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Original Article

Natural history and nest architecture of the fungus-farming ant genus Sericomyrmex (Hymenoptera: Formicidae)

JeŇ°ovnik, A., Chaul, J. & Schultz, T.

Abstract: The fungus-farming ant genus Sericomyrmex (Formicidae: Myrmicinae: Attini) contains 11 species distributed from northern Mexico to southern Brazil. Within their nests, all Sericomyrmex species grow highly specialized, obligately symbiotic fungi, which they use for food. Sericomyrmex is the youngest fungus-farming ant genus, the product of a recent, rapid radiation, with a crown-group age estimate of 4.3 million years. We review the literature and report newly acquired data on the natural history of Sericomyrmex, with a focus on nesting biology. We present data for 19 collected nests (16 complete and three partial excavations) of seven different Sericomyrmex species from Mexico, Costa Rica, Guyana, Peru, and Brazil. The nests of Sericomyrmex are subterra nean and consist of subelliptical to subspherical chambers connected by narrow tunnels, similar to those in most other attine ant genera. Chambers of the collected nests were 5 - 17 cm wide and 3.5 - 15 cm high, with average volumes of 96 - 1435 cm3. Total nest volume varied from 193 - 7179 cm3. Chambers occurred from 3 to 35 cm from the surface, but nests of S. parvulus Forel, 1912 were likely more than one meter deep at two localities where we were unable to finish excavations. In 18 out of 19 collected nests, at least some of the chambers were either directly underneath the nest entrance or offset by up to 10 cm, while in one S. bondari Borgmeier, 1937 nest they were displaced hori zontally > 2 m from the nest entrance. Indirect evidence suggests that such lateral displacement may be common in Sericomyrmex. We document the presence of an external waste midden in a nest of S. mayri Forel, 1912 in Guyana, the first such record for the genus. Based on 904 habitat records in our Sericomyrmex database, Sericomyrmex species inhabit a wide variety of habitats, but nine out of 11 species are more commonly collected in forested areas and are less often collected in very dry or open areas. Two species, S. scrobifer Forel, 1911 and S. maravalhas JeŇ°ovnik & SchulTz, 2017, are distributed almost exclusively in Brazilian savanna habitats, that is, cerrado.

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