Zootaxa 1201: 47–62 (2006)
www.mapress.com/zootaxa/
ISSN 1175-5326 (print edition)
Copyright © 2006 Magnolia Press
ISSN 1175-5334 (online edition)
ZOOTAXA
Three new species of Leptanilloides Mann from Andean Ecuador
(Formicidae: Leptanilloidinae)
DAVID A. DONOSO1, JUAN M. VIEIRA1 & ALEXANDER L. WILD2
1
Museo de Zoología, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Av. 12 de
Octubre y Roca, Aptdo. 17-01-2184, Quito, Ecuador, david_donosov@yahoo.com, vieiraroster@yahoo.com.
2
Department of Entomology, University of Arizona, Tucson, AZ 85721, USA, alexwild@email.arizona.edu.
Abstract
We report three new species of the ant genus Leptanilloides from Andean Ecuador. Leptanilloides
nomada sp. n. and L. caracola sp. n. are described from the worker caste, the latter from a unique
specimen; L. nubecula sp. n. is described from workers, males, and two gyne subcastes previously
unknown for the entire subfamily. Phenotypic variation in morphological characters in the new
species L. nomada and L. nubecula is more plastic than suggested by the traditional generic
diagnosis. These records represent the first case of three Leptanilloides species occurring in
sympatry. We discuss aspects of the army ant syndrome and its relevance to the genus
Leptanilloides.
Resumen
Tres nuevas especies del género de hormigas Leptanilloides son descritas a partir de especimenes
encontrados en Los Andes ecuatorianos. Leptanilloides nomada sp. n. y L. caracola sp. n. son
descritas en base a obreras, ésta última es descrita a partir de un sólo espécimen. L. nubecula sp. n.
es descrita en base a obreras, machos y dos subcastas de ginas previamente desconocidas para toda
la subfamilia. La variación fenotípica encontrada en algunos caracteres morfológicos de las nuevas
especies L. nomada y L. nubecula es más plástica de lo que sugiere la diagnosis genérica
tradicional. Estos registros constituyen el primer ejemplo de tres especies de Leptanilloides
viviendo en simpatría. Discutimos aspectos del síndrome de las hormigas legionarias y su
aplicación al género Leptanilloides.
Key words: Army Ants, Cloud Forest, Conservation, Ecuador, Leptanilloidinae, Otonga,
Systematics, Taxonomy.
Accepted by J. Longino: 21 Jan. 2006; published: 15 May 2006
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Introduction
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Leptanilloides is an uncommonly collected ant genus with subterranean habits in the New
World Andean and sub-Andean tropics. With cryptic and eyeless worker ants, the genus
was included in the ant subfamily Cerapachyinae (Brown 1975; Bolton 1990a, b) until
Baroni Urbani et al. (1992) justified the establishment of a separate subfamily,
Leptanilloidinae, hypothesized as the sister group to Cerapachyinae and all other members
of the dorylomorphs. The only apomorphy for the new subfamily provided by Baroni
Urbani et al. (l. c.) was the extremely reduced pygidium, represented by a small U-shaped
sclerite.
Brandão, Diniz et al. (1999) expanded our understanding of Leptanilloidinae and
described six new species that were arranged in two genera, Leptanilloides and
Asphinctanilloides. The reassessment, based on external and sting characters, added five
apomorphies supporting the subfamily: lateral blunt teeth on genae, metatibial gland
absent, gonostylus fused to the posterior arm of the oblong plate, several microtrichia plus
two longer sensillae at the presumed junction of gonostylus with posterior arm of oblong
plate, and base of sting shaft with a pair of long setae. Brandão, Diniz et al. (l. c.) also
established several apomorphies for both leptanilloidine genera. For Leptanilloides, two
apomorphies were proposed: propodeal dorsum at least two times longer than declivity
and abdominal segments 4 and 5 separated by a deep incision; while for
Asphinctanilloides, five apomorphies were established: postpetiole extremely reduced in
size with spiracle at midlength, spiracular plate median connection of the sting apparatus
with bilobed anterior region, quadrate plate apodeme wider than body of the plate, fulcral
arms absent, and basal ridge of sting not visible. Recently, Longino (2003) described a
new species, Leptanilloides mckennae Longino, from Costa Rica. Leptanilloides
mckennae expands the geographic distribution of the subfamily and also presents some
characters (i.e. very small postpetiole and posterior shifted postpetiolar spiracle) that have
been considered apomorphic for Asphinctanilloides.
