Platythyrea Roger, 1863

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 : 48-51

Platythyrea Roger

Fig. 3

Platythyrea Roger, 1863a: 172 (as genus). Type-species: Pachycondyla punctata Smith, F., 1858: 108 ; by subsequent designation of Bingham, 1903: 73.

Eubothroponera Clark, 1930: 8 (as genus). Type-species: Eubothroponera dentinodis Clark, 1930: 9 ; by original designation. Brown, 1975: 6 ( Eubothroponera as junior synonym of Platythyrea ).

Platythyrea is a moderately large (38 described extant species) pantropical genus and is the only member of Platythyreini . Platythyrea workers are notable for their rapid movement, arboreal habits and frequent presence of gamergates.

Diagnosis. Platythyrea workers are distinctive and not easily confused with those of other genera, though the genus lacks unequivocal autapomorphies. Diagnostic characters of Platythyrea workers and queens include (in combination) pruinose sculpturing, broad insertion of the clypeus between the frontal lobes and the consequently widely spaced frontal lobes and antennal insertions, laterally opening metapleural gland orifice, metatibiae with two pectinate spurs, toothed tarsal claws, and projection of the helcium from near midheight on the anterior face of A3. Pruinose sculpturing is rare within Ponerini (only present in some Leptogenys and in Belonopelta , both of which lack the high helcium and broad clypeal insertion of Platythyrea ), but is also shared with the proceratiine genus Probolomyrmex . Probolomyrmex differs from Platythyrea , however, in numerous characters, most obviously in its lack of frontal lobes and eyes, its single metatibial spur, its simple tarsal claws, and its lack of a stridulitrum on the pretergite of A4. In most Ponerini the clypeus is only narrowly inserted between the frontal lobes, but Thaumatomyrmex has a broad clypeal insertion (even broader than in Platythyrea ). Thaumatomyrmex otherwise differs dramatically from Platythyrea , and they are unlikely to be confused. A small number of genera in Ponerini have a relatively high helcium as in Platythyrea , but these genera all lack the broad clypeal insertion and pruinose sculpturing of Platythyrea . Finally, the Australian Platythyrea dentinodis species group (formerly Eubothroponera ) have a relatively low helcium, as in most Ponerini , and lack the fine pruinose sculpturing of most Platythyrea , but can be distinguished from Ponerini by their broad clypeal insertion and presence of two pectinate metatibial spurs.

Synoptic description. Worker. Small to very large (TL 4–20 mm; Brown, 1975) ants with the standard characters of Platythyreini . Mandibles triangular, edentate or with multiple distinct teeth on the masticatory margin, and often with a basal groove. Clypeus with a flat or convex anterior margin, and a broad posterior insertion between the frontal lobes. Frontal lobes moderately large and widely separated. Eyes large to moderate in size, located anterior to head midline. Metanotal groove usually obsolete, rarely present and shallowly impressed (e.g., P. lamellosa ). Propodeum broad dorsally, the posterior margins distinct and usually with a short blunt tooth at each posterodorsal corner. Propodeal spiracle usually round, rarely slit-shaped (e.g., P. lamellosa ). Metapleural gland orifice opening laterally, near the posteroventral corner of the propodeum, sometimes with a shallow lateral longitudinal groove. Metatibial spur formula (1p, 1p). Tarsal claws usually armed with a single preapical tooth. Arolia prominent and bright white. Petiole nodiform, the node usually much longer than wide, with parallel sides and a distinct dorsal face, the posterodorsal margin often bi- or tridentate. Helcium usually projects from near midheight on the anterior face of A3 (projects from lower down in the P. dentinodis group). Gaster with a moderate girdling constriction between pre- and postsclerites of A4. Stridulitrum present on pretergite of A4. Head and body usually uniformly pruinose (having a frosted appearance due to extremely dense fine punctations combined with a dense short pubescence), usually also with scattered foveolations, and usually with little to no upright pilosity. Members of the P. dentinodis group lack the pruinose condition and have denser upright pilosity. Color variable, yellowish brown to black. See descriptions by Brown (1975) and Bolton (2003) for further details of worker structure in Platythyrea .

