Chelaner leae

Monomorium leae is a generalist species with the capacity to persist in anthropogenic environments, such as gardens in outer suburbs of major cities. Regardless of the habitat, most nests are found in cryptic situations, i.e. under rocks, in moss, in rotten logs, and around the boles of trees. (Heterick 2001)

Identification
Heterick (2001) - Monomorium leae is arguably the most taxonomically difficult of the Australian Monomorium species, and shares with Monomorium sydneyense the distinction of having the greatest morphological plasticity. Sculpture and colour vary greatly among populations, and the ant's habitat ranges from tropical rainforest to dry Eucalyptus and Callitris woodland. Moreover, workers from the same nest differ in size and morphology. Larger workers often have an angulate propodeum and a rugose alitrunk, whereas smaller workers frequently possess a rounded propodeum and a smoother appearance.

Despite its morphological variability, however, the habitus of M. leae clusters around two basic forms: flavipes-insularis (found throughout temperate Australia) and hemiphaeum (predominantly found on the east coast of Australia). The two can be distinguished primarily by the depth of the metanotal groove: in flavipes-insularis this groove is no more than a furrow and is often almost completely obsolete (especially in large workers), whereas in hemiphaeum the metanotal groove is moderately to deeply impressed in all members of a nest series (see Andersen 1991c: 32-34). Other characteristics that usually separate flavipes-insularis from M. hemiphaeum sensu stricto include the following:

(1) head shape (typically rectangular in flavipes-insularis and rounded in hemiphaeum);

(2) the median clypeal sector between the antennal insertions (narrow and impressed in flavipes-insularis and wider and more protuberant in hemiphaeum);

(3) the anteromedial clypeal margin (straight or slightly emarginate in flavipes-insularis and rounded and projecting in hemiphaeum);

(4) the appearance of the petiolar node (cuneate or subcuboidal in flavipes-insularis and tumular in hemiphaeum);

(5) the appearance of the promesonotum seen in profile (flattened in flavipes-insularis and smoothly convex in leae);

(6) the appearance of the cuticle (mat and dull in flavipes-insularis and smooth and shining in hemiphaeum).

Finally, worker-queen intercastes are commonly present in nest series of hemiphaeum, but intercastes of flavipes-insularis appear to be rare. One intercaste from the Thomas River (Western Australia) belongs to the latter group. Despite these differences, however, there are many important similarities: such include the shape of the eyes and their position on the head, the notched frontal carinae under the frontal lobes, the long suberect setae on the antennal scapes, the number and appearance of the stout promesonotal setae, the five to eight transverse stria always present on the metapleuron (vestigial in some South Australian and Victorian populations), and the microstructure of the petiole and postpetiole. Furthermore, specimens referable to the type 'leae' show characteristics intermediate between flavipes-insularis and hemiphaeum. The leae morph resembles flavipes-insularis in the following respects: the propodeum often has a longer dorsal than declivitous surface, the propodeal angle is distinct, the shape and appearance of the head capsule are similar, the petiolar node is cuneate and sharply tapered, and allometric variation between workers within a nest is pronounced. However, leae shares with hemiphaeum the impressed metanotal groove, and smooth, glossy cuticle. In leae, moreover, the anteroventral petiolar process is rather large, compared with the smaller anteroventral petiolar process in flavipes-insularis. The type of leaecomes from Tasmania, but leae-like morphs are frequently encountered in New South Wales. This form has also been collected in Western Australia (Talyuberlup picnic ground and Dryandra State Forest).

Hemiphaeum-like forms can also be found in Western Australia, particularly the deep southwest. Specimens from the Porongurup and the Stirling Ranges have the impressed metanotal groove and the rounded propodeum of typical hemiphaeum, and even the same slightly brownish tinge on the frons. They are, however, rather smaller than the type, and the eyes are also smaller.