The male caste of Leptanilloidinae was described recently by Ward (2006), who linked
an unassociated male ant from a montane Costa Rican forest to L. mckennae workers using
molecular data. Ward (l. c.) also discussed the molecular similarities of leptanilloidines to
other dorylomorphs and the evolution and morphological convergences of ant assemblages
living in subterranean habitats (see also Ward 1994; López et al. 1994; Brady & Ward
2005). Brandão, Silva et al. (1999) review some aspects of the biology of this subfamily,
including observations suggestive of nomadic habits.
A recent discovery of two living colonies of Leptanilloides in Ecuador provided an
opportunity to observe aspects of their behavior and motivated the present work. In this
paper we describe three new sympatric species of Leptanilloides from an Andean cloud
forest in western Ecuador. In addition, we describe two distinct gyne subcastes of L.
nubecula sp. n. for the first time in the subfamily and provide a discussion of some
biological aspects of this subfamily.
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Materials and Methods
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The type series of L. nomada sp. n. was collected in December 2003 by ALW and JMV in
a private forest reserve, the Bosque Integral Otonga, on the western slopes of Ecuadorian
Andes. In June 2004 a second species, L. nubecula sp. n., was collected in the reserve by
DAD as part of an ant diversity survey. Finally, a single worker specimen of L. caracola
sp. n. was discovered while reviewing the ant collection at QCAZ museum.
Institutions mentioned in this study are abbreviated as follows: ALWC—Alexander L.
Wild personal collection, Tucson, Arizona, USA; BMNH—British Museum of Natural
History, London, United Kingdom; CASC—California Academy of Sciences, San
Francisco, CA, USA; LACM—Natural History Museum of Los Angeles County, Los
Angeles, California, USA; MCZC—Museum of Comparative Zoology, Harvard
University, Cambridge, Massachusetts, USA; MHNG—Muséum d’Histoire Naturelle,
Geneve, Switzerland; MZSP—Museu de Zoologia da Universidade de São Paulo, São
Paulo, Brazil; NHMB—Naturhistorisches Museum, Basel, Switzerland; NHMW—
Naturhistorisches Museum Wien, Vienna, Austria; QCAZ—Museo de Zoología de la
Pontificia Universidad Católica del Ecuador; UCDC—Bohart Museum of Entomology,
Davis, California, USA; USNM—National Museum of Natural History, Washington, DC,
USA.
Observations were made at 50x magnification with a Wild M5A dissecting
microscope at UCDC by ALW to the nearest .01 mm and at 66x on a Zeiss Stemi SV11
dissecting microscope at QCAZ by DAD to the nearest .02 mm. Worker measurements
and indices are based on Brandão, Diniz et al. (1999) but include some others from
Longino (2003) and Ward (2006): HL—head length, measured in full-face view, from the
anterior median clypeal border (not including the lamellate apron) to the median occipital
border; HW—maximum head width in full-face view; SL—scape length excluding the
condylar bulb; WL—mesosoma length from the base of anterior slope of pronotum to the
lower posterior angle of propodeum; FL—length of the fore femur; EL—length of
compound eye, as seen in full-face view; LHT—length of the metatibia in dorsal view,
excluding the medioproximal lobe; PL—petiole length, measured along line parallel to
tergosternal suture, from anterior-most to posterior-most visible portions of tergite; PPL—
postpetiole length, measured along line parallel to tergosternal suture, from anterior-most
to posterior-most visible portions of tergite; CI—cephalic index (HW × 100/HL); SI—
scape index (SL × 100/HW); REL—relative eye length (EL × 100/HL).
Specimens were imaged in an Auto-montage system (http://www.syncroscopy.com)
by April Nobile at CASC and by ALW at UCDC, and images have been placed online as
part of the Antweb database (http://www.antweb.org). For scanning electron microscopy
(SEM) of L. nubecula sp. n. ergatogyne, a specimen was washed in graded series of
acetone and critical point dried before metallization and observation in the MZSP SEM lab
by Lara Guimarães. Images were processed as TIFF files in Adobe Photoshop.
