Schistosoma intercalatum: an endangered species in Cameroon?

Despite the extremely wide distribution of both intermediate (snail) and definitive hosts, the species Schistosoma intercalatum has a highly restricted distribution in parts of West Africa (Cameroon, Equatorial Guinea, Gabon, Nigeria, Democratic Republic of Congo and S?o Tomé). Recent studies showed that the epidemiology of this species is very dynamic, including invasions and extinctions. This article reviews the epidemiology of S. intercalatum in Cameroon, where the species is endangered, and analyses its overall status in Africa. The possible reasons for the limited distribution of S. intercalatum are discussed.     

The peopling of São Tomé (Gulf of Guinea): origins of slave settlers and admixture with the Portuguese

The geographic origins of African slave settlers and the Portuguese genetic contribution to the population of S?o Tomé (Gulf of Guinea) were assessed through the analysis of beta-globin haplotypes in 44 chromosomes bearing the betaS allele and through the study of the genetic variation in eight autosomal markers (APOA1, AT3, FY, LPL, OCA2, RB1, Sb19.3, and GC) informative for admixture in a sample of 224 individuals. The observed betaS haplotype distribution (36.4% Bantu, 52.3% Benin, 4.5% Cameroon, 4.5% Senegal, and 2.3% atypical) is in accordance with the historical information on the major geographic sources of slave settlers of S?o Tomé, although it captures a more important contribution of Central-West Africa regions than previously anticipated. European admixture, estimated to be 10.7 +/- 0.9%, has created a considerable level of genetic structure, as indicated by the finding of significant linkage disequilibrium between 33% of unlinked marker loci pairs. Recent admixture was found to have an important contribution to these values, since removal of individuals with Portuguese or Cape Verdian parents or grandparents from the sample dropped the miscegenation level to 6.5 +/- 0.8% and reduced significant linkage disequilibrium to 11% of unlinked marker pairs. Taken together, these results indicate that the peopling of S?o Tomé might have provided one of the first examples of the combination of diverse African contributions and European admixture that emerged from the overseas population relocations promoted by the Atlantic slave trade.     

Relationships of Afroablepharus Greer, 1974 skinks from the Gulf of Guinea islands based on mitochondrial and nuclear DNA: patterns of colonization and comments on taxonomy

Partial sequences of three mitochondrial DNA genes, 12S rDNA, 16S rDNA and cytochrome b, and one nuclear gene, c-mos, were used to assess the phylogenetic relationships of species belonging to the genus Afroablepharus from the volcanic islands of the Gulf of Guinea (West Africa) and neighboring continental Africa. Additionally, partial sequences of cytochrome b were used to compare levels of sequence divergence within populations. The three forms from S?o Tomé, Príncipe and Annobon (one per island) are genetically distinct, with high levels of divergence, supporting the recognition of a distinct species in each island. Populations within each island contain very low levels of genetic diversity. These three forms form a monophyletic group suggesting a single initial colonization followed by radiation to the other islands, possibly from S?o Tomé to Príncipe and Annobon. This is contrary to what was found in other reptiles from these islands such as Mabuya (sensu lato) and Hemidactylus, which colonized the islands multiple times. Assuming a molecular clock for cytochrome b of about 2% divergence per million years (usually applied to Sauria), the lineage on Annobon island exceeds the age of the island, thus casting further doubt on this widely used divergence estimate. Partial sequences of c-mos showed no variation within islands. Five to seven sites were variable among islands, which is a high value further supporting the treatment of each island form as a distinct species.     

Variation in STR loci of the human myelin basic protein gene: north Portugal and São Tomé e Príncipe

Allele frequencies and a single-base substitution polymorphism for 3 short tandem repeat (STR) loci of the human myelin basic protein (MBP) gene were evaluated in North Portugal and S?o Tomé e Príncipe. Strong linkage disequilibrium between loci MBPB and MBPC was found. However, the patterns of nonrandom allelic associations were very different in the 2 populations: levels of haplotypic diversity and heterozygosity were higher in the S?o Tomé population. Similarly, a difference in the frequency of base substitution G-->A at position 124 was found: the frequency reached 4.1% in North Portugal and 0.5% in S?o Tomé. In both populations it was always found to be associated with haplotypes B10/C11 and B12/C9.     

