Distribution and Diversity of the Cryptic Ant Genus Oxyepoecus (Hymenoptera: Formicidae: Myrmicinae) in Paraguay with Descriptions of Two New Species

1 Biological Evaluation Section, Royal Belgian Institute of Natural Sciences, 29 street Vautier, 1000 Brussels, Belgium 2 Laboratory for Environmental Biology, The University of Texas, El Paso, TX 79968, USA 3 Department of Entomology, University of Illinois, 505 South Goodwin Avenue, Urbana, IL 61801, USA 4 Department of Evolutionary Biology and Ecology, Université Libre de Bruxelles, 50 Avenue Roosevelt, 1050 Brussels, Belgium

The genus is differentiated from other Solenopsidini by the 11-segmented antennae with a three-segmented apical club, the clypeus with four teeth, and the dentate propodeum [3]. In addition, the petiole and postpetiole nodes are high and often anteroposteriorly compressed [3].
The biology of the genus is poorly known, but three species (O. inquilinus [11], O. daguerrei [12], and O. bruchi [1]) are suspected to be inquilines of Pheidole or Solenopsis [1,7,11], although the exact nature of the relationship is unclear [3]. These three species are considered as "Vulnerable D2" [13], meaning they are suspected to be "facing a high risk of extinction in the wild in the medium-term future" because "their populations are characterized by an acute restriction in their area of occupancy (typically less than 100 km 2 ) or in the number of locations (typically fewer than five)." Due to the current rapid loss of biodiversity and uncertainty concerning the conservation status of social insects [14], data to increase our knowledge of threatened species are desperately needed.
Here, we report Oxyepoecus inquilinus for the first time from Paraguay and provide new distribution data for O. vezenyii and O. rastratus. Two new species are described.

Materials and Methods
The sampling of ant assemblages in the Chaco region of Paraguay was based on 560 Winkler and 720 pitfall samples collected between 2001 and 2004 in 11 localities along a 410 km transect beginning at Río Verde and ending at Fortín Mister Long close to the Bolivian border ( Figure 1) [15,16]. Sampling was always carried out at the end of the dry season (September-November). For Winkler extractions, the leaf litter present inside a one m 2 quadrat was collected and sifted Psyche and its fauna was extracted for 24 h. Pitfall traps consisted of 70 mm diameter drinking cups, containing water and a drop of detergent, operating for at least 24 hours. Vegetation corresponds to relatively well-preserved xeromorphic forests [17]. Elevation, mean annual rainfall and temperature, mean maximal temperature of the warmest month, and mean minimal temperature of the coldest month are provided for each locality [16].
Specimens from the Paraguayan oriental region were collected following previous techniques [10]. Data were supplemented by the examination of existing museum material [10]. Finally, data from the literature and the online specimen database http://www.antweb.org/ were added in order to provide a complete overview of the diversity and distribution of Oxyepoecus in Paraguay.

Measurements and Indices
All measurements are in millimeters. The abbreviations are as follows.
TL: Total length from the anterior margin of the head (in vertical position) to the posterior edge of the gaster measured in lateral view.
HL: Head length, measured in full face view, from the anterior margin of the medial lobe of the clypeus to the posterior border of the head (excluding the mandibles).
HW: Head width, the maximum width of the head measured in full face view, excluding the eyes.
EL: Eye length, the maximum diameter of eye.
PL: Petiole length, the maximum length of the node measured in dorsal view, starting at the base of the anterior face and ending at the base of the posterior edge.
PW: Petiole width, the maximum width of the node measured in dorsal view.
PPL: Postpetiole length, the maximum length of the node measured in dorsal view, as above.
PPW: Postpetiole width, the maximum width of the node measured in dorsal view.
WL: Weber's length, measured from the anterior edge of the pronotum to the posterior edge of the metapleural lobe.
The terminology is based on [18]. Holotypes, paratypes, and voucher specimens have been deposited at the Royal Belgian Institute of Natural Sciences, Brussels, Belgium, (RBINS), the University of Texas at El Paso (CWEM), the Alexander L. Wild

