The distribution of M and S molecular forms of Anopheles gambiae sensu stricto across Nigeria was determined. The molecular form of 40 to 45 specimens per locality from 9 localities was determined using mostly the same specimens from our recent study of genetic differentiation of A. gambiae across Nigeria (Onyabe & Conn, 2001). These samples were previously genotyped at 10 microsatellite loci, 5 located within chromosome inversions and 5 outside inversions. Both molecular forms occurred throughout the country, with no apparent relationship to the ecological transition from dry savannah in the north to humid forest in southern Nigeria. In all localities, however, 1 form or the other occurred virtually exclusively. No hybrids between forms were found. Across all loci, F(ST) values were as high within molecular forms as between forms. Regardless of molecular form, F(ST) values calculated across loci within inversions were much higher (range 0.0016 to 0.1988) than those calculated across loci outside inversions (range -0.0035 to 0.0260). Genetic distance was not significantly correlated with geographical distance within either form (P> 0.05). These observations suggest that, in addition to partial reproductive barriers between molecular forms, selection is a major factor shaping genetic differentiation of A. gambiae across Nigeria.
Anopheles gambiae Giles s.s. and Anopheles arabiensis Patton (Diptera: Culicidae) are major vectors of malaria in Nigeria. We used 1115 bp of the mitochondrial COI gene to assess their population genetic structures based on samples from across Nigeria (n = 199). The mtDNA neighbour-joining tree, based on F(ST) estimates, separated An. gambiae M and S forms, except that samples of An. gambiae M from Calabar clustered with all the An. gambiae S form. Anopheles arabiensis and An. gambiae could be combined into a single star-shaped, parsimonious haplotype network, and shared three haplotypes. Haplotype diversity values were high in An. arabiensis and An. gambiae S, and intermediate in An. gambiae M; all nucleotide diversities were relatively low. Taken together, patterns of haplotype diversity, the star-like genealogy of haplotypes, five of seven significant neutrality tests, and the violation of the isolation-by-distance model indicate population expansion in An. arabiensis and An. gambiae S, but the signal was weak in An. gambiae M. Selection is supported as an important factor shaping genetic structure in An. gambiae in Nigeria. There were two geographical subdivisions in An. arabiensis: one included all southern localities and all but two central localities; the other included all northern and two central localities. Re-analysing an earlier microsatellite dataset of An. arabiensis using a Bayesian method determined that there were two distinctive clusters, northern and southern, that were fairly congruent with the mtDNA subdivisions. There was a trend towards decreasing genetic diversity in An. arabiensis from the northern savannah to the southern rainforest that corroborated previous data from microsatellites and polytene chromosomes.
Helminth parasitc infections were investigated in 150 Anurans collected in parts of the Northern Guinea Savannah during thedry and wet seasons of 2016. The Anurans that were investigated included Amietophrynus regularis, Kassina senegalensis,Afrixalus vittiger, Xenopus tropicalis, Xenopus fischbergi, Pyxiecephalus cf. edulis, Hoplobatrachus occipitalis, Amniranagalamensis and Ptychadena pumilio. Overall prevalence of helminth parasites was 64% (94/150). Seven species ofhelminths belonging to three taxonomic classes were recovered: Monogenea 4%, Trematoda 19.33% and Nematoda 40.67%were identified. Eupolystoma alluaudi (30%) was the only monogenean recorded from the bladder of S. regularis. Tematodesfound were Diplodischus fishthalicus (53.49%) and Haematoloechus micrurus (67.45%) from the rectum and lungs of H.occipitalis, respectively. Nematodes included Camallanus microcephalus from the oesophagus and small intestine of X.fischbergi ( 62.96%) and X. tropicalis (100 %), respectively, Camallanus dimitrovi (25.58%) from the small intestine andrectum of H. occipitalis, an unidentified nematode from the oesophagus and small intestine of X. fischbergi (1.85%) and X.tropicalis (33.33%), and an Aplectana (85.00%%) species from the small intestine and rectum of S. regularis. Except forEupolystoma alluaudi, the infestation level was generally low. Parasite prevalence was higher during the wet (39.33%) thandry (24.67%) season and the difference was not significant (p = 0.17). The prevalence and infection intensity were lower thanthose reported from anurans in southern biotopes of Nigeria. The occurrence of Camallanus macrocephalus is a new recordfor Nigeria, while X. fischbergi and X. tropicalis are new host records for C. macrocephalus.
Keywords: Anurans, helminth, prevalence, Northern Guinea Savannah, Nigeria
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