Simopone species groups

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Based on Bolton, B. & Fisher, B.L. 2012. Taxonomy of the cerapachyine ant genera Simopone Forel, Vicinopone gen. n. and Tanipone gen. n. (Hymenoptera: Formicidae). Zootaxa, 3283, 1–101. PDF

The world fauna of Simopone can be divided into three distinct species groups based on the characters noted below. The largest of these is the emeryi group, distributed throughout sub Saharan Africa and Madagascar. It currently contains 20 species, of which 14 are Madagascan and 6 African. No single species is known to occur in both regions and species in this group tend to be large and powerfully built. The schoutedeni group, with 11 species, is peculiarly Afrotropical and consists of relatively small, uncommon species. The grandidieri group, though the smallest in terms of number of species (7), is by far the most widely distributed, with 1 Afrotropical, 1 Oriental, 2 Malagasy and 3 Malesian representatives.

Key to world species groups (workers)

1

  • Mesopleuron with a well defined and conspicuous transverse sulcus that divides it into anepisternum and katepisternum. Pygidium without a stout cuticular apical fork above the sting . . . . . 2
  • Mesopleuron without a transverse sulcus, the sclerite not divided into anepisternum and katepisternum. Pygidium with a stout cuticular apical fork above the sting. (Afrotropical, Malagasy) . . . . . emeryi group

2

  • Apex of pygidium margined by a row of denticles that are all approximately the same size. Anteroventral process of AII (petiole) not a lamina and without a fenestra. Outer margins of frontal carinae diverge from the line of the frontal lobes at their point of junction. Palp formula 5,3 where known. Setae on dorsal surfaces of mesosoma and abdomen usually sparse or absent. (Afrotropical, Malagasy, Oriental, Malesian) . . . . . grandidieri group
  • Apex of pygidium margined by a row of denticles, the median pair of which is enlarged. Anteroventral process of AII (petiole) a short lamina, with a fenestra. Outer margins of frontal carinae converge from the line of the frontal lobes at their point of junction. Palp formula 6,4 where known. Setae on dorsal surfaces of mesosoma and abdomen abundant. (Afrotropical) . . . . .schoutedeni group

Regional Keys

Key to Afrotropical Simopone Workers / Key to Known Afrotropical Simopone Queens

Key to Malagasy Simopone Species

emeryi species group

Characters of emeryi species group (workers)

1 Palp formula 6,4 (conradti, dux, grandis, latiscapa, marleyi, nonnihil, persculpta, rex, sicaria, silens, trita).

2 Mandibles sculptured, even if only feebly so.

3 With head in profile the parafrontal ridge fails to reach the anterior margin of the eye (i.e. it is confined to the area immediately behind the clypeus), or may be absent.

4 Mesopleuron without an impressed transverse sulcus that divides it into anepisternum and katepisternum.]

5 Propodeal spiracle is roughly circular to distinctly elliptical.

6 Pygidium with a distinct cuticular apical fork of two short, stout teeth.

7 Generally relatively large species, worker HW 0.74–2.18.It is interesting to speculate on the function of the pygidial fork. Its function could be to brace the apex of the abdomen against the cuticle of a victim immediately prior to stinging, and thus prevent the apex from sliding over the surface. Or it may act as a guide and brace for the sting when it is in use. From its position immediately above the sting it may serve to prevent lateral movement or slippage of the sting during insertion.

grandidieri species group

Characters of grandidieri species group (workers)

1 Palp formula 5,3 (elegans, grandidieri).

2 With head in profile the parafrontal ridge almost reaches the anterior margin of the eye (i.e. it is not confined to the area immediately behind the clypeus).

3 Outer margins of frontal carinae diverge from the line of the frontal lobes at their point of junction.

4 A distinct, impressed transverse sulcus is present on the mesopleuron that conspicuously divides the sclerite into an upper anepisternum and a lower katepisternum; this sulcus is continuous posteriorly with the sulcus that separates the mesopleuron from the metapleuron.

5 Propodeal spiracle is subcircular.

6 Propodeal dorsum and declivity are separated by an angle or blunt carina.

7 Anterior and dorsal surfaces of AII (petiole) are separated by a transverse carina.

8 Apex of pygidium is not hypertrophied and not isolated; dorsum of apex equipped with 4–6 small teeth.

9 Generally medium-sized species, worker HW 0.58–0.97.

Pilosity is sparse on dorsum except at apex of abdomen: sides of head between posterior clypeal margin and posterior corner lack setae; typically the dorsal mesosoma is without setae except for one at each pronotal humeral angle; tergite of abdominal segment IV at most with a basal pair and an apical pair only (reduced pilosity does not apply to bakeri, one of the extralimital species that belong to this group).

