University of Oulu

Laura Härkönen, Nico Alioravainen, Anssi Vainikka, Pekka Hyvärinen, Night reveals individuality in a shoaling fish, Behavioral Ecology, Volume 30, Issue 3, May/June 2019, Pages 785–791,

Night reveals individuality in a shoaling fish

Saved in:
Author: Härkönen, Laura1,2,3; Alioravainen, Nico4; Vainikka, Anssi4;
Organizations: 1Department of Ecology and Genetics, University of Oulu, Pentti Kaiteran katu 1, P.O. Box 3000, 90014 Oulu, Finland
2Department of Environmental Science, Policy, and Management, University of California, Berkeley, 130 Mulford Hall #3114, Berkeley, CA 94720, USA
3Aquatic population dynamics, Natural Resources Institute Finland (Luke), Paavo Havaksen tie 3, 90014 Oulu, Finland
4Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland
5Aquatic population dynamics, Kainuu Fisheries Research Station, Natural Resources Institute Finland (Luke), Manamansalontie 90, 88300 Paltamo, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 0.5 MB)
Persistent link:
Language: English
Published: Oxford University Press, 2019
Publish Date: 2020-10-01


Many animals rely heavily on visual cues from their environment, and therefore show circadian rhythmicity in their behavioral activities. In group-living animals, individuals’ activity rhythms must be synchronized not only with diel light–dark cycle but also with other group members. Increasing evidence has recently shown that circadian behaviors of animals are consistent within individuals and different between individuals, but the sources and consistency of diel activity variation in social context are less known. Using radio frequency identification technology, we recorded individual moving activity of the Eurasian perch (Perca fluviatilis) in randomly formed groups through 10 full diel cycles in seminatural environment. We found diel changes in variability and repeatability of behavioral activity both within and between the groups: individual differences in activity were more repeatable in nighttime, whereas group differences were more repeatable in daytime. The results suggest that collective group behavior in daylight obscures the expression of individuality, whereas the weak group effects in nighttime reveal a substantially wider continuum of individually consistent activity types. Our findings imply that 1) studying activity variation only on diurnal basis may underestimate the total activity variation among social individuals and may thus bias the repeatability estimates, and 2) accounting for diel variation in social effects may be essential for detecting ecologically realistic behavioral variation within and between animal groups. To conclude, this study highlights the complex interactions between circadian activity rhythms, individual behavioral differences, and group dynamics, and thereby provides new insights for understanding overall behavioral diversity in social animals.

see all

Series: Behavioral ecology
ISSN: 1045-2249
ISSN-E: 1465-7279
ISSN-L: 1045-2249
Volume: 30
Issue: 3
Pages: 785 - 791
DOI: 10.1093/beheco/arz015
Type of Publication: A1 Journal article – refereed
Field of Science: 1181 Ecology, evolutionary biology
Funding: This work was supported by the Academy of Finland (grant number 287700 to L.H.).
Academy of Finland Grant Number: 287700
Detailed Information: 287700 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2019. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. This is a pre-copyedited, author-produced version of an article accepted for publication in Behavioral Ecology following peer review. The version of record Laura Härkönen, Nico Alioravainen, Anssi Vainikka, Pekka Hyvärinen, Night reveals individuality in a shoaling fish, Behavioral Ecology, Volume 30, Issue 3, May/June 2019, Pages 785–791 is available online at: