Aenictus guineensis Santschi, 1924

Gómez, Kiko, 2022, A revision of the Afrotropical species of the Dorylinae ant genus Aenictus (Hymenoptera: Formicidae) based on the worker caste, Belgian Journal of Entomology 124, pp. 1-86 : 61-68

Aenictus guineensis Santschi, 1924

( Figs 1 A , 2 A, C , 43 A–D , 44 A–E , 51 )

Aenictus rotundatus st. guineensis SANTSCHI, 1924: 204 , fig. 7 (w.)

Syntype, GUINEA: Kakulima (Silvestri) (1w) [ CASENT0911438 ] NHMB [Examined] ; Syntype, same data (1w, beheaded) NHMB [Examined].

Aenictus guineensis TAYLOR et al., 2018: 10 [Raised to species]. Status confirmed here. Check below for discussion.

DIAGNOSIS. Its sparse, erect, long setae, the presence of a developed subpetiolar process and the lack of a developed propodeal ridge separates this species from the rest of the species present in the rotundatus complex, except for A. ugaduwensis sp. nov. and A. rotundatus , and separation is feasible only via index analysis. It is more slender and presents more rectangular heads than A. ugaduwensis sp. nov. (details under that species).

Aenictus guineensis is the western counterpart of the Southern and Eastern African A. rotundatus , and separating individuals can be difficult, especially with small, isolated individuals. TAYLOR et al., (2018) raised this form to species, but in my opinion with wrong or not detailed enough arguments to do so. I do respect his prevalence in this matter, though.

For more detailed information see discussion below.

There are some characteristics that may separate series of workers, but it’s a matter of comparison and very variable among individuals. Some of these for A. guineensis are a more developed propodeal ridge (but as a thin line at most in larger individuals), smoother mandibles (which can become shagreened in the most sculpted A. rotundatus ), more rectangular rounded subpetiolar process (against more shark-finned), slightly longer scapes and relatively more elongated petiole.

Clear separation can be obtained via index analysis (details in key and in page 65).

The type material [CASENT0911438] presents two labels, as A. rotundatus v. guineensis and as A. guineensis.

DESCRIPTION ( Figs 1 A , 2 A, 2 C, A–D , 44 A–E ). WORKER. HL: 0.63 [0.51-0.76]; HW: 0.54 [0.42-0.67]; SL: 0.45 [0.32-0.55]; WL: 0.98 [0.76-1.19]; PL: 0.24 [0.18-0.28]; PH: 0.17 [0.13- 0.20]; PPL: 0.18 [0.12-0.22]; PPH: 0.16 [0.12-0.21]; CS: 0.59 [0.46-0.71]; CI: 86 [80-90]; SIL: 70 [62-75]; SIW: 81 [77-86]; WL/HW: 179 [172-187]; PI: 137 [129-147]; PPI: 115 [100-128]; CSR: 152; (n=28).

With the characteristics of the rotundatus species complex and: scapes relatively long, almost reaching three quarters of the head (SL/HL~70). Funicular segments slightly longer than wide, the last three engrossing to the apical, which is about twice longer than wide. Head rectangular, longer than wide (CI~86), convex laterally and widest at the middle. Occipital line straight to slightly convex. Ventrolateral margin present, continuing behind the head to one fourth of its length. Mandibles triangular; with a long, sharp apical tooth followed by 5–6 triangular denticles. Clypeus a row of 6–10 conical teeth, clearly visible and longer than wide, decreasing to the sides, sometimes eroded. Frontal ridges present, not projecting frontally and not fused between the antennal sockets.

Pronotum convex, smoothly running into the straight mesonotum; mesopropodeal suture present and visible both laterally and dorsally, concave and meeting the propodeum at an angle; this with a very reduced but discernible anterior slope and elevated over the mesonotum; propodeal shape an elongated hexagon dorsally, widest in its anterior third over the propodeal spiracle, its sides often defined by weak rugulae. Transverse mesopleural groove not present. Mesometapleural suture present but very weak; propodeal ridge complete and present, except in the minima workers, where it can be reduced and faint; propodeal declivity concave below that line.

Petiole sessile with anterolateral ridges present, anterodorsal and dorsolateral ridges absent. Petiole ellipsoidal, rounded, anteriorly almost flat at 45 degrees and vertical posteriorly. Postpetiole subrectangular with rounded angles and vertical anterior and posteriorly, the posterior higher and less rounded, without carinae or ridges of any kind. Subpetiolar process developed with a bulky ellipsoidal process, followed by a lamellae variable in size from almost non-existent to about the size of the bulky process, rounded and pointing downwards.

Head, scapes, pronotum, mesonotum, dorsum of petiole and postpetiole, gaster and legs, smooth and shining; mandibles mostly smooth, variable rugulose in its upper half; propodeum, lateropetiole and lateropostpetiole alutaceus to reticulated, matt. Overall colour light brown to brown, slightly lighter at gaster and apex of funiculus.

Decumbent white setae, oriented backwards, present at head, dorsum of pronotum petiole, postpetiole and gaster. Dorsum of propodeum bare except for its posterior border, with 2–4 long erect setae. A few scattered, long, white, erect setae present at pronotum, petiole, postpetiole and gastral tergites, longer than petiole height. Scapes with white unequally long semierect setae, clearly longer than scape width.

SEPARATION BETWEEN A. guineensis AND A. rotundatus .

