Plumage colouration, testosterone and reproductive behaviour in the red bishop (Euplectes orix) [Elektronische Ressource] / von Alice Edler

Plumage colouration, testosterone and reproductive behaviour in the red bishop (Euplectes orix) [Elektronische Ressource] / von Alice Edler


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Plumage colouration, testosterone and
reproductive behaviour
in the red bishop (Euplectes orix)

Von der Fakultät für Mathematik und Naturwissenschaften
der Carl von Ossietzky Universität Oldenburg
zur Erlangung des Grades und Titels eines

Doktors der Naturwissenschaften (Dr. rer. nat.)

angenommene Dissertation

von Frau Alice Edler

geboren am 05. Mai 1977 in Nürnberg.


Gutachter: PD Dr. Thomas W. P. Friedl
Zweitgutachter: Prof. Dr. Peter H. Becker

Tag der Disputation: 15. September 2009


Dedicated to my parents.
For believing.
Ulrike Aidnik (1952 – 2005)
Werner Aidnik (1945 – 2006) Table of contents
Table of contents

General introduction 1
Introduction 2
Form and functions of carotenoids 2
Animal signals and signalling 4
Influencing factors on colour expression and variation 4
Immunocompetence and parasites 5
Testosterone and “badges of status” 7
Condition-dependent signalling 8
Objectives of the thesis 10
References 13

Chapter 1 – Individual quality and carotenoid-based ornaments in
male red bishops (Euplectes orix): plumage is not all that counts 18
Abstract 9
Introduction 20
Material and methods 23
Study species
Field methods 24
Plumage reflectance 25
Spectral analysis 26
Leukocyte profiles 27
Testosterone levels 28
Parasites 29
Statistical analysis 29
Results 31
Influences on plumage colouration 31
Age and colouration 34
Discussion 6
Plumage colouration 36
Plumage brightness 39
Plumage characteristics and their relation to age 42
Conclusion 44
i Table of contents
Acknowledgements 46
References 47

Chapter 2 – Reproductive behaviour in male red bishops (Euplectes
orix): how important is plumage colouration? 55
Abstract 56
Introduction 57
Material and methods 60
Study species and area 60
Field methods 61
Reflectance and spectral analysis 63
Parasites 64
Testosterone 65
Statistical analysis 66
Results 67
Territoriality 7
Territory tenure 7
Number of nests built 69 baccepted 71
Male attractiveness 71
Discussion 73
Territoriality 73
Territory tenure 74
Reproductive effort (number of nests built) 76
Reproductive success (number of nests accepted) 77
Male attractiveness (residuals of number of nests accepted
against nests built) 78
Conclusion 79
Acknowledgements 80
References 81

ii Table of contents
Chapter 3 – Plumage colouration, age, testosterone and dominance
in male red bishops (Euplectes orix): a laboratory experiment 86
Abstract 87
Introduction 88
Material and methods 91
Study species
Housing conditions 92
Body condition index and age 92
Reflectance measurements 93
Testosterone levels 94
Male-male contests 95
Manipulations 96
Video analysis 97
Statistical analysis 98
Results 99
Plumage reflectance 99
Testosterone levels 101
Relationships between measures of dominance 102
Contests 2007 103 2008
Effects of plumage manipulation on behaviour and contest
outcome 105
Discussion 107
Acknowledgements 111
References 12

Appendix 119
Appendix A – Wild red bishop males
Appendix A1 – Plumage characteristics 120
Appendix A2 – Testosterone, parasites, blood and BCI 123
Appendix A3 – Territoriality, tenure and reproductive behaviour 126
Appendix B – Aviary red bishop males
Appendix B1 – Plumage characteristics (2007) 129
Appendix B2 – Plumage characteristics (2008) 130
iii Table of contents
Appendix B3 – Age and testosterone (2007 and 2008) 133
Appendix B4 – Body condition and behaviour (contests 2007) 134
Appendix B5 – Body condition and behaviour (contests 2008) 138

Summary 141
Summary in English 142
Zusammenfassung auf Deutsch 145

Acknowledgements 149

Curriculum vitae 154

iv General introduction


1 General introduction

Over the last years, carotenoid-based plumage colouration has been the focus of
many studies. Insights have been given into what factors – such as immunological
and environmental ones – influence the expression of this plumage, thereby causing
an immense variation in ornaments. As red, orange or yellow plumage traits also
underlie intense inter- and intrasexual selection, their influence on such things as
reproductive effort and success or the outcome of male-male competition have also
been under intense scrutiny.

