Ants in the Azteca pittieri complex are the primary obligate inhabitants of C. alliodora throughout Costa Rica. In some areas character variation is discontinuous, suggesting discrete, parapatric species, but these differences are not stable geographically. In a plot of queen head length vs. head width (Figure), specimens from the Pacific lowlands form one cluster, specimens from above 500m near Monteverde form a second cluster, and specimens from the Atlantic lowlands and the Valle General form a third cluster somewhat intermediate between the first two. One queen from Santiago de Puriscal (swept from vegetation, and thus not known with certainty to be a C. alliodora ant) is discontinuously larger than all other queens examined.
Collections along an elevational transect (400-900m along the road from the Pan American Highway to Monteverde) revealed two phenotypes that could be interpreted locally as two species. One form has relatively small queens (Figure), and workers with the margin of the vertex shallowly excavated and the sides of the head nearly flat (Figure). The other form has relatively large queens, and workers with the margin of the vertex more deeply excavated and the sides of the head more convex. The two forms have a sharply parapatric distribution, with small-queen colonies occurring from 400-500m, and large-queen colonies occurring from 500-900m. In the narrow zone of sympatry both forms were found in adjacent trees, and founding queens of both forms were found in different nodes of the same small stump sprout or sapling. A similar pattern may occur on the more southern Pacific slopes, where one small and two large queens were collected near Palmar Norte (Figure).
Variation in queen propodeal pilosity is discordant with head shape. Queens from the Pacific side of Costa Rica, regardless of queen head shape, have dense pilosity on the propodeum (Figure). Queens from La Selva on the Atlantic slope have sparser propodeal pilosity, and it varies from a uniform covering to a discontinuous covering, with a few setae near the mesopropodeal suture, a gap with no setae, and a cluster of setae posterior to the spiracle (Figure). La Selva queens with the relatively shortest heads are indistinguishable from two queens collected from Hone Creek south of Limon, and these relatively small queens exhibit the extreme of propodeal pilosity reduction. Relatively larger queens tend to have more uniform propodeal pilosity.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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