Revisionary studies on the attine ant genus Trachymyrmex Forel. Part 3: The Jamaicensis group (Hymenoptera: Formicidae)

Abstract

We hereby revise the Jamaicensis group of species of Trachymyrmex (Myrmicinae: Attini), as the third part of our taxonomic revisionary studies on this fungus-growing ant genus. The species group we deal with here includes six taxa that share exclusively the antennal scrobes always reaching the posterior margin of the head and ending as two separate projections arising from the preocular and frontal carinae, giving the scrobe posterior region an “opened” appearance and an angular profile to the posterolateral corners, in frontal view. The Jamaicensis group is composed of Trachymyrmex atlanticus n. sp. (eastern Brazil), Trachymyrmex haytianus Wheeler & Mann, 1914 n. st. (Haiti, Jamaica), Trachymyrmex isthmicus Santschi, 1931 (Colombia, Ecuador, Panama), Trachymyrmex ixyodus n. sp. (northern Brazil, Suriname), Trachymyrmex jamaicensis (André, 1893) (Caribbean islands and southern USA), its synonyms (Trachymyrmex sharpii Forel, 1893; Trachymyrmex maritimus Wheeler, 1905 n. syn.; Trachymyrmex jamaicensis var. frontalis Santschi, 1925 n. syn., and Trachymyrmex jamaicensis cubaensis Wheeler, 1937 n. syn.), and Trachymyrmex zeteki Weber, 1940 (Colombia, Costa Rica, Ecuador, Panama). Trachymyrmex jamaicensis antiguensis Weber, 1938 is excluded from the Jamaicensis species group because it belongs to the Trachymyrmex Urichi species group. The only known Trachymyrmex fossil, T. primaevus Baroni Urbani, 1980, from the Dominican amber, does not belong to the Jamaicensis species group, as hypothesized earlier.

The molecular phylogenetics ofTrachymyrmexForel ants and their fungal cultivars provide insights into the origin and coevolutionary history of ‘higher‐attine’ ant agriculture

“…Intriguingly, M. holmgreni was reported by Gonçalves () to cut leaves of the grass Paspalum ancylocarpum Nees ex Steud. Mayhé‐Nunes & Brandão () likewise reported that grass clippings are used as a substrate for cultivating this species' fungus gardens and that grass clippings are also used to construct the turret that forms its nest entrance, an observation corroborated by Albuquerque et al . ().…”

“…Furthermore, the associations between L. gongylophorus and these ant species do not appear to be correlated with habitats occupied by extant species. Three species ( T. desertorum , T. smithi Buren and T. nogalensis Byers) occur in arid regions in North America (Rabeling et al ., ), one ( T. saussurei ) occurs in wet tropical forests in Mexico and northern Central America (Rabeling et al ., ), one ( M. opulentus ) occurs in wet forests from Guatemala to Amazonia (Mayhé‐Nunes & Brandão, ), and one ( P. diversus ) is found in wet forests in northern South America (Mann, ; Kempf, ; Brandão, ). The only geographic correlate of these observed ant–fungus associations is that none of them occurs south of Amazonia.…”

“…Diagnosis: Preocular and frontal carinae subparallel, extending to the posterior cephalic corner to form a more or less distinct antennal scrobe (Mayhé‐Nunes & Brandão, : figs 2, 5, 8, 11, 14; Mayhé‐Nunes & Brandão, : figs 9, 13, 25, 29, 33, 37; Mayhe‐Nunes & Brandão, : figs 1, 5, 9, 15, 19, 23; Rabeling et al ., 2007: figs 8B, 19B). In frontodorsal view, median pronotal spines absent or strongly reduced; when present, tooth‐like and fused at base; in some species apices of both teeth distinguishable, in others, both teeth entirely fused and only recognizable as a single median tooth (Mayhé‐Nunes & Brandão, : figs 11, 15, 27, 31, 35, 39; Mayhe‐Nunes & Brandão, : figs 2, 7, 11, 17, 21, 25). Dorsal surface of mandible smooth and shiny, without distinct striae; in some species [e.g. M. turrifex (Wheeler)] striae present at the base of the mandible. Eyes variable in size and often relatively flat. Widely distributed throughout South America (22 species), with five species in Central America [ M. isthmicus (Santschi), M. opulentus (Mann), M. squamulifer (Emery), M. turrifex (Wheeler), M. zeteki (Weber)], three in the Caribbean [ M. haytianus (Wheeler and Mann), M. jamaicensis (André), M. jamaicensis antiguensis (Weber)], and two in North America [ M. jamaicensis (André), M. turrifex (Wheeler)].…”

Biogeography of mutualistic fungi cultivated by leafcutter ants

“…versicolor , T. desertorum and T. arizonensis in Arizona, and the community of Clade‐A cultivars of diverse leafcutter species, T. intermedius and T. opulentus in northeast South America and in Central America. ( T. opulentus is labelled T. wheeleri in our Figure , but was synonymized by Mayhé‐Nunes & Brandão, .) Trachymyrmex intermedius ranges from Mexico to French Guiana, and T. opulentus ranges from Honduras to northern Brazil, so Clade‐A cultivation by these two Trachymyrmex species may occur in sympatry with the well‐studied leafcutter species in Panamá.…”

Evolution, systematics, and natural history of a new genus of cryptobiotic fungus‐growing ants

“…Simultaneous to, and potentially inspired by, the fundamental biological discoveries of Bates and his contemporaries, late 19th‐century entomologists described and classified many new species of fungus‐growing ants. Fundamental treatises of the 19th and early 20th centuries include taxonomic monographs and evolutionary hypotheses authored by foundational ‘attinologists’ such as Auguste Forel (, ,b), Carlo Emery (, , ), and William Morton Wheeler (, ), laying the basis for subsequent work by Borgmeier (), Gonçalves (), Kempf (, , , ), Kusnezov (), Wilson (), Brandão & Mayhé‐Nunes (, ), Mayhé‐Nunes & Brandão (, , , ), Rabeling et al . (, ), Klingenberg & Brandão (), Sosa‐Calvo & Schultz (), and Ješovnik & Schultz ().…”