Haplotype analysis of the apolipoprotein E and apolipoprotein C1 loci in Portugal and São Tomé e Príncipe (Gulf of Guinea): linkage disequilibrium evidence that APOE*4 is the ancestral APOE allele

The joint distributions of phenotypes from the apolipoprotein E gene (APOE) and from a closely linked restriction site polymorphism at the apolipoprotein C1 locus (APOC1) were studied in population samples from Portugal and S?o Tomé e Príncipe (Gulf of Guinea), a former Portuguese colony that was originally populated by slaves imported from the African mainland. The frequencies of the APOE alleles (*2, *3, and *4) in Portugal and S?o Tomé fitted the ranges of variation generally observed in European and African populations, respectively. Haplotype analysis showed that in both populations the strength of linkage disequilibrium was highest for the APOE*2 allele and lowest for the APOE*4 allele, suggesting that the origin of the APOE alleles followed a 4-->3-->2 pathway and thus providing independent confirmation of the results from sequence homology studies with nonhuman primates. In accordance with global trends in the distribution of human genetic variation, the European sample from Portugal presented more intense linkage disequilibrium between APOE and APOC1 than the African sample from S?o Tomé where, despite the short 4-kb distance that separates the 2 loci, the level of association between the APOC1 alleles and APOE*4 was nonsignificant.     

Raised houses reduce mosquito bites

BACKGROUND: In many parts of continental Africa house construction does not appear to impede entry of malaria vectors and, given their generally late biting cycle, the great majority of transmission takes place indoors. In contrast, many houses in S?o Tomé, 140 km off the coast of Gabon, are raised on stilts and built of wooden planks. Building on stilts is a time-honoured, but largely untested, way of avoiding mosquito bites. Exposure may also be affected by mosquito activity times and age composition of host-seeking females. A study was therefore undertaken on the island of S?o Tomé to determine if exposure to Anopheles gambiae, the only vector on the island, varied with house construction or time of the night. METHODS: A series of all-night landing collections were undertaken out of doors at ground level, inside houses at ground level, on the verandas of, and inside houses built on stilts. The gonotrophic age of an unselected sample of insects from the first three hours of landing collection (18:00-21:00) was determined by dissection. In addition, 1,149 miniature light-trap collections were obtained from 125 houses in the study area. Numbers collected were related to house construction. RESULTS: Biting of An. gambiae took place primarily outside at ground level. Less than one third of biting occurred inside houses. Houses built on stilts had half the number of An. gambiae in them compared to those built at ground level. Conversely houses with an eaves gap had more An. gambiae in them than houses without such a gap. Gonotrophic age did not affect house entry rates in An. gambiae. House construction affected Culex quinquefasciatus less than An. gambiae. Mean density per house, derived from a series of 1,490 randomly assigned light-trap collections, was over-dispersed with 18% of houses having 70% of the vectors. CONCLUSION: House construction plays an important role in determining exposure to malaria vectors in S?o Tomé. Neighbours can have very different exposure levels. Recommendations for improvement in control are given.     

Multilocus analysis of introgression between two sympatric sister species of Drosophila: Drosophila yakuba and D. santomea

Drosophila yakuba is widely distributed in sub-Saharan Africa, while D. santomea is endemic to the volcanic island of S?o Tomé in the Atlantic Ocean, 280 km west of Gabon. On S?o Tomé, D. yakuba is found mainly in open lowland forests, and D. santomea is restricted to the wet misty forests at higher elevations. At intermediate elevations, the species form a hybrid zone where hybrids occur at a frequency of approximately 1%. To determine the extent of gene flow between these species we studied polymorphism and divergence patterns in 29 regions distributed throughout the genome, including mtDNA and three genes on the Y chromosome. This multilocus approach, together with the comparison to the two allopatric species D. mauritiana and D. sechellia, allowed us to distinguish between forces that should affect all genes and forces that should act on some genes (e.g., introgression). Our results show that D. yakuba mtDNA has replaced that of D. santomea and that there is also significant introgression for two nuclear genes, yellow and salr. The majority of genes, however, has remained distinct. These two species therefore do not form a "hybrid swarm" in which much of the genome shows substantial introgression while disruptive selection maintains distinctness for only a few traits (e.g., pigmentation and male genitalia).     