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Results
Leptanilloides nomada Donoso, Vieira & Wild
Holotype worker deposited at QCAZ. Type locality: Ecuador, Cotopaxi Province,
Bosque Integral Otonga, 1960m, 79°0.197’W; 00°25.158’S, 02-Dec-2003, A. L. Wild & J.
M. Vieira, leg # AW2146. Pinned paratypes were deposited in the following museums:
ALWC, BMNH, CASC, LACM, MCZC, MHNG, MZSP, NHMB, NHMW, UCDC and
USNM. Additional paratypes are pinned or stored in 95% ethanol at ambient temperature
at QCAZ museum. See Figures 1, 2, 7–10.
FIGURES 1–6. Head in full-face view and lateral view of the body of Leptanilloides nomada (1–
2), L. nubecula (3–4) and L. caracola (5–6).
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Etymology: We chose the word nomada in allusion to the nomadic habits of
traditional shepherds (nom = to graze; nomad = shepherd; -a, gives a feminine ending to
the derivation [latin]).
WORKER
Diagnosis: Relatively large and slender. Genal teeth lacking. Clypeal lamella apron
straight. Antenna stout. Mesosoma prominent. Postpetiole relatively small. Hypostomal
teeth conspicuous, seen with head in ventral view. Abdominal segment 4 about the same
length as following segments combined. Dark reddish coloration.
Description: Head, in full frontal view, subquadrate and somewhat wider anteriorly
(CI 85–88). Lateral margins nearly straight and parallel. Posterior corners rounded and
posterior margin slightly concave. Clypeus short with anterior border almost straight and
bearing a concave translucent lamellae; with some setae projecting anteriorly. Frontal
carina short. Frontal lobes well developed and contiguous between antennal insertions.
Gena lacking carina. Mandibles slender, masticatory margin edentate, with distinct basal
and apical portions separated by a rounded angle. Eyes absent. Antenna stout and 12
segmented. Torulus conspicuous. Scape long and clavate, extending further than medial
distance to posterior margin. First funicular segment longer than broad, submoniliform,
gradually increasing in size toward apex but without forming a distinct antennal club.
Head in full face view bearing two hypostomal teeth, easily seen under clypeal translucent
lamella on ventrum.
Mesosomal dorsum long, slender and flattened. Pronotum stout, with a conspicuous
and flexible promesonotal suture. Metanotal groove obsolete. Mesonotum with large and
sclerotized lateral lamella. Propodeum long and unarmed. Propodeal declivity very short
and rounding into dorsal face. Propodeal spiracle conspicuous and rounded, in middle of
the sclerite. Metapleural gland evident but located under translucent (yellow) flanges
which are straight but rounded (not sharp) in posterior angle.
Petiole longer than postpetiole and as wide as long in dorsal view. Petiole with
straight sides and slightly narrowed from front to rear. In profile, petiolar tergite with two
dorsal portions (Figures 7–8). Anterior portion concave and the posterior portion convex.
Postpetiole with dorsal edge almost rounded (Figures 9–10). Anterior-ventral portion of
petiolar and postpetiolar sternite bearing a deep and rounded process. Petiolar spiracle
situated in anterior part of tergite. Postpetiolar spiracle situated anterior to midlength of
tergite in lateral view.
Metasoma robust. Abdominal segment 4 about the same length as following segments
combined. Tergite of abdominal segment 5 not ring-like but appearing to conceal
abdominal segment 6. Abdominal segments 4–5 and 5–6 separated by deep incisions.
Spiracle of abdominal segment 4 conspicuous and located at 2/5 length of tergite. Spiracle
of abdominal segment 5 and 6 less conspicuous and located more anteriorly than spiracle
of abdominal segment 4. Pygidium concealed by the preceding segment and U-shaped.
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Legs long (FL 0.50–0.52). Tibia enlarged apically. Tibia of foreleg with a long
pectinate spur. Metatibial gland absent. Tarsal claws simple.
