Introgressive hybridization of human and rodent schistosome parasites in western Kenya

Hybridization and introgression can have important consequences for the evolution, ecology and epidemiology of pathogenic organisms. We examined the dynamics of hybridization between a trematode parasite of humans, Schistosoma mansoni, and its sister species, S. rodhaini, a rodent parasite, in a natural hybrid zone in western Kenya. Using microsatellite markers, rDNA and mtDNA, we showed that hybrids between the two species occur in nature, are fertile and produce viable offspring through backcrosses with S. mansoni. Averaged across collection sites, individuals of hybrid ancestry comprised 7.2% of all schistosomes collected, which is a large proportion given that one of the parental species, S. rodhaini, comprised only 9.1% of the specimens. No F1 individuals were collected and all hybrids represented backcrosses with S. mansoni that were of the first or successive generations. The direction of introgression appears highly asymmetric, causing unidirectional gene flow from the rodent parasite, S. rodhaini, to the human parasite, S. mansoni. Hybrid occurrence was seasonal and most hybrids were collected during the month of September over a 2-year period, a time when S. rodhaini was also abundant. We also examined the sex ratios and phenotypic differences between the hybrids and parental species, including the number of infective stages produced in the snail host and the time of day the infective stages emerge. No statistical differences were found in any of these characteristics, and most of the hybrids showed an emergence pattern similar to that of S. mansoni. One individual, however, showed a bimodal emergence pattern that was characteristic of both parental species. In conclusion, these species maintain their identity despite hybridization, although introgression may cause important alterations of the biology and epidemiology of schistosomiasis in this region.     

Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues

While ocean acidification is predicted to threaten marine biodiversity, the processes that directly impact species persistence are not well understood. For marine species, early life history stages are inherently vulnerable to predators and an innate ability to detect predators can be critical for survival. However, whether or not acidification inhibits predator detection is unknown. Here, we show that newly hatched larvae of the marine fish Amphiprion percula innately detect predators using olfactory cues and this ability is retained through to settlement. Aquarium-reared larvae, not previously exposed to predators, were able to distinguish between the olfactory cues of predatory and non-predatory species. However, when eggs and larvae were exposed to seawater simulating ocean acidification (pH 7.8 and 1000 p.p.m. CO₂) settlement-stage larvae became strongly attracted to the smell of predators and the ability to discriminate between predators and non-predators was lost. Newly hatched larvae were unaffected by CO₂ exposure and were still able to distinguish between predatory and non-predatory fish. If this impairment of olfactory preferences in settlement-stage larvae translates to higher mortality as a result of increased predation risk, there could be direct consequences for the replenishment and the sustainability of marine populations.
Ecology Letters (2010) 13: 68–75     

REMARKABLE CONSERVATION OF INTERNALLY TRANSCRIBED SPACER SEQUENCES OF ARTHROSPIRA (“SPIRULINA” ) (CYANOPHYCEAE,CYANOBACTERIA) STRAINS FROM FOUR CONTINENTS AND OF RECENT AND 30‐YEAR‐OLD DRIED SAMPLES FROM AFRICA1

The internally transcribed spacer (ITS) sequences of 21 Arthrospira clonal strains from four continents and assigned to four different species (A. platensis, A. maxima, A. fusiformis, A. indica) in the culture collections were determined. Two main clusters, I and II, were differentiated by 49 positions out of 475 nt or 477 nt, respectively. Each cluster was further subdivided into two subclusters. Subclusters I.A and I.B were separated by two substitutions, whereas subclusters II.A and II.B were distinguished by four substitutions. After direct sequencing of the PCR products, three dried samples from Chad aged between 3 months and 35 years yielded a sequence belonging to subcluster I.A, as did a recent commercial product. The strains grown in production plants belonged to the same (sub)clusters as strains from culture collections, mainly I.A and II. PCR primers specific for each cluster and subcluster were designed and tested with crude cell lysates of Arthrospira strains. One dried sample (“dihé” 1) and a herbarium sample from Lake Sonachi (Kenya) only contained I.A sequences, whereas the commercial product was a mixture of the four genotypes and the other two dried samples contained minor polymorphisms characteristic of different clusters. Five clonal Arthrospira strains, thought to be duplicates, showed the simultaneous presence of the two forms of the four diagnostic positions that distinguish subclusters genotype II.A and genotype II.B. This is likely to be caused by multiple copies of the rDNA operon, in a intermediate stage of homogenization between subcluster II.A and subcluster II.B. The high conservation of ITS sequences is in contrast with the assignment to four different species, the great morphological variability of the strains, and their wide geographic distribution.     

