A natural timeless polymorphism allowing circadian clock synchronization in "white nights"

Area of Science:

• Chronobiology
• Animal behavior
• Evolutionary genetics

Background:

• Daily temporal organization, influenced by environmental rhythms and circadian clocks, confers a fitness advantage.
• Light:dark cycles synchronize circadian clocks, but adaptation to weak environmental cues, like constant light (LL), remains unclear.
• Drosophila, originating in Africa, have spread to regions with long summer days or LL, posing challenges to circadian clock function.

Purpose of the Study:

• To investigate how Drosophila adapt their circadian clock function under constant light (LL) conditions.
• To determine the role of a recently evolved natural timeless allele (ls-tim) in overcoming LL-induced clock disruption.
• To understand the functional significance of the less light-sensitive L-TIM protein in behavioral synchronization.

Main Methods:

• Comparative analysis of circadian clock function in Drosophila strains with ancient (s-tim) and evolved (ls-tim) alleles.
• Assessment of clock protein degradation (TIMELESS) under constant light (LL) conditions.
• Behavioral assays under semi-natural conditions simulating Northern European summers to evaluate synchronization capabilities.

Main Results:

• Constant light (LL) disrupts Drosophila circadian clock function by inducing CRYPTOCHROME-mediated degradation of TIMELESS (TIM).
• Temperature cycles can counteract LL's disruptive effects, but only in the presence of the less light-sensitive L-TIM, encoded by the ls-tim allele.
• Flies possessing the ls-tim allele successfully synchronize their behavior to semi-natural conditions mimicking Northern European summers, unlike those with the s-tim allele.

Conclusions:

• The evolved ls-tim allele, encoding less light-sensitive L-TIM, is crucial for enabling Drosophila behavioral synchronization under constant light (LL) conditions.
• This functional adaptation, overcoming LL-induced clock disruption, is likely the driving force behind the northward spread of the ls-tim allele.
• The study highlights the interplay between genetic evolution and environmental adaptation in maintaining circadian temporal organization.