Queen. Very similar to conspecific workers but usually winged, with the corresponding modifications of the thoracic sclerites and usually with ocelli (though they are sometimes absent, which is a unique condition among alate ant queens) ( Brown, 1975). Queens are ergatoid in some species and are completely absent in others (reviewed by Molet & Peeters, 2006).

Male. See descriptions by Brown (1975) and Yoshimura & Fisher (2007).

Larva. Described by Wheeler & Wheeler (1952, 1971a, 1976, 1989) and Villet et al. (1990a).

Geographic distribution. Platythyrea is pantropical, with some species also occurring in subtropical regions of the New World, Africa, Asia, and Australia ( Brown, 1975; Bolton et al., 2006).

Ecology and behavior. Platythyrea is an ecologically and behaviorally interesting genus. Unusually among ponerines, many Platythyrea species are arboreal, nesting in hollow branches or other preformed cavities in live or fallen trees, and foraging on tree trunks or other vegetation ( Brown, 1975; Djiéto-Lordon et al., 2001b; Yéo et al., 2006; Molet & Peeters, 2006). Some large African species (e.g., P. lamellosa ) are terrestrial and nest at the base of termitaria or under rocks ( Arnold, 1915; Brown, 1975). Platythyrea colonies are of the typical size for ponerines, with on average usually a few hundred workers or fewer ( P. conradti : 100 to 500 workers; Lévieux, 1976; Molet & Peeters, 2006; Yéo et al., 2006; P. lamellosa : 115 workers; Villet et al., 1990b; P. modesta : up to 50 workers; Djiéto-Lordon et al., 2001b; P. parallela : 50 workers; Wilson, 1959b; P. punctata : 23- 51 workers; Hartmann et al., 2005b; P. quadridenta : 19 workers; Ito, 1995; P. schultzei : 21 workers; Villet, 1991b; P. tricuspidata : 21 workers; Ito, 1995).

Platythyrea workers are very fast runners, and their speed combined with their potent venomous stings enable them to rapidly catch and subdue a wide range of prey ( Brown, 1975; Djiéto-Lordon et al., 2001a, 2001b). Some Platythyrea species are generalist predators (e.g., P. conradti: Yéo et al., 2006 ; Molet & Peeters, 2006; P. lamellosa: Villet, 1990c ; P. modesta: Djiéto-Lordon et al., 2001a, 2001b ), but many reportedly specialize on termites (e.g., Arnold, 1915; Brown, 1975) and at least one species ( P. arnoldi ) is apparently a specialist on adult beetles ( Arnold, 1915). In an unusual behavior, P. conradti workers collect nectar onto part of their body surface for transport to the nest; the liquid is retained via surface tension ( Déjean & Suzzoni, 1997). Lévieux (1983) lists an unidentified Platythyrea species as eating seeds, though this has not been confirmed ( Hölldobler & Wilson, 1990). Platythyrea workers typically forage individually (e.g., Villet, 1990c), but Djiéto-Lordon et al. (2001b) observed nestmate recruitment in P. modesta to aid in retrieval of large prey. Interestingly, workers of this species sometimes carry larvae directly to their prey, rather than bringing the prey back to their nest; this behavior is otherwise unknown within the Ponerinae . P. modesta conducts frequent emigrations to new nest sites, with recruitment occurring via use of chemical trails ( Djiéto-Lordon et al., 2001b). The use of chemical trails by other Platythyrea species has not been reported.

Platythyrea has perhaps the highest diversity of reproductive strategies known for any ponerine genus ( Villet, 1992b; Molet & Peeters, 2006). Nearly all examined Platythyrea species have gamergates, with the only exception being P. conradti , which is also the only Platythyrea species known to have ergatoid queens ( Molet & Peeters, 2006). In P. conradti , queens and workers aggressively interact to form a dominance hierarchy, but high-ranking workers do not reproduce unless the queen dies. Among those species known to have gamergates, some also have alate queens ( P. quadridenta , P. tricuspidata and P. arnoldi ; Villet, 1993; Ito, 1995), but some have gamergates only ( P. lamellosa , P. schultzei , and P. cf. cribrinodis ; Peeters, 1987; Villet et al., 1990b; Villet, 1991b, 1991c). In addition, the reproductive strategy of P. punctata is perhaps the most variable known for any ponerine species (see below). Villet (1990 c, 1991b, 1992b) examined the division of labor in colonies of P. cf. cribrinodis , P. lamellosa , and P. schultzei and found typical age-related polyethism in all species, with unmated workers of P. cf. cribrinodis laying only inviable haploid eggs.

