Ecological drivers and reproductive consequences of non-kin cooperation by ant queens

Abstract

The fitness consequences of joining a group are highly dependent on ecological context, especially for non-kin. To assess the relationships between cooperation and environment, we examined variation in colony reproductive success for a harvester ant species that nests either solitarily or with multiple, unrelated queens, a social strategy known as primary polygyny. We measured the reproductive investment of colonies of solitary versus social nesting types at two sites, one with primarily single-queen colonies, and the other with a majority of polygynous nests. Our results were consistent with the hypothesis that cooperative nesting by unrelated ant queens is likely a selection response to difficult environments, rather than a strategy to maximize reproduction under favorable conditions. Fewer colonies at the primarily polygynous site reproduced than at the site with primarily single queen nests, and those that did had lower reproductive investment, as measured by number and total mass of reproductives. Assessment of ecological conditions also support the harsh environment hypothesis. Colony density in the multi-queen population was higher, and nearest neighbor distances were lower for non-reproducing than reproducing colonies. To more directly test the hypothesis that colony reproduction was ecologically constrained, we experimentally supplemented food resources for a subset of colonies at the primary polygyny site. Supplemented colonies increased reproductive investment levels to equal that of colonies at the single-queen population, further indicating that environmental pressures are severe where primary polygyny is dominant, and may drive the evolution of non-kin cooperation in this context.

Intraspecific variation in colony founding behavior and social organization in the honey ant Myrmecocystus mendax

“…Primary polygyny has downstream costs to individual queens in term of sharing reproduction (Gadau andFewell 2009, Haney andFewell 2018). Per-capita production of sexual offspring is likely constrained by resource partitioning among nestmate queens.…”

Fecundity determines the outcome of founding queen associations in ants

“…Pleometrosis provides clear benefits, but these benefits are only inherited by the surviving queens, and the losing queens pay the great cost of dying without contributing to the next generation. Natural selection should thus favour queens that decide whether or not to join a pleometrotic association based on the relative benefits compared to individual foundation - these may differ across ecological contexts (Haney & Fewell, 2018) - and the likelihood of surviving the association. As fecundity appears to determine queen survival in L. niger , queens may have evolved the ability to assess the fecundity of potential partners.…”

Worker demography and behavior in a supercolonial ant colony: The case of the desert antCataglyphis niger

“…These apparent stochastic interactions raise many questions regarding the evolutionarily stable mechanisms in a polygyne supercolony. Most polygyne species are believed to have evolved due to ecological constraints (Haney & Fewell, 2018). However, in a few cases a genetic mechanism was found to be behind such polygynyfor example, "the social chromosome," a non-recombinant inversion that is present only in the polygyne form (Purcell, Brelsford, Wurm, Perrin, & Chapuisat, 2014;Wang et al, 2013).…”