Pristomyrmex mandibularis

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Pristomyrmex mandibularis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Pristomyrmex
Species: P. mandibularis
Binomial name
Pristomyrmex mandibularis
Mann, 1921

Pristomyrmex mandibularis casent0171044 profile 1.jpg

Pristomyrmex mandibularis casent0171044 dorsal 1.jpg

Specimen labels

At a Glance • Ergatoid queen  
 

This species occurs in rainforest and has been collected in litter berlesates; it nests beneath stones in small colonies (Mann, 1921). This species and Pristomyrmex tsujii are the only two Pristomyrmex species known from Fiji.

Identification

Wang (2003) - Worker. Masticatory margin of mandible lacking a diastema and possessing four teeth, of which the third tooth, counting from the apex, smallest; a strongly prominent tooth present about midway on the basal margin of mandible; petiole lacking a lateral longitudinal carina on each side; dorsum of head between frontal carinae usually smooth and shining.

Pristomyrmex mandibularis is endemic in Fiji. It possesses an ergatoid queen caste, which is not seen in the other species of the levigatus group; furthermore, its ergatoid queen has only one ocellus.

A member of the Levigatus species group

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Indo-Australian Region: Fiji (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

The biology of most Pristomyrmex species is poorly known. From Wang (2003): Most species of Pristomyrmex dwell in the rainforest, foraging as predators or scavengers. An Asian species, Pristomyrmex punctatus, however, occurs in open and disturbed habitats (e.g., bare hills, agricultural areas, and beaches). These ants prefer to nest in soil, litter, or rotten wood; in rotten parts of living trees; in dead standing trees; or around plant roots.

Pristomyrmex is of great interest because it exhibits several unusual biological and evolutionary phenomena. The absence of morphologically normal queens and reproduction primarily by unmated workers in P. punctatus {=P. pungens) is a highly unusual life history in the Formicidae. Ergatoid queens, a special wingless female caste morphologically intermediate between the queen and the worker, are present in at least four species: Pristomyrmex punctatus, Pristomyrmex africanus, Pristomyrmex wheeleri, and Pristomyrmex mandibularis; two of them (P. africanus and P. wheeleri) possess both queen and ergatoid queen castes.

Simulating death, slowness of movement, and nocturnal foraging has been recorded in Pristomyrmex (Donisthorpe, 1946; Taylor, 1965; Weber, 1941). Colony size varies greatly among species, ranging from about a dozen to several thousand workers (Donisthorpe, 1946; Itow et al, 1984; Mann, 1919; Taylor, 1965, 1968).

Castes

Queen

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • mandibularis. Pristomyrmex mandibularis Mann, 1921: 444 (w.) FIJI IS. Sarnat & Economo, 2013: 54 (q.m.). See also: Wang, M. 2003: 505.

Sarnat & Economo (2013):

Geographic variation. Like the worker of the species, which is discussed in Wang (2003) and Sarnat and Economo (2012), the alate queens of P. mandibularis vary substantially in size, shape, color and sculpture across the archipelago. The Viti Levu specimens are marked by sparse foveae, a median clypeal tooth that is smaller than the lateral teeth but still distinct, and tend towards the redder end of the color spectrum. The Vanua Levu, Koro and Lakeba specimens are moderately foveolate with a smaller and more blunted median clypeal tooth.

Comments. A puzzling taxonomic situation is presented by two alate queens from Gau occupying the extreme ends of the sculpture spectrum. Specimen CASENT0181910 lacks any distinct foveae on the head and mesosoma and is the least sculptured of the examined queens. Specimen CASENT0194557 is both exceptionally large (HW = 1.01 mm) and the mostly strongly sculptured of all examined Fijian Pristomyrmex queens, with well-defined foveae covering the head. The abundant pilosity on the head and mesosoma can be perhaps be explained by the greater number of piligerous foveae, but the length of the hairs is distinctly shorter than all other alate queens, including the aforementioned CASENT0181910 from Gau. Specimen CASENT0194557 also has shorter antennal scapes relative to its head width than any other examined alate queens of P. mandibularis or Pristomyrmex tsujii. The combination of gross morphological differences, morphometric disparity and sympatry of the two alate queens from Gau suggests that CASENT0194557 be assigned to a different species. We are reluctant however to describe a new species based on a single queen specimen. The aberrant measurements of CASENT0194557 are therefore reported separately from those collated from all other P. mandibularis alate queens.

Description

Worker

Wang (2003) - TL 2.68-3.49, HL 0.74-0.84, BW 0.76-0.88, CI 9.5-107, SL 0.61-0.74, SI 80-93, EL 0.11-0.14, PW 0.48-0.60, AL 0.68-0.90, PPW 0.20-0.25, PPL 0.16-0.19, PPI 121-133 (n = 33).

