Seasonal timing in different environments [Elektronische Ressource] : comparative studies in stonechats / vorgelegt von Barbara Helm

Helm, Charles Barbara

Sujets

• Biologie

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2002
• Nombre de lectures: 4
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Seasonal timing
in different environments:
comparative studies in Stonechats
Barbara Helm
Cover picture: Saxicola torquata
Photo: Nigel Blake
Barbara Helm Seasonal timing in different environments: comparative studies in Stonechats



Seasonal timing in different environments:
comparative studies in Stonechats




Dissertation der Fakultät für Biologie an der
Ludwig-Maximilians-Universität München



























vorgelegt von Barbara Helm

am 29. November 2002




































Gutachter

Prof. Dr. E. Gwinner
Prof. Dr. G. Neuweiler Heubl
Prof. Dr. E. Weiß


Tag der mündlichen Prüfung

11. April 2003 I
Table of Contents

Summary 1
Deutsche Zusammenfassung 4
Introduction 9
Four subspecies of Stonechats 11
Approaches used in the studies 16
Organization and scope of the dissertation 17
Prior publications of dissertation material 19

General methods 21
Birds and holding conditions 21
Photoperiodic conditions 21
Monitoring molt, derviation and analysis of variates 22
Quantitative genetic analyses 23
Monitoring migratory activity and derivation of data 24
Measuring growth and fluctuating asymmetry 24
Assessing the size of reproductive organs 25
Ringing recovery data 25

Studies of major life cycle events 27
Chapter 1: Growth and developmental precision in young Stonechats: differences
between subspecies and effects of short day length 29
Summary 29
Introduction 29
Material and methods 31
Nestling growth 31
Final size and developmental precision 32
Results 35
Growth of Siberian Stonechats 35
Final size and symmetry of Stonechats from four populations 35
Presence of FA in tarsus and P8 38
Influence of subspecies, sex and photoperiod on FA 39
Discussion 40
Growth of Siberian Stonechats 40
Size and FA of wing length 41
II
th
Final size of tarsus and the 8 primary 41
th
FA of tarsus and the 8 primary 43
Chapter 2: Postjuvenile molt under a tight seasonal schedule in Siberian
Stonechats 45
Summary 45
Introduction
Birds and methods 46
Results 48
Variations in molt timing 48
Effects of photoperiod 49
Family effects on the timing of molt 51
Comparison of molt timing among three Stonechat subspecies 53
Discussion 53
Chapter 3: Genetic control of molt timing: selection experiments with European
Stonechats (S.t. rubicola) 59
Summary 59
Introduction
Birds and methods 60
Selection regime 60
Statistical treatment 62
Results 64
Heritability estimates 64
Effects of hatching date 65
Discussion 66
Chapter 4: A new type of migrant? Migratory restlessness and postjuvenile molt in
Stonechats from the British Isles (S.t. hibernans) 73
Summary 73
Introduction 73
Materials and methods 75
Birds and methods 75
Analysis of nocturnal restlessness 76
Results 78
Postjuvenile molt 78
Nocturnal restlessness in Irish Stonechats 80
Temporal correlations between molt and migratory restlessness 86
Comparison with migratory restlessness of European Stonechats 86 III
Discussion 88
Timing of postjuvenile molt and migratory restlessness 88
Incidence of Zugunruhe 89
Timing of core migratory restlessness 92
Postbreeding nocturnal restlessness 94
Chapter 5: Movements of Stonechats from central Europe and the British Isles
(S.t. rubicola and hibernans): results from ringing recoveries 97
Summary 97
Introduction 97
Material and methods 100
Results 102
General patterns 102
Comparison of the three focal populations 105
Discussion 116
Chapter 6: Reproductive timing in European and Siberian Stonechats (S.t. rubicola
and maura) and its implications for hybridization of the two subspecies 119
Summary 119
Introduction 119
Material and methods 121
Results 122
Discussion 126
Outlook: Implications for timing under changing seasonal conditions 131

