Variation in sleep behaviour and its underlying causes: a study in a free-living blue tit

176 Pages·2012·0.84 MB·English

by  Corinna Loës

Variation in sleep behaviour and its underlying causes: a study in a
free-living blue tit population

Dissertation

der Fakultät für Biologie
der Ludwig-Maximilians-Universität
München

durchgeführt am Max-Planck-Institut für Ornithologie
Seewiesen

vorgelegt von
Corinna Loës
April 2012
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Erstgutachter: Prof. Dr. Bart Kempenaers
Zweitgutachter: Prof. Dr. Niels Dingemanse

Eingereicht am: 23.04.2012
Tag der mündlichen Prüfung: 04.07.2012
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Blue tit, Cyanistes caeruleus
Photo by Jan Wijmenga
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Table of contents

Summary …………………………………………………………………………………7
General Introduction …………………………………………………………………..11
Chapter 1 Variation in sleep behaviour in free-living blue tits,
Cyanistes caeruleus: effects of sex, age and environment ………….31
Chapter 2 Individual variation in sleep-wake rhythms in free-living
birds …………………………………………………………………67
Chapter 3 Individual variation in sleep behaviour in blue tits:
assortative mating and associations with fitness-related traits ……...89
Chapter 4 Search for informative polymorphisms in candidate genes:
clock genes and circadian behaviour in blue tits …………………..111
Chapter 5 Testing for associations between candidate genes for circadian
rhythms and individual variation in sleep behaviour in blue tits …..131
General Discussion ……………………………………………………………………153
Acknowledgements …………………………………………………………………...171
Author Contributions ………………………………………………………………...173
Addresses of Co-authors ……………………………………………………………..174
Curriculum Vitae ……………………………………………………………………..175
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Summary

Most if not all animals spend a considerable amount of their time within a 24-hour day in
the sleep state. Several benefits for the organisms have been ascribed to sleep and a
reduction in daily sleep amount can have various deleterious effects. However, the daily
sleep amount varies considerably between different species and varies also between
individuals within the same species. This has been mainly described in several human
populations and the underlying causes of the variation such as gender, age or genetic
variability have been reported in the literature. The focus of this dissertation is to provide
a detailed description of behavioural aspects of sleep in a wild bird population. Using
little infrared-sensitive cameras I recorded blue tits while roosting in nestboxes at night.

In chapter 1, I showed that the amount of sleep per night in blue tits follows
predominantly the length of the night, at least during the winter months from November
to March and is interrupted by many (short) awake phases. The reduction in sleep
duration between the longest and shortest night was about 4.8 hours and blue tits have to
be able to tolerate such reduced sleep amounts in the course of the season. My results
further demonstrate that in mid-winter during long nights the birds start to sleep relatively
late in comparison to sunset suggesting that they need to expand their activities as much
as possible to obtain enough food. Males and females clearly differ in their sleep
behaviour. This suggests that the sexes either differ in their sleep requirements, in their
sleep quality or in trade-offs with other activities. Repeated measurements of most of the
individuals allowed me to determine the individual consistency in sleep behaviour.

In chapter 2, I could show that environmental factors such as night temperature and
seasonal date not only influence temporal sleep parameters but also nocturnal sleep-wake
cycles. Nighttime sleep could be categorized into being rhythmic or arrhythmic and
differed in many aspects regarding this categorization. Birds showed significant
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repeatability in rhythmicity, suggesting a genetic basis of this trait, but the period length
of the rhythms was not repeatable.

After finding strong individual consistency and inter-individual as well as sex-specific
variation in temporal organization of sleep I investigated the influence of sleep
parameters on reproductive success in chapter 3. My results did not show any association
between variation in sleep behaviour and reproductive success in females, but I found
associations in males that contradicted my expectations. The probability of gaining extra-
pair paternity was higher in males that began to sleep earlier and slept longer. Further, I
showed that partners of a breeding pair were mated assortatively in regard to their
awakening times in the morning, but that broods of pairs with more dissimilar awakening
times had higher fledging success.

In the last chapter I aimed to examine the underlying genetic causes of the phenotypic
variability. Therefore, I needed to identify informative polymorphisms in candidate genes
of blue tits in a first step. In chapter 4, I describe the strategy that led to the identification
of eleven polymorphisms with a high potential of being functional in genes which are
involved in the regulation of circadian rhythms.

Finally, in chapter 5 I tested for associations between the described genetic
polymorphisms and sleep phenotypes. My results revealed four significant associations
between single nucleotide polymorphisms of three different genes and three sleep
phenotypes. However, the number of significant results and the most significant result in
my analyses could just as well have occurred by chance, given the large number of tests. I
can therefore neither give evidence for an association between the genetic and phenotypic
variations nor can I rule out such an association.

To conclude, in this dissertation I present several novel findings on the sleep behaviour of
wild birds, with a special focus on temporal sleep parameters. My findings provide new
insights on effects of environmental factors, sex, age and individuality on sleep behaviour
and on the relationship between sleep and reproductive success. On the other hand, the
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question about the genetic causes of inter-individual variation remains unanswered but
gives possibilities for future research.
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