Bothriomyrmex enigmaticus, Matthew Prebus & David Lubertazzi, 2016

Matthew Prebus & David Lubertazzi, 2016, A new species of the ant genus Bothriomyrmex Emery, 1869 (Hymenoptera: Formicidae) from the Caribbean region, European Journal of Taxonomy 211, pp. 1-12 : 4-9

Bothriomyrmex enigmaticus sp. nov.

urn:lsid:zoobank.org:act:A78CBE68-03A8-4A17-A0A7-44C76AC166F8

Figs 2 b–e, 3–4

Diagnosis

The following character combination distinguishes Bothriomyrmex enigmaticus sp. nov. from B. paradoxus : palp formula 2,3; medial lobe of clypeus not strongly projecting: flat, or with a broad, shallow concavity anteriorly. Long, paired setae on medial clypeal lobe separated by ⅔ their length or more. Eyes large: OI 23.1–24.7. Head box-like, with occipital corners narrowly rounded.

Etymology

The specific epithet is derived from the ancient Greek “αινιγματικός”, meaning “riddle”, and bears a double entendre: not only is this the second species in this genus with a paradoxical distribution, this species also presents a puzzling new perspective on the generic classification system of the tribe Bothriomyrmecini .

Type material examined

Holotype worker

DOMINICAN REPUBLIC: Provincia Maria Trinidad Sanchez, 7 km WSW El Factor , 19.29776° N, 69.94977° W ± 3 m, 195 m ± 5 m, 21 Jul. 2015, disturbed broadleaf moist forest, nest in dead top of live tree, M.M. Prebus # MMP01990 [ MCZ-ENT00035850 ].

Paratypes

DOMINICAN REPUBLIC: Provincia Maria Trinidad Sanchez, 9 workers, same collection as holotype [ CAS: CASENT0756066; INBio: CASENT0756067; LACM: CASENT0756068; MCZ: MCZ- ENT 00539146 , MCZ-ENT00539147; MNHNSD: MNHNSD 18.106 ; UCDC: CASENT0756071; USNM: CASENT0756072; ZIN: CASENT0755363].

Worker description

Measurements (n=11): CL 0.541–0.563 (0.554); ClyW 0.375–0.412 (0.395); CS 0.520–0.542 (0.531); CW 0.495–0.523 (0.508); dAN 0.181–0.215 (0.197); EL 0.124–0.137 (0.132); EW 0.096–0.109 (0.105); EYE 0.112–0.122 (0.118); F2W 0.062–0.070 (0.065); IF2 1.000–1.222 (1.117); MGr 0.019–0.030 (0.024); MW 0.318–0.357 (0.343); PoOC 0.251–0.274 (0.260); PH 0.214–0.250 (0.231); PrL 0.264– 0.296 (0.282); SL 0.407–0.434 (0.424); WL 0.572–0.617 (0.600).

Palp formula 2,3; distal maxillary palp segment roughly twice as long as basal ( Fig. 2 d). Medial hypostoma absent ( Fig. 2 e). Masticatory margin of mandible with 6 teeth and 1–2 denticles. Mandibles with short, curved setae similar to those on the anterior clypeal margin. Clypeus narrow: 0.10–0.11 mm high medially. Anterior clypeal margin flat, or with a broad, shallow concavity; bearing many short, curved setae; one long seta on each side of concavity, their bases separated by the length of the setae or more. Medial lobe of clypeus not strongly projecting. Posterior margin of clypeus even with anterior surfaces of antennal socket cavities. Antennal scapes short, not reaching the posterior margin of the head in full face view. Head slightly oblong (CL/CW 1.069–1.108), with lateral margins evenly convex; widest part of head in full-face view posterior to the compound eyes. Posterior head margin flat, becoming slightly concave medially; corners of head narrowly rounded, giving the entire head a blocky appearance. Head with two long setae on frons (longer than the first funicular segment) and two shorter setae on posterior clypeal margin (shorter than the first funicular segment), otherwise covered uniformly with short, dense, decumbant pubescence. Eyes large (EYE/CS 0.214–0.229), 8 ommatidia in longest row.

Posteroventral pronotum margin narrowly rounded. Metanotal groove deeply impressed. Propodeum high and rounded, with declivitous face roughly twice as long as dorsal face in profile; propodeal angle indistinct. Mesosoma covered uniformly with short, dense, decumbent pubescence.

Petiolar node in profile scale-like and strongly inclined anteriorly, with the anterior face much shorter than the posterior face ( Fig. 2 c). Ventral margin of petiole with a large lobe. Several setae present on the posteroventral margin of lobe.

