Question

A diurnal cycle of day and night called a circadian rhythm has the characteristics of a clock, with an oscillator and a coupler to link the clock and the rhythmic physiological process. Electric or chemical couplers had been proposed, but the chemical coupler appeared more likely or common as various studies had shown. The most telling evidence of chemical coupling between an oscillator and a circadian function was provided by Truman and Riddiford (1970), using the eclosion rhythm of two species of silkmoth. Methods • Used the silkmoths Hylaphora cecropia and Antherea pernyi and studied the effects of brain extracts, brain removal & reimplantation. Results

Questions 1. What hypotheses were being tested in the experiment? 2. What were the main results and did they address the hypotheses being tested? 3. What other interpretations can you draw from the data presented?

Answer 1

The study by Truman and Riddiford supported the hypothesis that chemical couplers from the brain control the circadian rhythms in silkmoths. The brain's influence on the internal biological clock and its impact on the synchronization of biological processes with Earth's daily cycle was demonstrated. Other interpretations suggest the vital role of the biological clock in regulating circadian rhythms.

The experiment conducted by Truman and Riddiford in 1970 aimed to test two hypotheses: the existence of a chemical coupler in circadian rhythms, and the effect of brain extracts, removal, and reimplantation on the eclosion rhythm of silkmoths. They used two species, Hylaphora cecropia and Antherea pernyi, and investigated the circadian rhythms associated with the eclosion (emerging of adult silkmoths from their cocoons) of these moths. The results showed that brain extracts, as well as brain removal and reimplantation, affected the eclosion rhythm, thus supporting the hypothesis that a chemical coupler, potentially from the brain, was involved in coordinating circadian rhythms with physiological processes.

Other interpretations that can be drawn from the data include the confirmation of an internal biological clock in these organisms that is influenced by the brain and its chemical signals. This intricate mechanism demonstrates how circadian rhythms are fundamental to the synchronization of biological processes with the Earth's 24-hour rotational period. The findings also hint at the profound effects brain chemistry has on regulating daily cycles of behavior and processes, emphasizing the fundamental role of the biological clock in maintaining circadian rhythms.