The evolutionary history of an iconic multispecies mutualism

Investigating how and when acacia ants started protecting host plants in return for food and shelter

GBIF-mediated data resources used : 23 species
Pseudomyrmex ferruginea Ryan Somma
Pseudomyrmex ferruginea by Ryan Somma via Wikimedia Commons. Licensed under CC BY-SA 2.0.

Certain species of ants nest inside specialized compartments of plants (domatia) and even receive food bodies from extra-floral nectaries of the host. In return, the ants aggressively patrol and protect the host plant against any and all intruders, including herbivores and competing plants.

In this study, researchers explore the evolutionary history of an iconic multispecies mutualism- between neotropical acacia ants (Pseudomyrmex ferrugineus group) and swollen-torn acacias (Vachellia spp.). Using genetic sequencing and phylogenetic analysis of 18 different ant species of Pseudomyrmex, the researchers infer the phylogeny of the ant species and estimate their ancestral ranges. The group as a whole appears to have diverged 12-14 millions years ago, and the domatium-nesting P. ferrigeneus subgroup is estimated to be about six million years old.

The researchers also estimated the ancestral range of 23 Vachellia host species using GBIF mediated occurrences. While the appearance of domatia in the host plant seems to have a single origin, the domatia-nesting trait unique to the P. ferrigeneus ants developed in two clades seperately, about three millions years apart.

Ward PS and Branstetter MG (2017) The acacia ants revisited: convergent evolution and biogeographic context in an iconic ant/plant mutualism. Proceedings of the Royal Society B: Biological Sciences. The Royal Society 284(1850): 20162569. Available at: