The circadian and endocrine systems influence many physiological processes in animals, but little is known on the ways they interact in insects. We tested the hypothesis that juvenile hormone (JH) influences circadian rhythms in the social bumble bee Bombus terrestris. JH is the major gonadotropin in this species coordinating processes such as vitellogenesis, oogenesis, wax production, and behaviors associated with reproduction. It is unknown however, whether it also influences circadian processes. We topically treated newly-emerged bees with the allatoxin Precocene-I (P-I) to reduce circulating JH titers and applied the natural JH (JH-III) for replacement therapy. We repeated this experiment in three trials, each with bees from different source colonies. Measurements of ovarian activity suggest that our JH manipulations were effective; bees treated with P-I had inactive ovaries, and this effect was fully recovered by subsequent JH treatment. We found that JH augments the strength of circadian rhythms and the pace of rhythm development in individually isolated newly emerged worker bees. JH manipulation did not affect the free-running circadian period, overall level of locomotor activity, sleep amount, or sleep structure. Given that acute manipulation at an early age produced relatively long-lasting effects, we propose that JH effects on circadian rhythms are mostly organizational, accelerating the development or integration of the circadian system.
Bibliographical noteFunding Information:
This study was supported by grants from the US-Israel Binational Agricultural Research and Development Fund ( BARD , number IS-4418-11 , and IS-5077-18 , to G.B.), the Israeli Science Foundation ( ISF , grant No. 1274/15 to G.B.) and the Planning and Budgeting Committee (PBC) Fellowship Program for Outstanding Chinese and Indian Post-Doctoral Fellows (to A.P).
© 2020 The Authors
- Bombus terrestris
- Bumble bee
- Circadian rhythms
- Juvenile hormone
- Locomotor activity