Highlighting the article written by M. Motro, U. Motro and D. Cohen in Insectes Sociaux
Written by Insectes Sociaux Editor-in-Chief, Michael Breed
Investigations of colony founding by groups start with the question: What happens if an animal that could survive perfectly well on its own is confined with others of the same species? Queens of the harvester ant species Messor semirufus typically found nests on their own, but occasional observations have been made of small groups of queens founding nests together. Many species of ant solitary queens initiate colonies, but in some species groups of queens come together and co-establish a nest. In this issue of Insectes Sociaux, Motro et al. (2017) investigate the outcomes of keeping M. semirufus queens in small groups. This study fits with a growing literature on how social cooperation might emerge when solitary animals are placed in groups by looking at success of group colony foundation in a species which normally does not express this behavior.
When animals have no option but to occupy the same space, the first obvious outcome is battle and possibly cannibalism. Second, the animals could ignore one another, perhaps only interacting if competing for a limited resource. Third, they could start working together to modify their environment, making it more suitable for habitation, and possibly they could collaborate in provisioning and caring for young.
This third outcome is highly significant to our understanding of the evolution of eusociality. If cooperation and division of labor emerges in a forced grouping, then many of the tools needed for successful eusocial living are already at hand. In some species of ant multiple queens come together to found nests. These groups work cooperatively and ultimately either transition to monogynous colonies via queen or worker culling of queens or become fully functional polygynous colonies. In these cases, whether the outcome is monogyny or polygyny, groups have survival advantages over single foundresses.
Motro et al (2017) found that pairs of M. semirufus queens performed less well than solitary queens at nest construction and that mortality was higher in pairs. Aggressive interactions, rather than cooperative behaviors emerged when ants were paired, suggesting that in this species queens attempt to usurp other queens’ nests, rather than joining for the benefits of mutual assistance. Crowding and difficult environmental conditions, exemplified by hard soil, favored co-founding in this species. Motro et al (2017) suggest that such forced associations could lead to selection for mutual tolerance, which is a critical first step in the emergence of cooperation.
Messor is a particularly interesting target for these experiments because similar studies have been conducted in another seed harvesting ant, Pogonomyrmex. The two genera are relatively phylogenetically distinct within the Myrmicinae (Ward et al. 2015) but have similar nesting and trophic biologies. Pogonomyrmex californicus queens found colonies singly at some locations (haplometrosis) and in groups at other locations (pleometrosis) (Overson et al 2014). The behavior of M. semirufus more closely resembles the haplometrotic populations of P. californicus.
Particularly notable about this study is that the data were collected a full quarter-century ago. This shows that careful studies with thorough documentation can retain their value. The value of this study perhaps even increased over time, as the theoretical framework about emergent cooperation developed and data were published on forced associations in other species of ant.
Studies of emergent cooperative behavior in groups of animals will continue to play a key role in improving our understanding of the evolution of social behavior. While this study of harvester ants found no advantage in living in groups, it reminds us that a key gateway to group living is social tolerance, and that even if ecological circumstances force animals into close proximity, there are other barriers to establishing a cooperative relationship. The evolution of the breakdown of those walls should play a key role in studies of social evolution.
Motro M, Motro U, Cohen D (2017) Forced associations by young queens of the harvester ant Messor semirufus during colony founding. Insect Soc. DOI 10.1007/s00040-017-0551-1
Overson R, Gadau J, Clark RM, Pratt SC, Fewell JH (2014) Behavioral transitions with the evolution of cooperative nest founding by harvester ant queens. Behav Ecol Sociobiol 68:21–30
Ward PS, Brady SG, Fisher BL, Schultz TR (2015) The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Syst Entomol 40:61–81. DOI: 10.1111/syen.12090