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Monomorium setuliferum species group
based on Bolton, 1987
Species
- Monomorium alamarum
- Monomorium ebangaense
- Monomorium hannonis
- Monomorium havilandi
- Monomorium macrops
- Monomorium notulum
- Monomorium setuliferum
- Monomorium xanthognathum
Diagnosis
Worker Monomorphic but with some size variation in any given series. Palp formula 2,2 (Monomorium alamarum, Monomorium setuliferum). Mandibles usually with 4 teeth, the basal tooth reduced to a small or minute denticle which is offset from the main row of 3 teeth. Basal denticle lost in one species (Monomorium havilandi) leaving the mandible 3-dentate. Mandibles longitudinally striate or rugose (smooth in Monomorium xanthognathum). Median portion of clypeus raised and weakly bicarinate, not strongly projecting forward and the anterior clypeal margin lacking prominent teeth or angles. Posteriorly the median portion of the clypeus broader than either frontal lobe where it passes between them. Cephalic sculpture variable, sometimes absent. Eyes moderate to very large (0.22-0.36 x HW) and situated in front of the midlength of the sides of the head. In profile the eyes usually conspicuously oblique and frequently reniform in shape. Head generally short and broad (CI > 85), but narrower in alamarum and Monomorium macrops. Scapes relatively short, SI usually < 90. Antennae with 12 segments, terminating in a strongly differentiated club of 3 segments. Propodeal dorsum smooth to reticulate-punctate , never transversely striate or rugose. Propodeal spiracle circular to subcircular. Petiolar spiracle at the node or immediately in front of the anterior face of the node. (Workers examined: all members of group.)
Female Characters as worker but alate when virgin and with fully developed flight sclerites; distinctly larger than conspecific worker. Eyes larger than worker and ocelli present. (Female examined: havilandi.)
Male Distinctly much larger than the con specific worker, closely approaching size of female. Mandibles with 3-4 teeth, the blades longitudinally rugose or striate. Palp formula 2,2 (Monomorium notulum). Antennae with 13 segments, the scape short cylindrical, two or more times longer than broad. First funicular segment shorter than remainder but not globular; remaining funicular segments cylindrical to barrel-shaped, elongate, not tapering or whip-like apically. Eyes large and at the midlength of the sides, with a broad space between their anterior margins and the clypeus (as in Fig. 25). Sides of head behind eyes converging to the broad occipital margin. With the head in full-face view the ocelli not breaking the occipital outline. Notauli absent but parapsidal furrows represented by a pair of unsculptured strips on the mesoscutum. HW slightly greater than maximum width of mesoscutum. Cross-vein m-cu absent from forewing. Axillae triangular, small and lateral on the dorsum. Propodeal spiracle small and circular. (Males examined: notulum, havilandi.)
species complexes
These Afrotropical species can be grouped into three complexes.
setuliferum complex
- Monomorium alamarum
- Monomorium ebangaense
- Monomorium hannonis
- Monomorium notulum
- Monomorium setuliferum
The complex contains three very closely related species ebangaense, notulum, and setuliferum, and a few peripheral but related taxa. The three named are very close indeed and may eventually prove to be expressions of a single plastic species. Within the group the three are characterized by a lack of standing pilosity on the head and body, presence of strong sculpture, possession of oblique eyes which may or may not be reniform, and presence of relatively broad heads and short scapes (CI 83-90; SI 81-90).
Peripheral to this triad is alamarum, which shares most of the above characters but has very reduced sculpture and a slightly larger head (CI 79-83) , and has a lower petiole node, although the significance of this last feature cannot be assessed at present. Also peripheral to the three species noted above is hannonis, a species obviously close to setuliferum but differing in the form of its sculpture and its development of dense pilosity. These five together may well represent a holophyletic group based on their sculpture and eye form, combined with the joint characters of the group diagnosis given above.
havilandi complex
The complex contains only havilandi and xanthognathum]], in which the large eyes are oblique, reniform in the latter but not so in the former. Scapes are relatively short (SI 70-82) and the broad head (CI 86-92) is smooth and unsculptured except for scattered hair-pits. Both species show numerous standing hairs on the head, alitrunk and gaster.
These two are grouped here on what are probably convergencies, and are not really closely related, but so little material of either is available for study that any pronouncements made now would amount to little more than speculation. Suffice to say that the havilandi worker is one of only two known Afrotropical species of Monomorium to have only 3 teeth on the mandible (the other being abyssinicum - now Trichomyrmex abyssinicus). It could have been derived from the setuliferum-complex above, or independently derived from the salomonis-group. The male, described by Arnold (1944), is of the salomonis-group form.
M. xanthognathum shows some resemblance to the destructor-group but has eyes which are too large and are wrongly shaped to allow its admittance to that group. Also, the diagnostic destructor-group character of possession of transverse sculpture on the propodeal dorsum is absent here. The discovery of the male of xanthognathum would help our understanding of its taxonomic position , but I would guess that the male would be salomonis-like rather than destructor-like.
macrops complex
This species has large eyes that are shifted forwards, but are only slightly oblique and are not reniform. The head is quite long (CI 78-80) but the scapes are relatively short (SI 84-90). Sculpture is extremely reduced on the head but present on the dorsal alitrunk; the head, alitrunk and first gastral tergite all retain standing hairs.
Certainly this species represents a development from the salomonis-group independent of any of those listed above. Its origins are presently very obscure but it seems a reasonable hypothesis that its resemblances to both of the complexes discussed above are the result of convergence rather than of real relationship.
Notes
This is a convenience group, erected to hold 8 southern African species which probably do not represent a holophyletic group but which are nonetheless linked by the characters listed above. The included species show, in the workers, features of both the salomonis-group and the destructor-group, but do not fall convincingly into either. Males on the other hand are most emphatically of the salomonis-group form and are in fact inseparable from those of members of that group. Based on material presently available the members of the setuliferum-group appear most likely to have been derived from two loci, or perhaps more, within the salomonis-group, but have converged on the destructor-group in a number of ways in the worker caste. See the notes under the introduction to the species-groups.