Cryptopone Emery, 1893

Schmidt, C. A. & Shattuck, S. O., 2014, The Higher Classification of the Ant Subfamily Ponerinae (Hymenoptera: Formicidae), with a Review of Ponerine Ecology and Behavior, Zootaxa 3817 (1), pp. 1-242 : 182-185

Cryptopone Emery

Fig. 42

Cryptopone Emery, 1893a : cclxxv (as genus). Type-species: Cryptopone testacea Emery, 1893a : cclxxv; by monotypy. Gen. rev.

Wadeura Weber, 1939: 102 (as genus). Type-species: Wadeura guianensis Weber, 1939: 103 ; by original designation. Wadeura as junior synonym of Cryptopone . Syn. nov.

Cryptopone is a moderately large genus (25 described species and subspecies) with a cosmopolitan distribution, though the species diversity is centered in Asia. Cryptopone workers are well-adapted to a hypogeic lifestyle, with small body size, reduced or absent eyes, flattened scapes, and traction setae on the mesotibiae.

Diagnosis. Cryptopone workers lack any obvious autapomorphic characters, but can be identified by the following characters (in combination): mandibles usually with a basal pit or fovea (absent in members of the former genus Wadeura , here newly synonymized with Cryptopone ), frontal lobes small and closely approximated, scapes flattened, eyes vestigial to absent, propodeum with a distinct dorsal face which widens posteriorly, metabasitarsus with simple setae but lacking spiniform or peg-like traction setae, and mesotibiae with stout traction setae (sometimes small and reduced to a few, but always present). Workers of Cryptopone most closely resemble those of Pseudoponera (a close relative of Cryptopone ), but differ most consistently in the presence of mesotibial traction setae. Similar traction setae occur in Centromyrmex , Feroponera , Promyopias , and Buniapone , but these genera all lack at least some portion of the diagnosis given above. Several other ponerine genera have basal mandibular pits, including Brachyponera , Euponera , and Hagensia , but these genera all lack mesotibial traction setae and have larger eyes, among many other differences.

Synoptic description. Worker. Very small to medium sized (TL 1.7–6.1 mm) ants with the standard characters of Ponerini . Mandibles triangular to subfalcate, usually with a small basal pit (absent in “ Wadeura ”) and without a basal groove. Anterior margin of clypeus broadly convex. Frontal lobes small and closely approximated. Scapes flattened. Apical segments of antennal funiculus often distinctly clubbed. Eyes greatly reduced or absent (in ” Wadeura ”). Metanotal groove reduced to a suture. Propodeum with a distinct dorsal face which widens posteriorly. Propodeal spiracles round to ovoid. Mesotibiae armed with stout traction setae. Metatibial spur formula (1p) or (1p, 1s). Petiole surmounted by a thick scale, its posterior face convex in dorsal view. Helcium sometimes projecting from near midheight of the anterior face of A3. Gaster with a moderate girdling constriction between pre- and postsclerites of A4. Head and body finely punctate, with some smooth and shining areas on the sides of the mesosoma, and with scattered to abundant short pilosity and dense pubescence. Color usually testaceous to orange, rarely black.

Queen. Similar to worker but slightly larger, alate, with ocelli and larger eyes, and with the other thoracic modifications typical of alate ponerine queens ( Brown, 1963). See additional details in Ogata (1987).

Male. See descriptions by Brown (1963) and Ogata (1987).

Larva. Described for various species by Wheeler & Wheeler (1952, 1971a, 1986b).

Geographic distribution. Cryptopone has a virtually cosmopolitan distribution, occurring in every major biogeographic region, though the species diversity is centered in East and Southeast Asia ( Brown, 1963; Bolton et al., 2006).

Ecology and behavior. Very little is known about the habits of Cryptopone , but based on morphology and anecdotal observations they are clearly hypogeic (e.g., Wheeler & Gaige, 1920). Cryptopone workers exhibit many classic characters of hypogeic ants, including small size, depigmentation, flattened scapes, vestigial eyes, and traction setae on the mesotibiae (e.g., Wheeler, 1933a). Reported field observations and collection data indicate that Cryptopone species nest in a diversity of microhabitats including rotting wood, polypore fungi, under grass, in leaf litter, in soil, or even inside termitaria ( Creighton & Tulloch, 1930; Forel, cited by Wheeler, 1933a; Smith, 1934; Weber, 1939; Wilson, 1958c; Terayama, 1999; Radchenko, 2005; Longino, 2013). Workers have been observed foraging in soil, leaf litter, and under moss or rocks ( Wheeler & Gaige, 1920; Wilson, 1958c; Radchenko, 2005; Longino, 2013). Haskins (1931) observed workers of C. gilva in laboratory conditions foraging in exposed conditions for brief periods, suggesting that they are not strictly hypogeic. Wilson (1958c) reported that workers of C. butteli are timid and slow moving, and Wheeler & Gaige (1920) noted similar behavior in workers of C. gilva and observed that they feign death; Smith (1934) also noted sluggish behavior in C. gilva . Cryptopone are most likely generalist predators, though observations of Cryptopone food preferences are scant. Imai et al. (2003) reported that C. sauteri is a predator of beetle and fly larvae.

