Melophorus Lubbock 1883

Heterick, Brian E., Castalanelli, Mark & Shattuck, Steve O., 2017, Revision of the ant genus Melophorus (Hymenoptera, Formicidae), ZooKeys 700, pp. 1-420 : 18-71

Genus Melophorus Lubbock 1883

Melophorus Lubbock 1883: 51. Type-species: Melophorus bagoti , by monotypy.

Erimelophorus Wheeler 1935: 71. (described as a subgenus of Melophorus ; junior synonym of Melophorus by Brown 1955: 474). Type-species: Melophorus wheeleri , by original designation.

Trichomelophorus Wheeler 1935: 71. (described as a subgenus of Melophorus ; junior synonym of Melophorus by Brown 1955: 474). Type-species: Melophorus hirsutus , by original designation.

Worker diagnosis.

Polymorphic ants characterized by a combination of long, J-shaped setae on the mentum, an elongate (often slit- or comma-shaped) propodeal spiracle, presence of a metapleural gland, antennal insertions abutting the posterior clypeal margin and three ocelli in an ocular triangle in all workers. The genus is taxonomically compact, and with the above characters taken into consideration, its members cannot be mistaken for any other group of ants. The descriptions below relate to the small minor worker and the large major worker. Media workers are of intermediate appearance but more closely resemble the minor worker.

Queen diagnosis.

Larger to smaller than the conspecific major worker. Palp formula, ocelli, appearance of antenna and number of antennal segments, and number of mandibular teeth are as for the conspecific major worker. Mesoscutum about as wide as long in species seen. Parapsidal lines parallel and usually distinct. Axillae small and widely separated, the separation much greater than their width. The wing is of the ' Camponotus ' form, with a radial cell, a first cubital cell and one submarginal cell. The cross-vein cu-a is present but the discoidal cell and cross vein m-cu are absent. Ergatoid or brachypterous queens have not been identified.

Male diagnosis.

(Caution: this diagnosis is based on only a small number of specimens that we have been able to identify as Melophorus males). Males with typical characteristics of males of this subfamily. The head bears an ocellar triangle that may be weakly turreted in some species, the antennal scape is usually longer to much longer than the head and the 13-segmented antenna is elbowed. The eyes are generally larger than those in the corresponding queen or major worker but not globose or bulbous in males seen. The mandible is 1- to 4-toothed in males seen; if 1-toothed, then apical tooth is prominent. The wing is as for the queen, but in one species a second small submarginal cell may be present, possibly limited to certain individuals. The parapsidal line is always present, weakly to strongly impressed; the notaulus is absent or present only as a median appendix arising from the base of the mesoscutum. The axillae are small and very widely separated from one another, the separation much greater than their width. Workerlike, wingless males are known for at least one desert-dwelling species.

Worker description.

