Leptanilloides atlanticus

The only known sample of this species includes 39 workers (six in alcohol) captured in a single pitfall trap set on the forest floor, at 800 m altitude. The collection point is a patch of secondary montane Atlantic Forest. The predominant climate in the region is humid, without a well-defined dry season; annual rainfall ranges from c.1860 to c.4400 mm (see Uehara-Prado et al. 2009 for site details).

Identification
Silva et al. (2013) - A member of the Leptanilloides biconstricta species-group. Leptanilloides atlanticus is similar to Leptanilloides biconstricta from Bolivia, but can be easily distinguished from it by the uninterrupted mesopleura and metapleura reticulation, versus fine, superficial and interrupted in L. biconstricta. Leptanilloides atlanticus also differs from L. biconstricta by the more densely foveolate head, with circa 20–30 foveolae covering a straight transverse line at head midlength, whereas there are only 10–20 in L. biconstricta. Additionally, L. atlanticus can be distinguished from L. biconstricta by the petiole as long as the postpetiole (petiole longer than postpetiole in L. biconstricta), comparatively smaller body size (best seen in head size and mesosoma length) and sternite on abdominal segment III anteriorly bulging (evenly rounded in L. biconstricta). Leptanilloides atlanticus is also similar to Leptanilloides femoralis from Venezuela, with which it shares a relatively enlarged femur (FFeW 0.07–0.08 in L. atlanticus, 0.08–0.09 in L. femoralis), and the fine microreticulate sculpture on the mesopleuron, propodeum and petiole. It can be distinguished from L. femoralis by the presence also of a subpetiolar process with an acute anteriorly projecting tooth (absent in L. femoralis). Leptanilloides atlanticus can be differentiated from Leptanilloides gracilis based on the shallow anterior constrictions of abdominal segments IV–VI in L. atlanticus, whereas they are deeply impressed in L. gracilis, and on the anteriorly bulging ventral margin of the abdominal segment III in L. atlanticus, whereas in L. gracilis the ventral margin is evenly rounded.

Leptanilloides atlanticus is similar to some other small species of the genus (mainly L. biconstricta, L. femoralis and L. gracilis). It can be identified by the following combination of traits: (1) sharply pointed flange over the metapleural gland, (2) mesopleura and metapleura reticulation not interrupted, (3) densely foveolate head, (4) petiole as long as the postpetiole, (5) enlarged fore femur, (6) abdominal segments IV–VI separated by shallow constrictions, (7) subpetiolar process with an acute, anteriorly projecting, tooth, (8) ventral profile of the subpetiolar process flat, and (9) sternite on abdominal segment III bulging anteriorly.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil.

Biology
Silva et al. (2013) - The description of L. atlanticus in the Brazilian Atlantic Forest brings new data to the biogeography of Leptanilloides. Most described species in the genus are known from the Andes, from the Andean foothills of Bolivia to higher altitudes in Colombia and Ecuador (Brandão et al. 1999; Donoso et al. 2006). Recently described Leptanilloides species expanded the range of the genus to Costa Rica (Longino 2003), Mexico and Guatemala (Borowiec and Longino 2011), and Venezuela (Borowiec and Longino 2011). Now, the present study shows that Leptanilloides also occurs in montane sites in south-eastern Brazil.

In particular, the first occurrence of Leptanilloides in the Brazilian Atlantic Forest implies a disjunct distribution pattern between Andean Leptanilloides and L. atlanticus. Similar biogeographical patterns have been described in studies on montane birds (Ribas et al. 2007), hylid frogs (Faivovich et al. 2005), the leptodactylid genus Ischnocnema (Padial et al. 2005), in rodents (Percequillo et al. 2011), and in butterflies (Brown 1987). Literature examples suggest a historical relationship between the Atlantic Forest Serra doMar and Austral Andean centres of endemism for hylid frogs, between Serra doMar and the Peruvian Andes for rodents, and between Serra doMar and the Andean Cordillera for birds (see discussion in Percequillo et al. 2011). Ribas et al. (2007) provided evidence that the spatiotemporal distribution of Pionus parrots, which display a very similar disjunct pattern, is linked to Andean tectonics and palaeoclimate changes through vicariance. Brown (1987) showed that there is high similarity between the south central Andes and south-eastern Brazil in several butterfly genera, and that this is a legacy of past climatic changes when a ‘bridge’ of suitable vegetation existed across northern Argentina, linking the Andes to the mountain chains in south-eastern Brazil.

There are also examples of disjunct distribution in plants. Safford (2007), analyzing the vascular plant genera of high-altitude grasslands in Brazil, concluded that their floristic similarity is greater with tropical Andean plants than with those of lowland and middle elevation areas of central and south-eastern Brazil. In montane and upper-montane Atlantic Forest areas, bryophytes with restricted distributions are preponderant, including many endemics and some showing disjunct distributions, with populations in the northern Andes and Central America (Santos and Costa 2010), probably reflecting the effects of long-distance dispersal by air currents and climatic similarities between the high-altitude grasslands and the northern Andes (Safford 2007; Santos and Costa 2010).

