A new species of the ant genus Bothriomyrmex Emery , 1869 ( Hymenoptera : Formicidae ) from the Caribbean region

Abstract. Bothriomyrmex enigmaticus sp. nov. is described from the island of Hispañola based on one nest collection. this is the first collection of the genus Bothriomyrmex (Emery, 1869) from the Caribbean region, and the second species to be described from the Americas. While sharing several characters with B. paradoxus (Dubovikoff & Longino, 2004) from Costa Rica and Honduras, B. enigmaticus sp. nov. diverges in several key characters, including palp formula. However, a morphometric comparison to Palearctic species of the tribe bothriomyrmecini suggests affinities to B. paradoxus, Chronoxenus wroughtoni (Forel, 1895) of the eastern Palearctic, and to a lesser extent an undescribed species of Arnoldius (Dubovikoff, 2005) from Australia and B. corsicus (Santschi,1923) of the western Palearctic.


Introduction
Bothriomyrmex (Emery, 1869), with 23 described species (Bolton, 2014), is a small genus of ants in the subfamily Dolichoderinae (Forel, 1878).With an unusual distribution, encompassing the Palearctic and Neotropic regions, Bothriomyrmex has been collected in a broad range of habitats, including grassland, savannah, lowland tropical moist forest and cloud forest.Nests typically occur in the soil, under rocks or in rotten wood.While little is known about the diet of many species, Santschi (1919) noted that Bothriomyrmex preferred a diet of sugar water, and observed a nest of B. crosi (Santschi, 1919) with nymphs of Tettigometra (Latreille, 1804), suggesting trophobiosis as one source of nutrition.Other details of the life history of many species remain obscure, but Forel (1873) was the first to observe a mixed colony of B. meridionalis (Roger, 1863) and Tapinoma erraticum (Latreille, 1798) in Switzerland.Later, in North Africa, Santschi (1906) observed that newly mated queens of Bothriomyrmex invade colonies of Tapinoma and usurp their nests by decapitating the queen over the course of several days, suggesting that at least in some cases Bothriomyrmex is a temporary social parasite.Due to the peculiar mandibular morphology of all known gynes in this genus, Seifert (2012) asserted that all species of Bothriomyrmex are temporary social parasites, with nest founding strategies similar to the one observed by Santschi.A study by Lloyd et al. (1986) suggested that the anal gland secretions of B. syrius (Forel, 1910) gynes facilitate their entrance into host nests, via chemical mimicry of the Tapinoma colony odor.
In 2004, a new species of Bothriomyrmex, B. paradoxus (Dubovikoff & Longino, 2004), was described from material collected in Costa Rica; further collections were made in mesophyll forest in Honduras during the 2010 Leaf Litter Arthropods of Meso-America (LLAMA) expedition.Prior to this, this genus was considered to be geographically restricted to the Palearctic, Oriental and Australian regions.Recently, Bothriomyrmex was separated into 3 geographically graded genera based on palp formula and gyne wing venation (see Table 1): Bothriomyrmex s.s., with 23 described species from the Palearctic region; Chronoxenus (Santschi, 1919), with 6 described species from the Oriental region; and Arnoldius (Dubovikoff, 2005), with 3 species from the Australian region (Dubovikoff 2005).Bothriomyrmex paradoxus, with palp formula 4,3 and a closed discoidal cell, is thought to be a member of Bothriomyrmex s.s.: indeed, a 2010 study in which the molecular phylogeny of the subfamily Dolichoderinae was estimated provided additional evidence for this argument (Ward et al. 2010, see Fig. 1).
In this article we describe a second species of Bothriomyrmex from the Americas.This species was found on the the island of Hispañola, marking the first record of this genus in the Caribbean region.Additionally, we utilize a morphometric dataset developed by Seifert (2012) in an effort to develop a hypothesis that could explain the disjunct distribution of this genus.

