Nesomyrmex asper

Identification
Longino (2006) - Costa Rican N. asper differs from South American N. asper in having a more elongate petiole. If further research reveals discontinuous variation, N. tristani (a synonym of N. asper) might emerge as a distinct Central American species. But Kempf noted that N. asper itself is highly variable, with two infraspecific synonyms. If N. tristani is distinct, then N. asper will probably resolve into multiple differentiated forms.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Costa Rica, Ecuador, Paraguay, Trinidad and Tobago, Venezuela.

Nomenclature

 *  asper. Leptothorax asper Mayr, 1887: 618 (w.q.m.) BRAZIL. Combination in L. (Goniothorax): Emery, 1896g: 59 (in key); in L. (Nesomyrmex): Kempf, 1959c: 414; in Nesomyrmex: Bolton, 2003: 272. Senior synonym of rufa, sulfurea: Kempf, 1959c: 414; of tristani: Longino, 2006b: 136.
 * rufa. Leptothorax (Goniothorax) asper var. rufa Emery, 1896g: 61 (w.q.) BRAZIL. Junior synonym of asper: Kempf, 1959c: 414.
 * tristani. Leptothorax (Goniothorax) tristani Emery, 1896g: 61 (w.q.) COSTA RICA. Combination in L. (Nesomyrmex): Kempf, 1959c: 415; in Nesomyrmex: Bolton, 2003: 272. Junior synonym of asper: Longino, 2006b: 136.
 * sulfurea. Leptothorax asper var. sufurea Forel, 1912g: 18 (w.) BRAZIL. [Justified emendation of spelling to sulfurea by Emery, 1924d: 250.] Junior synonym of asper: Kempf, 1959c: 414.

Longino (2006):

Kempf (1959) expressed doubt about the distinctness of the two species N. asper and Nesomyrmex tristani, but he saw evidence of two sympatric species in the vicinity of Caracas, Venezuela. One of the species matched his concept of N. asper. The other one differed from N. asper as follows:

“1) Longitudinal rugae on cephalic dorsum regular, more widely spaced, often fading out to a variable degree on front, vertex and occiput. 2) Rugae of thoracic dorsum usually less strikingly vermiculate, obsolescent on basal face of epinotum. 3) Epinotal spines shorter, more elevated and more diverging toward apex. 4) Petiolar node, as seen from the side, more depressed; broader, with sides diverging caudad, when seen from above. Each side postero-laterally with at least two prominent teeth. 5) Postpetiole laterally with two prominent teeth. 6) First gastric tergite generally distinctly transverse, broader than long.” This second form also matched Forel's N. asper antoniensis, from the Santa Marta region of Colombia, and additional material from Trinidad and Colombia. Kempf misidentified this second form as N. tristani, and illustrated N. tristani (figs. 11 and 15) with a worker from Trinidad.

The type locality of N. tristani is Costa Rica. I have examined abundant material from Costa Rica, and it all closely matches Kempf's description and illustration of N. asper. In Emery's description of the N. tristani worker, he states that the side of the postpetiole has two obtuse tubercles that are more or less distinct, which matches all the Costa Rican material I have seen. In contrast, workers from Colombia and Venezuela that I have examined have distinct acuminate teeth on the postpetiole, matching Kempf’s description of what he thought was N. tristani. I conclude that N. tristani is a junior synonym of N. asper, and that what Kempf thought was N. tristani is a distinct species. Forel's N. antoniensis is the valid name for the form.

Type Material
Syntype worker, queen, male: Brazil, Santa Catarina.