There are at least five other distinctive forms, including a beautiful bicoloured ant found in northern New South Wales and southern Queensland. Morphologically, this ant has the appearance of leae, but some larger specimens have a thickened petiolar node and a flattened promesonotum with a slightly projecting humeral rim or carina. Another variety, mainly found in the Australian Capital Territory, has a rugose propodeum and a subcuboidal node with dense transverse rugulae or microreticulation. Finally, the form most commonly encountered in the Eyre and Yorke Peninsulas is shining, smooth and dull brownish-orange in colour, with a rounded propodeum and without a trace of a metanotal groove. The petiolar node is very thin, and the eyes are rather small with fewer ommatidia ( <20) than possessed by most M. leae. In all cases, however, the ants share the characteristics of M. leae as defined in the key, and they are connected with other morphological variations by intermediates.

After hundreds of hours spent examining representatives of the various populations of M. leae, taken from all over Australia, I have found no discrete and unvarying morphological features that will separate them at a species level. This is despite the superficial appearance of separate species. Other taxonomic methods (such as allozyme analysis) may pick up consistent differences that would enable such sibling species to be identified. On the other hand, the queens of M. leae are much less variable between populations, and the males do not appear to differ much at all. Conversely, although the workers of Monomorium centrale superficially closely resemble the flavipes-insularis morph, the males are very ·different. Similarly with Monomorium euryodon, in which the reproductives lack the vein m-cu (always present in M. leae).

Monomorium forcipatum has been retained as a separate taxon for the present. However, a closer analysis of the members of the M. leae group could well see M. forcipatum synonymised under M. leae. The Monomorium melleum syntype workers have a dome-shaped promesonotum and a convex propodeum similar to that found in Monomorium kiliani. These features, while slight, separate them from the M. leae examined.

Heterick (2009) - Workers of the M. rubriceps group found in the SWBP are all yellow, orange or red; some species also have brown infuscation of the mesosoma. Monomorium leae is the most widespread and variable of these species, being found throughout Australia. Western Australia lacks the beautiful, bicoloured purplish brown-and-yellow race of the east coast rain forests and also the bright yellow form (formerly Monomorium hemiphaeum). Western Australian M. leae are orange to reddish, and exhibit some polymorphism. Larger workers have distinct propodeal denticles, while the propodeum is more rounded in smaller workers (which resemble yellow Monomorium sydneyense but with a 12-segmented antenna). In the SWBP, M. leae appears to be most abundant in more humid environments, e.g. near watercourses and around the boles of eucalypts in wetter parts of the south-west.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Fersch et al. (2000) described a queen polymorphism: winged and ergatoid

Nomenclature

 *  leae. Monomorium leae Forel, 1913g: 185 (w.q.) AUSTRALIA. Heterick, 2001: 429 (m.). Combination in M. (Notomyrmex): Emery, 1922e: 169; in Chelaner: Ettershank, 1966: 97; in Monomorium: Taylor, 1987b: 3. Senior synonym of hemiphaeum: Ettershank, 1966: 97; of flavipes, insularis: Heterick, 2001: 427.
 * hemiphaeum. Monomorium (Notomyrmex) hemiphaeum Clark, 1934c: 61, pl. 4, figs. 19, 20 (w.q.) AUSTRALIA. Junior synonym of leae: Ettershank, 1966: 97.
 * flavipes. Monomorium (Notomyrmex) flavipes Clark, 1938: 369, fig. 8 (w.q.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 96; in Monomorium: Taylor, 1987b: 2. Junior synonym of leae: Heterick, 2001: 427.
 * insularis. Monomorium (Notomyrmex) insularis Clark, 1938: 368, fig. 7 (w.q.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 97; in Monomorium: Taylor, 1987b: 3. Junior synonym of leae: Heterick, 2001: 427.

Worker
Heterick (2001) - HML 1.18-2.57; HL 0.46-0.91; HW 0.34-0.81; CeI 75-91; SL 0.31-0.69; SI 73-94; PW 0.24-0.58 (103 measured).