Almost nothing is known about the social organization of Cryptopone , but colonies are typically small ( C. butteli: Wilson, 1958c ; C. guianensis: Weber, 1939 ). Creighton & Tulloch (1930) observed a single colony of C. gilva with five dealate queens and stated that its colonies are small, and Smith (1934) similarly observed polygynous colonies of C. gilva but noted that its colonies could have as many as several hundred workers. Haskins (1931) also reported frequent polygyny in C. gilva . Nest emigrations are facilitated by social carrying in C. gilva ( Haskins, 1931) . Haskins (1931) gives many additional details of the habits of C. gilva , including the results of interesting experiments on its visual and auditory acuity.

Phylogenetic and taxonomic considerations. Cryptopone has had a somewhat complicated taxonomic history. In erecting Cryptopone, Emery (1893a ; also 1893b) noted the similarity of its type species, C. testacea , to Ponera . He distinguished the two genera by mandibular shape (the masticatory margin is shorter in C. testacea ) and by the relatively high articulation of the petiole with the gaster in C. testacea . Emery also compared C. testacea to Trapeziopelta (= Myopias ), noting the supposedly similar mandibular shape and high helcium. The subtriangular mandibles and high helcium of C. testacea have proven not to be universal in Cryptopone , nor is a high helcium common in Myopias , so these characters are less informative than Emery believed. Emery also considered the foursegmented club of C. testacea to be of taxonomic value.

Additional species were gradually added to Cryptopone until Wheeler (1933a) revised the genus, splitting off two species to form the new genus Pseudocryptopone (which he considered to be close to Ponera ), describing new species, and providing a revised diagnosis for the genera. Wheeler was the first to recognize the significance of the distinctive shape of the propodeum in dorsal view, of the stout mesotibial setae, and of the head shape. Based on the latter two characters, Wheeler believed that Cryptopone was closely related to Trachymesopus (= Pseudoponera ).

Wilson (1958c) discussed the relationship between Cryptopone and Trachymesopus and believed that they could be separated by three worker characters: the metatibial spur count (one in Cryptopone , two in Trachymesopus ), the shape of the mandibles (narrower and with more oblique masticatory margins in Cryptopone ), and the presence of eyes (absent in Cryptopone ). Brown (1963) noted the presence of stout setae on the mesotibiae and the presence of basal mandibular pits as being characteristic of the genus, recognized that Trachymesopus species with these traits are really Cryptopone , and transferred them to Cryptopone accordingly. More recently, Mackay & Mackay (2010) found the characters used to separate Cryptopone from related genera to be poor. They observed that many of these characters were too variable or difficult to see and therefore unambiguous interpretation and placement of some taxa within these genera was sometimes nearly impossible. As a result they synonymized Cryptopone with Pachycondyla . Mackay & Mackay (2010) also note that Wadeura guianensis , the type species of Wadeura , is basically a Cryptopone with unusual mandibles and because of this Wadeura does not warrant status as a full genus; they consider it to be a synonym of Pachycondyla .

To resolve these issues a broad range of species from across the world were examined. While some characters used to diagnose Cryptopone were found to be variable as noted by Mackay & Mackay (2010), we were able to develop a concise diagnosis for the genus and to produce keys which allow reliable identifications to be undertaken. Additionally, Schmidt's (2013) molecular phylogeny of the Ponerinae places Cryptopone as sister to Pseudoponera , a relationship that Wheeler (1933a) suggested, with no close relationship indicated to true Pachycondyla . Based on this we treat Cryptopone as a valid genus with Wadeura as its junior synonym. It should be noted that the true boundaries of Cryptopone and Pseudoponera are somewhat unclear, but morphological evidence does support this relationship (see the discussion of the Ponera genus group).

Our concept of Cryptopone nearly mirrors that of Brown, with the exception that we consider the genus Wadeura to be a probable junior synonym of Cryptopone . Wadeura (described by Weber, 1939), currently considered a junior synonym of Pachycondyla ( Brown, 1973) , is a small Neotropical group of three species. Though Schmidt (2013) did not sample Wadeura in his molecular phylogeny, the morphological similarities between Wadeura and Cryptopone are compelling and to our surprise have apparently not been noted previously. In most respects the three species of Wadeura are morphologically typical of Cryptopone , having the same dense punctate sculpturing, dense pubescence, depigmentation, head shape, convex anterior clypeal margin, small closely approximated frontal lobes, flattened scapes, vestigial eyes (actually completely absent in Wadeura ), anteriorly constricted propodeum and flat propodeal dorsum, round propodeal spiracles, simple posteriorly directed metapleural gland orifice, mesotibiae with stout spines, thick squamiform petiole, and the characters of the gaster. Wadeura differs from typical Cryptopone chiefly in mandibular shape (narrower and with longer teeth in Wadeura ), in the shape of the mesonotum (bulging in Wadeura , with the consequent appearance of a depressed propodeum), body size ( Wadeura is somewhat larger than most Cryptopone ), and metatibial spur count (one in Cryptopone , two in Wadeura ).

We do not consider the morphological differences between Wadeura and Cryptopone to be of genus-level significance, and interpret Wadeura as a lineage of Cryptopone (probably sister to C. gilva and C. guatemalensis ) which evolved larger size and possibly prey specialization, to fill a niche left empty in the Neotropics but filled by the superficially similar Promyopias in Africa and Buniapone in Southeast Asia (as suggested by Weber, 1939). Alternatively, Wadeura could actually be unrelated to Cryptopone and represent a remarkable case of convergence, though we do not find this hypothesis very credible.

Figures

FIGURE 42. Worker caste of Cryptopone rotundiceps: lateral and dorsal view of body and full-face view of head (CASENT0172100, April Nobile and www.antweb.org); world distribution of Cryptopone.