Scaling of body weight and fat content in fungus-gardening ant queens: does this explain why leaf-cutting ants found claustrally?

Abstract

Offspring traits are among the most important life history traits, yet we lack an adequate understanding of their role in social insect life history evolution. Colony founding in the fungus-gardening ants (Tribe Attini) is different from most other ant species because the queens forage during the founding phase. Queens of the most derived genus, Atta, are the only attines that exhibit the more typical claustral founding, where the queens seal themselves in a below-ground chamber and produce their first generation of workers with only body fat reserves. Here I report the dry weights, fat content and energetic value of newly mated queens of ten attine species. Published phylogenies were used to make inferences on the evolutionary transitions in this clade. It appears that the evolution of fungus-gardening was associated with the manufacture of smaller, leaner queens as basal taxa are characterized by small bodies that contain relatively less fat than derived taxa. Moreover, there appears to be an allometric function between fat, energetic content and dry weight, which means that for fatter and claustral queens to develop, they also must become larger.

Ant-fungal species combinations engineer physiological activity of fungus gardens

“…Colonies of both species were obtained by rearing newly mated queens collected immediately after mating flights (Seal, 2009;Seal and Tschinkel, 2007c) in 2010 and 2011. Colonies were maintained in plaster-lined boxes and fed ad libitum in a manner similar to previously published methods (Seal and Tschinkel, 2007a;Seal and Tschinkel, 2007b).…”

“…Queens were randomly assigned to either the Attamyces or Trachymyces condition and provided with ~50 g of garden (T. arizonensis queens) or 200 g of garden (A. texana queens; owing to the much larger size of Atta queens) (Seal, 2009) The experimental switches on T. arizonensis used in this study were conducted on eight colonies started with queens collected on 27-28 July 2011. Five of these were reared on Attamyces and three on Trachymyces.…”

“…Because Atta queens do not forage during the founding phase (Fernández-Marín et al, 2004;Seal, 2009), they were given substrate only after the first workers emerged. After worker emergence, colonies were connected to a foraging arena via a plastic tube and fed and cleaned at least twice a week.…”

“…One of the more profound evolutionary and ecological transitions occurred in the derived lineages (the 'higher Attini'), the most complex of which are found in the clade containing leaf-cutting ants (genera Atta and Acromyrmex). These ants exhibit large queens, pronounced variation in worker size and colony sizes of immense proportions (>1 million workers); as a result, fungus-growing ants may exert enormous ecological impacts (Hölldobler and Wilson, 2011;Meyer et al, 2011;Seal, 2009;Wilson, 1980;Wirth et al, 2003). Leaf-cutter ants generally cultivate a single species of fungus, called Attamyces bromatificus (hereafter, Attamyces) in its anamorph (vegetative, clonal) growth form and Leucocoprinus gongylophorus in its teleomorph (sexual) form Mueller et al, 2011b;Mueller et al, 1998).…”

Energy substrate used by workers of leaf-cutting ants during nest excavation

“…It is known that the accumulation of body reserves occurs through lipid storage, representing an important role in the evolutionary history of the tribe Attini, developing from a semiclaustral to a claustral founding (Seal 2009). Claustral founding queens do not forage and remain cloistered in their nests, rearing their offspring by metabolizing body reserves (Brown & Bonhoeffer 2003), as in the case of A. sexdens (Autuori 1942).…”