Leptogenys khammouanensis

This species is described from collections made from two caves of the Khammouan karst (Laos). It is characterized by a set of striking morphological characters (reduced eyes, light pigmentation, slender body and very elongated legs and antennae), which recall the troglobiomorphic traits of cave arthropods. The classical view that ants are rare and unimportant in caves is challenged. Ants are actually major and regular components of guano assemblages in many caves of the region, but none of these guano species exhibit cave-related adaptation in its external morphology. Conversely, ants are very rare in low-resources habitats, where only accidental occurrence of outside species are reported in Southeast Asia. Leptogenys khammouanensis has been found only in such an oligotrophic environment, very deep in the cave and far from any guano deposits. Its presence there, together with its troglobiomorphic traits, support the idea that Leptogenys khammouanensis is one of only two truly troglobitic ants (the other being Aphaenogaster gamagumayaa). (Roncin & Deharveng, 2003; Naka & Maruyama, 2018)

Identification
Roncin and Deharveng (2003) - The combination of reduced eyes, very pale color and elongate appendages isolates Leptogenys khammouanensis in its genus.

The general habitus of Leptogenys khammouanensis with very elongate head, mesosoma, petiole, antennae and legs is very similar to that of Leptogenys assamensis, a species that seems to be known only from the type series collected by Long in the Garo hills in Assam (E. India), and to Leptogenys ergatogyna, a forest species known from Zaire, Uganda and Cameroun and which presents few affinities to other African species (Bolton, 1975). However, Leptogenys assamensis and Leptogenys ergatogyna differ from L. khammouanensis by the presence in both species of the metanotal suture, the absence of a pair of enlarged, straight and hard setae on the clypeal lobe border, less mandibular teeth (no mandibular teeth in L. assamensis and only two apical teeth in L. ergatogyna) and by other characters (color, eyes size) discussed in the paragraph below concerning troglobiomorphic characters in Leptogenys.

One worker from the type locality possesses on the right side an abnormal eye of circular shape reduced to a single large ommatidia of 0.041 mm diameter.

Distribution based on Regional Taxon Lists
Oriental Region: Laos.

Biology
Lattke (2011) - L. khammouanensis may be a troglobitic species on account of the cave habitat, and several morphological traits associated with adaptation to an underground life such as elongate body and extremities, pale colored exoskeleton, and atrophied eyes. While such a possibility can not be ruled out, the suspect morphology is also found in several epigaeic foraging species of the genus. Hopefully future research into this Laotian Leptogenys will include intensive collecting in above ground habitats near the caves to rule out that cave populations are recent colonizations from epigaeic colonies that are simply exploiting an abundant food source.

Nomenclature

 *  khammouanensis. Leptogenys khammouanensis Roncin & Deharveng, 2003: 920, fig. 1 (w.) LAOS.

Worker
Holotype. TL 7.6, HL 1.54, HW 1.01, Cl 65, SL 1.99, Sl 197, EL 0.09, PrW 0.71, ML 2.55, PH 0.46, PL 0.77, LPI 59, DPW 0.32, DPI 0.40. Workers. TL 7.0-7.8, HL 1.54-1.65, HW 0.98-1.05 Cl 64-65, SL 1.94-2.12, SI 197-201, EL 0.09, PrW 0.66-0.74, ML 2.42-2.64, PH 0.45-0.50, PL 0.76-0.84, LPI 58-59, DPW 0.29-0.32, DPI 0.38-0.40.

Head elongate, quite narrow, slightly broadened anteriorly, broadest across the eyes, the sides feebly convex. Occipital margin passing to lateral margin by a regular curve. A low nuchal carina present. Eyes small, oval, composed of 15-20 ommatidia. Maximum diameter of eye 0.093 mm, about 0.09 x HW, that is less than the maximum width of the scapes (0.127 mm). Eyes well in front of the middle of head sides, with their posterior borders situated on the same level than the posterior end of the frontal carinae in full face view. Eyes position frontal, not overlapping the outlines of head sides in full-face view. Circumocular groove strongly developed. Mandibles not striated, weakly shining, with feeble puncturations more numerous near masticatory border. Masticatory margin of mandibles with 14 teeth: the two apical ones well developed and followed by three denticles, one tooth and a series of 8 small teeth and denticles. Basal margin of mandibles close to the basal tooth of the apical margin with small crenulations. Clypeus triangular, projecting anteriorly as a distinct lobe closing tightly against the basal border of the mandibles, and with its foremost part broadly truncated. A wide longitudinal carina present on the median portion of clypeus. Anterior border of clypeus bidentate due to two massive enlarged central setae and laterally a row of normal and straight setae, all much shorter than other cephalic setae. Antennal scapes extremely long surpassing the occipital margin by almost half their length, with numerous erect to subdecumbent hairs, most of them being half the scape width. Funicular segments elongate : length of segments 1-3 ca 0.254, 0.422, 0.355 respectively (the partly visible condylar bulb of the first antennal segment is exclude from this measurement). Funicular segment 11: length 0.232; width 0.131.

Mesosoma elongate. Pronotum widest behind the middle, narrower in front than behind. Mesonotum markedly elongate (dorsal length of mesonotum 0.659 mm, taken at the level of the anterior border of metathoracic spiracles) and approximately of the same length than pronotum length (collare excluded) in dorsal view. Mesosoma shallowly depressed between mesonotum and propodeal dorsum but without any trace of the transverse metanotal suture. A transverse carina present on the posterior end of the declivitous face of propodeum surrounding insertion of petiolar peduncle. A low longitudinal median carina is present on the mesosternum and is crossed by small wrinkles. Legs extremely long, with metafemur length (2.10 mm) exceeding gaster length.

Node of the petiole in dorsal view much longer than broad. Anterior part of the node with a carina separating it from the true anterior peduncle which is indeed very short. Dorsal outline of the anterior part of the node concave in lateral view. The node is widening progressively backward, giving to the anterior part of the node an aspect of false peduncle.

Gaster constricted between its first and second segment. Sting relatively short.

All body sculpture smooth. Body color light orange-yellow with small brown spots regularly spaced at the basis of body setae. Callow individuals yellow. Body with a dense pilosity especially on head, gaster and coxae, and with the longest hairs situated on clypeus, ventral surface of the head capsule and procoxae.

Type Material
Holotype worker, Laos: Tham (=cave) Nam Non (18.0270° N, 104.6883° E, coordinates from Brouquisse, 1999), alt. 185m, several km inside the cave, hand collecting, 15.11.1999, (LA0-070), J. Lorden and J.F. Vacquie.

Paratypes workers: 2 workers, same data; collected with holotype. The holotype of the new species is deposited in the Museum National d'Histoire Naturelle de Paris and the paratypes in the author's collection.

Etymology
From “Khammouan”, a province of Laos with beautiful calcareous landscapes, uncountable caves and subterranean rivers.

References based on Global Ant Biodiversity Informatics

 * Jaitrong W., B. Guenard, E. P. Economo, N. Buddhakala, and S. Yamane. 2016. A checklist of known ant species of Laos (Hymenoptera: Formicidae). Asian Myrmecology 8: 1-32. DOI: 10.20362/am.008019
 * Roncin E., and L. Deharveng. 2003. Leptogenys khammouanensis sp. nov. (Hymenoptera: Formicidae). A possible troglobitic species of Laos, with a discussion on cave ants. Zoological Science 20: 919-924.
 * Xu Z. H., and Q. J. He. 2015. Taxonomic review of the ponerine ant genus Leptogenys ROGER, 1861 (Hymenoptera: Formicidae) with a key to the Oriental species. Myrmecological News 21: 137-161.