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.