DOI: 10.5061/dryad.4xgxd259s
title: Shedding light on the threespine stickleback circadian clock

description: The circadian clock is an internal timekeeping system shared by most
 organisms, and knowledge about its functional importance and evolution in
 natural environments is still needed. Here, we investigated the circadian
 clock of wild-caught threespine sticklebacks (Gasterosteus aculeatus) at
 the behavioural and molecular levels. While their behaviour, ecology, and
 evolution are well studied, information on their circadian rhythms are
 scarce. We quantified the daily locomotor activity rhythm under a
 light-dark cycle (LD) and under constant darkness (DD). Under LD, all fish
 exhibited significant daily rhythmicity, while under DD, only 18% of
 individuals remained rhythmic. This interindividual variation suggests
 that the circadian clock controls activity only in certain individuals.
 Moreover, under LD, some fish were almost exclusively nocturnal, while
 others were active around the clock. Furthermore, the most nocturnal fish
 were also the least active. These results suggest that light masks
 activity (i.e. suppresses activity without entraining the internal clock)
 more strongly in some individuals than others. Finally, we quantified the
 expression of five clock genes in the brain of sticklebacks under DD using
 qPCR. We did not detect circadian rhythmicity, which could either indicate
 that the clock molecular oscillator is highly light-dependent, or that
 there was an oscillation but that we were unable to detect it. Overall,
 our study suggests that a strong circadian control on behavioural rhythms
 may not necessarily be advantageous in a natural population of
 sticklebacks and that the daily phase of activity varies greatly between
 individuals because of a differential masking effect of light.
description: GENERAL INFORMATION<br> Project title: Circadian activity
 and gene expression in the threespine stickleback<br> Authors:
 Marie-Pier Brochu and Nadia Aubin-Horth<br> Date of data collection:
 26/09/2019 - 09/06/2020<br> Location of data collection: Université
 Laval, Québec, Canada PROJECT DESCRIPTION AND
 METHODOLOGICAL INFORMATION<br> Using threespine sticklebacks
 (Gasterosteus aculeatus) caught in the wild population of the lac
 Témiscouata (Québec, Canada) in June 2019, we first quantified daily
 locomotor activity in individual fish under a 12 h light:12 h dark cycle
 (LD, lights on at 6:00 and lights off at 18:00) during 8 days and under
 constant darkness (DD) during 10 days. To do this, we individually placed
 18 fish in experimental 2 L tanks. Each tank was equipped with an infrared
 photoelectric sensor (E3Z-D67, Omron). Every time a fish interrupted the
 infrared light beam, it was counted as one movement. We quantified the
 locomotor activity of 54 individuals under LD (groups 1, 2 and 3) and of
 18 individuals under DD (group 1). Second, we quantified the expression
 rhythm of five clock genes (bmal1a, clock1b, clock2, per1b and cry1b) in
 the brain of sticklebacks under DD using qPCR (groups 2 and 3). To do
 this, we sampled the brain of four randomly selected individuals every 6 h
 throughout a 24-h cycle (6:00, 12:00, 18:00, 0:00), n=8/ time point).
 Please refer to the following publication for more information on the
 experimental design, methods and data analysis:<br> Brochu, M.-P.
 and Aubin-Horth N. (2021). Shedding Light on the Circadian Clock of the
 Threespine Stickleback. J. Exp. Biol. MISSING
 DATA<br> For all files, 6 individuals are missing because they died
 during experiments or were parasitized.<br> Group 1: ind.
 10.<br> Group 2: ind. 02 and 11.<br> Group 3: ind. 05, 14 and
 15. FILES DESCRIPTION<br> Filename:
 group_1_2_3_sex.csv<br> Description: sex identification<br>
 Variable list:<br> 1. Group ID<br> 2. Individual ID<br>
 3. Sex <br> Filenames: group_1_LD_activity.csv;
 group_2_LD_activity.csv; group_3_LD_activity.csv;
 group_1_DD_activity.csv<br> Description: number of movements per
 10-min interval during 8 days (LD) or 10 days (DD)<br> Variable
 list:<br> 1. Interval (1 to 144)<br> 2. Day<br> 3.
 Hour<br> 4. Minute (from the start of the interval)<br> 5.
 Ind01<br> 6. ... Filename:
 group_2_3_gene_expression.csv<br> Description: mean CQ values for
 the five clock genes studied and the reference gene (ubc)<br>
 Variable list:<br> 1. Group ID<br> 2. Individual ID<br>
 3. Time of brain collection (0:00, 6:00, 12:00 or 18:00)<br> 4. Mean
 CQ values for ubc<br> 5. Mean CQ values for period1b<br> 6.
 Mean CQ values for cry1b<br> 7. Mean CQ values for bmal1a<br>
 8. Mean CQ values for clock1b<br> 9. Mean CQ values for
 clock2
description: Please use the read.me file