Results
The following species of Oxyepoecus were collected in Paraguay ( Figure 1).
Diagnosis. Its worker morphology places this species within the rastratus species-group [4]. The reticulate-costulate dorsal surface of the head (Figures 2(a) and 2(d)) and the well-defined subpostpetiolar process, forming a pair of prominent blunt teeth (Figure 3 Lateral clypeal teeth are well developed, directed anteriorly; eye small, about 16-18 ommatidia, five ommatidia in greatest diameter; scape in repose failing to reach posterior border of head by about two maximum widths; sides of head nearly straight, parallel; frontovertexal margin slightly convex; pronotal shoulder gently angulate, marked with striae; notopropodeal (=metanotal) groove indistinct; propodeal angles developed, with two medium-sized acute teeth; subpetiolar process well-developed, lobe-like, directed ventrally; subpostpetiolar process well-developed, forming pair of blunt teeth, directed ventrally; nodes of petiole and postpetiole high and dorsally rounded, compressed anteroposteriorly; in lateral view, petiolar node higher than postpetiolar node; as seen from above, postpetiole much broader than petiole.

Body Color. Concolorous Reddish Brown.
Etymology. From Latin, bidens, referring to the subpostpetiolar process forming a pair of well-defined teeth. Distribution. Oxyepoecus bidentatus was found in three localities of the Paraguayan dry Chaco ( Figure 1). Because the maximal distance between localities was 340 km, O. bidentatus is suspected to be widely distributed in xeromorphic Chacoan forests, even if rarely found.  no gynes were found, suggests that this species nests in the soil, but workers forage in the leaf litter when abiotic conditions are favorable. Localities where the species was found have a mean annual rainfall and temperature ranging from 593 to 887 mm and from 23 to 25 • C, respectively [16]. [1]. Paraguay: Central: San Lorenzo, Lat: S 25.33, Long: W 57.55, 4.X.1979, Vaucher C., one worker, specimen code CASENT0178098, ALWC. The specimen has been imaged and is available on AntWeb (http://www.antweb.org/). [11] [7]. Paraguay: Itapúa: Santa María, no specific location information, 25.X.1982, Baud F., three workers, ALWC, one worker has been imaged and is available on AntWeb (http://www.antweb.org/), specimen number CASENT0178101. Mandible with four teeth, with diastema (gap) between basal and subbasal teeth; lateral clypeal teeth well-developed but small, not lobe-like, directed anteriorly; eye small, with about 18 ommatidia, five ommatidia in greatest diameter; scape in repose failing to reach posterior border of head by about two maximum widths; sides of head nearly straight, parallel, frontovertexal margin slightly convex; pronotal shoulder slightly marked with stria; inferior pronotal process well developed; notopropodeal groove poorly developed; propodeal angles developed, acute; subpetiolar process well developed, lobe-like, directed ventrally, anterior and posterior faces of petiole nearly parallel; two subpostpetiolar angles present, anterior and posterior faces of postpetiole nearly parallel; as seen from above, postpetiole much broader than petiole, postpetiole slightly angulate laterally.
Mandibles smooth and shiny, with few scattered punctures, most of dorsum of head with scattered coarse punctures, medial area smooth and glossy, mesonotum with longitudinal parallel striae, dorsopropodeum with fine transverse striae, lateropronotum mostly smooth and glossy, mesopleuron and lateropropodeum striolate, nodes of petiole and postpetiole smooth and glossy, posterior face of postpetiole transversely striolate, gaster smooth and glossy.    Comparison. This species is a member of the vezenyii species-group [3] defined principally in having a predominantly smooth and glossy dorsum of the head. It is very similar to the relatively common O. vezenyii, but can be easily distinguished as the promesonotum of O. vezenyii is nearly completely smooth and glossy (the dorsopropodeum of O. vezenyii has transverse striae as in O. striatus).
Oxyepoecus striatus appears most similar to O. browni, which has a similar sculptured promesonotum, short posterior propodeal face, moderately well-developed costulae between the frontal carinae, and a large lobe-like subpetiolar process. Oxyepoecus striatus can be separated as being smaller; the clypeal teeth are well defined, sharp, and directed anteriorly (not lobe-like and directed inward). The frontal lobes are more widely spaced than those of O. browni (separated by 0.11 mm) and the head is covered by coarse punctures (except for the smooth medial area).
Biology. The specimens were collected in three separate pitfall samples. The mean annual rainfall and temperature of the locality where the species was found were 887 mm and 23 • C, respectively [16]. [10]. In addition, the type specimen (worker) was collected in Paraguay (Concepción: Puerto Max Forel) [9].