Minor worker. Head. Head oval, square, cordate or rectangular, its posterior margin strongly convex to strongly concave. Compound eyes always present, usually medium to large (eye length generally 0.2 × length of side of head capsule ≥), rarely small. Eye shape elliptical across most species, often slightly reniform due to an invagination of cuticle on the outer margin of the eye, much more rarely ovoid, roughly circular or oval tending to elongate; in some populations of M. hirsutus eyes flattened and embedded in cuticular prominences when seen in full-face view, or projecting roundly or even bizarrely conical. In full-face view, eyes mostly situated in the upper half of the head capsule, rarely (mostly in very small minor workers) at about the midpoint of the capsule, but never anteriad of the midpoint. In profile, eyes usually placed ahead of the midline of the head capsule, less frequently at about the midline or fractionally in front of it, but never behind the midline. Three small ocelli always present. In full-face view, frontal carinae convex, concave, straight, convergent posteriad or divergent posteriad, sometimes raised (particularly near antennal insertion), vestigial beyond antennal insertions in a few taxa. Torulus (antennal sclerite) pedunculated in a couple of species but otherwise inconspicuous. Antenna always 12-segmented. Scape very variable in length, but usually attaining the posterior margin of the head capsule, and often extending well beyond it. Clypeus never longitudinally carinate, or with pro truding clypeal teeth but otherwise variable in appearance. Posterior margin of clypeus mostly arched and falling away from its mid-sector (i.e., between the frontal carinae), but lateral sectors of clypeus on same plane as mid-sector in a few species. Anterior clypeal margin often convex, with or without an anteromedial dimple, but concave, acuminate, spatulate and variously protrusive clypeal morphologies also occur. The midpoint of the clypeus may be notched, especially in the aeneovirens species-group. A clypeal psammophore of long setae (or ammochaetae) stretched across that sclerite is found in all Melophorus species, and may be located at any elevation, from at or just above the anterior clypeal margin to just under the posterior clypeal margin. Mandibular and gular psammophores of long, curved setae also usually present. Mouthparts. Palp formula mostly 6,4, but 3,4 and 3,3 also occur, maxillary palps variable in length from not reaching the hypostomal bridge to attaining the mesopleuron when they are fully extended. Apical segment of maxillary palp usually oblongiform, but may be narrow and acuminate or even vestigial and barely visible under a stereomicroscope. Mandible most commonly with five distinct teeth, but number of teeth and denticles ranges from four to over 15, mandible edentate except for apical tooth in one species. In five-toothed species apical tooth is nearly always much longer than remaining teeth and teeth 2 and 4 are typically longer than tooth 3 (teeth count taken from apical to basal tooth), basal tooth often offset and directed vertically. Masticatory margin usually vertical or weakly oblique, but strongly oblique in a few species. Mesosoma. Spines or denticles always absent from pronotum and mesonotum, present on propodeum only in M. majeri . Posterior pronotum planar, rounded or angled. Mesothoracic spiracles often opening on small dorsal prominences, these prominences stalk-like in M. hirsutus . Mesopleural process absent. Mesopleuron folds over onto flattened mesosternum without being demarcated by strong carina. Dorsal face of propodeum may be uniformly convex to flat, abruptly conical, or convex anteriad and flattened posteriad. Propodeal angle commonly absent, but may be sharply defined and is produced as denticles in M. majeri . Declivitous face of propodeum convex to flat, longer to shorter than dorsal face. Metanotal groove usually present, forming a weak to strong angle between the mesonotum and propodeum, but is absent or vestigial in a few species. Propodeal spiracle of variable appearance, but always prominent and longer than wide, usually situated at or near propodeal declivity, but nearer to midline of propodeum in some species-groups and in individual species. Petiole. Node always present. In profile, node often squamiform, but may be thicker, e.g., subcuboidal or triangular, and is typically directed posteriad. In full-face view, dorsum of node generally rounded, more rarely angulate, weakly acuminate or indented anteromedially. Petiole with a ventral lobe or keel. Gaster. First tergite vertical and somewhat overarching the petiole in dorsal view, with a small depression for receiving the rear of the node: Legs. Mesotibia and metatibia with one simple spur in most species, spurs reduced or absent in a few groups. General characters. Integument variable, from thick and sculptured to thin, flexible and glossy in very small minor workers of some species, mesonotum may be translucent. Sculpture, where present, predominantly consisting of microreticulation or fine striation, frank rugosity or larger striae found in very few species. Mesopleuron usually with some sculpture, even in otherwise smooth and glossy species. Appressed setae often small, and well-spaced, thick in some species producing pubescence and a silvery sheen in some lights. Erect setae tend to be short and bristly, more rarely fine, long; setae modified and spatulate or even clavate distally in a few species. Many species without erect setae on mesosoma and gaster, or with erect setae confined to margins of gastral tergites. Proventriculus. Proventriculus asepalous.

Major worker.

As for minor worker, but differing in the following particulars: Head. Usually planar or weakly concave, but may be strongly concave, never strongly convex. Head often strongly horizontally rectangular, distinctly broader than wide, especially in M. wheeleri species complex. Antennal scapes shorter than in corresponding minor worker, often barely exceeding or not even attaining the posterior margin of the head. Anterior margin of clypeus very variable and may be different to that of corresponding minor worker, often folded or turned back in large-headed species, one major worker with V-shaped anteromedial protuberance projecting anteriad. Mouthparts. Palps, if reduced, as for corresponding minor worker, but may be 3,2 (less than for minor worker) in one species. Otherwise, mouthparts as for corresponding minor worker in many species, but differing significantly in M. wheeleri and M. laticeps species complexes; here, major worker with powerful, truncate, inwardly curved mandibles with four to five teeth in taxa for which major worker is known (likely to be more in unconfirmed major worker of Melophorus species K (TERC)), basal margin folded over horizontally towards buccal cavity to form a planar surface that is delimited partially or fully along its length by a carina. Masticatory margin of mandible vertical, oblique or medially indented. (Characters of mesosoma and metasoma generally as for corresponding minor worker, but dorsal profile of mesosoma may vary, with pronotum and mesonotum generally more raised and convex. Erect setae nearly always present in major worker, even where the corresponding minor worker is glabrous).

Synopsis of Melophorus species

aeneovirens species-group

aeneovirens complex

aeneovirens ( Lowne 1865)

= constans Santschi 1928 syn n.

= insularis Wheeler 1934 syn n.

= iridescens ( Emery 1887) syn n.

= iridescens fraudatrix Forel 1915 syn n.

= iridescens froggatti Forel 1902 syn n.

attenuipes sp. n.

canus sp. n.

castaneus sp. n.

clypeatus sp. n.

curtus Forel 1902

fulgidus sp. n.

gibbosus sp. n.

griseus sp. n.

kuklos sp. n.

mullewaensis sp. n.

platyceps sp. n.

praesens sp. n.

rufoniger sp. n.

sulconotus sp. n.

tenuis sp. n.

teretinotus sp. n.

bagoti complex

bagoti Lubbock 1883

= Camponotus cowlei Froggatt 1896 comb. rev.

gracilipes sp. n.

nemophilus complex

nemophilus sp. n.

anderseni species-group

anderseni Agosti 1998

andersenioides sp. n.

chrysus sp. n.

subulipalpus sp. n.

biroi species-group

biroi complex

argus sp. n.

biroi Forel 1907

= fieldi propinqua Viehmeyer 1925 syn. n.

