Leptanilloides

Small hypogaeic blind ant predators with subterranean legionary habits. Their hypogaeic habits may, in concert with collecting techniques that have vastly undersampled ants with such a lifestyle, explain the paucity of information about these ants. Museum collections hold few specimens of these ants and there are also some oddly disjunct distributions for some species.

Identification
Brandão et al. (1999) - Ants with the following synapomorphies (only worker caste and larvae known): (1) propodeal dorsum at least 2 times longer than declivity; (2) gaster with segments 1 and 2, and 2 and 3 separated by deep incisions.

Similar to Asphinctanilloides.

Alitrunk flat without metanotal groove on dorsum; abdominal segments 5 and 6 (gaster segments 2 and 3) with a distinct, much narrower presclerite and wider postsclerite, resulting in constrictions between abdominal segments 4 and 5 (gaster segments I and 2), and 5 and 6 (gaster segments 2 and 3). . . . . Leptanilloides

Alitrunk flat with a metanotal groove on the dorsum; abdominal segments 5 and 6 without separation into pre and postsclerites and thus without constrictions between abdominal segments 4 and 5, and 5 and 6. . . . . Asphinctanilloides

Borowiec and Longino (2011) - Although originally the genus Asphinctanilloides had been differentiated from Leptanilloides by several characters (Brandão et al. 1999a), subsequent descriptions of new taxa somewhat blurred this distinction. At present at least presence of a deep metanotal groove and absence of a constriction between abdominal pre- and postsegments V and VI can be regarded synapomorphic for Asphinctanilloides. Ward and Brady (2009) discussed the subject in detail and noted that differentiation of Asphinctanilloides may render Leptanilloides paraphyletic.

Key to species
Key to Leptanilloides

Distribution
Neotropical.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
Anecdotal observations suggest these ants ("Leptanilloidinae" species) behave as army-ant like predators. These ants are likely to be largely subterranean, occasionally coming to the ground surface under debri (rocks, downed wood, etc.) while foraging or to allow mature sexuals (either males only or perhaps males and females) to leave their natal nest. Group predation, frequent colony migrations and synchronized brood cycles may also be part of their life history.

Brandão et al. (1999) - Leptanilloides is exclusively Neotropical, recorded from the Andean foothills at 440 m in Bolivia and in higher altitudes (> 3200 m and up) in Colombia and Ecuador. The biology is completely unknown, except some indication of army ant life style by the study of L. legionaria larvae. The strong girdling constrictions separating the three visible gastral segments is unique among leptanilloidine ants and a similar situation is only found in the cerapachyine Sphinctomyrmex, which has the armed pygidium not reduced. Although the larvae we have in hand are not well preserved, we found nothing similar to the larval haemolymph structure described by Masuko (1989) in Leptanilla japonica.

Donoso et al. (2006) - The army ant syndrome is defined as a combination of three discrete features: nomadism, obligate group-predation and queen dichthadiigyny. Brandão, Silva et al. (1999) provided indirect evidence that army-ant like behavior occurs in the subfamily Leptanilloidinae (=Dorylinae). First, they observed synchrony in larva production, which suggests nomadism. Second, two observations suggested group predatory behavior: 1) direct observation of group-predation by an Asphinctanilloides anae colony on an arthropod and 2) presence on larvae of mandibles with slender, sharp pointed teeth that facilitate being carried by workers. One of the worker paratypes of Leptanilloides legionaria Brandão et al. was preserved holding a larva in the fashion typical of army ants, with the larva slung ventrally under the body of the worker (Figure 6 in Brandão, Diniz et al. 1999), and our field observations confirm this behavior in Leptanilloides nomada and Leptanilloides nubecula. Our observations provide further evidence for synchrony in brood production, as noted by the presence of numerous (>100) larvae in a single growth stage during collections of L. nomada and L. nubecula. Also, our observations demonstrate for Leptanilloides subterranean habits, trail-following behavior, and nocturnal activity.