Frequency of the CCR5-delta32 mutation in the Atlantic island populations of Madeira, the Azores, Cabo Verde, and São Tomé e Príncipe

There is evidence that the CCR5-delta32 mutation confers protection against HIV-1 infection to homozygous individuals. It is believed that this mutation spread through Europe with the Vikings and that it has been subjected to positive selection, leading to a high frequency in Europe (approximately 10%). We carried out the present study to determine the 32-bp deletion allele and genotype frequencies of the CCR5 gene (CCR5-delta32) in the Atlantic island populations of Madeira, the Azores, Cabo Verde, and S?o Tomé e Principe. These Atlantic archipelagos were all colonized by the Portuguese in the 15th and 16th centuries, but the latter two received most of their settlers from the West African coast. The frequency of the CCR5-delta32 mutation varies between 0% in S?o Tomé e Príncipe and 16.5% in the Azores. The Azores Islands have one of the highest frequencies of homozygotes found in Europe (4.8%). There are significant differences (P < 0.05) between some of these populations, for example, between S?o Tomé e Príncipe and Cabo Verde, and even within populations (e.g., Portugal, Madeira, and the Azores).     

Phylogenetic relationships of Hemidactylus geckos from the Gulf of Guinea islands: patterns of natural colonizations and anthropogenic introductions estimated from mitochondrial and nuclear DNA sequences

Mitochondrial DNA (12S rRNA, 16S rRNA, and cytochrome b) sequences and nuclear sequences (C-mos and alpha-Enolase) were analyzed within all known Hemidactylus species from all three volcanic islands in the Gulf of Guinea that have never been connected to the continent. These comprise both endemic and widespread species. Our aim was to determine if the widespread species was introduced anthropogenically, to determine the number of distinct genetic lineages within the islands, and to determine if the endemic forms constituted a monophyletic group. Our results suggest that a previously undescribed species on S?o Tomé is the sister taxon to Hemidactylus newtoni, endemic to Annobon. Genetic variation between populations of Hemidactylus greefii from S?o Tomé and Principe is very high based on mtDNA sequences, but the forms cannot be distinguished using the nuclear DNA sequences. Hemidactylus mabouia appears to have been anthropogenically introduced to all three islands. The island endemics do not form a monophyletic group, suggesting multiple independent colonizations of the islands.     

Genetic variation in a compound short tandem repeat/Alu haplotype system at the SB19.3 locus: properties and interpretation

The genetic variation at a compound nonrecombining haplotype system, consisting of the previously reported SB19.3 Alu insertion polymorphism and a newly identified adjacent short tandem repeat (STR), was studied in population samples from Portugal and S?o Tomé (Gulf of Guinea, West Africa). Age estimates based on the linked microsatellite variation suggest that the Alu insertion occurred about 190,000 years ago. In accordance with the global patterns of distribution of human genetic variation, the highest haplotype diversity was found in the African sample. This excess in African diversity was due to both a substantial reduction in heterozygosity at the Alu polymorphism and a lower STR variability associated with the predominant Alu insertion allele in the Portuguese sample. The high level of interpopulation differentiation observed at the Alu locus (F(ST) = 0.43) was interpreted under alternative selective and demographic scenarios. The need for compatibility between patterns of variation at the STR and Alu loci could be used to restrict the range of selection coefficients in selection-driven genetic hitchhiking frameworks and to favor demographic scenarios dominated by larger pre-expansion African population sizes. Taken together, the data show that the SB19.3 Alu-STR system is an informative marker that can be included in more extended batteries of compound haplotypes used in human evolutionary studies.     

