Figure 5

Summary illustration. Interrelationship between the age-related decline in REM sleep (red line), and PCSK2 expression in the feather follicles and associated melanic feather spotting (•). For a given age (X), owlets with low PCSK2 expression (top) had low amounts of spotting and high amounts of REM sleep, whereas owlets with high PCSK2 expression (bottom) had high amounts of spotting and low amounts of REM sleep. In this respect, owlets expressing lower amounts of PCSK2 exhibited REM sleep amounts typical of younger birds, an altricial pattern of brain development, whereas owlets expressing higher amounts of PCSK2 exhibited REM sleep amounts typical of older birds, a precocial pattern of brain development.