Platythyrea punctata is a fascinating species from the standpoint of social and reproductive behavior, as it variously has alate queens, parthenogenetic intercaste queens, mated gamergates, and parthenogenetic workers ( Schilder et al., 1999a, 1999b; Hartmann et al., 2005b). In many populations of this species, reproduction occurs via thelytokous parthenogenesis ( Heinze & Hölldobler, 1995), which is not known to occur in any other ponerine. Workers in parthenogenetic colonies of P. punctata aggressively compete and form dominance hierarchies, with reproduction restricted to only a small number of high-ranking individuals and with workers attacking “surplus reproductives”, as communicated by their cuticular hydrocarbon profiles ( Heinze & Hölldobler, 1995; Hartmann et al., 2005a). The presence of worker policing in such colonies is surprising, since they are virtually clonal ( Schilder et al., 1999b) and therefore lack any genetic conflict among colony members (Hartmann et al., 2003). The reason for the reproductive conflict is that a reduced number of reproductives leads to increased colony productivity (Hartmann et al., 2003), favoring the maintenance of social control over reproduction.

The chemical ecology of Platythyrea has not been extensively studied, but Morgan et al. (2003) found that P. punctata lacks a Dufour’s gland and lacks volatile substances in its venom gland secretions.

Yéo et al. (2006) discovered an interesting commensal association between P. conradti and the myrmicine Strumigenys maynei , which nest together in the same branches. Strumigenys colonies were found in association with 75% of the examined Platythyrea nests. The Strumigenys workers apparently feed on refuse in the Platythyrea nest, and are moved without injury by Platythyrea workers if they attempt to feed on fresh prey brought into the nest.

Phylogenetic and taxonomic considerations. Roger (1863a) erected Platythyrea to house four species formerly placed in Pachycondyla or Ponera . He did not cite a type species, but Bingham (1903) later designated P. punctata (Smith, F.) as the type species. Some early authors placed Platythyrea in Ponerini (e.g., Forel, 1899; Wheeler, 1910), or even in Ectatommini ( Ashmead, 1905) , but Emery (1911) moved it to its own tribe, Platythyreini . Subsequent authors have followed Emery’s classification, and we continue to do so.

The sole junior synonym of Platythyrea , Eubothroponera , was described by Clark (1930) with the type species Eubothroponera dentinodis Clark (now Platythyrea dentinodis ). He placed into Eubothroponera several Australian species which he considered to be closely related to Bothroponera , of Tribe Ponerini . This is understandable, as the members of Eubothroponera (now the Platythyrea dentinodis group) differ from typical Platythyrea in their coarser sculpturing, denser pilosity, and especially in their relatively low helcium, which approximates the condition that is typical of most members of Ponerini .

Brown (1952) recognized the close relationship between Platythyrea and Eubothroponera and moved Eubothroponera into Platythyreini (along with Probolomyrmex and its eventual synonym Escherichia ), and later ( Brown, 1975) took the further step of synonymizing Eubothroponera under Platythyrea based on both worker and larval characters. Schmidt's (2013) molecular phylogeny of the Ponerini confirms this synonymy, as P. turneri (unequivocally a member of “ Eubothroponera ”, though it was never formerly placed there) is nested within Platythyrea . The phylogeny also confirms that Platythyrea and Probolomyrmex are not closely related, with their extensive morphological similarities presumably being due to convergence.

Figures

FIGURE 3. Worker caste of Platythyrea dentinodis: lateral and dorsal view of body and full-face view of head (CASENT0172409, April Nobile and www.antweb.org); world distribution of Platythyrea.