Australian Monomorium species groups

Based on: [[Media:Heterick 2001.pdf|Heterick, B. E. 2001.  Revision of the Australian ants of the genus Monomorium (Hymenoptera: Formicidae). Invertebrate Taxonomy. 15:353-459. PDF]]

The Australian Monomorium fauna consists of three clear aggregations of species. The first of these is the autochthonous Chelaner element. Several Chelaner species exhibit primitive features shared with some South American taxa. These include an anteriorly situated petiolar spiracle, a triangular mandible with up to six teeth, and the presence of complete notauli on the male mesoscutum. Overall, six species-groups can be identified among the Chelaner aggregations, and these include some easily recognisable complexes (e.g. the gilberti complex within the rubriceps-group, and the longiceps complex.

Here, a cluster of taxa is defined as a 'species-group' on the basis of several shared structural characters that appear to be synapomorphies for the group. 'Species-complexes' are defined by evident similarity, such that the component species can often only be separated on the basis of one or two minor characters (e.g. colour pattern or small but consistent differences in sculpture). Species-groups have either been assigned names already provided by Bolton (1987), or have been named after the earliest described species. The name of the most widespread and abundant taxon has been assigned to species-groups containing only undescribed species. The species-groups identified here include three that are given support from the cladistic analysis reported earlier in this paper (i.e. the bicorne-, kilianii-, and monomorium groups). Almost certainly M.falcatum, M. longinode, M. rubriceps and their allies represent three additional species-groups, and M. insolescens may constitute an additional group. The phylogenetic affinities of taxa clustered around M. longiceps are uncertain, but this complex shares several synapomorphies associated with members of the rubriceps-group. The bicorne-group includes species associated by Bolton (1987) with M. falcatum, but several important characters separate these two sets of taxa. Most notably, the pilosity and sculpture differ markedly. Moreover, the primitive mandibular dentition in the falcatum-group appears to be five (M. decuria), though it varies from three to five. Taxa in the bicorne-group always have four teeth. The species-groups originally lumped together under Chelaner will certainly require further revision. Additional information gained from the accurate identification of reproductives would be most helpful.

The rubriceps-group consists of those species linked by Bolton (1987) with M  forcipatum. The rubriceps and gilberti complexes are predominantly arboreal compared with a mainly terrestrial habit for the remainder of the rubriceps-group. The relatively small morphological differences between the rubriceps-gilberti complexes and taxa associated with M. leae may mask greater genetic differences. Monomorium crinitum possesses the elongate postpetiole of the kilianii-group, but has the general habitus of the rubriceps-group. Phylogenetically, this species may occupy an intermediate position between these two sets of taxa, although the cladistic analysis reported on in this work identifies it closely with M. kilianii.

The second element corresponds to the monomorium-group of Bolton (1987), though it is more morphologically variable on this continent than the species dealt with in Bolton's key to the Afrotropical members of the monomorium-group. Most of the constituent taxa are probably indigenous, though a few of the most abundant species, e.g. M. fieldi and M. laeve, may also occur in other Indo-Pacific countries. (I have seen tiny, yellow Monomorium from Malaysian rainforests that can scarcely be separated from M. laeve.) Monomorium rothsteini, M. sordidum and M. megalops possess more plesiomorphic features than the remainder of the Australian members of the monomorium-group This element is the most strongly supported in the cladistic analysis reported above, with more than half-a-dozen unambiguous synapomorphies shared by members of the group.

Bolton's (1987) key to the monomorium-group does not fit the Australian fauna very well. For example, M. sydneyense sometimes has sculptured mandibles, and M. nanum and associated species have reniform or anteriorly pointed eyes. Taxonomic features of the latter two groups leads to the suggestion that they are closely related to M. laeve, M. jieldi and the other taxa mentioned by Bolton as belonging to the monomorium-group, but they are excluded by the descriptions in his couplets. Monomorium nanum and other Australian members of the monomorium-group are superficially similar to species in the Afrotropical setuliferum-group, but differ in certain important respects (e.g. size, and the most common antennomere count of 11 in the Australian species compared with a uniform count of 12 in the setuliferum-group ). The eye shape is probably an example of convergent evolution.

The small Australian Monomorium pose particular difficulties for taxonomic analysis, not only because of their small size, but because of the probable convergence of many character states in many species. This may suggest relatively recent speciation. Unlike the more habitat-specific, larger Chelaner, nearly all of the monomorium-group members are abundant and widespread.

The third element includes species recently introduced into this country, usually by human agency. The destructor-group is represented in Australia only by the naturalised M. destructor, the salomonis-group by M. pharaonis, and the monomorium-group by M. floricola and possibly M. intrudens. The fossulatum-group is certainly represented by M. australicum, a probable import, and by at least one, if not two other species (i.e. M. fossulatum and possibly M. subcoecum). While these exotic species are included in the key to Australian Monomorium workers, discussion is limited to the members of the fossulatum-group. This is because M. australicum is the only species from the third element described from Australian material.

bicorne group

 * Monomorium anthracinum
 * Monomorium bicorne
 * Monomorium majeri
 * Monomorium pubescens
 * Monomorium rufonigrum
 * Monomorium striatifrons
 * Monomorium whitei

falcatum group

 * Monomorium decuria
 * Monomorium elegantulum
 * Monomorium falcatum
 * Monomorium lacunosum

insolscens group

 * Monomorium insolescens

kilianii group

 * Monomorium crinitum
 * Monomorium kiliani
 * Monomorium petiolatum
 * Monomorium shattucki
 * Monomorium tambourinense