The discovery of the L. nubecula gyne with a subdichtadiigyne habitus brings new data to the discussion of army ant origins. The leptanilloidine queen differs from true army ants in at least two respects: the gaster is not fully physogastric (maybe due to the relatively small number of workers in a normal leptanilloidine colony, or to a particular colony stage when collected), and the presence of eyes. However, in common with true army ants, leptanilloidine gynes are apterous and have an enlarged postpetiole and falcate mandibles. These characteristics suggest obligate fission as the reproductive strategy for Leptanilloides (see discussion in Gotwald 1995; Peeters & Ito 2001). Workers also show variable expression of typical army ant characters. Unlike true army ants, the colonies are not extraordinarily large, and there is no extreme polymorphism like some of the army ants. The Leptanilloidinae suggest a scenario for what the early stages of army ant evolution might have been.

The queen polymorphism (one true gyne plus several ergatogynes) found in L. nubecula is not new in the dorylomorphs (see Peeters & Ito 2001). Polygyny was reported for Neivamyrmex carolinensis (Rettenmeyer & Watkins 1978). In this species, polygyny was presumed to be correlated with special ecological limitations imposed by the tough environment in which the ants live. They occur at the northern limit of the range of army ants, and there may be a high rate of gyne death due to cold winters (Gotwald 1995). The cold conditions of the high Andean cloud forest may similarly favor polygyny in Leptanilloides.

The new species L. nomada and L. nubecula share strikingly similar character states with Leptanilloides mckennae and Leptanilloides legionaria with respect to external morphology. Shared characters include: 1) high reduction or lack of genal teeth, 2) petiolar form intermediate between Asphinctanilloides and Leptanilloides, 3) postpetiole smaller than petiole, 4) postpetiolar spiracle shifted backwards on anteromedian side of tergite, and 5) blunt flange over metapleural gland opening. These characters blur the distinction between Leptanilloides and Asphinctanilloides, an observation previously noted by Longino (2003) and Ward (2006). It is noteworthy that the males of the two species for which males are known differ greatly in mandible shape. The mandible of L. nubecula males are falcate while those of L. mckennae are subtriangular. The presence of sickle-shaped mandibles in L. nubecula males provides additional evidence that at least some Leptanilloides show trends toward stereotypical army ant morphology (see Ward 2006).

The discovery of three Leptanilloides species living in sympatry provides evidence of considerably more ecological diversity than was previously thought. The different Leptanilloides species may well be occupying distinct subterranean ecological niches. True army ants usually also occur as diverse communities of sympatric species (Gotwald 1995), although in that group as well little is known about how the different species partition local resources It is unknown whether these sympatric Leptanilloides speciated in sympatry or whether they co-occur as a result of secondary contact. In any case, the Otonga reserve and other Andean cloud forests are of extremely high importance for the study and conservation of Leptanilloides ants, a significance noted more generally by Myers et al. (2000) and documented for mammals (Jarrin 2001) and vascular plants (Jaramillo 2001).

Nomenclature

 *  LEPTANILLOIDES [Leptanilloidinae]
 * Leptanilloides Mann, 1923: 13. Type-species: Leptanilloides biconstricta, by original designation.

Worker
Small, slender, monomorphic. Head elongate, subquadrate, anterior portion of front rather strongly impressed. Clypeus short. Frontal carinm very short, fused between the antennm, separated anteriorly and bordering the antennal fossse. Cheeks with a strong carina, which proiects forward as a blunt tooth. Mandibles with distinct basal and apical portions separated by a rounded angle. Eyes absent. Antennee 12-jointed, stout, scape short, funiculus moderately thickened distally, joints submoniliform. Thorax long, slender and flattened; mesopinotum compressed laterally; promesonotal impression strong; mesopinotal impression obsolete. Epinotum unarmed. Petiole subcylindrical, not pedunculate. Postpetiole shorter and broader than the petiole. Gaster long and slender, the three segments visible from above separated by strong constrictions. Legs, long spines of anterior tibim very strongly pectinate, those of middle tibim small, of the posterior pair moderately pectinate. Claws simple.