Head and mesosoma dark reddish. Gaster lighter in color, to yellowish red. Body
bearing abundant white pilosity, denser dorsally than ventrally. Head, mesosoma, petiole,
and post-petiole densely foveolate. Body shining.
FIGURES 7–18. Petiole and postpetiole in lateral and frontal views. Worker of Leptanilloides
nomada (7–10). Worker (11–14) and ergatogyne (15–18) of L. nubecula.
Measurements (in mm) and indices: (holotype, min.-max. of 13 specimens): HL
0.68, 0.65–0.68; HW 0.59, 0.56–0.59; SL 0.42, 0.39–0.42; FL 0.51, 0.50–0.52; LHT 0.54,
0.53–0.57; WL 0.75, 0.72–0.77; PL 0.20, 0.19–0.21; PPL 0.17, 0.17–0.20; CI 87, 85–88;
SI 72, 68–73.
Comments: Known only from workers at the type locality. This species is reported as
Leptanilloides sp. EC1 in Ward (2006).
The type colony was collected at night from a series of subterranean trails and small
chambers along a trail-cut in a cloud forest. The trails emerged above ground for short
sections spanning several centimeters. Workers flicked their antennae in a manner similar
to that observed in ecitonine army ants. The colony contained numerous larvae at the
same stage of development, and workers carried the larvae slung underneath their bodies
in the same manner commonly observed among army ants (Gotwald 1995) and suspected
for other Leptanilloides species (Figure 6 in Brandão, Diniz et al. 1999).
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Leptanilloides nubecula Donoso, Vieira & Wild
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Holotype worker, male and gyne deposited at QCAZ. Type locality: Ecuador, Cotopaxi
Province, Bosque Integral Otonga, 1978m, 79°0.197’W; 00°25.158’S, 24-Jun-2004, D.A.
Donoso Leg. Under log. Some paratypes pinned and stored in the following museums:
CASC, MCZC, MZSP and UCDC. Additional paratypes are stored in 95% ethanol at
ambient temperature at QCAZ museum. See Figures 3–4, 11–28.
Etymology: The Latin word nubecula literally means little cloud and was chosen in
reference to the cloud forest where this species was first collected. This is a noun in
apposition.
WORKER
Diagnosis: Relatively large and slender ants. Polymorphic in color pattern. Without
genal teeth. Anterior clypeal margin and the lamella apron triangular. Hypostomal teeth
inconspicuous. Postpetiole relatively small. Abdominal segment 4 about the same length
as following segments combined.
Description: Head elongate and subrectangular (CI 75–79), slightly wider anteriorly.
Lateral margins of head nearly straight and parallel. Posterior corners rounded and
posterior border concave. Clypeus short with anterior margin triangular. Clypeal apron
translucent and triangular pointed anteriorly projecting some setae. Frontal carina very
short. Frontal lobes distinct, merging between antenna. Gena without teeth. Hypostomal
teeth present but inconspicuous on ventrum of head. Mandibles slender, with distinct
basal and apical portions separated by a rounded angle. Masticatory margin edentate,
although bearing several small denticles. Eyes absent. Antenna 12 segmented. Antennal
scape slender and extending further than medial distance to posterior margin. First
funicular segment longer than broad, submoniliform. Antenna gradually increases in size
toward apex but without forming a distinctive antennal club.
Mesosoma elongate, not slender and flattened. Pronotal suture conspicuous and
flexible. Metanotal groove obsolete. Propodeum unarmed, rounded and long. Propodeal
declivity very short and rounding into dorsal face. Propodeal spiracle conspicuous and
rounded, slightly below the middle of the sclerite. Metapleural gland noticeable, with
flanges rounded posteriorly.
Petiole in dorsal view longer than postpetiole, both segments subequal in width and
slightly narrowed from front to rear, lateral borders straight. In profile, segments heart
shaped, tergites always bigger than sternites. Petiolar sternite bearing large rounded
process. Postpetiole ventral process not as large as petiole process. Petiolar spiracle
situated at the anterior margin of the tergite (Figures 11–14).
