Rhythmic egg-laying behaviour in virgin females of fruit flies Drosophila melanogaster

Abstract

Fruit fly Drosophila melanogaster females display rhythmic egg-laying under 12:12 h light/dark (LD) cycles which persists with near 24 h periodicity under constant darkness (DD). We have shown previously that persistence of this rhythm does not require the neurons expressing pigment dispersing factor (PDF), thought to be the canonical circadian pacemakers, and proposed that it could be controlled by peripheral clocks or regulated/triggered by the act of mating. We assayed egg-laying behaviour of wild-type Canton S (CS) females under LD, DD and constant light (LL) conditions in three different physiological states; as virgins, as females allowed to mate with males for 1 day and as females allowed to mate for the entire duration of the assay. Here, we report the presence of a circadian rhythm in egg-laying in virgin D. melanogaster females. We also found that egg-laying behaviour of 70 and 90% females from all the three male presence/absence protocols follows circadian rhythmicity under DD and LL, with periods ranging between 18 and 30 h. The egg-laying rhythm of all virgin females synchronized to LD cycles with a peak occurring soon after lights-off. The rhythm in virgins was remarkably robust with maximum number of eggs deposited immediately after lights-off in contrast to mated females which show higher egg-laying during the day. These results suggest that the egg-laying rhythm of D. melanogaster is endogenously driven and is neither regulated nor triggered by the act of mating; instead, the presence of males results in reduction in entrainment to LD cycles.

• Egg-laying
• oviposition
• Drosophila
• circadian rhythm
• virgin
• mating

Acknowledgments

We acknowledge financial support from the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, and our parent funding body, the Department of Science and Technology, Government of India. We thank two anonymous reviewers for reading our manuscript and suggesting some very useful changes. We also thank Sheeba Vasu, Joydeep De, Koustubh Vaze Sheetal Potdar, Nikhil KL and Abhilash Lakshman for their constructive criticism and Nisha N. Kannan, Radhika Shinde, Madhuri Chauhan, and Komal Saxena for helping out with the fly transfers and egg counting in each assay. We are also exceptionally grateful to N. Rajanna and M.S. Muniraju for helping out with vial preparation and fly maintenance.