Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
Minor worker: head length 0.53mm, head width 0.48mm, scape length 0.41mm, Webers length 0.60mm (n=1). Head flattened behind; mesonotal suture absent; humeri barely produced as small tubercles; propodeal spines short; face smooth and shining; pronotum smooth and shining; katepisternum with center smooth and shining, margin foveolate; ventral half of side of propodeum smooth and shining, dorsal half and dorsum foveolate; gaster smooth and shining; dorsal pilosity abundant, moderately long, flexuous; color dark brown.
Major worker: head length 0.90mm, head width 0.82mm, scape length 0.46mm (n=1). Face dark brown; anterior half of face with subparallel, longitudinal rugae; rest of face smooth and shining; clypeus smooth; antennal scrobes present in the form of broad, shallow depressions beneath apices of scapes; scrobes smooth and shiny; hypostomal margin straight, with no median tooth, and pair of small teeth about half distance to recessed teeth flanking mandible bases (Figure); dorsal pilosity abundant; head with abundant, short setae projecting from sides of head in face view.
Similar species: at La Selva this species might be confused with P. tennantae. Minor workers of P. tennantae have relatively longer scapes, longer propodeal spines, larger propodeal spiracles, and longer dorsal setae. Major workers of P. tennantae have more extensive longitudinal rugae on the posterior face and the inner hypostomal teeth are stouter and closer together relative to the outer hypostomal teeth.
Range
Southern Brazil (type locality), Costa Rica. Costa Rica: Atlantic lowlands.
Natural History
This species occurs in lowland rainforest. The types were collected in Caraguatatuba forest reserve in the Brazilian state of Sao Paulo. In Costa Rica there are few records, all from La Selva Biological Station and vicinity. Workers have been collected in Malaise traps, Winkler samples, and canopy fogging samples. One nest series was collected at La Selva, from under loose bark of a large, leaning, dead Cecropia trunk. The bark was intact but easily sloughing in big sheets.
Comments
Pheidole lucaris has a strikingly disjunct distribution. Costa Rican material was compared with the types and the match is strikingly close. Among other similarities, the shape of the hypostomal margin and the form of the innner hypostomal teeth are very similar. In Costa Rica, many Pheidole species have the inner hypostomal teeth large and closely spaced near the midline, and many species have the inner hypostomal teeth thin, sharp, and widely spaced, closer to the outer hypostomal teeth than to the midline. The inner teeth of P. lucaris are small and exhibit spacing that is intermediate between the aforementioned groups.
Several mechanisms could cause the observed disjunction. (1) The two populations are not the same species and instead are the result of extreme morphological convergence. (2) The species is only apparently disjunct due to undersampling. (3) The species is truly disjunct, and the disjunction due to long-distance dispersal. Neither population occurs in disturbed or synanthropic habitats, typical hallmarks of recently introduced species. (4) The species is truly disjunct due to vicariance. It could have been formerly widespread in the Neotropics, but has gone extinct over the large central part of its range, perhaps due to displacement by new forms originating in Amazonia.
Page authors:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
Stefan Cover, Museum of Comparative Zoology, Harvard University, Cambridge MA 02138 USA. scover@oeb.harvard.edu
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