Population genomic evidence that human and animal infections in Africa come from the same populations of Dracunculus medinensis

BackgroundGuinea worm–Dracunculus medinensis–was historically one of the major parasites of humans and has been known since antiquity. Now, Guinea worm is on the brink of eradication, as efforts to interrupt transmission have reduced the annual burden of disease from millions of infections per year in the 1980s to only 54 human cases reported globally in 2019. Despite the enormous success of eradication efforts to date, one complication has arisen. Over the last few years, hundreds of dogs have been found infected with this previously apparently anthroponotic parasite, almost all in Chad. Moreover, the relative numbers of infections in humans and dogs suggests that dogs are currently the principal reservoir on infection and key to maintaining transmission in that country.Principal findingsIn an effort to shed light on this peculiar epidemiology of Guinea worm in Chad, we have sequenced and compared the genomes of worms from dog, human and other animal infections. Confirming previous work with other molecular markers, we show that all of these worms are D. medinensis, and that the same population of worms are causing both infections, can confirm the suspected transmission between host species and detect signs of a population bottleneck due to the eradication efforts. The diversity of worms in Chad appears to exclude the possibility that there were no, or very few, worms present in the country during a 10-year absence of reported cases.ConclusionsThis work reinforces the importance of adequate surveillance of both human and dog populations in the Guinea worm eradication campaign and suggests that control programs aiming to interrupt disease transmission should stay aware of the possible emergence of unusual epidemiology as pathogens approach elimination.     

Theoretical habitat templets, species traits, and species richness: aquatic macrophytes in the Upper Rhône River and its floodplain

• 1 The objective of this study, which is based on forty-two species of hydrophytes and helophytes, is to investigate: (i) relationships among species traits; (ii) habitat utilization by species; (iii) the relationship between species traits and habitat utilization; (iv) trends in species traits in the framework of spatial–temporal habitat variability, and if trends match predictions from the river habitat templet; and (v) trends in species richness in the framework of spatial–temporal habitat variability, and if trends match predictions of the patch dynamics concept.
• 2 Two data sets were used for this analysis: species traits (mainly reproductive and morphological characteristics) were documented from the literature; and species distribution across eight habitat types was from field surveys conducted in the floodplain of the Upper Rhone River, France. This information was structured by a fuzzy coding technique and analysed by ordination methods.
• 3 Several species traits, which are related to disturbances and reflect resistance (e.g. attachment to soil or substrate) or resilience (e.g. potential for regeneration of an individual), are closely related for aquatic macrophytes.
• 4 Habitat utilization by aquatic macrophytes separates the habitat types along a gradient of connectivity with the main channel, which corresponds to a gradient in flood disturbance frequency and the permanence of the different water-bodies.
• 5 The relationship between species traits and habitat utilization is highly significant, indicating that a particular set of habitat types is used by taxa with a particular set of species trait modalities.
• 6 Observations in one habitat templet (in which scaling of the templet is primarily based on water level fluctuations for the temporal variability axis and on substrate characteristics for the spatial variability axis) generally do not support predictions on trends in species traits but do support predictions on trends in species richness.
• 7 Observations in an alternative habitat templet (in which scaling of the templet is based on frequency of flood scouring for the temporal variability axis and on heterogeneity of the substrate for the spatial variability axis) support theoretical predictions on trends for about half of the species traits for which predictions were available. However, trends in species richness in this alternative habitat templet are only partly in agreement with predictions.

     

Biosynthesis of phycobiliproteins. Incorporation of biliverdin into phycocyanin of the red alga Cyanidium caldarium

14C-labelled biliverdin IX alpha was administered to cultures of Cyanidium caldarium that were actively synthesizing photosynthetic pigments in the light. Between 9 and 12% of the phycobiliprotein chromophore produced in such cultures was derived from exogenous biliverdin. These results demonstrate that biliverdin is an intermediate in the biosynthesis of phycobiliproteins.     

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia II. LH and testosterone concentrations before and after GnRH

Plasma LH and testosterone (T) concentrations were measured before (basal) and two hours after (peak) GnRH stimulation in 52 Bos indicus strain bulls between one and two years of age. The animals comprised 13 1 2 Brahman, 20 3 4 Brahman, 8 1 2 Sahiwal and 11 3 4 Sahiwal cross bulls and samples were collected at approximately seven week intervals. Basal- and peak-T concentrations increased between one and two years of age, and basal LH concentrations decreased; no changes in peak LH were noted over time. Peak-T concentrations were significantly correlated with scrotal circumference (SC), sperm per ejaculate and seminal fructose. Significant genotype differences were noted, Sahiwal cross bulls had higher peak-T concentrations at puberty than Brahman cross bulls.     

