What is the process called when an organism's free-running cycle is altered to align with a different rhythm?

The process of aligning an organism's free-running cycle with a different rhythm is known as entrainment. Entrainment refers to the synchronization of an organism's internal biological clock with external environmental cues, such as light and temperature changes. This adjustment allows organisms to align their physiological processes, like sleep-wake cycles and breeding patterns, with the natural cycles in their environment, ultimately enhancing their survival and reproductive success.

This phenomenon is particularly important in species that rely on environmental cues to determine their behavior and physiological states. For instance, many animals exhibit entrainment to the light-dark cycle of the day, adjusting their internal clocks to optimize their activity during daylight hours and rest at night.

The other possible answers reflect concepts related to biological rhythms but do not specifically address the mechanism of aligning an internal cycle with an external rhythm. Synchronization and regulation pertain to the general process of maintaining rhythm but do not convey the specific action of adjusting a free-running cycle. Phase shifting describes a change in the timing of biological rhythms but does not encompass the broader process of aligning with external environmental signals as entrainment does.