Leptanilloides Mann, 1923

Borowiec, Marek L., 2016, Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae), ZooKeys 608, pp. 1-280 : 125-129

Taxon classification Animalia Hymenoptera Formicidae

Leptanilloides Mann, 1923

= Amyrmex Kusnezov, 1953, syn. n.

= Asphinctanilloides Brandão, Diniz, Agosti and Delabie, 1999, syn. n.

Type-species.

Leptanilloides biconstricta , by original designation.

This is a lineage of subterranean ants from Central and South America. Its members had been extremely rarely encountered before collecting methods targeting soil-dwelling ants were popularized: 17 out of the 19 currently known species were described after 1998.

Diagnosis.

Worker. The workers of Leptanilloides are rather variable but can be distinguished from all other dorylines by a combination of promesonotal Pronotomesopleural suture variously developed but often conspicuous, propodeal spiracles positioned low, lack of metanotal groove , absence of propodeal lobes, and small and unarmed pygidium. The positioning of the propodeal spiracle may be rather high on the sclerite in some species and so these could conceivably be mistaken for small Neivamyrmex . The latter, however, can be distinguished by a complete lack of a promesonotal Pronotomesopleural suture in dorsal view and abdominal segment IV much larger than the succeeding segment V, with no apparent constrictions between abdominal segments IV, V, and VI. Although some larger Leptanilloides species can have an inconspicuous promesonotal Pronotomesopleural suture, those will have visible constrictions on the gaster and abdominal segment IV and that segment is never much larger than succeeding gastral segments.

Male. The males of Leptanilloides are distinct in their extreme reduction of tegulae. The wing venation is reduced and unusual among dorylines because of the combination of costal cell (C) present in fore wing and discal cell always being open. The males of Leptanilloides also lack conspicuously bispinose abdominal sternite IX (subgenital plate) characteristic of almost all other male dorylines.

Description.

Worker.Head: Antennae with 12 segments. Apical antennal segment not enlarged, not broader and longer than two preceding segments combined. Clypeus with cuticular apron. Lateroclypeal teeth absent or present. Parafrontal ridges absent or reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum without median notch or concavity. Proximal face of stipes projecting beyond inner margin of sclerite, concealing prementum when mouthparts fully closed. Maxillary palps 2- or, rarely, 1-segmented. Labial palps 2-segmented. Mandibles triangular, with teeth or triangular with median tooth. Eyes absent. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Posterior head corners dorsolaterally immarginate. Carina surrounding occipital foramen ventrally absent or present. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Promesonotal connection variable, with Pronotomesopleural suture present, weakly differentiated, immobile or with Pronotomesopleural suture conspicuous and complete, but immobile, or with Pronotomesopleural suture complete and mobile. Pronotomesopleural suture visible, unfused up to notal surface. Mesometapleural groove weakly impressed to deeply impressed and conspicuous. Transverse groove dividing mesopleuron absent. Pleural endophragmal pit concavity absent. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma absent. Metanotal depression or groove on mesosoma present. Propodeal spiracle situated low on sclerite. Propodeal declivity without distinct dorsal edge or margin and rectangular in posterior view. Metapleural gland with bulla visible through cuticle. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate or marginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at posttergite and axial or slightly supraaxial. Prora simple, not delimited by carina, a simple U-shaped margin, or a V-shaped protrusion. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III variable, more than half size of succeeding segment IV, which is weakly constricted at presegmental portion (uninodal waist) or abdominal segment III about half size of succeeding segment IV, which is strongly constricted at presegmental portion (binodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like, not sculptured or a gradual concavity, not gutter-like. Abdominal segment IV not conspicuously largest segment. Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite equally well visible in lateral view. Girdling constriction between pre- and posttergites of abdominal segments V and VI absent or present. Girdling constriction between pre- and poststernites of abdominal segments V and VI absent or present. Pygidium small, reduced to narrow strip, without impressed medial field and simple, not armed with cuticular spines or modified setae. Hypopygium unarmed. Legs: Mid tibia with single simple/barbulate spur, with single pectinate spur, or rarely with two simple spurs. Hind tibia with pectinate spur or rarely with one barbulate and one pectinate spur. Hind basitarsus not widening distally, circular in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland present as oval patch of whitish cuticle. Metabasitarsal gland absent. Hind pretarsal claws simple. Polymorphism: Monomorphic.