Mandibles usually smooth and shining. A prominent tooth present about midway on the basal margin of mandible. Clypeus flat and unsculptured. Anterior clypeal margin with a median tooth and two lateral teeth; the median tooth, in size, similar to or smaller than the others. Ventral surface of clypeus usually with a weak transverse ruga. Palp formula 1,3. Frontal carinae extending to the level of the posterior margins of the eyes. Antennal scrobes absent. Frontal lobes slightly expanded. Eyes moderately sized. Occipital margin straight or feebly concave in full-face view. Pronotum unarmed. Propodeum with a pair of short to moderately long spines. Metapleural lobes triangular. Petiole node in profile high, higher than long, with the anterodorsal angle being an apex and the dorsum posteriorly rounding into the posterior surface, its anterior peduncle slightly longer than or about as long as the node . Postpetiole in profile high, about two times as high as long, rounded dorsally. In dorsal view, postpetiole transrectangular. Dorsum of head between the frontal carinae usually smooth and shining but sometimes with a few small and shallow punctures. Sometimes a few foveolate punctures bordering the frontal carinae, present on the genae and around the eyes. Dorsum of alitrunk smooth and shining. Petiole and postpetiole smooth and shining, each lacking a lateral longitudinal carina on each side. Gaster unsculptured. Dorsal surface of head with numerous erect to suberect long hairs. Some of similar hairs present on the dorsum of alitrunk, a pair on the petiole, one to two pairs on the postpetiole, and a few on the first gastral tergite. A few pairs of forward-projecting hairs present near the anterior clypeal margin. Scapes and tibiae with numerous erect to suberect hairs. Color reddish-brown to blackish-brown.

Queen

Sarnat & Economo (2013) - Alate queen. Measurements (n = 10): TL 3.22–3.65, HW 0.80–0.86, HL 0.77–0.85, CI 99–106, SL 0.64–0.74, SI 79–88, EL 0.14–0.18, PW 0.61–0.67, ML 0.82–0.96, PeH 0.22–0.26, PeL 0.14–0.18, PeI 58–76, PpH 0.26–0.29, PpL 0.16–0.19, PpI 59–69. Measurements of aberrant specimen CASENT0194557: TL 4.10, HW 1.01, HL 0.96, CI 105, SL 0.77, SI 77, EL 0.19, PW 0.76, ML 1.06, PeH 0.30, PeL 0.17, PeI 58, PpH 0.32, PpL 0.21, PpI 65.

Conforming to the generic Pristomyrmex definition detailed in Wang (2003) with the following specifications. Closely resembling worker in the structure of the mandibles, clypeus, petiole, postpetiole and gaster in addition to sculpture, color and pilosity with the following differences. Distinctly larger. Eyes much larger with diameter composed of ca. 12 facets. Three ocelli present. Posterior head margin flat to weakly concave. Median clypeal tooth distinct to nearly absent. Mesosoma marked with wing sclerites and dorsal sutures. Propodeal spines significantly smaller than those of worker; present as large and broad distinct angles approximately equal in size to propodeal lobes. Dorsum of head entirely free of foveae to covered in abundant well-defined foveae. Dorsum of mesosoma with more than 10 pairs of erect hairs.

Wang (2003) - Ergatoid. TL 3.32, 3.40; HL 0.84, 0.84; HW 0.82, 0.82; CI 98, 98; SL 0.66, 0.73; SI 80, 89; EL 0.14, 0.15; PW 0.54,0.56; AL 0.78, 0.82; PPW 0.23,0.24; PPL 0.19, 0.21; PPI 114, 121 (n = 2).

Generally similar to worker, color and pilosity as in the worker, but the head with one ocellus, alitrunk in dorsal view with a promesonotal suture, mesonotum more convex, and propodeal armaments shorter than in the conspecific worker.

Male

Sarnat & Economo (2013) - Measurements (n = 21): TL 2.55–3.22, HW 0.51–0.61, HWE 0.63–0.75, HL 0.48–0.6, CI 97–113, SL 0.14–0.21, SI 26–34, EL 0.21–0.25, PW 0.53–0.73, ML 0.8–1.08, PeH 0.14–0.19, PeL 0.27–0.38, PeI 178–234, PpH 0.18–0.23, PpL 0.13–0.17, PpI 64–83.

Conforming to the generic Pristomyrmex definition detailed in Wang (2003) with the following specifications. Head, including the eyes, broader than long. Dorsal portion of occipital margin raised into a transverse carina from which no short lengths of longitudinal carinae originate. Frontal carina weak, terminating before reaching the posterior level of the eye. Clypeus with a median longitudinal carina and 1–3 pair of lateral carinae extending towards the anterior margin. Anterior clypeal margin flat to weakly convex. Mesoscutum with distinct notauli forming a Y-shape. Parapsidal furrows reduced to weak impressions. Scuto-scutellar sulcus with 7–10 narrow longitudinal ridges visible in dorsal view. Propodeum armed with a pair of strong tubercles or small teeth. Propodeal lobes obtusely triangular with a blunt or rounded apex; usually more developed than propodeal teeth. Middle and hind tibiae lacking spurs. Petiole in profile cuneiform with a weakly developed and broadly convex node. Peduncle long. Postpetiole in profile nodiform with a steeply convex anterior face and shorter, more gently sloped posterior face. In dorsal view subrectangular and broader than long. Entirely smooth and shiny. All dorsal surfaces with abundant long erect to suberect hairs. Legs and scapes with numerous erect or suberect short hairs. Color black to blackish brown with lighter brown appendages and gaster. Wings infuscated.

Type Material

Wang (2003) - Syntype workers, Fiji Is.: Viti Levu, Nadarivatu, 1915-1916 (W. M. Mann) (American Museum of Natural History, Los Angeles County Museum of Natural History, Museum of Comparative Zoology, National Museum of Natural History) [examined].

References