Gracilidris pombero Wild, 2006

Wild, A. L. & Cuezzo, F., 2006, Rediscovery of a fossil dolichoderine ant lineage (Hymenoptera: Formicidae: Dolichoderinae) and a description of a new genus from South America., Zootaxa 1142, pp. 57-68 : 62-66

Gracilidris pombero Wild & Cuezzo, sp. nov.

(worker Figs. 1-8, 10; nest Fig. 9; distribution Fig. 11)

Type material examined

Holotype. Worker. Paraguay, Pte. Hayes: 5k SE Pozo Colorado . 140m. 23°33.129' S 58°45.853' W, 5. xii.2002, A.L. Wild acc. no. #1766 ( IBNP).

Paratypes. Series of 20 workers, same data as holotype, acc. nos. #1734 , 1736 , 1766 ( ALWC, BMNH, CASC, IFML, LACM, MCZC, MHNG, MZSP, UCDC, USNM).

Additional material examined

Argentina: Santiago del Estero: Copo National Parq . (5w, IFML). Brazil: Bahia: Ilheus , CEPEC, specimen not directly examined, ( photographic internet record, #4830 : http:// research.amnh.org/entomology/social_insects/tempcepecline.html, available in 2002 and apparently offline as of August 2005). Maranhao: Balsas , Gerais de Balsas 08°34' S 46°42.6' W xi.1999-iii.2000, Brandao et al (2w, MZSP). Mato Grosso: Mpio. Varzea Grande, Souza Lima , 25.i.1985, J. C. Trager (3w, MZSP). Sao Paulo: Agudos , xii.1957, C. Gilbert (2w, MZSP).

Worker measurements

Holotype: HL 0.87, HW 0.67, SL 0.94, FL 0.87, LHT 0.95, PW 0.53, WL 1.28, OI 5.4, SI 141, CI 76.

Others (n = 14): HL 0.80-0.93, HW 0.62-0.71, SL 0.89-1.08, FL 0.72-0.99, LHT 0.89-1.14, PW 0.47-0.57, WL 1.16-1.46, OI 4.0-6.9, SI 138-154, CI 76-81.

Worker description

As given in the generic description, but with the following additional details: Head in full frontal view longer than broad (CI 76-81) and quadrate-oval in shape. Lateral margins evenly convex and the head no wider posterior to than anterior to the eyes. Compound eyes large (OI 4.0-6.9), consisting of 130-150 ommatidia, situated near the longitudinal midpoint of the head in full frontal view. Anterior clypeal margin usually bearing a single straight, short, forward-projecting median seta, a longer pair of setae just lateral of the midline that are about half the length of the masticatory margin of the mandibles, and an irregular number (2-6) of small setae lateral to these (Fig. 6).

Mandibular dentition variable but usually as follows: strong apical tooth, a smaller subapical tooth, a small third tooth, a strong fourth tooth, and the remaining 3 teeth small, spaced more or less evenly along the masticatory margin and separated from each other by 1-3 denticles. Basal angle of the mandible indistinct and bearing 2-4 denticles.

Dorsal surfaces of ant head, mesosoma, and metasoma devoid of erect setae, except abdominal segment 6 which bears a pair of setae oriented posteriorad. Entire surface of body including legs, antennal scapes, and the proximal half of the mandibles covered in a dense, fine pubescence. Pubescence also contains fine appressed hairs twice as long as the adjacent hairs, and evenly spaced about as far apart as their length over the body and appendages (Fig. 8). These can be difficult to see without the correct lighting, and are most visible on the gaster. Ventral surfaces of the mesosoma, coxae, and metasoma with a few erect setae. Integument shagreened, ant appearing dull to lightly shining but never opaque.

Color varying from body and appendages dark brown (Paraguay, Bahia, Maranhao), to head and gaster light brown with the mesosoma and petiole testaceous (Sao Paulo, Mato Grosso). Trochanters, tarsi and ventrum of petiole lighter than body, light brown to almost white.

Discussion

Body proportions and color vary geographically among populations of G. pombero . In particular, specimens from Paraguay and Argentina are darker and have relatively shorter appendages than Brazilian specimens. Given that this variation is allopatric, however, and given the limited material available for study, we feel it is preferable to place all forms within a single species until more material becomes available.

Biology

In the two collection series where nesting information was noted (the Paraguayan type series and the Mato Grosso series), colonies were in soil with the nest entrance consisting of a small earthen turret. The turret of the type series nest in Paraguay was only a few millimeters tall and opened at ground level on one side (Fig. 9), so that the nest entrance was cryptic and concealed from above. There appeared to be only one nest entrance. A low level of activity at the entrance of the type series nest and the small number of workers (n = 25) collected during a partial nest excavation suggests a small colony size.

The collection records of G. pombero indicate that it inhabits low scrub forests of the type found in cerrado and chaco habitats. The specimens from Maranhao were collected at a sardine bait in cerrado scrub forest near the edge of a soybean field. The specimen from Bahia, Brazil was collected in a small primary forest fragment in a Cocoa plantation. The Mato Grosso, Brazil collection was from grazed cerrado, and the Paraguayan type series came from a lightly grazed Copernicia alba palm forest in the humid chaco.

Gracilidris ants are probably noctural, which may partly explain their rarity in collections. At the type locality, single foraging workers were collected at dusk and after dark on two separate nights, and visual searches and baits during the day at the same location did not yield any workers. In the field, workers appear elongate, their gaster held horizontally (Fig. 10), and their movements are smooth and deliberate.

Reproductive castes, brood, colony structure, and life history are unknown.

Etymology

Pombero is a mythical nocturnal figure in Guarani folklore. The name is applied here as a noun in apposition in reference to the nocturnal activity pattern of this species.