Accumulation of polyunsaturated fatty acids by cladocerans: effects of taxonomy,temperature and food

1. Zooplankton are important in transferring dietary nutrients, including polyunsaturated fatty acids (PUFA), up through aquatic food webs. 2. We tested the hypothesis that the taxonomic composition of zooplankton affects the retention and subsequent transfer of PUFA from upwards through the food web. Using laboratory experiments, we investigated dietary PUFA accumulation and bioconversion capacities of six cladoceran species (Ceriodaphnia sp., Daphnia longispina, Daphnia magna, Daphnia pulex, Scapholeberis mucronata and Simocephalus vetulus) fed on two diets (Scenedesmus obliquus and Cryptomonas sp.) that differed in their PUFA profiles. We performed experiments at two different temperatures (14 and 20 °C) to assess the role of temperature in the trophic transfer of PUFA. 3. There was little variation in the concentrations of PUFA in these cladocerans which were controlled by dietary PUFA supply. Moreover, as expected, the concentrations of PUFA in all cladoceran species were higher at low temperature. 4. However, even if the composition of PUFA in the cladoceran species generally corresponded to that in their diet, preferential accumulation of some PUFA was recorded in all these taxa. When fed on a highly unsaturated fatty acid‐deficient diet, all the cladocerans showed some ability to convert C18‐PUFA into arachidonic acid and eicosapentaenoic acid. Interspecific variation in the ability to accumulate and bioconvert PUFA in cladocerans was more pronounced at low temperature (14 °C) for both diets. 5. Our results strongly suggest that in heterogeneous habitats with food partitioning between co‐existing cladocerans, foraging behaviour may affect the transfer of PUFA more strongly than interspecific variation in accumulating and/or bioconverting dietary PUFA.     

Short‐term effects of CO2 and O2 on citrate metabolism in illuminated leaves

Although there is now a considerable literature on the inhibition of leaf respiration (CO₂ evolution) by light, little is known about the effect of other environmental conditions on day respiratory metabolism. In particular, CO₂ and O₂ mole fractions are assumed to cause changes in the tricarboxylic acid pathway (TCAP) but the amplitude and even the direction of such changes are still a matter of debate. Here, we took advantage of isotopic techniques, new simple equations and instant freeze sampling to follow respiratory metabolism in illuminated cocklebur leaves (Xanthium strumarium L.) under different CO₂/O₂ conditions. Gas exchange coupled to online isotopic analysis showed that CO₂ evolved by leaves in the light came from ‘old’ carbon skeletons and there was a slight decrease in ¹³C natural abundance when [CO₂] increased. This suggested the involvement of enzymatic steps fractionating more strongly against ¹³C and thus increasingly limiting for the metabolic respiratory flux as [CO₂] increased. Isotopic labelling with ¹³C₂‐2,4‐citrate lead to ¹³C‐enriched Glu and 2‐oxoglutarate (2OG), clearly demonstrating poor metabolism of citrate by the TCAP. There was a clear relationship between the ribulose‐1,5‐bisphosphate oxygenation‐to‐carboxylation ratio (v_o/v_c) and the ¹³C commitment to 2OG, demonstrating that 2OG and Glu synthesis via the TCAP is positively influenced by photorespiration.     

Physical forces constrain the depth distribution of the abundant native mussel Elliptio complanata in lakes

1. Unionid mussels often account for a large portion of benthic biomass and contribute to nutrient cycling and sediment processes, but are thought to be limited to shallow areas (<2–3 m). 2. The depth distribution and body size of Elliptio complanata were compared in seven Canadian Shield lake basins of different sizes to test what factors determine the upper and lower limit of their depth range. Specifically, I tested whether (i) the upper range of their distribution is limited by exposure to winds and wave action and (ii) the lower range of their distribution is limited by the depth of the thermocline or by the boundary of mud deposition. 3. The average depth distribution of E. complanata shifted to greater depths in larger lake basins. When comparing individual transects, maximum mussel density was found deeper at more exposed sites. Mussel size decreased with increasing depth and was larger, on average, in larger lake basins. These results suggest that physical forces limit the upper range of mussel distribution in lakes. 4. The maximum depth at which mussels were found in different lakes was closely related to thermocline depth. However, mussels were commonly observed below the predicted depth of the mud deposition boundary. The thermocline limits the lower range of mussel distribution in lakes, probably by limiting food availability and by determining water temperature. Substratum type does not limit the lower distribution of mussels. 5. These results suggest that unionid mussels are present in the deeper parts of the littoral zone, especially in large lakes. Therefore, comparisons of mussel populations between sites and between lakes would be biased unless the full depth distribution of these mussels is considered. These results also suggest that long‐term changes in the thermal structure of lakes could affect the range of unionid mussel populations and their functional role in littoral ecosystems.