Metasoma short and compact. Abdominal segment 4 about the same length as
following abdominal segments combined. Abdominal segment 5 not ring-like but
conceals abdominal segment 6. Abdominal segments 4–5 and 5–6 separated by
constrictions. Spiracle of abdominal segment 4 conspicuous and located at 1/3 length of
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tergite. Spiracle of abdominal segment 5 conspicuous and located more anteriorly.
Spiracle of abdominal segment 6 easily seen and located very anterior in the tergite.
Pygidium concealed by preceding segment and displaying typical U-shape.
Legs long (FL 0.53–0.56). Tibia enlarged apically. Tibia of foreleg with a long and
pectinate spur. Metatibial gland absent. Claws simple.
FIGURES 19–24. Leptanilloides nubecula ergatogyne. Head in lateral view and a close up of the
hypostomal teeth (19–20). Lateral detail of the petiole, note the shape of the postpetiole (21).
Lateral view of the body (22). Tergite of abdominal segment 7 (23). A detail of the clypeus (24).
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FIGURES 25–28. Full face view of head and lateral view of body of the male (25-26) and gyne
(27–28) of Leptanilloides nubecula.
Body color varies from testaceus to reddish brown, always shining. Head and
mesosoma always darker than gaster. Head foveolate. Mesosoma and abdomen finely and
sparsely foveolate. Head, body and appendages with abundant short, erect, light hairs.
Measurements (in mm) and indices: (holotype, min.-max. of 5 specimens): HL 0.69,
0.69–0.72; HW 0.54, 0.54–0.56; SL 0.42, 0.42–0.44; FL 0.54, 0.53–0.56, LHT 0.60, 0.59–
0.65; WL 0.87, 0.86–0.90; PL 0.17, 0.15–0.17; PPL 0.11, 0.11–0.15; CI 78, 75–79; SI 78,
76–81.
GYNE
Diagnosis: Subdichtadiigyne. Approximately 1/4 larger than workers. Head rounded,
lateral borders convex. Compound eyes present and comprised of about 10 facets.
Mandibles subtriangular, masticatory margin edentate. Clypeal lamella apron present.
Apterous, wings and wing buds absent. Petiole enlarged, taller and broader but similarly
proportioned to worker petiole but without dorsal or lateral horns typical of ecitonine and
doryline gynes. Distinct postpetiole absent, third abdominal segment broadly attached to
following segments, with tergosternal fusion. Petiolar and postpetiolar spiracles located as
in workers. Promesonotal suture present and articulated. All segments covered with
dense pubescence. See Figures 27–28.
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Measurements (in mm) and indices: (one gyne measured): HL 0.78; HW 0.74; SL
0.44; LHT 0.75; WL 1.08; PL 0.20; CI 94; SI 59.
ERGATOID GYNE
Diagnosis: Similar to workers but lighter in color and lacking a separate postpetiole
(Figure 21–22). Gaster enlarged. Ovarioles present but not active. See Figures 15–24.
Measurements (in mm) and indices: (min.-max. of 3 specimens measured): HL 0.62–
0.65; HW 0.53; SL 0.41–0.42; LHT 0.59–0.60; WL 0.78–0.81; PL 0.11–0.12; CI 85–81;
SI 77–80.
MALE
Diagnosis: Mandibles falcate and overlapping at closure. The masticatory margin
edentate. Genal teeth and hypostomal teeth lacking. 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; metapleural
gland reduced and inconspicuous; propodeal spiracle small, circular, positioned at about
midheight of propodeum. Medial vein diverging from radial vein more anteriorly than in
L. mckennae; hindwing lacking closed cells. Integument mostly smooth and shiny, with
scattered piligerous punctures; pilosity common on most of body, head and mandibles,
suberect to decumbent. See Figures 25–26.
Measurements (in mm) and indices: (One male measured): HL 0.32; HW 0.32; SL
0.14; EL 0.14; FL 0.36; LHT 0.40; WL 0.64; PL 0.11; CI 100; SI 41; REL 45.
Comments: The type series was a colony found at 2000 hr under a rotten log. A
second colony, with males, was found on a second excursion to the same study site. The
diagnosis of the ergatogynes may be incomplete in reference to color and other age-related
traits, as the collected ergatogyne individuals were teneral, showing pale coloration,
absence of abdominal fat bodies, and undeveloped ovaries.
