcer (BU) disease, a necrotizing skin disease caused by the environmental pathogen Mycobacterium ulcerans (MU). Empirical and anecdotal observations have linked BU incidence to landscape disturbance, but potential relationships have not been quantified as they relate to land cover configurations.

Methodology/Principal Findings

A landscape ecological approach utilizing Bayesian hierarchical models with spatial random effects was used to test study hypotheses that land cover configurations indicative of anthropogenic disturbance were related to Buruli ulcer (BU) disease in southern Benin, and that a spatial structure existed for drivers of BU case distribution in the region. A final objective was to generate a continuous, risk map across the study region. Results suggested that villages surrounded by naturally shaped, or undisturbed rather than disturbed, wetland patches at a distance within 1200m were at a higher risk for BU, and study outcomes supported the hypothesis that a spatial structure exists for the drivers behind BU risk in the region. The risk surface corresponded to known BU endemicity in Benin and identified moderate risk areas within the boundary of Togo.

Conclusions/Significance

This study was a first attempt to link land cover configurations representative of anthropogenic disturbances to BU prevalence. Study results identified several significant variables, including the presence of natural wetland areas, warranting future investigations into these factors at additional spatial and temporal scales. A major contribution of this study included the incorporation of a spatial modeling component that predicted BU rates to new locations without strong knowledge of environmental factors contributing to disease distribution.     

The single Andigenum origin of Neo-Tuberosum potato materials is not supported by microsatellite and plastid marker analyses

Neo-Tuberosum refers to cultivated potato adapted to long-day tuberization and a syndrome of related morphological and physiological traits, developed by intercrossing and selection of short-day adapted potatoes of the Solanum tuberosum Andigenum Group, native from the Andes of western Venezuela to northern Argentina. This re-creation of the modern potato helped support the theory of an Andigenum Group origin of potato in temperate regions and the possibility to access the largely untapped diversity of the Andigenum Group germplasm by base broadening breeding. This Neo-Tuberosum derived theory, the re-creation of the modern potato from Andigenum germplasm, has been universally accepted for almost 40 years, and has had tremendous impact in planning some breeding programs and supporting phylogenetic conclusions in cultivated potato. We show, with microsatellite (simple sequence repeat, SSR) and plastid DNA marker data, that Neo-Tuberosum germplasm is closely related to Chilotanum Group landraces from lowland south-central Chile rather than to Andigenum Group germplasm. We interpret this quite unexpected result to be caused by strong rapid selection against the original Andigenum clones after unintended hybridization with Chilotanum Group germplasm. In addition, we show that Neo-Tuberosum and Andigenum Group germplasm did not serve to broaden the overall genetic diversity of advanced potato varieties, but rather that Neo-Tuberosum lines and lines not using this germplasm are statistically identical with regard to genetic diversity as assessed by SSRs. These results question the long-standing Neo-Tuberosum derived theory and have implications in breeding programs and phylogenetic reconstructions of potato. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intra-specific variability and the competition–colonisation trade-off: coexistence, abundance and stability patterns

Intra-specific variability often produces an overlap between species distributions of individual performances which can influence competition relations and community dynamics. We analysed a two-species competition–colonisation model of vegetation with intra-specific variability in juvenile growth. On each patch colonised by both species, the winner was the juvenile with higher individual growth. Intra-specific variability disproportionately favoured the more fecund species because the tail of its distribution represented more individuals. In some cases, this process could even lead to a reversal of competition hierarchy and exclusion of the species with higher mean juvenile performance. In the space of species 2 mean growth and fecundity traits, the combinations of traits allowing coexistence with species 1 appeared close to an ideal trade-off curve. Along this curve, species 2 and species 1 coexisted at similar abundance. The balance of relative abundances diminished with the distance of species 2 from this curve. For a given level of relative species performances, coexistence stability increased continuously as species differentiation increased. In contrast to classical models that exhibit abrupt changes of equilibrium community properties when species traits vary, our model displayed continuous changes of these properties in relation to the balance of life traits within and among species. Intra-specific variability allows flexible patterns of community dynamics and could explain discrepancies between observations and classical theories.     

Differential gene expression in two potato lines differing in their resistance to Phytophthora infestans

Horizontal resistance to late blight in the potato is a primary objective of many breeding programs. Knowledge of the physiological and biochemical mechanisms underlying it, however, is scarce. The purpose of the present study was the identification of these physiological and biochemical factors in plant material obtained by crossing a late blight resistant Solanum phureja clone with a susceptible dihaploid of S. tuberosum subsp. tuberosum. The mRNA RT-PCR differential display method was used to compare the gene expression patterns of a resistant hybrid with that of a susceptible one. By sequence homology, we identified several genes with diverse functions, including genes known to be involved in resistance or stress responses and genes known to be involved in primary or secondary metabolism.     

Characterization of herpes simplex virus type 1 thymidine kinase mutants selected under a single round of high-dose brivudin

A broad variety of herpes simplex virus type 1 clones was selected under a single round of high-dose selection with brivudin. Mutations in the thymidine kinase (TK) genes consisted of 42% frameshift mutations within homopolymer repeats of G's and C's and single nucleotide substitutions (58%) that produced stop codons (Q261 and R281) or a new codon at the site of the substitution (A168T, R51W, G59W, G206R, R220H, Y239S, and T287 M). The A168T change, associated with an altered TK phenotype, proved to be the most commonly selected substitution. For the different mutants, a correlation between phenotype, genotype, and in vivo neurovirulence was observed.