Oriental and Malesian fauna of Simopone. Four certain extralimital species of Simopone have been described to date, three from the Malesian region and one from the Oriental. All four belong to the grandidieri group, by far the most widespread group of the genus, which also contains one Afrotropical member (laevissima) and two species from Madagascar (elegans, grandidieri). All four extralimital species exhibit the characters noted under the definition of that group. In particular, all have a distinct transverse sulcus on the mesopleuron, broad, transversely flattened frontal lobes and carinae, similarly shaped AII that lacks a lateral carina, and relatively sparse pilosity. Like the Afrotropical laevissima, two of these four species appear to have fairly well developed scrobes and all have a strong transverse sulcus on the metapleuron that continues the line and intensity of the mesopleural transverse sulcus. The scrobes are perhaps least well represented in oculata, which in this respect more closely resembles the Malagasy species elegans and grandidieri. The Oriental and Malesian species all appear to be rare and are known only from their holotypes, or from just one or two specimens. Radchenko (1993) has provided a key to workers of the four species (bakeri, chapmani, gressitti and oculata).

schoutedeni species group

Characters of schoutedeni species group (workers)

1 Palp formula 6,4 (annettae, brunnea, dryas, miniflava, wilburi).

2 Mandibles unsculptured, smooth with scattered small pits.

3 With head in profile the parafrontal ridge reaches, or almost reaches, the anterior margin of the eye (i.e. it is not confined to the area immediately behind the clypeus).

4 Eyes with numerous short but conspicuous setae that arise between the ommatidia.

5 A distinct, impressed transverse sulcus is present on the mesopleuron that conspicuously divides the sclerite into an upper anepisternum and a lower katepisternum; this sulcus is continuous posteriorly with the sulcus that separates the mesopleuron from the metapleuron.

6 Promesonotal suture is represented across the dorsum by a line of minute cuticular ribs or a line of adjacent punctures; line of suture is conspicuous to faint. Metanotal groove is at most a very faint, almost effaced line, but usually is entirely absent.

7 Propodeal spiracle circular or very nearly so.

8 Anteroventral process of AII (petiole) in profile consists of a short lamina that has a roughly oval fenestra near its midlength; the posteroventral corner of the process is dentiform or short-spiniform.

9 Pygidium with a small, insignificant apical fork of two or four teeth that are usually only slightly larger than the other marginal denticles.

10 Generally relatively small species, worker HW 0.46–0.80.

In addition, all examined specimens of this group, except for a couple of workers of wilburi, have a small patch of pale, thin cuticle on the side of the pronotum. The patch is roughly oval to crudely elongate-triangular and is located on the anterior half of the sclerite, usually just below its mid-height. No trace of this patch occurs in any species of the grandidieri group that has been seen. Most members of the emeryi group have no equivalent of this patch, but something that may be similar can be seen in grandis, and some specimens of Malagasy species have a reddish spot on the cuticle in a similar position, but this seems variable within species.

Each of the eleven species assigned to this Afrotropical endemic group is represented by very few specimens; in several cases only single specimens are known. This tends to make the assessment of species limits rather difficult, because normal variations in sculpture, shapes of particular body parts, size-related variation, and so on are impossible to assess. However, in wilburi 12 specimens, including a queen, are known from five different localities, the longest series of which contains six workers. In this series some size-variation is apparent, but the morphology remains consistent. Similarly, the five workers known of annettae, from four localities, are also quite uniform. These consistencies, compared and contrasted to the different morphological modifications seen in other specimens, are taken as the template by which the species-rank taxonomy of the group is currently arranged. It may be that some of the species currently represented only by singletons will eventually be found to show size-related variation, so the taxonomy will need re-assessment when longer series, and particularly nest-series, have been accumulated.

Identification of species

The eleven species currently included in the schoutedeni group are best separated by the characters in the key, but at least one alternative system may be used. Seven of the eleven species have fine ground sculpture on the head between the eyes that is arranged into minute, irregular, roughly parallel longitudinal striolae or costulae, usually right across the interocular space. These minute costulae run between, and sometimes through, the broad shallow foveolate punctures that also occur in this area. Of the seven, fulvinodis is immediately isolated by its unique colour pattern and dryas by its long, narrow AIII and its small, relatively anteriorly located eyes. Of the remaining five species in this complex, schoutedeni is the only one to exhibit AII with parallel straight sides in dorsal view, so that the anterior and posterior widths of AII are almost exactly the same. In amana, annettae and wilburi the anterior width of AII is less than the posterior width, often obviously so, and all three are smaller than schoutedeni. S. wilburi has larger, more prominent eyes than amana and annettae, and annettae has AII broader than long, whereas in wilburi and amana AII is longer than broad.

The other four species lack conspicuous longitudinally arranged ground sculpture between the eyes, but small patches of disorganised microsculpture may be present, and even one or two tiny, isolated longitudinal striolae may occur. Of these, miniflava is quickly isolated by its uniformly yellow colour and brunnea has the punctures on the tergite of AIII reduced to widely separated pin-pricks, rather than the closely packed foveolate punctures that are more characteristic of the group. S. vepres is larger than occulta (e.g. HW 0.69 versus 0.49) and has larger, more prominent eyes. In addition, AII in vepres is broader posteriorly than anteriorly, whereas in occulta the two widths are almost exactly the same.