= marius Forel 1910 syn. n.

castanopus sp. n.

compactus sp. n.

cuneatus sp. n.

dicyrtos sp. n.

graciliceps sp. n.

gracilis sp. n.

latinotus sp. n.

lissotriches sp. n.

longiceps sp. n.

macrops sp. n.

microreticulatus sp. n.

minimus sp. n.

mjobergi Forel 1915

postlei sp. n.

propebiroi sp. n.

turbineus sp. n.

brevignathus complex

brevignathus sp. n.

marmar sp. n.

quadratus sp. n.

fieldi complex

ankylochaetes sp. n.

bruneus McAreavey 1949

eumorphus sp. n.

fieldi Forel 1910

fulvidus sp. n.

gilliatensis sp. n.

hirsutipes sp. n.

incisus sp. n.

inconspicuus sp. n.

isaiah sp. n.

lanuginosus sp. n.

longipes sp. n.

major Forel 1915 stat. n.

microtriches sp. n.

orthonotus sp. n.

paramorphomenus sp. n.

perthensis Wheeler 1934 stat. n.

sericothrix sp. n.

setosus sp. n.

solitudinis sp. n.

sulla Forel 1910 stat. n.

turneri Forel 1910

= pillipes Santschi 1919 syn n.

= turneri aesopus Forel 1910 syn. n.

= turneri candidus Santschi 1919 syn. n.

vitreus sp. n.

oblongiceps complex

oblongiceps sp. n.

wheeleri complex

brevipalpus sp. n.

caeruleoviolaceus sp. n.

cerasinoniger sp. n.

chauliodon sp. n.

diversus sp. n.

hexidens sp. n.

laticeps Wheeler 1915

parvimolaris sp. n.

pelorocephalus sp. n.

prominens sp. n.

purpureus sp. n.

('species K’ [TERC])

wheeleri Forel 1910

= omniparens Forel 1915 syn. n.

xouthos sp. n.

fulvihirtus species-group

barbellulatus sp. n.

fulvihirtus Clark 1941

ludius species-group

hirsutus complex

hirsutus Forel 1902

ludius complex

ludius Forel 1902

pusillus sp. n.

translucens sp. n.

majeri species-group

majeri Agosti 1998

potteri species-group

macroschismus sp. n.

pelecygnathus sp. n.

potteri McAreavey 1947

Total: 93 species

Removed from Melophorus

scipio Forel 1915 (to Prolasius ) comb. rev.

Key to Melophorus species based on workers

The key to species is based on workers, as species-level separation of the other adult castes is not only extremely difficult, but of very limited utility. Moreover, the reproductive castes of the less common species have either not been collected or are often unable to be associated with workers (since most material examined has come from trapping or opportunistic hand collection, rather than from nests). Major and minor workers of a specific Melophorus taxon have been included in the measurements where possible. However, for some uncommon species only minor or major workers are known. (Note. 'species K’ (TERC) and other Melophorus specimens held in the TERC Collection were not available as loan material except under restrictive conditions that were not acceptable to the authors of this paper.

Descriptions. (Unless otherwise stated, specimens mentioned under 'other material examined’ are housed in the Australian National Insect Collection [ANIC]. Curtin Ant Collection material [designated ‘JDM’] is now the property of the Western Australian Museum [WAM]).

Melophorus aeneovirens species-group

This includes what are probably the most morphologically generalised Melophorus , with ancient traits. The M. aeneovirens species-group is comprised of three complexes (aenovirens, bagoti , and nemophilus ). Most members of the group are elongate and gracile and include the predominant Melophorus species in cooler, wetter and more heavily forested environments, especially on the east coast, as well as parts of the Torresian zone. While some taxa have broad geographic ranges, others are known from a few collections only and appear to be highly localised. With the exception of a cluster of species around M. curtus (i.e., M. praesens , M. rufoniger and M. tenuis ) the species are readily recognisable and do not pose great taxonomic difficulties.

Phylogenetically, the genetics of the M. aeneovirens species-group are highly congruent with the morphology. Despite only successfully sequencing several species, we obtained a representative species for each of the species complexes and here show that each complex is monophyletic. The M. aeneovirens complex is the most basal complex (well supported by the three- and five-gene trees), and the M. nemophilus and M. bagoti clades are sister complexes, which is reflected in the similarity in their morphological features.

Melophorus aeneovirens complex

Among all the M. aeneovirens complexes, this is the most speciose. The members of the complex are grouped together, based on several morphological features (particularly, the appearance of the anterior margin of the clypeus, the mandible, placement of the ammochaetae and the sloping appearance of the propodeum). The three-gene tree (Suppl. material 1) is the most telling when it comes to explaining the phylogeny of this complex. Based on the information derived from the successfully sequenced species, M. canus and M. griseus are sister species and the most highly derived. Interestingly, M. praesens is sister to M. platyceps in this gene tree, despite significant morphological differences (flattened body, short labial palps, etc.) that appear to place M. platyceps in its own complex.