The first fossil replete ant worker establishes living food storage in the Eocene

Worker specialization extends the behavioral and ecological repertoire of ant colonies. Specialization may relate to colony defense, brood care, foraging, and, in some taxa, storage. Replete workers swell the crop and gaster to store liquid food, which can be accessed by other colony members through trophallaxis. This storage ability, known as repletism, has independently evolved across several ant lineages, but the temporal history of this trait has not yet been investigated. Here, we describe the first fossil replete in the extinct species Leptomyrmex neotropicus Baroni Urbani, 1980 preserved in Miocene-age Dominican amber. Together with new evidence of repletism in L. neotropicus’ extant sister species, Leptomyrmex relictus Boudinot & al., 2016, we reconstruct the pattern of acquisition and descent in this storage-linked trait. Our ancestral-state reconstruction suggests that Leptomyrmex acquired replete workers in the Eocene and may therefore represent the earliest instance of so-called “honeypot” ants among all known ants, both living and extinct.