STUDIES ON THE CYTOSPECIES AND DISTRIBUTION OF Simulium damnosum COMPLEX (DIPTERA: SIMULIIDAE) IN PARTS OF NIGERIA, CAMEROON AND EQUATORIAL GUINEA

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Date
1998-07
Authors
BASSEY, STELLA AME EKPENYONG
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Abstract
Cytotoxanomic studies of members of the Simulium damnosum complex was carried out in parts of Nigeria, Cameroon and Equatorial Guinea to determine cytospecies status and distribution across different bio-climatic zones and across country boundaries. These three neighbouring West African countries were studied in view of the importance of the knowledge of vector species abundance and distribution in onchocerciasis endemic areas and how their migratory activities affect control programmes. Sampling sites for the study was chosen within a broad transect from the northern extremes of distribution in Nigeria through its southern bio-climatic zones into south west Cameroon near Mount Cameroon and further south to parts of the island of Bioko in Equatorial Guinea. Sites in Nigeria cut across both savannah and forest zones while in Cameroon and Equatorial Guinea all sites fell within the forest zone. Larval samples were collected from these sites and cytospecies status determined by the observation of the inversion pattern of their polytene giant chromosomes. In Nigeria four cytospecies were observed, S. squamosum, S. sirbanum, S. damnosum s.s. and S. yahense with frequency distribution of 58%, 21.3%, 17.3% and 3.3% respectively. Cytospecies observed in Cameroon were S. squamosum (84%) and S. mengense (16%). I n the island of Bioko, there was observed the existence of a single cytospecies which is confined to the S. squamosum sub-species and closely related to S. yahense. This cytospecies was found to have no fixed inversion differences from either S. squamosum or S. yahense but differed from both in the pattern of sex-linkage of inversion 2-L18 which here was Y-linked . Distribution of the Nigerian cytospecies in relation to the different bio-climatic zones showed S. squamosum and S. yahense to be more restricted to the forest with frequencies of 98% and 100% respectively. Simulium damnosum V exhibited a wide distributional range, spanning through forest (57.7%) and savannah (42.3%) areas. Simulium sirbanum occurred more in the savannah ( 98.4%) zones. Further more, in the forest zones of Nigeria, S. squamosum was found to consist of two different populations, one with a sex-linked chromosome variation on the centromere of chromosome one, and the other population did not have this variation. Measurement of physical and chemical parameters of the water in the some breeding sites in Nigeria showed slight differences between the features for the forest and savannah zones. It is apparent from results of this study that in Nigeria S. squamosum and S. yahense are restricted to the forest zones whereas S. damnosum s.s. and S. sirbanum, typical savannah cytopecies are becoming significant in the forest zones. This may be a reflection of a change in environmental conditions, a factor which may partly explain why cytospecies like S. sanctipauli and S. soubrense reported to occur in Nigeria by other researchers were not observed. Interestingly, S. mengense was not observed in Nigeria and no sexlinked chromosomal variation was observed in any of the S. squamosum samples from Cameroon. The above observations together with the uniqueness of S. mengense to Cameroon and Bioko type S. yahense to Bioko indicate that in spite of the proximity of these countries, there is still some geographic limit to the movement of the S. damnosum cytospecies.
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A dissertation submitted to the postgraduate school, Ahmadu Bello University, Zaria in partial fulfillment for the requirements of the award of a Doctor of Philosophy in Biology. DEPARTMENT OF BIOLOGICAL SCIENCES, AHMADU BELLO UNIVERSITY ZARIA, KADUNA STATE, NIGERIA. JULY 1998
Keywords
STUDIES,, CYTOSPECIES,, DISTRIBUTION,, Simulium damnosum,, COMPLEX (DIPTERA: SIMULIIDAE),, PARTS,, NIGERIA, CAMEROON,, EQUATORIAL GUINEA.
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