Reanalysis of Filter-Feeding Behavior of Caddis Fly (Brachycentrus) Larvae Reveals Masking and Circadian Rhythmicity

Data published on the subjectively determined presence or absence of circadian periodicity in feeding of Brachycentrus occidentalis Banks, an aquatic insect belonging to the order Trichoptera, were reanalyzed by statistical methods based on the cosine model. The 4h data for 5 days of synchronized environmental conditions followed by 5 days of constant conditions (using original values and purified values after removal of an 8h component attributed to the feeding schedule) were quantified for rhythm characteristics by the least-squares fit of cosines. A circadian rhythm was highly significant during synchronized conditions (light-dark and cycling water temperature) and in continuous light when water temperature continued to cycle. A circadian rhythm in the percentage of larvae feeding during continuous light and constant water temperature, which had not been observed by visual inspection in the original data, was detected in the unmasked data with a "free-running" period not overlapping 24.0h (95% confidence limits from 18.95h to 21.66h). Effects of masking brought about by manually feeding the larvae every 8h were statistically significant under both synchronized and constant environmental conditions. (Chronobiology International, 15(6), 595-606, 1998)