A supplement to the Anophelinae of Africa south of the Sahara (Afrotropical Region).

Speciation in the Anopheles gambiae complex is reviewed and discussed with emphasis on the patterns of chromosomal differentiation, particularly at the intraspecific level. The significance of inversion polymorphism in gambiae and arabiensis (the two species of greatest medical importance) is evaluated with reference to recent field investigations carried out in Nigeria. In both sibling species some of the inversions show clinical geographical changes in frequencies, with evident correlations with climatic conditions and vegetation zones. Microgeographical variations in species distribution and in intraspecific inversion frequencies are also present, which appear mostly related to man-made environmental contrasts. Parallel indoor-/outdoor collections of samples from polymorphic populations of arabiensis and gambiae show that adult mosquitoes carrying certain inversion karyotypes do not distribute at random in relation to the human environment, being significantly more frequent in outdoor than in indoor samples, or vice-versa. Optimal habitat choice appears to be involved in such variations of indoor resting behaviour, since the chromosomal types carried by less endophilic individuals are those more adapted to humid climates, i.e. those which tend to avoid the higher nocturnal saturation deficit of the indoor environment. This phenomenon, producing non-uniform exposure of the vector population to residual insecticides sprayed in houses, might explain the mediocrity of the results of malaria control projects based on house-spraying against endophilic vectors in the African savannas.

Chromosomal differentiation and adaptation to human environments in the Anopheles gambiae complex

Two new species within the Anopheles gambiae complex are here described and named. Based on molecular and bionomical evidence, the An. gambiae molecular "M form" is named Anopheles coluzzii Coetzee & Wilkerson sp. n., while the "S form" retains the nominotypical name Anopheles gambiae Giles. Anopheles quadriannulatus is retained for the southern African populations of this species, while the Ethiopian species is named Anopheles amharicus Hunt, Wilkerson & Coetzee sp. n., based on chromosomal, cross-mating and molecular evidence.

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Anopheles coluzzii and Anopheles amharicus, new members of the Anopheles gambiae complex.

Historically, members of the Anopheles gambiae complex from Ethiopia have been identified chromosomally as either A. arabiensis or A. quadriannulatus. Recent collections from the Jimma area in Ethiopia, south-west of Addis Ababa, revealed 29 specimens of A. quadriannulatus based on the standard polymerase chain reaction (PCR) identification method. ‘Wild’ females were induced to lay eggs and the progeny reared as individual families. Resulting adults were cross-mated to a laboratory colony strain of A. quadriannulatus originating from the Kruger National Park, South Africa. Hybrid progeny were obtained only from the colony female x Ethiopian male cross. This cross produced a female/male sex ratio of 0.48. Male offspring were sterile and ovarian polytene chromosomes from hybrid females showed typical asynapsis as expected in interspecific crosses within the A. gambiae complex. The X chromosomes, although apparently having homosequential banding patterns, were usually totally asynapsed. All autosomes were homosequential. The lack of inversion heterozygotes, in both the wild and hybrid samples, may simply be a reflection of the small sample size. Until such time as the Ethiopian species can be formally described and assigned a scientific name, it is provisionally designated Anopheles quadriannulatus species B because of its close similarity to this species.

The Anopheles gambiae complex : A new species from Ethiopia

Abstvact A multivariate approach has been used to study morphological variation in the blue and orange-form species of rock crab of the genus Leptograpsus. Objective criteria for the identification of the two species are established, based on the following characters: width of the frontal region of the carapace; width of the posterior region of the carapace (rear width); length of the carapace along the midline; maximum width of the carapace; and the depth of the body. The first canonical variate, which differentiates between the two species, represents a contrast between the carapace width relative to the width of the front lip and the depth of the body; the blue-form species has a greater relative carapace width than has the orange form. The second canonical variate, which presents a contrast between the rear width and the carapace length, identifies males and females within each species; males have a greater relative carapace length than have females. All individuals, including 20 not used in the study, were correctly identified for colour form. The clear separation of the blue and orange forms achieved by canonical analysis supports the previously determined specific status of the two forms.

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Mr.G. Davidson

Papers

The Anopheles gambiae complex