Prey attraction in a generalist microbial predator,Dictyostelium discoideum

Generalist predators often live in environments that vary in the type and abundance of prey species. The prey species in turn vary in their susceptibility and suitability to predation. How do generalists navigate this variation in prey abundance and profitability and seek out their preferred prey? We investigated this in the soil protistDictyostelium discoideum, a generalist predator of many species of bacteria. Despite their generalist diet, amoebas experience considerable variation in growth rate on their prey bacteria. We tested if amoebas innately prefer the more profitable prey bacteria. We found that the levels of chemoattraction of naïve amoebas towards prey bacteria increased with increasing growth rate of the amoebas on those bacteria. This suggests thatD. discoideumamoebas have an innate prey preference that is adaptive. Next, we tested how experience with prey bacteria affects chemoattraction in amoebas. Given the number of bacterial species in soil, learning from experience should be advantageous. However, we found no evidence for learning; instead amoeba preference in learning experiments was partially explained by innate attractiveness of the prey bacteria. Our results suggest that generalist amoebas are innately attracted to the more profitable prey bacteria and this innate attraction cannot be overridden by recent experience.