Anopheles (Cellia) moucheti Evans

Harbach, Ralph E. & Wilkerson, Richard C., 2023, The insupportable validity of mosquito subspecies (Diptera: Culicidae) and their exclusion from culicid classification, Zootaxa 5303 (1), pp. 1-184 : 69-70

Anopheles (Cellia) moucheti Evans

subspecies moucheti Evans, 1925b —original combination: Anopheles marshalli var. moucheti (specific status by Evans 1931). Distribution: Burundi, Central African Republic, Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Ghana, Kenya, Republic of the Congo, Rwanda, Sierra Leone, South Sudan, Tanzania, Uganda ( Wilkerson et al. 2021, Cameroon, Guinea and Nigeria are excluded).

subspecies nigeriensis Evans, 1931 —original combination: Anopheles moucheti var. nigeriensis . Distribution: Cameroon, Guinea, Niger, Nigeria ( Wilkerson et al. 2021) .

Anopheles moucheti was originally described as a variety of An. marshallii ( Theobald, 1903a) and elevated to species status by Evans (1931). The taxon was described from a series of adult males and females from the Belgium Congo, present-day Democratic Republic of the Congo. The holotype male was collected at Buta, which today is a city and capital of Bas-Uiele Province located in the northern area of the country. When Evans recognized moucheti as a distinct species, she also described nigeriensis as a variety of the species based on a series of syntypes (“co-types”), including one male and two females with associated larval and pupal exuviae, collected at Yaba, a suburb of Lagos, Lagos State in southern Nigeria. Townson (1990) verified the presence of nine syntypes in the Natural History Museum, London— two females from Yaba, and two males, two females and three larvae from near Lagos.

Gillies & de Meillon (1968) and Gillies & Coetzee (1987) did not distinguish the adults of moucheti sensu stricto and nigeriensis in their keys to the Anopheles of the Afrotropical Region; however, they did distinguish the larvae based on the development of head seta 3-C—with three or more branches in moucheti sensu stricto and single, occasionally bifid in nigeriensis . The complete chaetotaxy of the larvae, and also the pupae, has not been 8studied comparatively. Gillies & de Meillon (1968) specified that nigeriensis “Differs from the nominate subspecies only in the following characters: Pharynx [cibarium]: Spines on pediment of cone apparently rather longer. Wing: In a series of specimens from Lagos, reared from eggs and with associated larvae from the same eggbatch (C. D. Ramsdale), a 6th pale fringe spot is present in 4 out of 5 females. Outer clypeal hairs [seta 3C]: Simple or bifid apically. We have not been able to confirm Evans’s description of the mesonotal hairs as being narrower than in the type form.”

The taxonomic history of An. moucheti (Moucheti Complex, Brunhes et al. 1998 b) involves the closely related An. bervoetsi D’Haenens, 1961 , which was originally described as a subspecies of moucheti . It was afforded specific status by Gillies & de Meillon (1968) based on distinctive features of the larva, and returned to subspecific status by Brunhes et al. (1998 b), who also considered nigeriensis to be a synonym of moucheti : “All of these [published] observations lead us, at least while awaiting new information, to consider An. moucheti as a polymorphic species and An. moucheti nigeriensis as a synonym of An. moucheti Evans, 1925 [translated from the French].” In agreement with Gillies & de Meillon, bervoetsi was reinstated as a separate species by Antonio-Nkondjio et al. (2008) based on high levels of differentiation between 10 microsatellite loci of non-coding DNA.

Kengne et al. (2007) investigated the use of the mitochondrial cytochrome oxidase b (CytB) gene and the ribosomal internal transcribed spacers ITS1 and ITS2 to distinguish bervoetsi , moucheti sensu stricto and nigeriensis , which were recognized as subspecies of moucheti at the time. The results of their study suggested that moucheti sensu stricto occurs in the forested areas of central Africa while bervoetsi and nigeriensis are only found in areas of the Democratic Republic of the Congo and Nigeria, which encompass their type localities, respectively. For ITS1, the mean genetic distance was found to be greater between nigeriensis and bervoetsi (0.166) than between moucheti sensu stricto and bervoetsi (0.141), and lower between moucheti sensu stricto and nigeriensis (0.084). The authors stated that “This degree of differentiation between morphological forms is relatively high, indicating significant genetic divergence among the three taxa, which is comparable with that among species.” In comparison, the ITS2 sequences exhibited a lower degree of divergence, ranging from 0.03 between moucheti sensu stricto and nigeriensis to 0.063 between moucheti sensu stricto and bervoetsi . Sequence differences included 30 fixed indel or substitutions between moucheti sensu stricto and bervoetsi , 29 between nigeriensis and bervoetsi , and 16 between moucheti sensu stricto and nigeriensis . For the CytB gene, 26 fixed differences in the first codon position were identified among the three forms. The CytB gene sequences, in agreement with the ITS2 sequences, showed consistent but low divergence of 0.035 –0.047 between the three forms. The authors concluded that “The concordance of genetic variability of the three markers and the lack of intraspecific geographical variation suggests that the three members of the group are true species.” In summary they stated that “The three genomic regions revealed sequence differences between the three morphological forms similar in degree to the differences shown previously for members of other anopheline species groups or complexes (genetic distance d = 0.047–0.05 for CytB, 0.084 –0.166 for ITS1 and 0.03–0.05 for ITS2).” In view of the genetic evidence, we are suprised that Kengne et al. did not formally elevate nigeriensis to specific rank. But having said that, the taxonomic status of nigeriensis was not relevant to the objective of their study, which was to elucidate molecular means for distinguishing and identifying the three nominal forms.

Despite the available morphological, molecular and distribution data, nigeriensis continued to be recognized as a subspecies ( Harbach 2018; Coetzee 2020; Irish et al. 2020; Wilkerson et al. 2021). In fact, nigeriensis as a separate entity has largely been ignored, e.g., in the recent list of countries in which Afrotropical species of Anopheles have been recorded ( Irish et al. 2020), the authors stated “As An. nigeriensis refers to a subspecies of An. moucheti , it is not included here.”

In view of the morphological, distributional and in particular the molecular distinctions detailed above, we are compelled to formally recognize nigeriensis as a separate species of the Moucheti Complex: Anopheles (Cellia) nigeriensis Evans, 1931 . Anopheles nigeriensis is not currently included as a species in the Encyclopedia of Life and should be added to the list of species of the genus. As currently understood, the Moucheti Complex includes three species, bervoetsi D’Haenens , moucheti Evans and nigeriensis Evans.