Male.Head: Antennae with 13 segments. Clypeus with or without cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical. Maxillary palps unknown. Labial palps unknown. Mandibles falcate or, more rarely, elongately triangular, edentate, or intermediate. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Carina surrounding occipital foramen ventrally absent. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Notauli absent. Transverse groove dividing mesopleuron absent. Propodeal declivity reduced, without distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes absent. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle immarginate. Helcium in relation to tergosternal Pronotomesopleural suture placed at posttergite or at Pronotomesopleural suture and axial. Prora simple, not delimited by carina. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III more than half size of succeeding segment IV; latter weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV absent, i.e. pre- and postsclerites indistinct. Cinctus of abdominal segment IV absent, not impressed. Girdling constriction between pre- and postsclerites of abdominal segments V and VI absent. Abdominal segment IV not conspicuously largest segment. Abdominal sternite VII simple. Abdominal sternite IX simple or cleft, with lateral apodemes reduced, only medial apodeme conspicuous, short. Genitalia: Cupula short relative to rest of genital capsule and of approximately equal length on both dorsal and ventral surfaces. Basimere broadly fused to telomere, with sulcus discernable at junction or no sulcus trace at junction, and ventrally with left and right arms abutting. Telomere gradually tapering toward apex. Volsella gradually tapering toward apex. Penisvalva laterally compressed, rounded at apex. Legs: Mid tibia with single simple/barbulate spur or with single pectinate spur. Hind tibia with single pectinate spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal glands absent. Hind pretarsal claws simple. Wings: Tegula absent or extremely small. Vein C in fore wing present. Pterostigma narrow or broad. Abscissa R·f3 absent. Abscissae Rs·f2-3 present, connecting with Rs+M&M·f2. Cross-vein 2r-rs present, differentiated from Rs·f4 by presence of Rs·f2-3. Abscissae Rs·f4-5 present, fused in absence of 2rs-m. Abscissa M·f2 in fore wing contiguous with Rs+M or absent. Abscissa M·f4 in fore wing absent or present, not reaching wing margin. Cross-vein 1m-cu in fore wing absent. Cross-vein cu-a in fore wing present, arising from Cu and distal to, at or near M·f1. Vein Cu in fore wing present, with only Cu1 branch prominent. Vein A in fore wing with abscissa A·f1 present. Vein C in hind wing absent or present. Vein R in hind wing absent. Vein Sc+R in hind wing absent or present. Abscissa Rs·f1 in hind wing absent or present, shorter than 1rs-m. Abscissa Rs·f2 in hind wing absent or present, not reaching wing margin. Cross-vein 1rs-m in hind wing absent. Vein M+Cu in hind wing absent. Abscissa M·f1 in hind wing absent. Abscissa M·f2 in hind wing absent. Cross-vein cu-a in hind wing absent. Vein Cu in hind wing absent. Vein A in hind wing absent.

Gyne. The queens of Leptanilloides collected so far have been ‘subdichthadiiform’, or wingless ergatoids with eyes and hypertrophied gaster, including abdominal segment III. The gynes possess eyes but no ocelli. See description of Leptanilloides erinys gyne in Borowiec and Longino (2011); Donoso et al. (2006) also reported blind intercastes in addition to a subdichthadiigyne in Leptanilloides nubecula .

Larva. Larva was described by Brandão et al. (1999a). Presence of cocoons unknown.

Distribution.

Leptanilloides is a genus found throughout Central America, from Chiapas, Mexico to Panama, and from scattered, mostly high-elevation records from Bolivia, Colombia, Ecuador, and Venezuela. It is also present in the Amazon Basin and one species has been described from the Atlantic forest habitat of São Paulo, Brazil. A recent collection from western Texas ( MacGown et al. 2015) is a remarkable range extension for this lineage.

Taxonomy and phylogeny.