Aenictus guineensis was raised to species in TAYLOR et al. (2018:10). The reasons given were: ‘This species is some 75-80% of the size of the Eastern Africa species A. rotundatus and has a notably more rectangular head and a flatter profile to the petiole among other differences.’

Fig. 45 and Fig. 46 show the measurements done on 28 workers of A. guineensis and 44 of A. rotundatus including types of both species. Regarding size and head shape (HW/HL), no significant difference can be appreciated. Also, the petiolar profile is similarly flat (Figs 43 C, 44 C, 57 C). If ‘flatter profile’ does not refer to shape but to height, PH by itself does not separate the species (Fig. 45 B), but is quite useful as an index (PI=PL/PH, Fig. 46A). Except for values between 125 and 135 it can separate both species easily, but for values between them a more thorough analysis is needed.

Morphometric analysis was performed to assess if both species can be morphologically separated. PCA analysis did not produce any separation ( Fig. 47 ). This result does not prove that they are the same species, just that PCA analysis cannot find an easy separation between them.

A more sophisticated analysis (Nest Centered Cluster Analysis) was performed ( CSOSZ & FISHER, 2016). In this case, separation between Eastern African and Western African nests was possible in 100% of the cases ( Fig. 48 ), so it seems to provide strong evidence that they can be two different morphological entities.

Best Index Analysis was performed as in BAUR & LEUENBERGER (2011) to find the couple of indexes that produce the best possible separation, which resulted to be PH/PL and WL/SL ( Fig. 49 ). LDA and Leave One Out analysis performed with these new variables also produced a neat separation between both species ( Fig. 50 ).

The discriminant function 26.225*PH/PL+8.680WL/SL-40.524, separates both species in 100% of the tested samples, being positive for A. rotundatus and negative for A. guineensis. Based on these data, A. guineensis is considered here a good species.

OTHER MATERIAL EXAMINED. IVORY COAST: • Comoe 06/2004 (Moretto). Savanne (4w), MSNM. NIGERIA: • 16 km N of Mokwa 04/10/1976 (Longhurst) (3 pins, 3w each) [ NHMUK012849321 to NHMUK012849323 ] BMNH • Ibadan 10/10/1973 (Critchley) (1w) [ NHMUK012849324 ] BMNH. SENEGAL: • Kedougou, Dande (2) ( Dindefelo ) 450m, 12.36583, -12.32917 29/09/2016. Hand (Gomez, K). Savannah (+20w in ethanol), Foraging under stone [ KG03386 ] KGPC • same data (2 pins, 1 w each) [ KGCOL00579 , KGCOL00580 ] KGPC • same data (2w) [ KGCOL00575 ] KGPC • same data (3w) [ KG03386A06 ] AFRC • same data (3w) [ KG03386A07 ] CASC • same data (2 pins 3w each) [ KGCOL00576 , KGCOL00577 ] KGPC • same data (4w) [ KGCOL00578 ] KGPC • Neménick, Niokolo Koba 10 km W ( Niokolo Koba NP), 13.0764, -12.78196 01/08-07/11/2018. Winkler (Diallo, A.). Savannah (1w) [ KG03821B01 ] KGPC • Thies, Mboro 2m, 15.14438, -16.86874 06/09/2018. Hand (Menchetti, M.). Cultives nr. savannah (2w), Foraging [ KGCOL 00574] KGPC.

DISTRIBUTION. West Africa, known from Senegal to West Nigeria ( Fig. 51 ).

Figures

Fig. 1. Mandibular and clypeal shapes for the different species groups. A, gr. rotundatus (Aenictus guineensis, CASENT0876634). B, gr. koloi (Aenictus koloi, sp. nov., KGCOL00552). C, gr. eugenii (Aenictus eugenii, CASENT0235822). D, gr. eugenii (Aenictus mvuvii, sp. nov., CASENT0350555). E, gr. popeyei (Aenictus popeyei, sp. nov., CASENT0810234). F, gr. decolor (Aenictus decolor, CASENT0317077). G, gr. asantei (Aenictus asantei, NHMUK012849241). H, gr. rixator (Aenictus rixator, CASENT0907030).

Fig. 2. Head sculpture and femora shapes. A, C, Aenictus guineensis (CASENT0876634). B, Aenictus xegi sp. nov. (NHMUK012849243). D, Aenictus susanae sp. nov. (CASENT0406729).

Fig. 43. Aenictus guineensis, minor worker, type (CASENT0911438). A, head, dorsal view. B, habitus, lateral view. C, mesosoma, petiole and postpetiole, lateral view. D, mesosoma, petiole and postpetiole, dorsal view.

Fig. 44. Aenictus guineensis, major worker (CASENT0876634). A, head, dorsal view. B, habitus, lateral view. C, mesosoma, petiole and postpetiole, lateral view. D, mesosoma, petiole and postpetiole, dorsal view. E, mandibles and clypeus, dorsal view.

Fig. 51. Distribution of A. guineensis.

Fig. 47. Principal Component Analysis (PCA) results for A. guineensis and A. rotundatus.

Fig. 48. Nest Centered Cluster Analysis (NCCA) results for A. guineensis and A. rotundatus.

Fig. 49. Best Index Analysis separation between A. guineensis and A. rotundatus, showing the discriminant boundary.

Fig. 50. LDA allocation results for A. guineensis and A. rotundatus.