Despite several cases in the literature in which it was possible to show that the observed disjunct patterns reflect real distributions, we cannot discount the possibility that the apparent disjunct distribution pattern observed in Leptanilloides results from an insufficient collecting effort applied to the subterranean environment; these ants may be much more common and widespread than presently known. Amyrmex (known only from males) may be identical either to Leptanilloides or Asphinctanilloides (Ward and Brady 2009); the apparent distribution gap of South American Leptanilloides should be reconsidered if Amyrmex is synonymous with Leptanilloides.

Castes
Known only from the worker caste.

Nomenclature

 *  atlanticus. Leptanilloides atlantica Silva, Brandão, Feitosa & Freitas, 2013: 3, figs. 1A-D, 2A-F (w.) BRAZIL.

Worker
(holotype): HW0.25, HL 0.34, SL 0.15, ML 0.41, PW 0.16, PL 0.11, PPL 0.11, FFeW 0.07, FFeL 0.19, HFeL 0.21, HTiL 0.23, AIVW 0.24, CI 74.51, SI 60.53.

(15 measured): HW 0.24–0.25, HL 0.34–0.36, SL 0.14–0.16, ML 0.39–0.41, PW 0.15–0.17, PL 0.11–0.12, PPL 0.09–0.11, FFeW 0.07–0.08, FFeL 0.19–0.20, HFeL 0.20–0.21, HTiL 0.21–0.23, AIVW 0.23–0.25, CI 66.67–73.08, SI 57.89–66.67.

With the character states of Dorylomorphs, Leptanilloidinae and Leptanilloides (Borowiec and Longino 2011) and with the body and appendages yellowish-brown covered by short, moderately abundant, subdecumbent to appressed hairs; somewhat longer hairs located on the anterior portion of the cephalic capsule. Dorsal surface of head with a longitudinal median line devoid of any sculpture. Head, mesosoma, petiole, postpetiole and gaster comparatively densely foveolate; head with circa 20–30 foveolae covering a straight transverse line at head midlength. Mesopleura and metapleura and propodeum entirely reticulate; petiole reticulate except on the dorsal face. Gaster smooth and shiny.

Head longer than broad. Lateral margins of head modestly convex and almost subparallel; occipital corners rounded; vertexal margin slightly convex. Clypeus with some setae projecting anteriorly. Mandibles short, with distinct basal and masticatory margins separated by a rounded angle; masticatory margin concave, bearing minute denticles; external margin of mandibles convex; dorsal surface with scattered piligerous punctures and short setae. Palp formula 2,2 (count in situ). Antennal scape short and clavate, about one-third of the total length of head, covered by evenly distributed piligerous punctures; first funicular joint incrassate, slightly longer than the second; apical segment about twice as long as the preceding segment.

Mesosoma subrectangular. Pronotum with the promesonotal suture conspicuous, complete and flexible. Metanotal groove not impressed. Posterior face of propodeum relatively short, meeting the dorsal face in a rounded and unarmed angle. Flange over the metapleural gland opening sharply pointed posteriorly. Tibiae enlarged apically; mid tibia with one simple and hind tibia with one pectinate spur.

Petiole slightly longer than broad; anterior face slightly concave in lateral view; in dorsal view, lateral margins straight; petiolar spiracle small and inconspicuous, set near the anterior rim of tergite subpetiolar process with an acute, anteriorly projecting tooth. Postpetiole relatively large, as long as the petiole, subquadrate in lateral view; anterior face concave medially and straight posteriorly, in dorsal view lateral margins diverging posterad; sternite spiracle set anteriorly on the tergite.

Abdominal segments IV, V and VI similar in length; abdominal segments III and IV broader than long in dorsal view.

Type Material
Holotype worker BRAZIL, SP, Santo André, Paranapiacaba, Reserva Biológica do Alto da Serra de Paranapiacaba, 23°46’18’’S, 46°20’24’’ W, 800 m above sea level, Atlantic Forest, 12 January 2007; Uehara-Prado M. col.; Pitfall trap #K4; []. Paratype workers Thirty-two point-mounted specimens with the same data as the holotype, [MZSP (26), ZUEC (2), (1),  (1),  (1),  (1)].

Etymology
The type series was collected in a locality in the Atlantic Forest biome, and hence its name.

References based on Global Ant Biodiversity Informatics

 * Silva R. R., R. M. Feitosa, C. R. F. Brandao, and V. L. Freitas. 2013. The first Leptanilloides species (Hymenoptera: Formicidae: Leptanilloidinae) from eastern South America. Journal of Natural History http://dx.doi.org/10.1080/00222933.2012.763058