Myxomycetes have an allorecognition system that can only discriminate between intraspecies

Myxomycetes are multinucleate unicellular organisms. They form a plasmodium that moves by protoplasmic flow and prey on microorganisms. When encountering intraspecifics, the plasmodium has the capacity for "fusion", actively approaching and fusing its cells, or "avoidance", altering its direction to avoid the other individual. This is an allorecognition ability. However, it remains unclear whether the range of allorecognition extends to other species, and its ecological significance is also obscure. Here, we conduct a quantitative evaluation of contact responses from closely related species of plasmodium to clarify the recognition range of the allorecognition system in Myxomycetes. Behavioral assays demonstrate that the allorecognition system recognizes individuals within the same species while failing to recognize those of different species. The allorecognition is an extremely narrow and inward-focused mechanism, arguing for a highly specialized system of self-other recognition.