C20orf9-003 (ACI-1), a gene localized on chromosome 20q13.12 encoding for a 49 kD cytoplasmic protein with a putative nucleotide binding site.

Murine NGD5 is a gene identified from NG108-15 cells which is postulated to be involved in opioid receptor function. Here we report the cloning and characterization of a cDNA C20orf9-003 (ACI-1) encoding the human orthologue of the mouse NGD5. Analysis of the genomic structure revealed that C20orf9-003 (ACI-1) contains 13 exons and 12 introns, spanning 52.5kb of genomic DNA and is a variant of C20orf9. Chromosomal localization of human C20orf9-003 (ACI-1) assigned this gene to chromosome 20q13.12. Genes at this locus have been associated with the progression and possibly the development of various cancers. In addition several linkage studies support the possibility that one or more genes affecting obesity are located in 20q13. No function can be clearly assigned to C20orf9-003 (ACI-1), however, the protein has a cytoplasmic subcellular location and the secondary structure contains a Rossman fold like feature which is found in many nucleotide binding proteins.     

Engineering a twist in 9,10-diethynylanthracenes by steric interactions.

A series of 9,10-bis(phenylethynyl)anthracenes decorated with sterically demanding tert-butyl substituents have been prepared and spectroscopically characterised. We demonstrate that the introduction of two bulky substituents in the ortho position of the phenyl rings effectively locks the ground state into a conformation in which the three rings are orthogonal. Fluorescence spectroscopy reveals evidence for partial planarisation of this compound in the excited state at ambient temperature, but this is prevented in low temperature solvent glasses.     

Process length variation in cysts of a dinoflagellate,Lingulodinium machaerophorum,in surface sediments: Investigating its potential as salinity proxy

A biometrical analysis of the dinoflagellate cyst Lingulodinium machaerophorum [Deflandre, G., Cookson, I.C., 1955. Fossil microplankton from Australia late Mesozoic and Tertiary sediments. Australian journal of Marine and Freshwater Research 6: 242–313.] Wall, 1967 in 144 globally distributed surface sediment samples revealed that the average process length is related to summer salinity and temperature at a water depth of 30 m by the equation (salinity/temperature) = (0.078?average process length + 0.534) with R² = 0.69. This relationship can be used to reconstruct palaeosalinities, albeit with caution. The particular ecological window can be associated with known distributions of the corresponding motile stage Lingulodinium polyedrum (Stein) Dodge, 1989. Confocal laser microscopy showed that the average process length is positively related to the average distance between process bases (R² = 0.78), and negatively related to the number of processes (R² = 0.65). These results document the existence of two end members in cyst formation: one with many short, densely distributed processes and one with a few, long, widely spaced processes, which can be respectively related to low and high salinity/temperature ratios. Obstruction during formation of the cysts causes anomalous distributions of the processes. From a biological perspective, processes function to facilitate sinking of the cysts through clustering.     

Phylogeography of the Guinea multimammate mouse (Mastomys erythroleucus): a case study for Sahelian species in West Africa

Aim To investigate the phylogeographical structure of the Guinea multimammate mouse, Mastomys erythroleucus (Temminck, 1853), a widespread murid rodent in sub‐Saharan (Sahel and Sudan) savannas, for a better understanding of the impacts of geographical and historical factors on the evolutionary history of this species, in the context of the growing database of phylogeographical studies of African savanna mammal species. Location Sahel and Sudan savannas, Africa. Methods We sequenced the whole cytochrome b gene in 211 individuals from 59 localities distributed from Senegal to Ethiopia. Sequence data were analysed using both phylogenetic (several rooted tree‐construction methods, median‐joining networks) and population genetic methods (spatial analyses of molecular variance, mismatch distributions). Results Haplotypes were distributed into four major monophyletic groups corresponding to distinct geographical regions across a west–east axis. Diversification events were estimated to have occurred between 1.16 and 0.18 Ma. Main conclusions Vicariance events related to the fragmentation of savanna habitats during the Pleistocene era may explain the phylogeographical patterns observed. Genetic structure was consistent with a role of major Sahelian rivers as significant barriers to west–east dispersal. Recent demographic expansions probably occurred during arid phases of the Holocene with the southward expansion of savannas.     

Étude chimiotaxonomique de deux espéces nouvelles de Hazunta (Apocynaceae)

Twenty-two indole alkaloids have been isolated from two new Hazunta species (Apocynaceae). Apparently, five of them are bis-indoles of a previously unknown structure.