Adelomyrmex tristani

Adelomyrmex tristani is a common cloud forest ant throughout Central America. It is most often collected in Winkler samples, but may also occur at baits.

Identification
Longino (2012) - Adelomyrmex tristani was recognized by Fernández (2003) as highly variable and likely consisting of multiple cryptic species. Large community samples taken by the LLAMA project revealed that at several sites in Central America, two sympatric species occur that both key to A. tristani. In this work I hypothesize two broadly sympatric species, each of which shows substantial geographic variation. In general, when the two species co-occur, A. tristani is the smaller of the two, with shorter, denser, more reclining pilosity, especially on the face and gaster. Adelomyrmex paratristani is larger, with longer, sparser, more erect setae. Where the range of A. tristani overlaps with A. paratristani, the queen has the mesonotum largely smooth and shining, while A. paratristani has the mesonotum largely longitudinally rugose, with an anteromedian triangular patch that is smooth and shining.

In the southern part of the range, where it does not overlap with A. paratristani, the queens have mesonotal sculpture like A. paratristani. In broad terms, A. tristani shows centers of abundance along the Pacific side of Central America, in the Sierra de Chiapas, the Guatemalan volcanoes from Volcan Atitlán to the mountains east of Guatemala City, the Sierra de Comayagua in Honduras, western and southern Nicaraguan mountains, and the mountains of Costa Rica. It becomes a rare element as one moves inland and eastward. In contrast, A. paratristani dominates the core mountain areas of northern Nicaragua, Honduras, Guatemala, and central Chiapas.

Two populations sampled by the LLAMA project are distinctive variants. The population on the south slope of Volcán Atitlán has very short propodeal spines, reduced to short, 90° angles, and the pilosity is very short. Populations in the Sierra de Chiapas to the north and the mountains around Guatemala City to the east have more developed, acute propodeal spines, and the pilosity is slightly longer. A population near La Unión, Guatemala, in Zacapa Department, has relatively sparse, erect gastral pilosity, like A. paratristani, and the dorsal promesonotal rugae are weak, on some specimens leaving a smooth shiny region anteromedially. The population is clearly differentiated from the local version of A. paratristani, in pilosity and size. HW of A. tristani in this population is 0.48–0.56 mm. The local population of A. paratristani has HW 0.62–0.68, and the pilosity is longer.

Key to Adelomyrmex of the New World mainland

Distribution
Longino (2012) - Mexico to Costa Rica, AntWeb images of a specimen from an Ecuadorian cloud forest look like A. tristani, and thus the range may extend into South America.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Guatemala, Honduras, Mexico, Nicaragua.

Biology
Longino (2012) - At multiple sites in Central America it occurs in sympatry with Adelomyrmex paratristani, a species whose range is contained largely within the range of A. tristani. There is a tendency for A. tristani to be most abundant in regions peripheral to the range of A. paratristani. There is some geographic variation in both A. tristani and A. paratristani, such that both could be split into multiple allopatric or parapatric species in the future, but currently there is no evidence for multiple sympatric forms within the current definition of A. tristani.

Adelomyrmex tristani is most abundant in the northern part of its range, in the Cordillera de Chiapas, extending into the mountains of western Guatemala. It is abundant in cloud forest from 1500-2000 m, occurring in up to 70% of quantitative miniWinkler samples. It occurs as high as 2700 m at Cerro Huitepec near San Cristobal de las Casas, Chiapas.

Castes
Males have yet to be collected.

Nomenclature

 *  tristani. Apsychomyrmex tristani Menozzi, 1931b: 269, fig. 6 (w.) COSTA RICA. Fernández, 2003b: 30 (q.). Combination in Adelomyrmex: Kempf, 1972a: 18. Senior synonym of brevispinosus: Longino, 2012: 32.
 * brevispinosus. Adelomyrmex brevispinosus Fernández, in Fernández & Mackay, 2003: 596, figs. 1-3 (w.) COSTA RICA. Junior synonym of tristani: Longino, 2012: 32. See also: Fernández, 2003b: 15.

Longino (2012) - Adelomyrmex brevispinosus was differentiated from A. tristani by a small median smooth spot on the dorsal promesonotum. Specimens were reported from Costa Rica and Chiapas. However, specimens of A. brevispinosus from these two different regions otherwise look identical to their respective surrounding populations of A. tristani, paralleling the geographic variation. I conclude that A. brevispinosus falls within the intraspecific variability of A. tristani.

Worker
Fernández (2003) - (n=40). HL 0.53-0.73 HW 0.45-0.65 SL 0.29-0.41 EL 0.05-0.08 WL 0.53-0.73 GL 0.63-0.92 TL 2.00-2.84 CI 90-91 SI 55-63.

Head with posterior margin weakly flat to feebly concave. Mandibles with 5 to 6 teeth decreasing in size from the apical teeth. Tooth of basal margin of mandible not protuberant, smaller than subapical masticatory tooth. Eyes small, with 7 to 22 facets. Hypostomal tooth small but visible. Promesonotum slightly convex, higher than propodeal dorsum; metanotal groove well marked. Lateral sides of pronotum angulated. Propodeal spiracle rounded. Propodeum sloping, with the spines variable in size and shape, from low, triangular to long and narrow. Petiole high, with anterior side sloping and posterior side more or less feebly convex; sometimes petiole nearly quadrate, with anterior and posterior faces nearly parallel. Postpetiole campaniform with a ventral transverse ridge toothlike as seen in profile. Sting well developed. Mandibles dorsally with moderate longitudinal rugulations. Clypeal plate smooth and shining. Head frons longitudinally rugulate, head sides irregularly rugulated and mixed with punctures. Promesonotal dorsum variously sculptured, from longitudinal fine rugulae to longitudinal to strong coarse costae, in some workers the rugae or striae mixed, anteriorly oblique to transverse, in a few workers only a very few central longitudinal rugae visible. Promesonotal rugae or striae mixed with punctures. Propodeal declivity transversely rugulated between propodeal spines. Declivitous face of propodeum from smooth to covered with transverse rugae. Petiole and postpetiole normally transversely rugulated, sometimes times dorsally smooth and shining. Legs and gaster smooth and shining.

Hairs yellowish, long and flexuous on the body, more short and appressed on antennae and legs. Body black, dark brown or brown, legs light brown, tarsi yellowish.

Queen
Fernández (2003) - HL 0.75 HW 0.66 SL 0.45 EL 0.11 WL 0.84 GL 1.05 TL 3.22 CI 88 SI 68.

As worker with the following differences: Mandibles with all teeth of masticatory border of similar size. Three ocelli present. 12–13 ommatidia in the largest diameter of eye. Pronotum laterally costulated. Promesonotum longitudinally costulated with areas smooth and shining variable, from anterior half to nearly all promesonotum. Metanotum longitudinally costulated. Mesopleurae with longitudinal costulation and areas smooth and shining. Propodeum costulated longitudinally in the sides, transversely in the declivitous face.