Brandão et al. (1999) - Alitrunk flat, with a metathoracic-propodeal suture visible on sides of sclerite that may be represented by a faint depression, but never a groove; propodeal dorsum at least 2 times longer than declivity, the faces separated by an attenuate angle; petiole (2nd abdominal segment) longer than high; postpetiole spiracles situated forward of midlength of the segment; abdominal segments 5 and 6 with a distinct, much narrower presclerites and wider postsclerites, resulting in constrictions between abdominal segments 4 and 5, and 5 and 6 ( Figs 2, 4, 6, 8); spiracular plate median connection of sting apparatus with anterior margin convex or straight; furcula in the shape of an U ( Figs 59, 67) and weakly sclerotized; lateral wing-shaped projections absent; sting with bulb base rounded.

Borowiec and Longino (2011):

Antennae with 12 segments.

Apical antennal segment slender, not swollen; round in cross-section.

Clypeus with well developed, translucent lamella (apron).

Lateroclypeal teeth (same as “genal” teeth in Donoso et al. 2006) present or absent.

Parafrontal ridges absent or weakly developed.

Preocular grooves absent.

Frontal carinae vertical, very reduced and fused, completely exposing antennal sockets.

Antennal scrobes absent.

Maxillary palps two-segmented, except in gracilis, where apparently weakly fused and forming one segment; labial palps two-segmented (palp formula 1,2 or 2,2) (in situ count in gracilis, femoralis and legionaria, also reported by Brandao et al. 1999a).

Mandibles subtriangular, edentate or with small, blunt teeth on both masticatory and basal margins.

Eyes absent.

Ocelli absent.

True occipital margin concealed behind vertex in full face view.

Ventrolateral margins of head with carina encircling the foramen only.

Head ventrally with carina complete around foramen magnum, evenly rounded.

Pronotal flange not separated from collar by distinct ridge.

Promesonotal connection complete and apparently flexible (biconstricta, caracola, erinys, femoralis, gracilis, improvisa, sculpturata) or partly to almost completely fused and not flexible (legionaria, mckennae, nomada, nubecula).

Propleura and mesopleura distinctly separated, the connection continuous with promesonotal portion.

Mesometapleural sulcus usually visible, weakly impressed and running towards metanotal sulcus, anepisternum not delineated dorsally or posteriorly.

Transverse mesopleural sulcus absent.

Posterior head, mesosoma, petiole and abdominal segment III immarginate.

Petiole laterally above spiracle immarginate.

Petiole anterodorsally immarginate.

Helcium narrow, posterior face of petiole and anterior face of abdominal segment III well-developed.

Abdominal segment III smaller or much smaller than succeeding segment IV, which is constricted at the presegmental portion.

Abdominal segment III anterodorsally immarginate.

Abdominal segment IV not conspicuously the largest segment.

Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite are equally well visible in lateral view.

Cinctus of abdominal segment IV simple, not cross-ribbed.

Girdling constriction posterior to abdominal segment IV present on sternites V and VI

Abdominal tergite VII (pygidium) reduced and short, unarmed.

Abdominal sternite VII (hypopygium) unarmed.

Mid tibia with one simple spur, hind tibia with single pectinate spur (most species) or both tibiae with two simple spurs (only gracilis) (spur formula 1s,1p or 2s,2s).

Middle and hind basitarsus not widening distally, circular in cross-section.

Posterior flange of hind coxa not produced as raised lamella.

Metatibial gland present, reduced (observed in erinys and nubecula).

Metabasitarsal sulcus absent.

Pretarsal claws simple.

Larva
Brandão et al. (1999) - (description based on larva of Leptanilloides legionaria, see below). First 5 abdominal segments clearly differentiated from another; posterior somites indistinct (Fig. 48). Long (50 μm) unbranched, smooth, slightly curved hairs, and a continuous covering of very small (less than 10 μm) unbranched, smooth, slightly curved to flexuous hairs. Head longer than wide (Fig. 49); genae bulging and frons depressed (Fig. 50); antennae relatively long, almost as long as mandibles, with 2 apical sensillae; labrum circular or heart-shaped in face view, elongate. Mandibles without striae or spinules, their outer border furnished with 6 slender sharp-pointed teeth; apical and subapical teeth longer than remaining (Figs 49, 51). Maxillae without paxiliform or digitiform palp, with apical sensillae.