Formicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Costa Rica (common in mid to upper elevation wet forest in Cordillera Volcanica Central northward through Cordillera de Tilaran and Cordillera de Guanacaste; also known from Cerro Rincon on the Osa Peninsula, but so far not collected from Cordillera de Talamanca; on Atlantic slope known to be a rare element of the fauna at La Selva Biological Station at 50m elevation, becoming much more common in Braulio Carrillo National Park, above 500m elevation).
Identification
Minor worker: scapes with fine, completely appressed setae/pubescence, and with 3-10 differentiated erect setae scattered along shaft of scape; cheeks with projecting erect setae; sides and dorsum of pronotum both flat and meeting at a rounded angle (sharper angle than JTL-010); sides of pronotum without erect setae; dorsal and posterior faces of propodeum subequal in length, flat, meeting at a distinct angle; first gastral tergite with moderately abundant erect white or clear setae; underlying pubescence fully appressed, and sharply differentiated from erect setae, highly variable in density (see note); integument of first gastral tergite varies with pubescence, from shagreened in forms with dense pubescence to feebly shagreened and shining in forms with weak pubescence; color variable, with mesosoma being darkest, appendages, malar area, and scapes being lightest, and gaster being intermediate; specimens from cloud forest areas darkest, often a dark red brown throughout; specimens from lowlands often more brightly colored, with dark mesosoma and nearly yellow legs and scapes.
Major worker: head subcircular; face yellow up to eyes or beyond; clypeus not protruding, flat to weakly convex in lateral view; face and cheeks with abundant short stiff setae; face finely granular/punctate, becoming smooth and shiny on cheeks.
May grade into JTL-016 (see note below).
Similar species: JTL-027, JTL-016, JTL-010.
Natural History
This is a very common species in mid to upper elevation wet forests. I have collected it dozens of times as foragers on low vegetation and as an opportunistic cavity nester. I often find nests in dead branches, dead wood, and very frequently in chambers under epiphyte mats. The species can occur both in second growth vegetation and in the canopy of trees in primary forest. It seems to prefer well-insolated portions of the habitat, and is rare in the shaded understory. Unlike Camponotus JTL-016, I have never found this species nesting in live stems. For example, I have never found it in Cecropia internodes, in spite of extensive survey work. Nests are often small, usually no more than a few dozen workers, but colonies may be polydomous and thus it is difficult to say how large colonies can get.
Notes
The species as construed here exhibits very sharp clinal variation. Specimens from Monteverde community area, Santa Elena, and the San Luis Valley have dense yellow pubescence on the first gastral tergite. Specimens from the ridge crest cloud forest above Monteverde have almost no pubescence. Specimens from Penas Blancas have weak pubescence. Specimens from La Selva have pubescence intermediate between specimens from Penas Blancas and specimens from the Monteverde community. Could this be related to thermoregulation? Does yellow pubescence decrease heat absorption? Other ant species that inhabit highly insolated habitats often have dense yellow pubescence on the gaster: Camponotus sericeiventris, JTL-059, and Pachycondyla villosa are examples. Is there selection for reduced pubescence where it is cloudy and/or cold?
This is basically an upland version of JTL-027, differing mainly in more pilosity on cheeks. However, it is more common in fogging samples from La Selva than JTL-027. Perhaps this is because it is more generalized in its nesting habits than JTL-027, nesting in dead wood as well as under epiphytes.
I cannot reliably distinguish minor workers of JTL-017 and JTL-016. Major workers of the two species seem very distinct around Monteverde, with the former having a relatively rounded head, flat clypeus, and yellow up to the eyes, while the latter has a more rectangular head, protruding clypeus, and is all black. However, collections from other parts of the country show a large amount of variation. In particular, some majors of what I am identifying as JTL-016 have a more rounded head, a less protruding clypeus, and a bit of yellow near the mandibular insertions. One can imagine some of these traits having a clear adaptive significance. The subquadrate head and protruding clypeus of JTL-016 majors make sense in light of its tendency to nest in stems rather than under epiphyte mats. The majors may be somewhat phragmotic, using their heads to block narrow nest entrances or tunnels. But cause of the morphological variability among these forms is unknown. There could be multiple cryptic species that are well separated genetically, or distinct genetic clusters in some areas and not in others, or distinct clusters with some hybridization, or abundant polymorphism within panmictic populations with some kind of ecological sorting occurring during nest establishment in different substrates.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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