Mycocepurus smithii

A wide ranging member of its genus it has been shown that asexual reproduction, which is know from many populations, has secondarily evolved numerous times. (Rabeling et al. 2011)

Identification
This is one of the two species in which the workers lack the well-developed promesonotal spines in the center of the crown. Generally there is a very low, sharp crest in this region. In most cases, it can be separated from the other species that lacks these spines, the Brazilian Mycocepurus obsoletus, on the basis of the distributions. Otherwise, it can be separated by the lateral pronotal spines, which are long and sharp, not short and blunt as in M. obsoletus. Specimens that have bumps in the center of the crown of spines, could be confused with Mycocepurus tardus, but can be usually separated as M. tardus has definite promesonotal spines. The females have small lateral pronotal spines, and tiny inferior lateral pronotal spines. The females are slightly larger than those of Mycocepurus curvispinosus (~ 3 mm total length). Additionally the propodeal spines are bent slightly downward. These characters would easily separate it from females of M. curvispinosus. (Mackay et al. 2004)

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, French Guiana, Greater Antilles, Guadeloupe, Guyana, Haiti, Honduras, Lesser Antilles, Mexico, Nicaragua, Panama, Paraguay, Peru, Puerto Rico, Saint Lucia, Suriname, Trinidad and Tobago, Venezuela.

Habitat
Ranging from open, disturbed areas, burned rain forest, sub-deciduous tropical forests, to tropical rain forests, and moist gullies.

Biology
Mackay et al. (2004) provides the following synopsis - Kempf (1963) reviewed the biology of this species. It nests only in the soil (Torres 1989), often with the entrance surrounded by a turret. Specimens in México are often found nesting under stones. The nest cavity is very small, only a few cm in diameter, and is connected with several fine, threadlike, tunnels. The nest may be as deep as a meter. There are often several nests in a single area, which suggests a single large nest with multiple entrances. The colonies are polygynous. The small, sluggish workers carry dry leaves, caterpillar dung (Kempf, 1963) and bat dung (Levins et al. 1973) back to the nest, where they culture their fungus. Populations vary greatly over time, and they may be abundant in some areas (Torres 1989, Majer, 1997). This species may be associated with the leaf-cutting ant Atta sexdens, and is often found in the same habitat as Mycocepurus goeldii, with which it has mixed mating swarms, although hybridization apparently does not occur. This species apparently tolerates a number of other species in its nest, including Mycocepurus curvispinosus, Solenopsis sp. (thief ants) and Acropyga sp. It forages together with M. curvispinosus.

Kellner et al. (2015) - Mycocepurus smithii is an unusual attine ant since it is the only known asexually reproducing fungus-farming ant (Himler et al. 2009; Rabeling et al. 2009), such that each colony is comprised of a single ant clone tending a garden with a single fungus clone (Kellner et al. 2013).

In our study population in central Panama, we found a total of 11 ant clones and 9 fungus clone lineages in 52 colonies. Phylogenetic analyses suggested that ant colonies regularly exchange fungal cultivars or domesticate novel fungi from free-living populations into symbiosis (Kellner et al. 2013).

Our analysis of bacterial communities of M. smithii colonies from the field shows that colonies of ants and fungus gardens are distinct from their surroundings, and that the microbiome of ants and fungus gardens is mostly dominated by the genera Lactobacillus and Pantoea. Another discovery was the lack of significant differentiation between ant- and garden-associated bacterial communities, which contrasts with the findings of similar analyses on the higher derived attine Trachymyrmex septentrionalis (Ishak et al. 2011a), where ant- and garden-associated bacteria formed distinct communities. These results suggest that M. smithii ants and symbiotic fungi may exchange bacteria when the ants move through their gardens or ingest garden material with the result that the bacterial communities are homogenized to a greater extent than in the higher attine T. septentrionalis. Mycocepurus smithii bacterial communities were also clearly separated from the surrounding nestwalls and adjunct soil from outside the nests; thus, the bacteria found on ants and gardens are not the result of accidental contamination from environmental sources such as the surrounding soil. This suggests that the ants are able to shape their own microbial environment, and most likely control the microbial communities on their cuticle and on the gardens by grooming off unwanted harmful bacteria (Ferńandez-Maŕın et al. 2009).

Our analysis of fragments of a single fungus garden shows that microbial communities within M. smithii gardens are not homogeneous. Gardens of M. smithii have a hanging structure, with curtain-like strands hanging from the ceiling of the nest cave, which is unlike the relatively solid globule-shaped gardens typical of most leaf-cutting ants and other higher derived attines (Seal and Tschinkel 2008). Within a single strand, the fungus grows from top to bottom (the ants elongate the strand as it grows). Because M. smithii in the field and in the lab start new gardens in the center of a chamber ceiling rather than near the ceiling periphery, it is likely that each garden has an age profile from the inside to the outside (central older parts, peripheral younger parts). The nine garden fragments analyzed clustered into five likely groups, with the central (presumably older) parts forming one of these groups.

Haiti
From Wheeler and Mann (1914): Several workers....were taken at Cape Haitien and Diquini. The nests in the latter locality were in the form of small craters and were located in clay soil in a moist spot in a gully formed by a small stream. Several colonies were nesting in an area about 25 ft. square, but in no other place in the neighborhood. At Cape Haitien only a single colony was found and this was nesting in a road leading across the mountains and nearly at the summit.

Nomenclature

 *  smithii. Atta (Mycocepurus) smithii Forel, 1893g: 370 (w.) ANTILLES. Kempf, 1963b: 425 (q.). Combination in Mycocepurus: Wheeler, W.M. & Mann, 1914: 42. Senior synonym of attaxenus, bolivianus, borinquenensis, eucarnitae, manni, reconditus, tolteca, trinidadensis: Kempf, 1963b: 425.
 * borinquenensis. Atta (Mycocepurus) smithi var. borinquenensis Wheeler, W.M. 1907c: 718 (w.) PUERTO RICO. Combination in Mycocepurus: Emery, 1924d: 335. Junior synonym of smithii: Kempf, 1963b: 425.
 * tolteca. Atta (Mycocepurus) smithi var. tolteca Wheeler, W.M. 1907c: 718 (w.) MEXICO. Junior synonym of smithii: Kempf, 1963b: 425.
 * eucarnitae. Mycocepurus smithii var. eucarnitae Forel, 1913l: 235 (w.) CUBA. Junior synonym of smithii: Kempf, 1963b: 425.
 * attaxenus. Trachymyrmex attaxenus Menozzi, 1936b: 85 (w.q.) BRAZIL. Junior synonym of smithii: Kempf, 1963b: 425.
 * reconditus. Mycocepurus reconditus Borgmeier, 1937b: 246, figs. 34-36 (w.q.) BRAZIL. Junior synonym of smithii: Kempf, 1963b: 425.
 * trinidadensis. Mycocepurus smithi var. trinidadensis Weber, 1937: 378, fig. 1 (w.q.) TRINIDAD. Junior synonym of smithii: Kempf, 1963b: 425.
 * bolivianus. Mycocepurus bolivianus Weber, 1938b: 155, fig. 8 (w.) BOLIVIA. Junior synonym of smithii: Kempf, 1963b: 425.
 * manni. Mycocepurus manni Weber, 1938b: 156, figs. 1, 2 (q.) BOLIVIA. Junior synonym of smithii: Kempf, 1963b: 425.