Slime molds solve traffic problems without a brain and weigh up to 20 kilograms
A slime mold has no brain, yet species like Physarum polycephalum have been used to model traffic networks, and the group shows behaviours usually linked to animals that think. One plasmodial species, Brefeldia maxima, can reach 20 kilograms as a single giant cell packed with thousands of nuclei.
Slime mold is a label of convenience rather than a family. The organisms it covers are scattered across five distant branches of the eukaryote tree, from Amoebozoa to the Stramenopiles, and share a lifestyle: single cells that come together, by aggregating or fusing, into bodies that make spores. Estimates settle on about 1,000 species, while environmental DNA suggests 1,200 to 1,500. Being small and soft, they have left almost no fossils.
The largest are the Myxogastria, the only ones easily seen and the source of the slimy name. Each is one enormous cell with no internal walls, its cytoplasm streaming along strands and periodically reversing direction. Fuligo septica, nicknamed dog vomit slime mold, spreads as a yellow mass over bark mulch after heavy rain. Cellular slime molds live differently: their amoebae roam alone until food runs out, then swarm into a tiny slug that crawls toward light and becomes a fruiting body. Some amoebae turn into spores, while others die to form the stalk that lifts them up.
Thomas Panckow gave the first description in 1654, calling one a fast-growing fungus. Heinrich Anton de Bary grouped them as Mycetozoa, Ernst Haeckel put them in his new kingdom Protista in 1868, and George Willard Martin still argued in 1932 and 1960 that they came from fungi. In 1992 Patterson and Sogin proposed that the dictyostelids branched off before plants, animals and fungi.
They turn up nearly everywhere: 24 species in Chile's Atacama Desert, 46 in the Sonoran, dictyostelids in Arctic and Antarctic soils. Phytomyxea parasites cause cabbage club root, and Sphindidae beetles eat nothing but slime molds. Reproduction gets complicated too. Physarum polycephalum carries three mating genes, two with thirteen variants each and one with three, so a single individual can release cells of up to eight genetic types. In Ecuador some species have traditionally been eaten.
Source: Slime mold