Conclusions 137

Acknowledgements 143

References 145

List of publications in biology 161

Curriculum Vitae 163
IV 1
Summary

Birds must time their seasonal activities precisely to best match the specific
conditions of their temporal environments. Local populations often differ in seasonal
timing. To understand adjustments to temporal environments, I compared major events in
annual cycles among four populations of a model species, the Stonechat (Saxicola
torquata). The studies were carried out on captive Stonechats from African, Central
European, Irish and Siberian populations. Among these populations, time-pressure is
presumably highest in long-distance migrant Siberian Stonechats that stay on the breeding
grounds for the shortest time. Central European and Irish Stonechats migrate short
distances and hence have a longer breeding season. In addition, Irish Stonechats are partial
migrants so that for parts of the population migration is not a necessary component of
their seasonal organization. African Stonechats are year-round residents. By comparing the
populations' temporal organization I aimed to contribute to an understanding of how
seasonal timing can be modified and how modifications of one life cycle stage affect
others.
The dissertation consists of six studies exploring the first annual cycle of
Stonechats, from hatching until reproduction. The first section is dedicated to growth and
developmental precision in the young. I compared growth of time-constrained Siberian
Stonechats to that of other subspecies to assess if seasonal pressure accelerates
development. Wing growth was faster than in the other subspecies and hence differed in
the predicted direction. However, body mass grew just as fast in African nestlings which
presumably were subject to the lowest seasonal pressure. Therefore, seasonal pressure may
accelerate growth, but other selection pressures may have similar effects. A possible cost of
fast growth could be reductions of size or developmental precision. I compared fluctuating
asymmetry (FA) and final size of tarsus and wing among the four populations. In addition,
birds were kept under two photoperiods indicating different seasonal pressure. A
significant amount of FA was present, but FA differed neither among populations nor in
response to day length. In contrast, wing size but not tarsus size of European and Siberian
Stonechats was significantly reduced under time pressure. These results suggest that
nestlings from late clutches incur the price of a reduced wing span to compensate for some
of their delay.
The next major developmental stage is postjuvenile molt. The great plasticity in the
Stonechats’ body molt timing in response to photoperiodic cues can be described by
reaction norms. One study in my dissertation investigates molt under a tight seasonal
schedule in Siberian Stonechats. Siberian Stonechats molted faster and at earlier ages than
their conspecifics. Under short day length molt was not advanced but its duration was
2
greatly reduced. Siberian Stonechats differed from other subspecies in their reaction norms
to photoperiod in a way that may be related to requirements of their temporal
environments. For Siberian Stonechats, duration but not the timing of molt was highly
2
heritable. In a second study, I tested the heritability (h ) of molt timing in European
Stonechats in selective breeding experiments. Initial results of the long-term experiments
2
confirmed high h and suggested a correlated selection response of photoperiodic reaction
norms. Micro-evolutionary mechanisms of timing adjustments in Stonechats may hence
proceed through adjustments of photoperiodic reaction norms.
After molt, migratory Stonechats set out on their journey to wintering grounds. In a
case study of Irish Stonechats I related migratory restlessness to the timing of postjuvenile
molt. Because of their partially migrant behavior, I expected individual differences among
birds in Zugunruhe and in molt timing. Unexpectedly, all Irish Stonechats showed
pronounced migratory restlessness. Timing of molt and migratory urge were closely
correlated. The birds initiated Zugunruhe soon after the peak of molt but before its
completion. In addition, many birds showed low levels of restlessness coinciding with the
time of juvenile dispersal. The consistently migratory behavior of Irish Stonechats contrasts
with observations from other partially migrant passerines but needs to be tested more
rigorously. A consolidation of results would imply a more differentiated approach to the
regulation of partial migration. In this study I introduced new techniques for the analysis
of nocturnal activ