Tyrannomyrmex

A colony of Tyrannomyrmex has finally been discovered! See the biology section of Tyrannomyrmex rex for a report on the details of this species from Wong and Yong (2017). The colony contained less than 30 workers and, based on laboratory observations, this species is apparently nocturnal. Their observations led to their suggesting (Wong and Yong 2017) The paucity of records for Tyrannomyrmex species is likely attributable to their small colony size (i.e. 30 individuals including workers and brood in our T. rex colony), as well as their nesting habits in moist rotting wood under leaf-litter - an environment likely to be missed by conventional ant collection methods such as leaf-litter sampling, pitfall traps, and even direct hand sampling. The suspected nocturnal activity patterns of Tyrannomyrmex species may further reduce their chances of being discovered, and their potentially specialised yet unknown trophic preferences might explain their absence from bait collections thus far. In general, remarkably similar combinations of ecological and behavioural idiosyncrasies have been suggested for other rarely collected ant genera (e.g. Tatuidris in Donoso 2012).

Identification
Fernández (2003) -Tyrannomyrmex possesses a unique combination of traits which separate it from other myrmicines: modified setae along the internal border of the mandibles and mandibles with two teeth, apical and subapical, with the rest of the masticatory border lacking teeth. The modified setae are reminiscent of some of the Adelomyrmex, but in Tyrannomyrmex the setae are thick, nonspatulate, and cylindric. The antennal club is not easily-defined. At first glance it appears to be 2-segmented, but the last segments under careful examination might also be interpreted as 3-segmented.

Borewiec (2007) described the species Tyrannomyrmex dux, finding it had regular and not modified setae along the internal border of the mandibles.

Distribution
Known from Malaysia, India and Sri Lanka.

Biology
In 2003, Fernández described a new genus and species, Tyrannomyrmex rex from peninsular Malaysia based on a single specimen collected from leaf litter at Negri Sembilan, Pasoh Forest Reserve in 1994 (Fernández, 2003). This ant has subsequently been found in Singapore. A second species, Tyrannomyrmex dux has been described based on a single specimen collected from leaf litter in southern India in 1999 (Borowiec, 2007). A third species, Tyrannomyrmex legatus was collected from leaf litter in Sri Lanka (Alpert, 2011). In addition, Brian Heterick recognized a single male collected from a light trap in the Philippines in 1965 as possibly representing an unknown male of Tyrannomyrmex.

Workers are found in leaf litter. The biology of these rare ants is poorly known. Jacquemin et al. (2015) suggested the genus appeared to be restricted to pristine or relatively undisturbed forests but discovery of a Tyrannomyrmex rex colony in a secondary forest does not lend support to this idea.

Morphology
Jacquemin et al. (2015) - As previously noted (Fernández, 2003; Borowiec, 2007), the genus seems to lack a functional metapleural gland, a structure unique to ants and playing a key role in sanitation and chemical defense (Yek & Mueller, 2011). This gland has been secondarily lost is some ant lineages, mostly in social parasites and arboreal formicines, probably because their life histories render them less exposed to pathogens than ground-dwelling species (Yek & Mueller, 2011 and references therein). Its absence in Tyrannomyrmex, a probable hypogean genus, suggests either that these ants could be social parasites or that they possess other protections against pathogens as observed for instance in some Camponotus (Walker & Hughes, 2011) and Polyrhachis species (Graystock & Hughes, 2011). Additional material and anatomical studies are obviously required to test these hypotheses.

Nomenclature

 *  TYRANNOMYRMEX [incertae sedis in Myrmicinae]
 * Tyrannomyrmex Fernández, 2003a: 2. Type-species: Tyrannomyrmex rex, by original designation.

Worker

 * Mandibles with two teeth in the masticatory border, apical and smaller subapical. No teeth onin the basal margin of the mandible.
 * Inner ventral margin of masticatory border of mandibles with setae. Setae can be normal or modified.
 * Clypeus devoid of carinae.   Foveolae may be present.
 * Palpal formula 2, 2.   Confirmed.
 * Compound eyes small, reduced to a few ommatidia.
 * Antennae 11-segmented with an ill-defined 3-segmented club.
 * Frontal carinae and antennal scrobes absent.
 * Mesosoma without grooves.
 * Propodeal lobes large and round.
 * Sting large and robust.