Octostruma triangulabrum

Octostruma triangulabrum
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Attini
Genus:	Octostruma
Species:	O. triangulabrum
Binomial name
Octostruma triangulabrum Longino, 2013 Specimen Label

Octostruma triangulabrum occurs in montane wet forest habitats, in both mesophyl cloud forest and wet pine-oak forests, throughout the central Chiapas highlands. It occurs from 900–2750 m elevation and can be moderately abundant (up to 13% of 1 m2 plot litter samples in quantitative sampling). It is only known from Winkler and Berlese samples of sifted leaf litter. (Longino 2013)

Identification

Longino (2013) - With the characters of Octostruma wheeleri and Octostruma triquetrilabrum. Differing from O. wheeleri in the presence of 8–12 spatulate setae on face (6 on O. wheeleri) and shallow reticulate rugulose sculpture on face and dorsal pronotum (nearly smooth on O. wheeleri). Differing from both species in a pair of spatulate setae on the mesonotum (lacking in O. wheeleri and O. triquetrilabrum).

Keys including this Species

• Key to Octostruma species

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: 18.5333° to 16.94866°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

Neotropical Region: Mexico (type locality).

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Longino (2013) - This species and Costa Rica's Octostruma triquetrilabrum are extremely similar allopatric forms, differing only in the presence or absence of mesonotal setae. Intensive sampling of the litter fauna in cloud forest sites in Nicaragua, Honduras, and Guatemala has failed to reveal additional populations. Both together are quite similar to the lowland Octostruma wheeleri. Octostruma triangulabrum is sharply parapatric with O. wheeleri (see Comments under O. wheeleri).

Explore Overview of Octostruma biology  Longino (2013) - Brown and Kempf (1960) summarized the biology of basicerotines as follows: The basicerotines all come from tropical or subtropical areas, and predominantly from mesic habitats, particularly rain forest, where they live primarily in the upper layers of the soil and in the soil cover, including large and small pieces of rotten wood. They are fairly common in soil cover berlesates. Nests have been found in snail shells, and in the peaty masses gathered about epiphytic ferns above the ground level. So far as is known, colonies are small, consisting of one or more dealate—or rarely ergatoid—females, and a few workers. Judging from the structure of the workers and females, one would suppose that they were predaceous on small arthropods... Besides this summary, the behavior of three basicerotine species has been studied. Wilson (1956) observed a small captive colony of Eurhopalothrix biroi, a New Guinea species. Workers moved slowly and captured a variety of small, soft-bodied prey, including spiders, symphylans, entomobryid Collembola, campodeids, and hemipteran nymphs. Wilson and Brown (1984) observed a captive colony of Eurhopalothrix heliscata, a species from Singapore. The colony contained over 400 workers, multiple alate and dealate queens, several adult males, and brood. Foraging workers acted "rather like miniature ferrets," readily wedging themselves into small crevices. They foraged solitarily, attacking a variety of prey but mostly termites. They used their sharply-toothed mandibles to abruptly snap onto appendages of prey, maintaining purchase and slowly reaching around with the gaster to sting the prey. The strongly sclerotized labrum was also employed to press against the clamped appendage. The behavioral repertoire was limited. There did not appear to be trophallaxis, as workers and larvae fed directly from prey in the brood chambers. Nor did there appear to be any form of alarm communication. While there was generally an increase in the number of foragers when clusters of prey were presented, there was no evidence of any pheromone-based recruitment. Workers were non-aggressive and responded to disturbance by tucking the appendages and becoming immobile, often for minutes at a time. Wilson and Hölldobler (1986) studied captive colonies of Basiceros manni from Costa Rica and observed behavior not substantially different from E. heliscata. Foraging workers of many basicerotines are often encrusted with a firmly bonded layer of soil, which is thought to function as camouflage, enhancing crypsis (Hölldobler & Wilson, 1986). Knowledge of the basic natural history of these ants has hardly progressed since the observations of Wilson, Brown, and Hölldobler. More specimens are now available for examination due to quantitative litter sampling, enhancing knowledge of basicerotine diversity and distribution, but discovering nests remains exceedingly difficult. Quantitative samples of 1 m2 litter plots reveals that small basicerotines can be very frequent, occurring in over 50% of samples in some cases, but never in large numbers. Individual samples usually contain fewer than ten workers, and workers are often accompanied by dealate queens. These results suggest that colonies, at least among New World species, are usually small, with tens of workers. Less than half of the species of Octostruma have their queens described. Ergatoid queens are known from some species. Males are known from collections for some species but none have been described. The mating biology of these ants and how common ergatoid queens are across the genus and within colonies is not known. ‎

Castes

Known only from the worker caste.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• triangulabrum. Octostruma triangulabrum Longino, 2013: 52, figs. 1A, 3A, 5J, 38, 43 (w.) MEXICO.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

