ARTICLE Analysis of the Population Structure of Anopheles funestus (Diptera: Culicidae) from Western and Coastal Kenya Using Paracentric Chromosomal Inversion Frequencies LUNA KAMAU, 1 RICHARD HUNT, 2 AND MAUREEN COETZEE 2 J. Med. Entomol. 39(1): 78Ð83 (2002) ABSTRACT Intotal,324 Anopheles funestus Gilesspecimenscollectedfromsevenhousesinwestern KenyaandsevenincoastalKenyawerescoredfortheirparacentricchromosomalinversionswiththe aimofdeterminingthelevelofgeneticdifferentiationbasedontheseinversions.Housesineacharea werewithina2-kmradius.Thetwoareasare 700kmapart.Onlyinversions2a,3a,3b,and5awere foundtobepolymorphic.Levelsofpolymorphismvariedgreatlybetweeninversions.Therewereno signiÞcant deviations from Hardy-Weinberg expectations for samples from individual houses at one siteorwhendataforhousesineachareawerepooled.Overall,thelevelofdifferentiationbetween westernandcoastalKenyawassigniÞcant,suggestingthatthetwopopulationsaregeneticallyisolated. Results based on inversion 2a alone were, however, not consistent with this conclusion. Founder effectsandselectionagainstthe2ainversionarediscussedaspossibleexplanationsforthisdiscrepancy. KEY WORDS Anopheles funestus, malaria, chromosomal inversions, variability, Kenya MALARIACONTINUESTO beamajorhealthconcerninthe tropics. Anopheles funestus Gileshasbeenshowntobe an important malaria vector, in some cases playing a more important role than An. gambiae Giles and An. arabiensis Patton (e.g., Fontenille et al. 1997). An. funestus isamemberofaspeciescomplexcomprising at least nine members, the adults of which are not easily distinguished on the basis of morphological characteristics (Gillies and De Meillon 1968; Gillies and Coetzee, 1987) although some species may be distinguished using larval characteristics. The mem- bers of this complex are An. funestus, An. vaneedeni Gillies&Coetzee, An. parensis Gillies, An. aruni Sobti, An. confusus Evans & Leeson, An. rivulorum Leeson, An. fuscivenosus Leeson, An. leesoni Evans, and An. brucei Service. Traditionally, the only other method for distinguishing members of the An. funestus group have been by chromosomal inversion karyotypes (Green and Hunt 1980, Green 1982). More recently, however, single-strand conformation polymorphism (SSCP)analysishasbeenusedtoidentifyfourmem- berofthisgroup(Koekemoeretal.1999).Ofthenine species in the complex, An. funestus has the widest distribution. This mosquito is also highly anthropo- philic (Gillies and De Meillon 1968). Characterization of vector populations in terms of reproductiveunitsisafundamentalstepinthedevel- opmentofvectorcontrolstrategiesthatarebasedon the genetic manipulation of vectorial capacity. An understanding of genetic differentiation and gene ßow in natural mosquito populations is crucial to de- termininghowfarintroducedgeneswillspread,which in turn is important in determining the spatial and temporal scale required for gene introductions. Knowledgeofpopulationgeneticstructureisalsouse- ful in predicting the spread of insecticide resistance associated with particular genes. Thecharacterizationofpopulationsintermsofba- sic reproduction units can be achieved by measuring among-population genetic variability, using any of several genetic markers. In the study reported here, Þxed paracentric inversion karyotypes were used to differentiatebetweenthevariousmembersofthe An. funestus groupandthenpolymorphicinversionsused to study population genetic structure. Materials and Methods Study Site Description. Twositeswereusedinthis study:AheroinwesternKenya(34° 30ÕE;0° 5' S)and MagaoniinKwaledistrictofcoastalKenya(39° 30ÕE; 4° 10ÕS).Eachsiteistraversedbyapermanentfresh waterstreamwithvegetationßoatingalongthesides. Several small ponds with tall reeds are also found in both areas. In addition, Ahero is a rice-growing area whereirrigationiscarriedoutintermittently.Previous studiescarriedoutinthesetwoareasindicatethat An. 1 Center for Biotechnology Research and Development, Kenya Medical Research Institute, P.O. Box 54840, Nairobi, Kenya. 2 Medical Entomology, Department of Clinical Microbiology and InfectiousDiseases,SchoolofPathologyoftheSouthAfricanInstitute for Medical Research, P.O. Box 1038, Johannesburg, 2000, and the UniversityoftheWitwatersrand,Johannesburg,PrivateBag3,WITS, 2050, South Africa. 0022-2585/02/0078Ð0083$02.00/0  2002 Entomological Society of America Downloaded from https://academic.oup.com/jme/article/39/1/78/878882 by guest on 22 December 2022