Elsevier

Animal Behaviour

Volume 94, August 2014, Pages 161-166
Animal Behaviour

Essay
Sleep, sleep timing and chronotype in animal behaviour

https://doi.org/10.1016/j.anbehav.2014.05.001Get rights and content

Highlights

  • Sleep and sleep timing are prospering fields in psychology.

  • Ideas from this field can be translated to animal behaviour.

  • Similarities and differences between animals and humans are shown.

  • Research topics are proposed.

In humans, sleep duration and sleep timing have been identified as interesting facets of individual differences and of personality. Sleep duration and sleep timing are different constructs. For example, compare two individuals both sleeping for 6 h: one may sleep from 2300 to 0500 hours and the other from 0100 to 0700 hours. One can assess the midpoint of sleep in these two subjects which is the midpoint in clock time between sleep onset and awakening. These ideas have already been picked up in a handful of studies. Sex differences have been found in birds in the same direction as in humans with males sleeping for less time. Contrasting effects have been found in relation to mating: in humans, late chronotype men have the highest mating success, whereas in birds, earlier chronotypes gain higher mating success. Many sleep parameters are related to assortative mating in humans and similar but weaker relationships have been found in birds. Ontogenetic studies show that sleep–wake behaviour changes during adolescence in humans. Such changes have also been found in other mammals ranging from primates to rodents. Factors determining sleep–wake patterns could be environmental, such as temperature, sunrise or sunset or even artificial light at night. Artificial lighting at night leads to an earlier wake up and singing time in blackbirds, Turdus merula, whereas light at night makes humans wake up later. As a conclusion, I show some parallels and differences in the study of sleep timing between animals and humans and encourage further studies, in both field and laboratory settings.

Section snippets

Chronotype as a Personality Aspect

Sleep timing or chronotype has been described as an interesting aspect of personality (Matthews, 1988). The term ‘personality’ was first used for humans, but animal personality is also an increasing field of study, with articles by Gosling and John (1999) and Gosling, Kwan, and John (2003) being an important starting point. The first reviews (e.g. Réale, Reader, Sol, McDougall, & Dingemanse, 2007) labelled these personality aspects as temperament, a definition paralleled, for example, by

Chronotype in animals

In laboratory animals, there is some evidence for the existence of chronotypes (Aschoff and Wever, 1962a, Labyak et al., 1997, Wicht et al., 2014). For example, Aschoff and Wever (1962a) reported individual differences in chaffinches, Fringilla coelebs. Labyak et al. (1997) examined 15 variables of circadian activity and temperature for diurnal degus, Octodon degus: they noted similar chronotype variations as described for humans with extreme individuals differing by one or more standard

Physiological aspects

In nonhuman animals, chronotype has not yet been studied extensively in relation to hormone measures or other physiological measures in field studies. However, there is some evidence for such relationships from humans, both men and women from laboratory and field settings. First, body temperature was lower at night and the lowest core body temperature (the point of lowest temperature) was earlier in the night in morning than in evening types, both in the laboratory (Baehr, Revelle, & Eastman,

Ontogenetic aspects and sex differences

Ontogenetic aspects have been discussed in detail for humans, and it has been found that there are two significant changes in sleep–wake behaviour during adolescence (Roenneberg et al., 2004). First, with the onset of puberty, children very quickly become evening oriented around the age of 12–14 years (Carskadon et al., 1998, Randler, 2011). This has been supposed to be related to pubertal changes in hormone secretion, although this idea has not been convincingly tested. Second, at the end of

External abiotic environmental influence

Large seasonal differences in sleep timing of 4.8 h between summer and winter have been found in blue tits, and these differences are much larger than in humans. In humans at around 69° latitude in Norway (Tromsø), the difference was only some 8 min which was an unexpected result (see Johnsen, Wynn, Allebrandt, & Bratlid, 2013). A similar effect as in the blue tits was expected (but with a weaker difference of 30 min or 1 h). Environmental factors determining sleep–wake patterns could be

Sexual selection and mating

The sex differences in sleep–wake variables in the blue tit were considered as an effect of sexual selection, similarly to humans (Randler et al., 2012a). Blue tit males that ‘went out of bed’ earlier had a higher mating success (Poesel, Kunc, Foerster, Johnsen, & Kempenaers, 2006). This is supported by Helm and Visser (2010) who reported that the shorter free-running period length (shorter than 24 h in dim light) may be a consequence of sexual selection. Offspring from extrapair matings had

Correlates and evolutionary consequences

Health-related aspects have been revealed in relation to chronotype and sleep duration in different studies in humans (e.g. Lázár et al., 2012), late risers having worse health. For example, being overweight or obese has been linked with evening orientation and increased stress hormones (Lucassen et al., 2013) or generally an unhealthy diet (Kanerva et al., 2012). Also, health problems have been found with eveningness: there was a predisposition in evening types to type 2 diabetes, while

Conclusions and further topics

What can psychologists learn from animal studies on sleep behaviour? Animals are less restricted or influenced by social schedules (e.g. work or school in humans) and the comparison of results from animals and humans may help researchers assess social aspects of sleep behaviour and their importance for the circadian rhythm. More social animals, such as baboons or meerkats, might have higher synchronization in their sleep–wake behaviour than solitary species. What can be learnt from studies on

Acknowledgments

I am grateful to Ana Sendova-Franks for her encouragement, and I am specifically thankful to the three referees with their views helping to clarify the logic of this essay.

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