Leptanilloides caracola Donoso, Vieira & Wild
Holotype worker deposited at MCZC. Type locality: Ecuador, Cotopaxi Province, Bosque
Integral Otonga, 2200m, 78°0.95’W; 00°0.32’S, 04-Abr-1997, EX: D3, I. G. Tapia & P.
Ponce Leg. Only one specimen examined. See Figures 5–6.
Etymology: Name in reference to a popular character in local folklore. Noun in
apposition.
WORKER
Diagnosis: This species can be recognized by its minute size, light brown color,
absence of genal teeth and large postpetiole.
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Description: Head elongate and subquadrate (CI 78), slightly wider anteriorly. Lateral
margins of head nearly straight and parallel. Posterior corners rounded and posterior
border slightly concave. Clypeus short with anterior border straight, lamella apron
triangular. Frontal carina very short, fused between the antenna, separated anteriorly and
bordering the antennal fossa. Gena without blunt teeth. Mandibles short, masticatory
margin edentate, with distinct basal and apical portions separated by a rounded angle.
Eyes absent. Antenna stout, 12 segmented. Scape short and clavate, extending about 3/8
the distance to occipital borders. Funiculus moderately narrow. First funicular joint
rounded, broader and longer than the second. Antennal joints submoniliform, gradually
increasing in size toward apex but not forming an antennal club.
Mesosoma long, slender and flattened. Pronotum conspicuous, with a flexible
promesonotal suture. Metanotal groove obsolete. Sides of mesonotum sclerotized.
Propodeum unarmed. Propodeal declivity very short and rounding into the dorsal face.
Propodeal spiracle round, situated in the middle of the sclerite. Metapleural gland flanges
conspicuous, translucent and posteriorly rounded.
Petiole distinct. Petiole smaller than postpetiole in dorsal view. Petiole very slightly
narrowed from front to rear and with straight sides. Postpetiole more narrowed from front
to rear. In profile, petiolar tergite with two dorsal portions. Anterior portion large and
concave and posterior portion convex. Postpetiole in profile with dorsal edge rounded.
Antero-ventral portion of the petiolar sternite with a deep and rounded process.
Postpetiole without anteroventral process. Petiolar and postpetiolar spiracle not easily
seen.
Metasoma long and slender. Abdominal segments 4–6 subequal in length in dorsal
view and separated by strong constrictions. Pygidium concealed by the preceding segment
and U-shaped.
Tibia enlarged apically. Tibial spur of foreleg long and pectinate. Metatibial gland
absent. Claws simple.
Body color shining light yellowish brown. Head with abundant punctures. Mesosoma
and abdomen more finely and sparsely punctate. Head, body and appendages with
abundant, rather coarse, short and erect, brownish hairs.
Measurements (in mm) and indices: (only holotype measured): HL 0.40; HW 0.31;
SL 0.18; FL 0.22; LHT 0.24; WL 0.47; PL 0.12; PPL 0.16; CI 78; SI 58.
Comments: Data found on the label (i.e. EX:D3) indicates the specimen was collected
in a pitfall trap in second growth forest (I. G. Tapia, pers. com.).
Discussion
Few phenomena have attracted such attention from myrmecologists as the army ant
syndrome (Wilson 1958, 1971; Gotwald 1995; Brady 2003; Brady and Ward 2005). 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
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indirect evidence that army-ant like behavior occurs in the subfamily Leptanilloidinae.