Second, third and fourth tergites of gaster with long, erect setae arising from the middle of the tergite: two on the second, six on the third and fourth. First four sternites of gaster also bearing two long setae similar to those found on the tergites. Pubescence similar to the rest of the body, but becoming longer on the posterior margins of the sclerites.

Uniformly light brown; coxae and legs somewhat lighter.

Larva description

Shape dolichoderoid. Body with two ventrolateral protuberances on prothorax which are fused ventrally by a narrow ridge; setae very short and limited to the prothorax; 8 pairs of spiracles. ( Fig. 4).

Key to Neotropical Bothriomyrmex species based on workers

1. Palp formula 4,3 (see fig. 3d in Dubovikoff & Longino 2004); medial lobe of clypeus strongly projecting beyond the lateral lobes; anterior margin evenly rounded to flat, never concave medially; paired long setae on anterior margin of medial lobe separated by less than ⅔ of their length ( Fig. 2 a) ……………………………………………………… B. paradoxus ( Dubovikoff & Longino, 2004)

– Palp formula 2,3 ( Fig. 2 d); medial lobe of clypeus weakly projecting; anterior margin flat to broadly concave medially; paired long setae on anterior margin of medial lobe separated by ⅔ of their length or more ( Fig. 2 b) ……………………………………………… B. enigmaticus sp. nov.

Distribution and ecology

Bothriomyrmex enigmaticus sp. nov. is known from one collection on the north side of the island of Hispañola ( Fig. 5 ). The sampling took place in July 2015 during a Museum of Comparative Zoology expedition to the Dominican Republic. The new ant species was discovered while based at a guardhouse in the Toro Palomo sector on the SE side of the Loma Guaconejo Scientific Reserve, near the village of La Peonía, at 195 m in elevation. M. Prebus collected a partial nest containing workers and brood from decomposing wood at the top of a 1.5 m tall live sapling in the middle of a path leading west from the guardhouse. The habitat was scrubby secondary growth, roughly 100 meters from a more mature secondary lowland moist forest. Tapinoma litorale (Wheeler, 1905) was abundant in this habitat; due to the superficial similarity of these two species, Bothriomyrmex enigmaticus sp. nov. was mistaken for T. litorale in the field. The nest was not mixed; it consisted solely of B. enigmatus .

Taxonomic notes

Dubovikoff & Longino (2004) came to the conclusion that Bothriomyrmex paradoxus is a member of the Palearctic Bothriomyrmex s.s. based on palp formula and wing venation. They also noted that it doesn’t fit perfectly into species groups in this region: a deeply impressed metanotal groove is found in the B. gibbus (Soudek, 1925) group, but the gyne of B. paradoxus also has short, suberect setae on the mesosoma and gaster, which is typical of the B. syrius (Forel, 1910) group. With its large eyes, deep metanotal groove, and nesting preference, B. enigmaticus sp. nov. appears to be closely related to B. paradoxus . However, it diverges from the latter in several characters, most notably palp formula. Referring to Shattuck (1992), it appears that a palp formula of 6,4 is probably pleisiomorphic in the Dolichoderinae . Within the tribe Bothriomyrmecini there is a trend in palp reduction in Arnoldius , Bothriomyrmex and Chronoxenus ( Table 1 ) that becomes apparent when they are compared with Loweriella ( Shattuck, 1992) and Ravavy (Fisher, 2009) , which have palp formula 6,4 and 6,3. It is possible that a palp formula of 4,3 is plesiomorphic in the clade of ( Bothriomyrmex + Chronoxenus + Arnoldius ), with the latter two genera having undergone subsequent reductions. Within other genera of the Dolichoderinae , e.g., Technomyrmex (Mayr, 1872) and Azteca (Forel, 1878) , palp formula can be highly variable, making generic diagnoses based on this character alone problematic. While the reproductives (and therefore the wing venation) of B. enigmaticus sp. nov. remain unknown, if the worker were to be classified based on the current generic diagnoses, one might be inclined to place it in Chronoxenus based solely on palp formula. However, the similarities between B. enigmaticus sp. nov. and B. paradoxus mentioned above are striking, suggesting that these two species are sister taxa and palp formula is a labile character.

Figures

Fig. 2. Clypeal structure. a. Bothriomyrmex paradoxus (Dubovikoff & Longino, 2004) (JTLC 000003511). b. B. enigmaticus sp. nov. (MCZ-ENT 00035850); arrows indicate the insertion points of long setae on anterior clypeal margin. c. Petiole. d. Mouthpart dissection. e. Ventral view of head capsule of B. enigmaticus sp. nov. (MCZ-ENT 00035850). Photo credit for 2 a: Michael Branstetter. All scale bars represent 0.2 mm.

Fig. 5. Known distribution of Bothriomyrmex paradoxus (Dubovikoff & Longino, 2004) and B. enigmaticus sp. nov.