Comparing ape densities and habitats in northern Congo: surveys of sympatric gorillas and chimpanzees in the Odzala and Ndoki regions

The conservation status of western lowland gorillas and central chimpanzees in western equatorial Africa remains largely speculative because many remote areas have never been surveyed and the impact of emergent diseases in the region has not been well documented. In this study, we compared ape densities and habitats in the Lokoué study area in Odzala National Park and the Goualougo Triangle in Nouabalé-Ndoki National Park in northern Republic of Congo. Both of these sites have long been considered strongholds for the conservation of chimpanzees and gorillas, but supposedly differ in vegetative composition and relative ape abundance. We compared habitats between these sites using conventional ground surveys and classified Landsat-7 ETM+ satellite images. We present density estimates via both standing-crop and marked-nest methods for the first time for sympatric apes of the Congo Basin. The marked-nest method was effective in depicting chimpanzee densities, but underestimated gorilla densities at both sites. Marked-nest surveys also revealed a dramatic decline in the ape population of Lokoué which coincided with a local Ebola epidemic. Normal baseline fluctuations in ape nest encounter rates during the repeated passages of marked-nest surveys were clearly distinguishable from a 80% decline in ape nest encounter rates at Lokoué. Our results showed that ape densities, habitat composition, and population dynamics differed between these populations in northern Congo. We emphasize the importance of intensifying monitoring efforts and further refinement of ape survey methods, as our results indicated that even the largest remaining ape populations in intact and protected forests are susceptible to sudden and dramatic declines.     

G6PD deficient alleles and haplotype analysis of human G6PD locus in São Tomé e Príncipe (West Africa)

A population sample from S?o Tomé e Príncipe (West Africa) was screened for the G6PD-deficient variants A- (376G/202A), Betica (376G/968C), and Santa Maria (376G/542T). G6PD locus haplotype diversity was also investigated using six intragenic RFLPs (FokI, PvuII, BspHI, PstI, BclI, NlaIII) and a (CTT)n microsatellite 18.61 kb within the G6PD locus. The estimated frequencies of the G6PD*B normal allele, the G6PD*A variant (376G), and the G6PD*A- allele were 0.698, 0.194, and 0.108, respectively. G6PD variants Betica and Santa Maria were not found. Similar levels of microsatellite diversity were found on variants G6PD*B and G6PD*A (H = 0.61 and 0.68, respectively), indicating a similar age for both alleles. All G6PD*A- alleles share the RFLP-microsatellite haplotype ++(-)+(-)+/195, the same haplotype described in nearly all the *A-alleles from sub-Saharan, Mexican Mestizo, and Portuguese populations, consistent with a single and recent origin of the G202A mutation on this *A haplotype.     

Historical biogeography and phenotype‐phylogeny of Chroodiscus (lichenized Ascomycota: Ostropales: Graphidaceae)

Aim To analyse the historical biogeography of the lichen genus Chroodiscus using a phenotype‐based phylogeny in the context of continental drift and evolution of tropical rain forest vegetation. Location All tropical regions (Central and South America, Africa, India, Southeast Asia, north‐east Australia). Methods We performed a phenotype‐based phylogenetic analysis and ancestral character state reconstruction of 14 species of the lichen genus Chroodiscus, using paup * and mesquite ; dispersal–vicariance analysis (DIVA) and dispersal–extinction–cladogenesis (DEC) modelling to trace the geographical origin of individual clades; and ordination and clustering by means of pc‐ord , based on a novel similarity index, to visualize the biogeographical relationships of floristic regions in which Chroodiscus occurs. Results The 14 species of Chroodiscus show distinctive distribution patterns, with one pantropical and one amphi‐Pacific taxon and 12 species each restricted to a single continent. The genus comprises four clades. DIVA and DEC modelling suggest a South American origin of Chroodiscus in the mid to late Cretaceous (120–100 Ma), with subsequent expansion through a South American–African–Indian–Southeast Asian–Australian dispersal route and late diversification of the argillaceus clade in Southeast Asia. Based on the abundance of extant taxa, the probability of speciation events in Chroodiscus is shown to be extremely low. Slow dispersal of foliicolous rain forest understorey lichens is consistent with estimated phylogenetic ages of individual species and with average lengths of biological species intervals in fungi (10–20 Myr). Main conclusions The present‐day distribution of Chroodiscus can be explained by vicariance and mid‐distance dispersal through the interconnection or proximity of continental shelves, without the need for recent, trans‐oceanic long‐distance dispersal. Phylogenetic reconstruction and age estimation for Chroodiscus are consistent with the ‘biotic ferry’ hypothesis: a South American origin and subsequent eastward expansion through Africa towards Southeast Asia and north‐eastern Australia via the Indian subcontinent. The present‐day pantropical distributions of many clades and species of foliicolous lichens might thus be explained by eastward expansion through continental drift, along with the evolution of modern rain forests starting 120 Ma, rather than by the existence of a hypothetical continuous area of pre‐modern rain forest spanning South America, Africa and Southeast Asia during the mid and late Cretaceous.     