Form and functions of carotenoids

Carotenoids are a special group of organic pigments with unique properties, functions
and actions. There are over 700 known carotenoids, divided into two groups –
xanthophylls and carotenes. In order to understand their biological importance, it is
necessary to understand the relationship between structure, properties and function.
Carotenoids belong in the category of tetraterpenoids, meaning they consist of 40
carbon atoms. These are in the form of a polyene chain, which is sometimes
terminated by rings. Carotenoids containing oxygen are classified as xanthophylls,
whilst those without typically contain only hydrogen and carbon and are grouped
under the term “carotenes”, of which the most famous one is probably β-carotene.
The observed colour of carotenoids – ranging from pale yellow through bright orange
to a deep red – is directly linked to their structure. The double-bonded carbon atoms
interact with one another via conjugation, a process in which electrons in the
molecule are able to move freely across the molecule. With an increasing number of
double bonds between the carbon atoms, electrons have more space to move. This
leads to a decrease in the absorbed ranges of energies of light and more frequencies
of light are absorbed from the short end of the spectrum of visible light, resulting in a
redder appearance (Britton et al. 2008).
Originally, carotenoids evolved in archaebacteria to provide support in lipid
membranes and later in photosynthetic organisms as light-harvesting pigments for
photosynthesis (Vershinin 1999) by extending the wave length range of light that
could be harvested and thereby improving photosynthesis (Britton et al. 2008).
2 General introduction
Further, as they are highly reactive to oxidizing agents and free radicals, carotenoids
serve an important function as free-radical scavengers. Through this, they protect
sensitive systems against oxidative damage, forming the basis of anti-oxidant action
(Burton & Ingold 1984, McGraw 2006, Britton et al. 2008), as well as protecting the
immune system during immune cell activation and proliferation (Chew 1993, Hughes
Also, and most importantly for this thesis, carotenoids play a vital role in the world of
colour. The yellow, orange and red colouration caused by these pigments is a wide-
spread phenomenon in the animal world and can be found in insects, fish and birds,
the classic examples being canaries, greater flamingos and gold fish. Animals,
however, cannot synthesize carotenoids and need to consume them as an important
part of their diet. These ingested pigments can then be metabolized accordingly,
meaning that the carotenoids found in tissues are not necessarily the ones ingested
(Brush 1990). A classic example for this is the modification of lutein and zeaxanthin
into the “canary xanthophylls” as the yellow pigments found in the yellow feathers of
canaries, which was first described by Brockman and Völker (1934). The range of
carotenoid colouration in the animal kingdom serves several purposes, such as
warning and advertising (Summers & Clough 2001, Blount et al. 2003, Casagrande
et al. 2006, Bezzerides et al. 2007, Pike et al. 2007, Blount et al. 2009).
After melanins, carotenoids are the second most frequent pigments in bird
colouration and were first ascribed as colourants to egg yolk (Willstatter & Escher
1912) and only later to feathers (Brockman & Völker 1934), legs and beaks
(Lonnberg 1938) and eyes (Hollander & Owen 1939). Different carotenoids lead to
different colours, with astaxanthin, canthaxanthin and adonirubin being responsible
for red colouration, while lutein, zeaxanthin and the canary xanthophylls result in
yellow colouration. While all birds naturally circulate carotenoids as a result of
inevitable dietary uptake, only a few of them actually incorporate these pigments into
various integumentary tissues. Also, for the most part, if pigments are deposited, they
are only deposited in certain body regions. In the house finch (Carpodacus
mexicanus) for example, carotenoids only give colour to the crown, breast and rump,
while the remaining feathers are melanised. Further, certain carotenoids can be
targeted, meaning that only specific pigments are actually used for colouration, even
if several others are also consumed (McGraw et al. 2003). The use of carotenoids in
ornamental traits has been proposed to be due to their physiological and chemical