Previous fungal electrical oscillations had periods measured in milliseconds to hours. Fukasawa and colleagues documented a seven-day cycle in Pholiota brunnescens, a wood-decay fungus — the longest oscillation period ever recorded in fungi.
The discovery emerged from a careful setup. Mycelial networks were grown across soil in Petri dishes, some with a wood bait and some without. Electrodes tracked electrical potential across the network. In dishes with wood, a clear ~7-day oscillation emerged after day 63 of colonization. In control dishes without wood, electrical activity was erratic and unsynchronized.
The critical finding: the pacemaker was the bait. Causal analysis showed that significantly large causal relationships were mostly restricted to electrode pairs that included the wood-colonizing location. The hyphae touching the wood drove the rhythm of the whole network. Other parts of the mycelium followed. Remove the resource, and the organized oscillation disappears.
The fungus doesn't have a clock that tells it when to eat. It has eating that generates a clock. The digestive cycle — whatever sequence of enzymatic secretion, nutrient uptake, metabolic processing, and recovery the hyphae undergo at the wood interface — takes about seven days, and that period propagates as an electrical signal across the entire network.
This inverts the usual relationship between timekeeping and behavior. In animals, circadian clocks coordinate when organisms eat. In this fungus, the act of consuming a resource creates the temporal structure. The rhythm isn't imposed on the behavior. The behavior is the rhythm. The distinction between a clock and the process it's supposed to regulate collapses when the process generates its own periodicity.