Discussion
Seven Oxyepoecus species are recorded from Paraguay. Two of them are new species described in this paper: O. bidentatus and O. striatus from the rastratus and vezenyii speciesgroups, respectively. These species-groups now include eight and 12 species, respectively. Oxyepoecus bidentatus was found in three localities, 20 to 340 km away from each other, indicating that this species may be widely distributed within the Paraguayan dry Chaco. Oxyepoecus striatus is only known from the type locality.
Oxyepoecus rastratus was documented from South and South-East Brazil and from Eastern Paraguay [4]. Its presence at T. Enciso N.P. increases its range nearly 700 km to the West. In addition, samples in the dry Chaco and in the Paraná forest suggests that this species may be present in a variety of biomes.
Oxyepoecus reticulatus has been recorded in a dozen localities in South and Southeastern Brazil, mainly in relatively dry forests [4]. The Paraguayan data increase its distribution by nearly 360 km to the West.
Oxyepoecus bruchi was collected in 1948 and 1953 in Argentina (Córdoba and Tucumán provinces) and more recently (2003) in Brazil (Palhoça, Santa Catarina State) [3,4,7]. Only one specimen was collected in 1979 in Paraguay (Central). Although the species was rarely collected, its distribution seems potentially large. Nevertheless, O. bruchi appears locally rare, justifying its vulnerable status [13]. This species is suspected to be an inquiline of the ants Pheidole rosae (named Ph. silvestrii in [7]) and Ph. obtusopilosa [1,7,11], but these species were not present in our samples and, to our knowledge, have not been collected in Paraguay [10].
Oxyepoecus inquilinus was sampled in two localities of the Paraguayan dry Chaco. In the literature, O. inquilinus was reported from two savanna localities of the Brazilian Cerrado [7], one Brazilian pasture [4], one anthropogenic area (i.e., the "Jardin del Instituto Miguel Lillo") from the Argentinean Tucumán province [11], and one locality in the Bolivian Bení Department [7]. In addition, one worker closely related to O. inquilinus was collected in a savannamorichal habitat from Colombia, but its specific status awaits further investigation [2]. Finally, O. inquilinus was recently sampled in a Valdivian forest of Chile [5]. If the identity of the Colombian specimen is confirmed, O. inquilinus is the most broadly distributed species of the genus. In fact, its Colombian and Chilean localities represent both the northernmost and southernmost limits of distribution for the entire genus. Although data are insufficient to determine the exact requirements of this species, O. inquilinus seems to be present both in open and closed habitats, in degraded and pristine ecosystems, and in dry and wet areas. The distribution of this species seems large but discontinuous, and O. inquilinus is apparently locally rare, justifying its vulnerable status [13]. O. inquilinus is suspected to be inquiline in Pheidole radozskowskii nests [11]. At T. Enciso N.P., the same Winkler sample collected two workers of O. inquilinus and 11 workers of Ph. radozskowskii. However, at Nueva Asunción the latter was not recorded in our 60 Winkler and 60 pitfall samples, suggesting that O. inquilinus is not restricted to this host species.
With the exception of the Paraguayan type specimen [9], Oxyepoecus vezenyii is exclusively known from Brazil where it was sampled in different ecosystems over a large spatial scale [3,4]. The presence of this species in the Paraguayan dry Chaco increases its range nearly 400 km to the West.
In this study, Oxyepoecus individuals were mainly collected using the Winkler extraction method. This technique is highly effective for sampling minute and cryptic ant species which were previously suspected to be rare before the development of the method [20,21]. This may be the case for Oxyepoecus species [3]. Nevertheless, in dry forests the Winkler sampling is strongly influenced by the rainfall regime, and a recent rainfall may increase its efficiency both in terms of species collected and species occurrences [15]. Teniente Enciso National Park was the single locality of the dry Chaco sampled a day after a rainfall. This bias may be the reason why a relatively large number of Oxyepoecus species and individuals were collected in this park and just a few in the other dry Chacoan localities. We hypothesize that using the Winkler method during the rainy season of the Paraguayan dry Chaco (December-April) [22] will increase the probability of collecting Oxyepoecus.
Oxyepoecus ants appear diversified and well established at Teniente Enciso National Park, where 58 individuals Psyche representing four species were collected during a single sampling session (03-05.XI.2001). This locality may hence constitute a promising reference site to undertake studies concerning these poorly known myrmicinae. Moreover, the presence of O. inquilinus at T. Enciso N.P. emphasizes the biological conservation importance of this park.