Alternative life-histories in a socially polymorphic ant

Abstract

Social organisms vary greatly in the number of breeders per group; yet, the causes and consequences of this variation remain poorly known. Here, we show that variation in social structure is tightly linked with changes in several fundamental life-history traits within one population of ants. Multiple-queen colonies of Formica selysi were much more populous than single-queen ones. They also occurred in areas of higher nest density, had longer colony lifespan, produced smaller queens that presumably disperse less, and invested less in reproductive individuals relative to workers. These multiple changes in life histories are consistent with a shift in the mode of colony foundation and the degree of philopatry of queens. They may also provide various fitness benefits to members of multiple-queen colonies and are likely to play a central role in the evolution and maintenance of polymorphic social structures.

Effects of the social environment on the survival and fungal resistance of ant brood

“…Each queen usually mates with one male, rarely with two (Chapuisat et al 2004;Schwander et al 2005). The number of workers per colony is highly variable, with approximately ten times more workers in colonies headed by multiple queens than in colonies headed by a single queen (Rosset and Chapuisat 2007). Workers from singlequeen (=monogyne) colonies are also significantly larger than workers from multiple-queen (=polygyne) colonies (Schwander et al 2005) and have a slightly higher activity in one component of the immune system causing bacterial growth inhibition, even when controlling for body size (Castella et al 2010).…”

Covariation between colony social structure and immune defences of workers in the ant Formica selysi

“…The transition from monogyny to polygyny is generally associated with major changes in dispersal, colony demography, nest density and relative investment in reproduction and maintenance (Hölldobler and Wilson, 1977;Keller, 1993;Rosset and Chapuisat, 2007). Such changes at the colony level may result in modifications of individual characteristics, including physiological traits.…”

“…We sampled workers in monogyne and polygyne field colonies and measured three major components of their immune system, the bacterial growth inhibitory activity, bacterial cell wall lytic activity and prophenoloxidase activity. We predicted that workers originating from monogyne colonies should have higher levels of immune defences than workers originating from polygyne colonies, because workers from monogyne colonies were more resistant to a fungal challenge (Reber et al, 2008), were significantly larger (Schwander et al, 2005) and represented a higher energetic investment for the colony (Rosset and Chapuisat, 2007). In addition, we also examined if the three components of the immune system varied significantly among colonies.…”

Can alternative pathways mediate the influence of queen number on nestmate discrimination in ants?

“…On the other hand, the influence of the social origin of an intruder on aggressiveness could be a by-product of other intruders' traits that are under selection pressures specific to monogyne or polygyne colonies. 17,18 For instance, the costs of nepotistic behaviors of workers over the care of brood from different matrilines in polygyne colonies 19 could select for an egg-signal that prevent workers from discarding eggs according to their maternal origin and by doing so, could trigger the general tolerance of polygyne eggs by foreign workers. Alternatively, the partial overlap of other socially-selected signals of monogyne and polygyne colonies could explain the lower aggression observed between workers from the same versus different social forms.…”