Head. Head square or rectangular to rounded; vertex slightly concave, or planar; frons smooth and shining with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae. Compound eyes circular or subcircular, or elliptical; (viewed from front) compound eyes set in posterior half of head capsule, or set in anterior half of head capsule; (viewed laterally) compound eyes set at midline of head capsule; eye moderate, eye width 0.5-1.5x greatest width of antennal scape. Antennal segments 12; club three-segmented. Anteromedial clypeal margin straight or slightly emarginate, median clypeal carinae not produced as teeth or denticles. Longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles. Posteromedial clypeal margin level with posterior surface of antennal fossae to extending slightly posteriad of posterior surface of antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes parallel straight. Venter of head capsule without elongate, basket-shaped setae. Palp formula 2,3. Maximum number of mandibular teeth and denticles: five; mandibles (viewed from front) triangular and smooth, with piliferous punctures; basal tooth not enlarged; basal angle indistinct; apical and basal mandibular margins meeting in tooth or denticle.

Alitrunk. Promesonotal sculpture present in form of microreticulation and striolae on and around katepisternum, otherwise promesonotum smooth and shining; dorsal promesonotal face evenly convex to convex anteriad, otherwise flattened; erect and suberect promesonotal setae greater than 10; setulae decumbent and subdecumbent. Mesonotal suture absent. Metanotal groove present as feebly impressed furrow between promesonotum and propodeum to present as distinct and deeply impressed trough between promesonotum and propodeum. Propodeal sculpture present as faint microreticulation with few striae, mainly on lower lateral surface, or present as uniform rugosity, with well defined costulae on declivitous face of propodeum; dorsal propodeal face sloping posteriad, with wedge-shaped flattening or shallow depression that is widest between propodeal angles; processes absent (propodeum smoothly rounded in profile or with slight hump at propodeal angle) to absent (propodeum angulate in profile), or present on posterior propodeal angles as small denticles or sharp flanges; lobes present as blunt flanges. Propodeal angle absent, or present; declivitous face of propodeum flat, or longitudinally concave between its lateral margins. Erect and suberect propodeal setae 5-1 0; propodeal setulae absent, or decumbent and subdecumbent. Propodeal spiracle lateral and about midway between metanotal groove and declivitous face of propodeum; vestibule conspicuous through cuticle.

Petiole and postpetiole. Petiolar spiracle lateral and slightly anteriad of petiolar node. Petiolar node cuboidal, or conical, dorsally rounded, or cuneate, dorsally rounded, or tumular and inclined anteriad; sculpture absent, petiolar node smooth and shining, or present in form of microreticulation. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 1: 1 to near 3:4. Anteroventral process present as pronounced spur, or slender carina that tapers posteriad. Ventral lobe present in some individuals. Height ratio of petiole to postpetiole near 3:4; height-length ratio of postpetiole near 2:1 to near 1:1. Sculpture absent on dorsum, at least: postpetiole smooth and shining, or present in form of microreticulation. Ventral process present and distinct.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour variable, with several distinctive colour morphs connected in a continuum by intermediate forms. Distinctive morphs include: (1) Monomorium flavipes (southern mainland states): tawny yellow to bright orange with lighter coloured legs; (2) Monomorium hemiphaeum (eastern Australia) shining amber, and with progressively more extensive infuscation, found along a cline reaching northern Qld; (3) Monomorium leae (Tasmania): castaneus with fulvous legs. A striking colour morph also occurs in rainforest in the Lamington Plateau, mountains in southeast Qld, Mt Bellenden Ker in northeast Qld, and possibly elsewhere. In this morph the alitrunk, petiole and postpetiole are deep russet to piceous, the head and appendages are deep yellow to orange, and the gaster is orange, occasionally with brown bands near the tergal margins. This colour pattern is also found in Monomorium tambourinense and several species in the M. rubriceps-group. Worker caste monomorphic but variable in size, with series of intercastes between largest and smallest workers (monophasic allometry).

Queen
Heterick (2001) - HML 2.15-3.08; HL 0.67-0.93; HW 0.54-0.83; CeI 81-94; SL 0.39-0.67; SI 71-90; PW 0.41-0.83 (20 measured).

