Octostruma montanis

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

Octostruma montanis P casent0627340.jpg

Octostruma montanis D casent0627340.jpg

Specimen Label

Octostruma montanis is a cloud forest species known from two sites: Cerro Musún in southern Nicaragua and Monteverde in Costa Rica. Cerro Musún is an isolated mountain surrounded by largely deforested lowlands. The slopes from 700 m elevation to the peak at 1400 m are a protected reserve. The LLAMA project carried out Winkler sampling across the full elevational range of the reserve, and O. montanis was restricted to parts of the reserve above 1100 m. In Monteverde in the Cordillera de Tilarán, northern Costa Rica, O. montanis occurs in the ridge crest cloud forest at 1500 m elevation, but not lower. All collections are from Winkler samples of sifted litter and rotten wood from the forest floor. (Longino 2013)

Identification

Face lacking transverse arcuate carina; basal five teeth of mandible acute; apex of labrum bilobed; face typically with 6 spatulate setae (8 in Octostruma cyrtinotum), seta-bearing pits along vertex margin large; filiform setae lacking on petiole, postpetiole, first gastral sternite; anterior half of dorsal face of propodeum convex, demarcating impressed metanotal groove; mesonotum lacking spatulate setae (with a pair in O. cyrtinotum). (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

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


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.

  • montanis. Octostruma montanis Longino, 2013: 43, figs. 1C, 3B, 5P, 32, 43 (w.) NICARAGUA.

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

Three worker series from Reserva Musún in Nicaragua are uniform in face setal pattern. Two worker series, each of two workers, are known from Monteverde, Costa Rica, and they vary in setal pattern. One series is identical to the Musún specimens, with the same number and disposition of setae, and the same enlarged seta-bearing pits. The other has only the posteromedian seta pair and the pits are not enlarged. The seta pair at the lateral vertex angles and the pair near the eyes are missing and there are no differentiated pits at these sites, so their absence is probably not due to wear. This setal pattern is the same as Octostruma planities, which occurs in the nearby dry-forest lowlands. In all other characters the specimens are like other O. montanis specimens.

Description

Worker

HW 0.73–0.78, HL 0.69–0.72, WL 0.80–0.85, CI 106–109 (n=4). Differing from Octostruma cyrtinotum in the characters of the Diagnosis (see the identification section above); otherwise similar in most respects to O. cyrtinotum.

Type Material

Holotype Specimen Labels

Holotype worker: NICARAGUA, Matagalpa: RN Cerro Musún, 12.97796, -85.23242, ±50 m, 1350 m, 1 May 2011, wet cloud forest, ex sifted leaf litter (R.S.Anderson#2011-008) California Academy of Sciences, unique specimen identifier CASENT0627340]. Paratype workers: same data CASC, CASENT0623873; National Museum of Natural History, CASENT0627338; Museum of Comparative Zoology, CASENT0627339; Museu de Zoologia da Universidade de Sao Paulo, CASENT0627341]; same data except 12.97056, -85.23388, ±20 m, 1120 m, 2 May 2011 (LLAMA, Wm-D-01-1-06) Instituto Nacional de Biodiversidad, CASENT0639986; University of California, Davis, CASENT0639988; CASC, CASENT0639990; John T. Longino Collection, CASENT0639991.

Etymology

The name refers to its restriction to montane habitats. It is a dative plural noun 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