Bactrocera invadens (Diptera: Tephritidae), a new invasive fruit fly pest for the Afrotropical region: host plant range and distribution in West and Central Africa

In 2003, the invasive fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) (Drew et al. 2005), of possible Sri Lankan origin, has been detected in the East and about 1 yr later in West Africa. In regular surveys in Benin and Cameroon covering 4 yr, samples from 117 plant species across 43 families have been obtained. Incubation of field-collected fruits demonstrate that in West and Central Africa (WCA) B. invadens is highly polyphagous, infesting wild and cultivated fruits of at least 46 species from 23 plant families with guava (Psidium spp.), mango (Mangifera spp.), and citrus (spp.), and the wild hosts tropical almond (Terminalia catappa L.), African wild mango (Irvingia gabonensis (Aubry-Lecomte) Baill.), and sheanut (Vitellaria paradoxa C.F.Gaertn.) showing the highest infestation index. B. invadens occurs in 22 countries of WCA with new records for Angola, Central African Republic, the Congo, DR Congo, Equatorial Guinea, Gabon, Gambia, Guinea Bissau, Mali, Mauritania, Niger, and Sierra Leone. Overall, the pest has spread across a North-South distance of ?5,000 km representing a contiguous area of >8.3 million km(2) within WCA. B. invadens has adapted to a wide range of ecological and climatic conditions extending from low land rainforest to dry savanna. Because of its highly destructive and invasive potential, B. invadens poses a serious threat to horticulture in Africa if left uncontrolled. Moreover, the presence of this quarantine pest causes considerable restrictions on international trade of affected crops.     

Quantitative trait loci affecting the difference in pigmentation between Drosophila yakuba and D. santomea

Using quantitative trait locus (QTL) mapping, we studied the genetic basis of the difference in pigmentation between two sister species of Drosophila: Drosophila yakuba, which, like other members of the D. melanogaster subgroup, shows heavy black pigmentation on the abdomen of males and females, and D. santomea, an endemic to the African island of S?o Tomé, which has virtually no pigmentation. Here we mapped four QTL with large effects on this interspecific difference in pigmentation: two on the X chromosome and one each on the second and third chromosomes. The same four QTL were detected in male hybrids in the backcrosses to both D. santomea and D. yakuba and in the female D. yakuba backcross hybrids. All four QTL exhibited strong epistatic interactions in male backcross hybrids, but only one pair of QTL interacted in females from the backcross to D. yabuka. All QTL from each species affected pigmentation in the same direction, consistent with adaptive evolution driven by directional natural selection. The regions delimited by the QTL included many positional candidate loci in the pigmentation pathway, including genes affecting catecholamine biosynthesis, melanization of the cuticle, and many additional pleiotropic effects.     

Genetic polymorphism and forensic parameters of nine short tandem repeat loci in Ngöbé and Emberá Amerindians of Panama

