Nest architecture, fungus gardens, queen, males and larvae of the fungus-growing ant Mycetagroicus inflatus Brandão & Mayhé-Nunes

Abstract

All known fungus-growing ants (tribe Attini) are obligately symbiotic with their cultivated fungi. The fungal cultivars of “lower” attine ants are facultative symbionts, capable of living apart from ants, whereas the fungal cultivars of “higher” attine ants, including leaf-cutting genera Atta and Acromyrmex, are highly specialized, obligate symbionts. Since higher attine ants and fungi are derived from lower attine ants and fungi, understanding the evolutionary transition from lower to higher attine agriculture requires understanding the historical sequence of change in both ants and fungi. The biology of the poorly known ant genus Mycetagroicus is of special interest in this regard because it occupies a phylogenetic position intermediate between lower and higher ant agriculture. Here, based on the excavations of four nests in Pará, Brazil, we report the first biological data for the recently described species Mycetagroicus inflatus, including the first descriptions of Mycetagroicus males and larvae. Like M. cerradensis, the only other species in the genus for which nesting biology is known, the garden chambers of M.inflatus are unusually deep and the garden is most likely relocated vertically in rainy and dry seasons. Due to the proximity of nests to the Araguaia River, it is likely that even the uppermost chambers and nest entrances of M. inflatus are submerged during the rainy season. Most remarkably, all three examined colonies of M. inflatus cultivate the same fungal species as their congener, M. cerradensis, over 1,000 km away, raising the possibility of long-term symbiont fidelity spanning speciation events within the genus.

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

“…Although it seems initially surprising that this obligately ant‐associated fungal species is found across such a broad geographic range and in both wet and dry habitats, similar patterns have been observed in other ant‐cultivated fungi and may in fact be the norm (e.g. Rabeling, ; Ješovnik et al ., ; Sosa‐Calvo et al ., ). It is possibly significant that the fungal species associated with X. explicatus is the sister group (along with another, more closely related species) to the derived ‘ amabilis‐mayri ’ fungal cultivar group, which may comprise a single fungal species grown by a disproportionately large number of Trachymyrmex and Sericomyrmex species across a wide geographic range (Ješovnik et al ., ).…”

Rediscovery of the enigmatic fungus-farming ant "Mycetosoritis" asper Mayr (Hymenoptera: Formicidae): Implications for taxonomy, phylogeny, and the evolution of agriculture in ants

“…In addition, the males of Mycetophylax asper , which were unknown at the time of Kempf (17) revision of the Cyphomyrmex strigatus group, have 12-segmented antennae, a deviation from the ancestral condition of 13 found in most fungus-farming ants. Although this condition occurs in other members of the former Cyphomyrmex strigatus -group ( Mycetophylax faunulus , Mycetophylax auritus ) and in Mycetophylax conformis [ 34 ], it remains unclear whether this shared reduction is due to homology or homoplasy because (i) Mycetophylax morschi and Mycetophylax simplex males are reported to have 13-segmented antennae [ 34 ] and (ii) the 12-segmented condition has arisen independently multiple times in the Attina, including in Mycetagroicus inflatus , species of Sericomyrmex , Trachymyrmex opulentus [ 23 , 34 , 36 ], and some social parasites [ 84 – 86 ].…”

“…Results from the fungal molecular phylogenetic analyses indicate that the fungal species cultivated by Mycetophylax asper falls within Clade 2 of the lower attine cultivars ( Fig 9 , left and center trees) [ 42 , 88 ]. More specifically, the fungal cultivar of Mycetophylax asper belongs to Clade 2, subclade F ( Fig 9 , center and right trees) of Mehdiabadi et al, [ 41 ], likely a single fungal species that is also cultivated by Cyatta abscondita [ 7 ], Kalathomyrmex emeryi , Mycetagroicus cerradensis [ 43 ], Mycetagroicus inflatus [ 36 ], Mycocepurus smithi , Myrmicocrypta buenzlii , and two species in the former Cyphomyrmex strigatus group ( Mycetophylax faunulus and Mycetophylax strigatus ) [ 41 ]. Curiously, the ITS fungal strains most closely related to those cultivated by the forest-dwelling Mycetophylax asper are also cultivated by cerrado-dwelling species ( Cyatta abscondita , Mycetagroicus inflatus , Mycetagroicus cerradensis , and Kalathomyrmex emeryi ), in some cases thousands of kilometers away.…”

Revision of the fungus-farming ant genus Sericomyrmex Mayr (Hymenoptera, Formicidae, Myrmicinae)

“…Males of Sericomyrmex can be separated from most other attine males by the presence of 12 antennal segments, deviating from the usual 13 segments in the males of most attine species, and from the 11 segments found in males of some social parasites ( Gallardo 1916 , Schultz et al 1998 , Rabeling and Bacci 2010 ). However, 12 antennal segments occur in parallel in Cyphomyrmex (e.g., C. faunulus Wheeler and C. auritus Mayr), Mycetophylax conformis Mayr, Mycetagriocus inflatus Brandão & Mayhé-Nunes, and Trachymyrmex opulentus ( Mayr 1887 , Wheeler 1925a , Ješovnik et al 2013 , Klingenberg and Brandão 2009 ). Males of Sericomyrmex can be separated from the other attine ant males with 12-segmented antennae by the following: presence of long, flexuous hairs on most of the body (no hair or very short and sparse hair in M. inflatus , Cyphomyrmex , Mycetophylax , and Trachymyrmex ); dull, light brown integument, faintly reticulate and not strongly sclerotized (strongly sclerotized and dark brown to black in C. faunulus and M. conformis , light brown but costate on head and mesosoma in Trachymyrmex ), scutellum with flat to slightly notched posterior margin, but never with sharp and long posterior processes (as in Trachymyrmex , C. faunulus ), smooth posterior cephalic corners (with a small sharp denticle in C. faunulus and C. auritus ).…”

“…Morphological terminology and measurement indices follow Snodgrass (1910), Tulloch (1929), Bolton (1994), Schultz and Meier (1995), Mackay et al (2004), Rabeling et al (2007), Sosa-Calvo and Schultz (2010), and Ješovnik et al (2013). Male genitalia terminology follows Boudinot (2013).…”