Exploiting new terrain: An advantage to sociality in the slime mold Dictyostelium discoideum

Identifying benefits to cooperation is important in studying social evolution. When the social amoebae of Dictyostelium discoideum starve, they aggregate to form multicellular slugs that migrate towards the soil surface to form fruiting bodies. Multicellularity in D. discoideum is thought to help provide protection from predators and aid in the dispersal of reproductive spores. Here we show an additional benefit of local dispersal. Utilizing D. discoideum's phototactic behavior, we induced slug migration over bacteria and show that this passage results in the removal of bacteria. Time-lapse video revealed that slugs do not dissociate on contact with bacteria, rather cells sloughed from the migrating slugs consume the prey and reproduce. Using an aggregation mutant, we show that the cells slugs shed are able to reach and colonize food sources solitary amoebae cannot. We propose that the exploitation of local food patches is an important selective benefit favoring multicellularity in D. discoideum