Abbreviations of depositories
The material upon which this study is based is located and/or was examined at the following institutions: the type material of the new species and all imaged specimens are uniquely identified with specimen-level codes affixed to each pin (e.g.CaseNt0636109).Digital color images and measurements were taken using a Leica MZ 12.5 stereo microscope equipped with a JVC KY-F75 digital camera and Syncroscopy Auto-Montage software (version 5.0).All images were taken by the authors, except where indicated.
The images and specimen data presented are available online and can be viewed on AntWeb (www.antweb.org).Measurements and indices are presented as minimum and maximum values, expressed in mm to three decimal places, with arithmetic means in parentheses.The following measurements are derived from those used by Seifert (2012) and Dubovikoff & Longino (2004).= F2 divided by the maximum width of second funicular segment (excluding pubescence) in dorsal view MGr = Depth of metanotal groove/depression in profile view; the upper reference line extends between the highest points of mesonotum and propodeum perpendicular to which depth measuring is performed.Use of transmitted light ensures the most accuracy MW = Pronotal width: maximum width of pronotum measured in dorsal view PoOc = Postocular distance: distance from the transverse level of posterior eye margin to hind margin of head, measured medially PH = Petiole height: maximum height of the petiole in profile view, including protruding lobe on the ventral margin PrL = Propodeal length: distance from most caudal point of posterior propodeum (a dentiform paramedian structure on both sides of petiolar junction) to hind the margin of the metanotal groove SL = Scape length: maximum antennal scape length excluding basal condyle and neck WL = Weber's length: the diagonal length of the mesosoma in profile from the point at which the pronotum meets the cervical shield to the posterior basal angle of the metapleuron

Measurements
The varying degree of inclination of pubescence and pilosity is often of high diagnostic value throughout a broad spectrum of ant genera.In this context we use the terms "erect", "suberect", "subdecumbent", "decumbent", and "appressed" following the usage in Wilson (1955).

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.Palp formula 2,3; distal maxillary palp segment roughly twice as long as basal (Fig. 2d).Medial hypostoma absent (Fig. 2e).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: 0.10-0.11mm 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.

Type
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.

PREBUS M. & LUBERTAZZI D., Caribbean Bothriomyrmex
Petiolar node in profile scale-like and strongly inclined anteriorly, with the anterior face much shorter than the posterior face (Fig. 2c).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.

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.

Discussion
this is the first record of Bothriomyrmex from the Caribbean region, and the second species to be described from the Americas.Until very recently, this genus was considered to be limited strictly to the Palearctic region.An estimation of the phylogeny, biogeography and divergence times of the Dolichoderinae (Ward et al. 2010) suggested that the split between B. paradoxus and the Palearctic species, B. saundersi (Santschi, 1922), occurred between 5 and 15 mya, excluding a simple explanation of vicariance by continental drift.One hypothesis that could reconcile the current distribution and phylogeny of this group is that characters such as short antennal scapes, compact propodeum and deep metanotal groove are plesiomorphic to (Bothriomyrmex + Chronoxenus + Arnoldius), while having large eyes is a trait that is plesiomorphic to (Chronoxenus + Bothriomyrmex), which have subsequently become reduced in some species.If this is the case, the most plausible explanation for the current distribution is that Bothriomyrmex was once much more broadly distributed in the Americas, and went extinct in the Nearctic part of its range in recent times.

Table 1 .
Dubovikoff (2005)acters separating three closely related genera in the tribe Bothriomyrmecini, based onDubovikoff (2005).*2,3 in Bothriomyrmex enigmaticus sp.nov.(thisstudy).PREBUS M. & LUBERTAZZI D., Caribbean Bothriomyrmexirrespective of the pigmentation status, measured in oblique lateral view EW = Eye width: minimum diameter of compound eye including all structurally visible ommatidia irrespective of the pigmentation status, measured in oblique lateral view EYE = Eye size: arithmetic mean of EL and EW F2 = Median length of 2 nd funicular segment in dorsal view; take care to measure median length because of unequal length of the segments' sides.Use the highest optical resolution available IF2