Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Southern half of continental USA, Mexico, Costa Rica, Trinidad, Argentina, Chile, Cuba, Jamaica, Dominican Republic, Puerto Rico, Saint Vincent.
Identification
Eyes usually composed of 1-3 partially fused facets; eyes situated relatively far forward on sides of head; face with dense small puncta, sublucid; mesonotum weakly convex, with distinct impression at propodeal suture; petiolar node a thickened scale, with weakly converging anterior and posterior faces, and a broadly rounded dorsum; color usually dark brown to black. Measurement data.
I tentatively separate a form I call JTL-008, which tends to be somewhat shinier, with more dilute pubescence, and with the eyes shifted relatively farther forward, to the point where they almost rest on the anterior margin of the head capsule (figure, a=opacior s.s., b=JTL-008) (Images of JTL-008: worker lateral view (reduced, original); worker face view (reduced, original)).
I also place here two workers collected by P. S. Ward (collection number 7650), from 500m elevation in Carara Biological Reserve. I refer to them as JTL-015. These workers have measurements that match opacior, but the color is light red brown, and the petiolar node is high, thin, and scale-like, much different from the typical opacior petiole. One worker has dense long pilosity on the undersurface of the head, but I examined other material of opacior, and the length and abundance of this pilosity was highly variable. The dorsal face of the propodeum is strongly sloping and curves gradually into the posterior face, unlike other opacior collections in which the dorsal and posterior faces meet at a more pronounced angle. The eyes are larger than other opacior material, composed of about 5-6 facets on one worker, and around 10 facets on the other. These differences strongly suggest this is a distinct species, but I postpone judgement until more material is obtained. (Images of JTL-015: worker lateral view (reduced, original); worker face view (reduced, original)).
Natural History
The form I call opacior s.s. seems to have a preference for synanthropic and seasonally dry habitats. I have scattered collections from Costa Rica, as follows:
Santa Rosa National Park: in Winkler sample collected by P. S. Ward.
Finca La Pacifica, a dry-forest riparian habitat: in Winkler sample of sifted litter from the forest floor.
Carara Biological Reserve: in Winkler sample collected by P. S. Ward.
Casa Plastico, a 600m elevation wet site on the Atlantic slope, in young second growth at the edge of a pasture: under a mossmat at the base of a tree.
A coffee farm near Heredia in the Central Valley: collected in studies of coffee farm fauna by Ivette Perfecto.
Sirena in Corcovado National Park, a lowland wet forest site: in Winkler sample of sifted litter from the forest floor.
A roadside in Monteverde, where an isolated and epiphyte-laden tree had recently fallen: a nest was under epiphytes near the ground.
La Selva Biological Station, a mature lowland wet forest site: a nest was under epiphytes on a dead branch recently fallen from the canopy.
Fila Cruces near San Vito: a nest was under a stone at the edge of a gravel road through pastures and scrubby forest.
Parque Nacional, a small landscaped park in the middle of San Jose: among a collection of stray foragers.
In contrast, the form JTL-008 I know from La Selva and the adjacent slope of Volcan Barba to about 900m, the Penas Blancas Valley east of Monteverde, and the Wilson Botanical Garden near San Vito. It inhabits mature wet forest, and I usually encounter it in Winkler samples of sifted litter from the forest floor. At La Selva, I collected a nest from beneath the thin, loose bark of some dead wood on the ground.
The form JTL-015 was from a Winkler sample of sifted litter from the forest floor.
I tentatively associate an ergatoid male with form JTL-008. It was obtained in a Winkler sample from the Penas Blancas Valley, along with many workers of JTL-008.
Taxonomic Notes
Hypoponera opacior is probably a species complex; a brief perusal of collections from throughout its range reveals abundant geographic variation in details of color, pilosity, and eye size. For example, Californian material that has traditionally been identified as opacior can be separated into two or three distinct species (P. S. Ward, pers. comm.). This pattern suggests an older lineage whose current distribution is the result of vicariance rather than recent dispersal, at least over parts of its range. It is also possible that some parts of the range are the result of recent dispersal. For example, is its current distribution on many Caribbean islands a result of old vicariance or recent introductions?
The variability I observe in Costa Rica is possibly a reflection of this same combination of older resident populations in mature forest sites, and more recently introduced forms in synanthropic habitats. Alternatively, recent selection may be driving the correlated patterns of morphology and habitat.
In Kempf (1972), the distribution of trigona is southern Brazil (numerous states), Argentina (numerous states), Bolivia, and Costa Rica. The distribution for trigona opacior is many caribbean islands, and scattered localities in the mainland Neotropics (but not including Costa Rica). Kempf (1962) carefully described the lectotype of trigona. He did not observe the type of the subspecies opacior, but stated "[opacior] seems specifically distinct from trigona if the current idea about its nature is correct." Kempf did not list the Costa Rican record of trigona in his 1962 paper, and I do not know the basis for his listing it in 1972. Nor do I know how he distinguished trigona from opacior. I am calling Costa Rican material opacior and not trigona, because of its similarity to North American material of opacior and the geographic proximity to the type locality.
Although Kempf still listed opacior as a subspecies of trigona in 1972, it has been listed as a species-rank taxon by Taylor (1968), Smith (1979), and Bolton (1995). Bolton attributes the new status to Kempf 1962.
Type Data
Ponera trigona var. opacior Forel 1893:363. Syntype worker, queen: West Indies, St. Vincent.
Literature Cited
Bolton, B. 1995. A new general catalogue of the ants of the world. Cambridge, Mass.: Harvard University Press, 504 pp.
Forel, A. 1893. Formicides de l'Antille St. Vincent. Recoltees par Mons. H. H. Smith. Trans. Entomol. Soc. Lond. 1893:333-418.
Kempf, W. W. 1962. Miscellaneous studies on neotropical ants. II. (Hymenoptera, Formicidae). Studia Entomol. 5:1-38.
Kempf, W. W. 1972. Catalogo abreviado das formigas da regiao Neotropical. Stud. Entomol. 15:3-344.
Smith, D. R. 1979. Superfamily Formicoidea. Pp. 1323-1467 in: Krombein, K. V., Hurd, P. D., Smith, D. R., Burks, B. D. (eds.) Catalog of Hymenoptera in America north of Mexico. Volume 2. Apocrita (Aculeata). Washington, D.C.: Smithsonian Institution Press, pp. i-xvi, 1199-2209.
Taylor, R. W. 1968. Nomenclature and synonymy of the North American ants of the genera Ponera and Hypoponera (Hymenoptera: Formicidae). Entomol. News 79:63-66.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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