Each fall, millions of monarch butterflies from across the Eastern United States use a time-compensated sun compass to direct their navigation south, traveling up to 2,000 miles to an overwintering site in a specific grove of fir trees in central Mexico. Scientists have long been fascinated by the biological mechanisms that allow successive generations of these delicate creatures to travel such long distances to a small region roughly 300 square miles in size.
Understanding the relationship between genes, behavior and physiological adaptations in monarchs may also lead to new insights into similar connections in humans. Circadian clocks, for instance, are a crucial component in the complex time-compensated sun compass system governing a monarch’s ability to navigate long distances, and are now understood to play a pivotal role in human biology. Temporal variations in hormone levels, pharmacokinetics and disease processes, such as the increased incidence of heart attacks in the early morning, reveal the prominent influence of the circadian clock on human physiology. Understanding the molecular mechanisms of the circadian clock has already helped reveal how clock gene mutations contribute to disorders of the timing of sleep, and new insights could illuminate how clock gene mutations contribute to diseases such as major depression and seasonal affective disorder.