HW 0.73–0.78, HL 0.68–0.73, WL 0.82–0.89, CI 106–109 (n=5). Labrum sides straight, strap-like lateral portions converging from base to apex, fused apically (not bilobed, at most with minute notch apically), joined medially by thin translucent cuticle; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth, basal rim of dorsal surface slightly offset from base of tooth 1, forming small denticle, teeth 1–5 acute, similar in shape, teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles; dorsal surface of mandible roughened; ventral surface flat and parallel to clypeus apically, twisting basally to nearly perpendicular orientation basally, smooth and shining; interior surface concave, smooth and shining; scape flattened, with pronounced anterobasal lobe, dorsal surface roughened, dull; clypeus with broad, shallow emargination anteriorly; clypeus and face shallowly, irregularly rugulose, generally matte, tops of face rugulae sublucid; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, strongly delimited dorsally, posteriorly, and ventrally with sharply defined thin cuticular rim; compound eye small, circular, composed of about 7 ommatidia; distinct carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; scrobe floor faintly foveolate, matte; vertex margin anterior to occipital carina smooth, sublucid (top of head, not visible in face view); occipital carina extends anteriorly on ventral surface of head to level of compound eye; undersurface coarsely rugose.

Promesonotum moderately convex in profile, promesonotal suture not impressed, promesonotum with broad, weak, longitudinal impression; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces; dorsal face weakly convex; propodeal spines well-developed, in the form of acute flattened perpendicular plates, extending ventrally as thin carinae; single well-defined transverse carina extends between propodeal spines, separating dorsal and posterior faces of propodeum; propodeal spiracle medium-size, diameter less than width of base of propodeal spine, located below propodeal spine and abutting to somewhat separated from posterior margin; all surfaces of mesosoma matte except posterior face of propodeum, which is shiny; dorsum of promesonotum irregularly shallowly rugulose laterally, smooth medially, dorsal and posterior face of propodeum smooth, lateral pronotum smooth; meso- metapleuron and side of propodeum confluent, smooth.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node subquadrate to triangular, with long sloping dorsal face, posterior face short to absent; anteroventral margin with acute to peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole shallowly rugulose, matte; first gastral tergite densely punctate, tergal puncta smaller posteriorly, interspaces sublucid; first gastral sternite smooth, matte anteromedially, punctate posteriorly.

Anterior labral lobe with radiating tuft of soft, thick, translucent, capitate setae of unequal length projecting from apex; each larger mandibular tooth with fully appressed seta running length of tooth; anterior margin of scape with about 8 stiff clavate setae; clypeus and face with fine, sparse fully appressed ground pilosity; face typically with 10 erect clavate setae arranged as in; pronotum lacking erect setae; mesonotum with a pair of erect clavate setae; mesotibia with about 5 clavate seta of variable length at apex; petiole, postpetiole, first gastral tergite lacking erect setae; ground pilosity of first gastral tergite short, sparse, fully appressed; first gastral sternite with abundant clavate setae clustered on posterior half, anterior half devoid of setae.

Color dark red brown.

Type Material

Holotype Specimen Labels

Holotype worker: Mexico, Chiapas: Nahá, 16.96291, -91.59335, ±2 km, 950 m, 10 Jun 2008, mesophil forest, ex sifted leaf litter (LLAMA, Wm-A-07-all) California Academy of Sciences, unique specimen identifier CASENT0608768. Paratype workers: same data John T. Longino Collection, CASENT0608761; same data except 16.97417, -91.58592, ±50 m, 950 m, 14 Jul 2007 (J. Longino#6047-s) Colección Entomológica de El Colegio de la Frontera Sur, JTLC000009758; National Museum of Natural History, JTLC000009759]; 16.97417, -91.58592, ±50 m, 950 m, 14 Jul 2007 (R. S. Anderson#2007-013) Museum of Comparative Zoology, CASENT0602034; 16.96313, -91.59337, ±50 m, 985 m, 8 Jun 2008 (LLAMA, Wa-A-07-1-06) Museu de Zoologia da Universidade de Sao Paulo, CASENT0627348; University of California, Davis, JTLC000014462]; 16.96318, -91.59337, ±50 m, 985 m, 8 Jun 2008 (LLAMA, Wa-A-07-1-07) Colección de Artrópodos, CASENT0627349; CASC, CASENT0627350; 16.94866, -91.59392, ±50 m, 930 m, 8 Jun 2008 (LLAMA, Wa-A-07-2-08) CASC, JTLC000014488.

Etymology

The name refers to the triangular labrum that is not bilobed at the apex. It is a noun in apposition and thus invariant.

References

• Longino, J.T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699, 1-61. doi:10.11646/zootaxa.3699.1.1

References based on Global Ant Biodiversity Informatics

• Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
• Longino J. T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699(1): 1-61.
• Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/