Head. Head square or rectangular; vertex slightly concave, or planar; frons smooth and shining with combination of appressed setulae and erect and suberect setae, or smooth and shining with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae, or microreticulate and striolate with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae. Compound eyes circular or subcircular to elliptical; (viewed from front) compound eyes set in anterior half of head capsule; (viewed laterally) compound eyes set posterior of the midline of head capsule; eye large, eye width greater than 1.5x greatest width of antennal scape.

Alitrunk. Mesoscutum in profile evenly convex, or convex anteriad; thereafter flattened, or evenly flattened. Mesoscutal pilosity consisting of dense in curved setulae and setae, or consisting of decumbent and subdecumbent setulae anteriad and erect and suberect setae posteriad; dorsal appearance of mesoscutum smooth and shining; length-width ratio of mesoscutum and scutellum combined near 2:1, or near 4:3. Axillae contiguous or nearly so, or separated by distance less than half greatest width of scutellum. Propodeal sculpture present as faint microreticulation with few striae, mainly on lower lateral surface, or present as uniform rugosity, with well defined costulae on declivitous face ofpropodeum; dorsal propodeal face flattened. Propodeal processes absent (propodeum angulate in profile), or present on posterior propodeal angles as small denticles or sharp flanges; lobes present as blunt flanges. Propodeal angle present. Erect and suberect propodeal setae greater than 10; propodeal setulae decumbent and subdecumbent. Propodeal spiracle lateral and nearer declivitous face of propodeum than metanotal groove, or lateral and about midway between metanotal groove and declivitous face of propodeum.

Wing. Wing veins tubular and strongly sclerotised; vein m-cu present as an entire vein enclosing first discoidal cell; vein cu-a present.

Petiole and postpetiole. Petiolar spiracle lateral and slightly anteriad ofpetiolar node, or lateral and positioned in pedicel well anteriad of petiolar node. Petiolar node cuboidal, or conical, dorsally rounded, or cuneate, dorsally rounded, or cuneate, sharply tapered; sculpture absent, petiolar node smooth and shining, or present in form of microreticulation. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 2:1 to near 4:3. Anteroventral process present as pronounced spur, or slender carina that tapers posteriad. Height ratio of petiole to postpetiole near 1:1 to near 4:3; height-length ratio of postpetiole near 2: 1 to near 1: 1. Sculpture absent on dorsum, at least: postpetiole smooth and shining, or present in form of microreticulation; ventral process present and distinct.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour variable; often uniformly orange or tawny yellow or bicoloured orange and brown/piceous. Brachypterous alates not seen. Ergatoid or workerfemale intercastes seen and examined.

Male
Heterick (2001) - HML 1.27-2.04; HL 0.49-0.78; HW 0.52-0.78; CeI 96-108; SL 0.13-0.18; SI 20-29; PW 0.41-0.88 (11 measured).

Head. Head width-mesoscutal width ratio near 1: 1. Compound eyes protuberant and elliptical; (viewed laterally) compound eyes set at midline of head capsule; ocelli not turreted. Ratio of length of first funicular segment of antenna to length of second segment near 1:2 to near 1:3. Maximum number of mandibular teeth and denticles: three.

Alitrunk. Mesoscutum in profile convex anteriad, thereafter flattened; dorsal appearance of mesoscutum smooth and shining, or finely microreticulate; mesoscutal pilosity consisting of long, dense setae. Parapsidal furrows vestigial, or present and distinct; notauli present. Axillae separated by distance more than half greatest width of scutellum.

Wing. Wing veins tubular and strongly sclerotised; vein m-cu present as an entire vein enclosing first discoidal cell; vein cu-a present.

Petiole and postpetiole. Petiolar spiracle lateral and slightly anteriad of petiolar node. Sculpture absent, petiolar node smooth and shining; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 1:1 to near 3:4. Anteroventral process always absent or vestigial; ventral lobe always absent. Height-length ratio of postpetiole near 2:1 to near 4:3; sculpture absent on dorsum, at least: postpetiole smooth and shining to present in form of microreticulation; ventral process absent or vestigial, or present and distinct.

Gaster. Pilosity of first gastral tergite consisting mainly of decumbent and subdecumbent setulae.

General characters. Chocolate.