Nine STR loci (CSF1PO, TPOX, TH01, F13A01, FESFPS, VWA, D16S539, D7S820, and D13S317) were analyzed in unrelated Ng?bé and Emberá Amerindians of Panama. The chi-square test demonstrated statistically significant differences (P < 0.001) in the allele frequencies for all markers except one (D16S539; P < 0.01). Both populations shared their alleles with the highest frequencies in seven loci. However, there were also noticeable differences at the TPOX locus, which showed its highest frequencies at alleles 11 (0.48) and 6 (0.54) for the Ng?é and Emberá, respectively. Interestingly, these alleles are present in one population and are absent in the other, suggesting that they could be distinctive for each population. These results demonstrate that, despite the fact that each population belongs to a different linguistic stock [Chibchan (Ng?bé) and Chocoan (Emberá)], both retain strong similarities in their allele-frequency distributions. Three loci (TPOX, VWA, and F13A01) in the Ng?bé and two loci (TH01 and TPOX) in the Emberá departed from Hardy-Weinberg equilibrium. The analysis of the STR markers demonstrates that, despite their low levels of genetic polymorphisms, most of them could be informative for forensic purposes, showing a combined power of discrimination of 0.9999 for both Amerindian populations. However, powers of exclusion in the Ng?bé were very low, particularly at the TH01 (0.04) and FESFPS (0.08) loci. The combined powers of exclusion were 0.9338 and 0.9890 for the Ng?bé and the Emberá, respectively. Furthermore, the combined typical paternity index in the Ng?bé was considerably low (2.58), and in the Emberá it was 40.44, which is also very low. The low genetic polymorphism levels suggest that theuse of additional loci supplementing the battery of the nine loci is recommended for paternity and forensic tests in both populations, particularly for the Ng?bé.     

Time and origin of cichlid colonization of the lower Congo rapids

Most freshwater diversity is arguably located in networks of rivers and streams, but, in contrast to lacustrine systems riverine radiations, are largely understudied. The extensive rapids of the lower Congo River is one of the few river stretches inhabited by a locally endemic cichlid species flock as well as several species pairs, for which we provide evidence that they have radiated in situ. We use more that 2,000 AFLP markers as well as multilocus sequence datasets to reconstruct their origin, phylogenetic history, as well as the timing of colonization and speciation of two Lower Congo cichlid genera, Steatocranus and Nanochromis. Based on a representative taxon sampling and well resolved phylogenetic hypotheses we demonstrate that a high level of riverine diversity originated in the lower Congo within about 5 mya, which is concordant with age estimates for the hydrological origin of the modern lower Congo River. A spatial genetic structure is present in all widely distributed lineages corresponding to a trisection of the lower Congo River into major biogeographic areas, each with locally endemic species assemblages. With the present study, we provide a phylogenetic framework for a complex system that may serve as a link between African riverine cichlid diversity and the megadiverse cichlid radiations of the East African lakes. Beyond this we give for the first time a biologically estimated age for the origin of the lower Congo River rapids, one of the most extreme freshwater habitats on earth.     

Parthenogenesis in schistosomatidae

Among which species, in what situations and how, does parthenogenesis occur in the biology of reproduction of schistosomes? Here, José Jourdane, Daniéle Imbert-Establet and Louis Albert Tchuem Tchuenté review the literature on parthenogenesis in schistosomes, and debate the evolutionary aspects of this type of reproduction.     

Phylogenetic position and biogeography of Hillebrandia sandwicensis (Begoniaceae): a rare Hawaiian relict

The Begoniaceae consist of two genera, Begonia, with approximately 1400 species that are widely distributed in the tropics, and Hillebrandia, with one species that is endemic to the Hawaiian Islands and the only member of the family native to those islands. To help explain the history of Hillebrandia on the Hawaiian Archipelago, phylogenetic relationships of the Begoniaceae and the Cucurbitales were inferred using sequence data from 18S, rbcL, and ITS, and the minimal age of both Begonia and the Begoniaceae were indirectly estimated. The analyses strongly support the placement of Hillebrandia as the sister group to the rest of the Begoniaceae and indicate that the Hillebrandia lineage is at least 51-65 million years old, an age that predates the current Hawaiian Islands by about 20 million years. Evidence that Hillebrandia sandwicensis has survived on the Hawaiian Archipelago by island hopping from older, now denuded islands to younger, more mountainous islands is presented. Various scenarios for the origin of ancestor to Hillebrandia are considered. The geographic origin of source populations unfortunately remains obscure; however, we suggest a boreotropic or a Malesian-Pacific origin is most likely. Hillebrandia represents the first example in the well-studied Hawaiian flora of a relict genus.     

Abstracts

S. M. Stigler 317 The Pedigree of the International Biometric Society Pour le 60(ème) anniversaire de la Société Internationale de Biométrie, nous proposons un regard en arrière sur la vision de la Biométrie posée par son premier Président, R. A. Fisher, à partir de notes prises dans un cours qu'il a donné en 1935-36.