Octostruma gymnogon

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

Octostruma gymnogon P casent0627379.jpg

Octostruma gymnogon D casent0627379.jpg

Specimen Label

Octostruma gymnogon is a montane species. It occurs mostly in mature cloud forest. On the Barva Transect in Costa Rica it shows a sharp elevationally parapatric distribution with Octostruma amrishi and is restricted to elevations above 400 m. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. Dealate queens and intercaste workers occasionally occur together with workers in litter samples. Additional comments are included under Octostruma balzani. (Longmino 2013)

Identification

Longino (2013) - Mandible with 8 teeth, tooth 1 a broad blunt lamella, strongly differentiated from tooth 2, teeth 2–5 acute, similar in shape, with denticles between them; teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles (O. balzani complex); face setation, lacking erect setae on posterolateral margins of head (present in Octostruma balzani, Octostruma megabalzani, and Octostruma trithrix) and on the posteromedian margin (present in Octostruma amrishi); mesosomal dorsum lacking a pair of erect setae (present in O. balzani, O. megabalzani, and O. trithrix); metanotal groove not impressed in profile view (impressed in O. balzani and O. megabalzani).

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Costa Rica (type locality), Guatemala, Honduras, Nicaragua, Panama.


Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

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

Nomenclature

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

  • gymnogon. Octostruma gymnogon Longino, 2013: 33, figs. 1E, 3D, 5D, 24, 42 (w.q.) COSTA RICA.

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

Description

Worker

HW 0.62–0.68, HL 0.56–0.59, WL 0.62–0.68, CI 109–114 (n=6). Matching in almost every respect the description for O. balzani, except the differences outlined in the Diagnosis and key. Octostruma gymnogon is generally darker brown than either O. amrishi or O. balzani.

Queen

HW 0.66, HL 0.60, WL 0.79, CI 110 (n=1). Similar in all respects to Octostruma balzani.

Type Material

Holotype Specimen Labels

Holotype worker: COSTA RICA, Alajuela: Casa Eladio, Rio Peñas Blancas, 10.31667, -84.71667, ±2 km, 800 m, 26 Apr 1987, primary wet forest, sifted leaf litter (J. Longino#1579-s) Instituto Nacional de Biodiversidad, unique specimen identifier CASENT0627379]. Paratype workers, queen: same data INBC, CASENT0627380; same data except (J. Longino#1578-s) California Academy of Sciences, Los Angeles County Museum of Natural History ENT 143374; National Museum of Natural History, LACM ENT 143375; 27 Apr 1988 (J. Longino#2015-s) Museum of Comparative Zoology, LACM ENT 143379; Museu de Zoologia da Universidade de Sao Paulo, LACM ENT 143380]; 10 May 1989 (J. Longino#2529-s) Colección de Artrópodos, INBIOCRI001281404; Escuela Agricola Panamericana, INBIOCRI001281422; 23 May 1990 (J. Longino#2701-s) University of California, Davis, INBIOCRI001282517; 2 Mar 2004 (J. Longino#5278-s) CASC, JTLC000005383; John T. Longino Collection, JTLC000005390.

Etymology

The name refers to the lack of a spatulate seta on the posterolateral vertex margin. 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