First, they observed synchrony in larva production, which suggests nomadism. Second,
two observations suggested group predatory behavior: 1) direct observation of grouppredation by an Asphinctanilloides anae Brandão et al. 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 L. 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 L. nomada and L. 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 (Emery) (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 L. mckennae Longino and L. legionaria Brandão et al. 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
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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 character states shown by Leptanilloides have important consequences for the
reconstruction of army ant evolution. Dorylomorphs comprise a well-supported group of
ant subfamilies which includes army ants and relatives (Bolton 2003). The current view
sets Leptanilloidinae as the sister group to the remainder of the dorylomorphs
[Cerapachyinae + (true army ants)] (Brady and Ward 2005). This phylogenetic placement
makes Leptanilloidinae an important taxon of reference for studies on the evolution of
cerapachyines and of the more highly specialized true army ants, especially under some
models of character evolution (Cunningham 1999). In particular, the observations
reported here imply that some army ant traits, including eyelessness in the worker,
specialized gyne morphology, and the form of brood carrying, may have been present in
the ancestral dorylomorph. However, the presence of large eyes and small, unspecialized
gynes in some Cerapachys species (Brown 1975) raise the alternate scenario, that
Leptanilloides may represent a case of parallel evolution and convergence on true army
ants. Ward (2006) suggests that the leptanilloidine lineage is older than the approximately
105 million year old army ant lineage, as estimated from molecular dating analysis (Brady
2003). If true, they predate the complete fragmentation of Gondwana. Since
leptanilloidine ants have not been recorded outside of the Neotropics, the group may well
have gone extinct elsewhere.
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).
Key to species of Leptanilloides based on the worker caste
1
Postpetiole in profile much shallower dorsoventrally than adjoining fourth abdominal
segment (Figures 2, 4); postpetiolar spiracle shifted posteriad on anteromedian side of
tergite (Figures 9, 13); genal teeth absent or very reduced in size (Figure 3), body size
relatively large [HL 0.68–0.70]..................................................................................... 2
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4
5
6
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7
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Postpetiole in profile nearly as deep dorsoventrally as fourth abdominal segment (Figure 6); postpetiolar spiracle situated forward on the tergite; genal teeth usually present
and large (except in L. caracola), body size relatively small [HL 0.40–0.50] ............ 5
Head subquadrate [CI 85–88]; lateral margins nearly straight and parallel (Figure 1);
propodeal declivity short and straight, propodeum with dorsal and posterior faces
clearly differentiated (Figure 2) ................................................... L. nomada (Ecuador)
Head subrectangular [CI 75–80]; lateral margins rounded (Figure 3); propodeal declivity usually rounded without clear distinction between dorsal and posterior face (Figure
4) .................................................................................................................................. 3
Lateral margins of the head rounded; posterior margin of the head slightly concave;
head sculpture fine, at most 10-12 shallow foveolae across face at midlength (Figure 5
in Brandão, Diniz et al. 1999) .................................................L. legionaria (Colombia)
Lateral margins of the head slightly rounded; posterior margin of the head deeply concave; head sculpture more coarse, with at least 15 foveolae across face at midlength . 4
Without hypostomal teeth.......................................................L. mckennae (Costa Rica)
With hypostomal teeth (Figures 19–20) ...................................... L. nubecula (Ecuador)
Flange over metapleural gland opening rounded posteriorly; head sculpture coarse,
about 20 deep foveolae across face at midlength.......................................................... 7
Flange over the metapleural gland opening sharply pointed posteriorly; head sculpture
variable .......................................................................................................................... 6
Petiole, in lateral view, longer than postpetiole; head sculpture shallow, with 15 foveolae across face at midlength (Figure 7 in Brandão, Diniz et al. 1999)............................
.................................................................................................. L. biconstricta (Bolivia)
Petiole, in lateral view, as long as postpetiole; head sculpture deeper, with 25 foveolae
across face at midlength (Figure 1 in Brandão, Diniz et al. 1999) .................................
.............................................................................................. L. sculpturata (Colombia)
Genal teeth very small or reduced; mandibular teeth not developed, masticatory margin edentate (Figure 5) ................................................................ L. caracola (Ecuador)
Genal teeth present (Figure 16 in Brandão, Diniz et al. 1999); mandibular teeth well
developed (Figure 16 in Brandão, Diniz et al. 1999)................ L. improvisa (Ecuador)
Acknowledgments
We thank Alvaro Barragán, Miriam Rivera and Giovanni Onore for access to laboratories
in the QCAZ Museum. We thank Dr. Carlos Brandão, who kindly facilitated SEM images
of the L. nubecula ergatogyne and commented carefully on a last draft. April Nobile
provided Auto-montage images. The Pontificia Universidad Católica del Ecuador
provided funding through Project # A312 to DAD and JMV. ALW traveled to Ecuador
with support from United States National Science Foundation grant # 0234691.
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