Repeatability of circadian behavioural variation revealed in free-ranging marine fish.

Josep Alós,Martina Martorell-Barceló,Andrea Campos-Candela

doi:10.1098/rsos.160791

Abstract

Repeatable between-individual differences in the behavioural manifestation of underlying circadian rhythms determine chronotypes in humans and terrestrial animals. Here, we have repeatedly measured three circadian behaviours, awakening time, rest onset and rest duration, in the free-ranging pearly razorfish, Xyrithchys novacula, facilitated by acoustic tracking technology and hidden Markov models. In addition, daily travelled distance, a standard measure of daily activity as fish personality trait, was repeatedly assessed using a State-Space Model. We have decomposed the variance of these four behavioural traits using linear mixed models and estimated repeatability scores (R) while controlling for environmental co-variates: year of experimentation, spatial location of the activity, fish size and gender and their interactions. Between- and within-individual variance decomposition revealed significant Rs in all traits suggesting high predictability of individual circadian behavioural variation and the existence of chronotypes. The decomposition of the correlations among chronotypes and the personality trait studied here into between- and within-individual correlations did not reveal any significant correlation at between-individual level. We therefore propose circadian behavioural variation as an independent axis of the fish personality, and the study of chronotypes and their consequences as a novel dimension in understanding within-species fish behavioural diversity.

Highlights

Humans show consistent and repeatable between-individual differences in their average level of circadian behaviours, such as awakening time, rest onset or rest duration, defining different chronotypes [1,2]
The rest onset was only affected by the longitude of the centre of the home range suggesting that individuals living in higher longitudes had a delayed rest onset
The study of the covariates affecting circadian behavioural variation in free-ranging pearly razorfish suggested that awakening time, rest duration and daily travelled distance were affected by the spatial awakening time rsos.royalsocietypublishing.org R

Summary

Introduction

Humans show consistent and repeatable between-individual differences in their average level of circadian behaviours, such as awakening time, rest onset or rest duration, defining different chronotypes [1,2]. While Stuber et al [16] found low Rs in circadian-related behaviours in great tits, Parus major, Stuber et al [17] and Steinmeyer et al [15] found consistent between-individual differences and high Rs in great tits exposed to predation risk and blue tits, Cynistes caeruleus, respectively. These recent evidences of chronotypes in terrestrial animals have provided a novel dimension in relation to chronobiology to understand individual behavioural diversity and many ecological and evolutionary processes [10,18]. Fishes, the existence of chronotypes (i.e. the assessment of the repeatability in traits like a wakening time, rest onset or rest duration) has never been explored in the wild

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