Comparative studies of tidal rhythms. ix. the modifying roles of deuterium oxide and azadirachtin on circalunidian rhythms

The influence of deuterium oxide was tested on the persistent activity rhythm of the fiddler crab Uca pugilator. It caused reductions in the amount of activity expressed by 82% of the animals; and increased the period lengths of 73% of the crabs. U. pugnax individuals were subjected to azadirachtin injections. The substance caused the activity peaks of 40% of the crabs to split, produced period shortening in 13%, and period lengthening in 7%. Ten percent of the azadirachtin treated animals became arrhythmic. Ethanol (here used as a solvent for azadirachtin), known to modify circadian rhythms, had no effect on circalunidian rhythms, however, the crabs received only very small, one‐time injections. The results obtained are used as support for a working hypothesis stating that the same clock type may govern both circadian and circalundian rhythms.