The adaptive significance of adjusting behavioral activities to the right time of the day seems obvious but is under debate. Our data provides evidence that proper timing of eclosion, a vital behavior of the fruit fly Drosophila melanogaster, requires a functional molecular clock under quasi-natural conditions.

We compared eclosion profiles and assessed eclosion rhythmicity in wildtype flies (CS) and clock-related mutant strains (per⁰¹, pdf⁰¹, han⁵³⁰⁴) under laboratory and outdoor conditions. In the laboratory, flies were entrained in either light-dark cycle (LD12:12) or warm (25°C)-cold (16°C) cycle  (WC12:12), and tested under entrainment or constant conditions using TriKinetics Drosophila Eclosion Monitors. For outdoor assays, a WEclMon system was used and experiments were performed between July-Octobre 2014 and July-Octobre 2016.

Flies with a defective molecular clock showed impaired rhythmicity and gating under natural temperate conditions in Würzburg/Germany even in the presence of a full complement of abiotic Zeitgebers. We also found that eclosion rhythmicity cannot be entrained by daily cycles in relative humidity. Low relative humidity also did not or only weakly affect the ability of the flies to eclose and unfold their wings.

Our results suggest that the presence of natural Zeitgebers is not sufficient, and a functional molecular clock is required to induce stable temporal eclosion patterns in flies under temperate conditions with considerable day-today variation in light intensity and temperature. Temperate Zeitgebers are, however, sufficient to functionally rescue a loss of PDF-signalling.

The data set belongs to the publication:

Ruf F, Mitesser O, Mungwa ST, Horn M, Rieger D, Hovestadt T, and Wegener C (2021) Natural Zeitgebers Under Temperate Conditions Cannot Compensate for the Loss of a Functional Circadian Clock in Timing of a Vital Behavior in Drosophila. Journal of Biological Rhythms 36: 271–285. DOI: 10.1177/0748730421998112.

Outdoor eclosion measurements were carried out with the WEclMon system. Laboratory eclosion measurement were carried out using TriKinetics Eclosion monitors.

Abiotic factors were measured using 145S dataloggers (MSR Electronics).