Leptanilloides mckennae

Ward, P. S., 2007, The ant genus Leptanilloides: discovery of the male and evaluation of phylogenetic relationships based on DNA sequence data., Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions. (Memoirs of the American Entomological Institute 80), pp. 637-649 : 642-643

DESCRIPTION OF LEPTANILLOIDES MCKENNAE MALE

Head broader than long, with large eyes that occupy the anterior half of sides of head; mandibles slender, elongate-triangular, and overlapping at closure (Figure 1), masticatory margin edentate and rounding into unarmed basal margin; external margin of mandible weakly concave; maxillary palps 2 - segmented; labial palps difficult to discern in situ but apparently similarly reduced; genal teeth and hypostomal teeth lacking; anterior margin of clypeus with a prominent, subtriangular, translucent lamella, bluntly pointed medially and with an anterior-posterior extension at this midpoint that is subequal to scape width; posterolateral margin of clypeus well marked, but posteromedial boundary obscure; antennal sockets horizontal and exposed, and located close to the anterior clypeal margin; antenna 13 - segmented, each segment much longer than wide; scape and ultimate antennal segment subequal in length, each 0.12 × total length of antenna and 2.2 × length of the second antennal segment; front of head immediately posterior to antennal sockets slightly depressed, and furnished medially with a low, blunt, longitudinal ridge, probably homologous with the elevated frontal carinae of the worker; lateral ocelli separated from median ocellus by about their diameters.

Mesosoma with usual complement of sclerites (Figure 2); pronotum U-shaped in dorsal view and reduced anteromedially to a thin horizontal strip, set well below the level of the mesonotum; pronotum triangular in profile, with pointed posterior apex; mesonotum lacking notauli, but with a darkened, weakly impressed anteromedial suture; parapsidal sutures present; parascutal carina poorly developed and terminating before the transcutal cleft; axillae not meeting medially, connected by a narrow furrow; tegula very small and inconspicuous; mesopleuron lacking oblique transverse sulcus and hence not divided into anepisternum and katepisternum, but lower third of mesopleuron with a broad longitudinal furrow (possibly an artifact of cuticular collapse); boundary between metapleuron and propodeum effaced posteriorly; metapleural gland reduced and inconspicuous; propodeal spiracle small, circular, positioned at about midheight of propodeum and as far back as the posterior extremity of the metanotum. Legs slender (LHT / HL ~ 1.5); mesotibia and metatibia each with a single spur, barbulate and pectinate, respectively; tarsal claws lacking preapical tooth.

Wings somewhat infuscated and with reduced venation (Figure 3); pterostigma present; forewing with one submarginal cell; closed discal (medial) cell lacking, i. e., m-cu crossvein absent; veins M and Cu diverging distal to crossvein cu-a by a distance greater than the length of the crossvein; hindwing lacking closed cells; anterior margin of hindwing with 3 - 4 hamuli; jugal lobe absent.

Metasoma long and slender; abdominal segment 2 (petiole) subquadrate in profile (Figure 2), longer than high or wide, and only weakly constricted posteriorly (helcium thus apparently quite broad); spiracle on abdominal segment 2 located at anterodorsal extremity; abdominal segment 3 larger than petiole, and not developed as postpetiole nor separated from abdominal segment 4 by a marked constriction; abdominal spiracle 3 located on anterior third of tergite; abdominal segments 2 and 3 with tergosternal fusion; abdominal segment 4 lacking tergosternal fusion; segment 4 with short but distinctly differentiated presclerites; spiracle present on anterior half of tergite 4; abdominal segments 5 and 6 apparently lacking differentiated presclerites, and not separated from succeeding segments by constrictions; abdominal spiracles 5 and 6 small and inconspicuous but exposed, i. e., visible at anterior margins of respective tergites, under normal distension; abdominal tergite 8 (pygidium) small and simple but visible dorsally, not wholly covered by abdominal tergite 7; cerci absent; subgenital plate (abdominal sternite 9) with posterior margin broadly concave but not bifurcate; anterior margin of subgenital plate with mesial apodeme better developed than lateral apodemes; basal ring not hypertrophied; paramere long and slender with upturned apex (Figure 2), about 1.5 × petiole length; volsella simple, lobelike, lacking differentiated cuspis.

Body size small; total length, excluding appendages, approximately 2.7 mm; integument mostly smooth and shiny, with scattered piligerous punctures; pilosity common on most of body, suberect to decumbent. Color: yellowish-brown, dorsum of head a contrasting dark brown; abdominal segments 4 - 8 medium brown.

Comparison of the two males

The two males were closely comparable in terms of external morphology, the chief difference between them being larger eye size in the Arenal male (see measurements below). Head shape, antennal proportions, integument sculpture, color, and overall habitus were otherwise very similar. The preceding description is a composite for the head, wings and genitalia, and is based on the Arenal male alone for other details.

Measurements (in mm) and indices:

HW HL SL LHT CI SI REL REL 2

P. N. Arenal 0.639 0.472 0.242 0.724 1.35 0.38 0.54 0.40

Estacion Cacao 0.592 0.452 0.221 — 1.31 0.37 0.47 0.36

Comments

To the extent that the Leptanilloides mckennae male is representative it suggests the following provisional diagnosis for males of the subfamily Leptanilloidinae : mandibles elongate-triangular and edentate; palp formula 2,2 or less; antennae 13 - segmented; anterior clypeal lamella present; pronotum triangular in profile, U-shaped in dorsal view, and narrow and strap-like anteromedially; notauli absent; mesopleuron lacking oblique transverse suture; petiole nodiform; postpetiole absent; abdominal spiracles 5 and 6 visible under normal distension; posterior margin of subgenital plate emarginate; cerci absent; mesotibia and metatibia each with single apical spur; forewing with one submarginal cell and no discal (medial) cell.

Several features of the Leptanilloides mckennae male match those of the worker caste of the same species, such as the well developed, medially pointed clypeal lamella; the form of the tibial spurs; the location of the abdominal spiracles; and overall body size (2.7 mm long versus ~ 3.1 mm in the worker). General traits of the Leptanilloides male that provide support for placement of the genus in the dorylomorph group include tergosternal fusion of abdominal segments 2 and 3 (but not 4); exposure of abdominal spiracles 5 and 6 under normal distension; absence of cerci; and simplified volsella. Interestingly the Leptanilloides male also shares some specific attributes with army ant males including a triangular pronotum (in profile); reduced parascutal carina; absence of an oblique transverse sulcus on the mesopleuron; and relatively small tegula. In other respects, however, Leptanilloides lacks some of the key characteristics of male army ants such as large size (relative to workers), elongate and sickle-shaped mandibles, robust metasoma, and modified genitalia.