Leptanilloides was described with one species, Leptanilloides biconstricta , in 1923 ( Mann 1923). Subsequently a closely related genus Asphinctanilloides was described, along with new Leptanilloides species ( Brandão et al. 1999a). Asphinctanilloides was originally differentiated from Leptanilloides by several characters. The genus Amyrmex , known only from males, was originally placed erroneously in the Dolichoderinae ( Ward and Brady 2009). Recent descriptions of additional Leptanilloides species reveal greater morphological diversity of the genus and blur the distinction from Asphinctanilloides ( Longino 2003, Donoso et al. 2006, Borowiec and Longino 2011). Because of this it has been suggested that Leptanilloides may eventually prove paraphyletic with regards to Asphinctanilloides and it has already been shown to be paraphyletic with respect to Amyrmex (see Ward and Brady 2009). No Asphinctanilloides have ever been included in a molecular analysis but it is possible that the males described as Amyrmex in fact correspond to Asphinctanilloides . Here I propose synonymy of both Amyrmex and Asphinctanilloides under Leptanilloides . Leptanilloides in this new sense is easily identified in both worker and males and guarantees more stable taxonomy in the face of potential paraphyly issues, although it encompasses morphologically disparate forms. It is possible that future workers will feel justified to split this genus once again after a better understanding of worker and male diversity is attained. Delsinne et al. (2015) provide the most recent key to species of Leptanilloides excluding Asphinctanilloides , but the species that were placed in the latter can still be identified using Brandão et al. (1999a).

The phylogenetic position of Leptanilloides within Dorylinae was difficult to ascertain with Sanger sequencing data ( Brady et al. 2014) but genomic data suggest that it forms a clade with Sphinctomyrmex and New World army ants. Several species have been included in morphology-based and molecular phylogenies ( Brandão et al. 1999a, Ward 2007, Ward and Brady 2009, Delsinne et al. 2015, MacGown et al. 2015, Borowiec, in prep.) but the availability of fresh material precludes a comprehensive analysis.

Biology.

Leptanilloides nomada was observed foraging at night in partly subterranean, partly exposed, columns but the ants did not carry any prey ( Donoso et al. 2006). In Leptanilloides nubecula the colonies are apparently polygynous, with subdichthadiigyne queens and intercastes present ( Donoso et al. 2006), but a complete colony of Leptanilloides erinys contained only single subdichthadiiform queen ( Borowiec and Longino 2011). Brood apparently develops in synchrony, as all nest collections so far contain larvae of uniform size ( Brandão et al. 1999a, b, Donoso et al. 2006, Borowiec and Longino 2011). Brandão et al. (1999b) summarized the scant information available on species then classified in Asphinctanilloides . They report workers of Leptanilloides anae moving in columns similar to that of army ants, preying on an unidentified, dismembered arthropod under cow dung. This would suggest that this species may not be a specialized predator of other ants, like most dorylines, although it is clear that more observations are needed. As evidence for hypogaeic habits Brandão et al. (1999b) note that where intensive surveys of leaf litter ants have been carried out specimens have not been collected by that method but only from soil samples. Specimens have also been extracted from stomachs of subterranean amphisbaenians, giving further evidence for the underground lifestyle.

Species of Leptanilloides

Leptanilloides amazona Brandão, Diniz, Agosti and Delabie, 1999: Brazil, comb. n.

Leptanilloides anae Brandão, Diniz, Agosti and Delabie, 1999: Brazil, comb. n.

Leptanilloides atlantica Silva, Brandão, Feitosa and Freitas, 2013: Brazil

Leptanilloides biconstricta Mann, 1923: Bolivia

Leptanilloides caracola Donoso, Vieira and Wild, 2006: Ecuador

Leptanilloides chihuahuaensis MacGown, Schiefer and Branstetter 2015: United States

Leptanilloides copalinga Delsinne and Donoso 2015: Ecuador

Leptanilloides erinys Borowiec and Longino, 2011: Ecuador

Leptanilloides femoralis Borowiec and Longino, 2011: Venezuela

Leptanilloides golbachi Kusnezov, 1953: Argentina, comb. n.

Leptanilloides gracilis Borowiec and Longino, 2011: Mexico

Leptanilloides improvisa Brandão, Diniz, Agosti and Delabie, 1999: Ecuador

Leptanilloides legionaria Brandão, Diniz, Agosti and Delabie, 1999: Colombia

Leptanilloides manaura Brandão, Diniz, Agosti and Delabie, 1999: Brazil, comb. n.

Leptanilloides mckennae Longino, 2003: Costa Rica

Leptanilloides nomada Donoso, Vieira and Wild, 2006: Ecuador

Leptanilloides nubecula Donoso, Vieira and Wild, 2006: Ecuador

Leptanilloides prometea Delsinne and Donoso, 2015: Ecuador

Leptanilloides sculpturata Brandão, Diniz, Agosti and Delabie, 1999: Colombia