Egg Shape in Birds
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Egg Shape in Birds Jamie Edward Thompson A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of PhilosophyďLJWƵďůŝĐĂƚŝŽŶ The University of Sheffield Faculty of Science Department of Animal and Plant Sciences March 2020 &ŽƌĂlways providing a positive mindset when it comes to discussing my goals and aspirations &ŽƌĂlways being the one to say ‘you can’ and ‘you will’ This is for you Nanna. Contents Contents Summary iii Acknowledgements iv-v Declaration vi-x Chapter 1 Introduction 1 1.1. Background 2-4 1.2. Avian Egg Shape 5-13 1.2.1. Describing and Quantifying Egg Shape 5-7 1.2.2. What are the potential drivers of egg shape diversity? 7-10 1.2.3. The case of the Common Guillemot’s pyriform egg 10-13 1.3. Thesis Layout 13-16 1.4. Acknowledgement of collaborative work within the thesis 16 Chapter 2 Accurately quantifying the shape of birds’ eggs 29 Biggins, J. D., Thompson, J. E. and Birkhead, T. R. (2018). Ecology and Evolution, 8, 9728-9738. Chapter 3 Wade’s Birds of Bempton Cliffs and his observations 45 on Guillemot (Uria aalge) eggs Birkhead, T. R. and Thompson, J. E. (2019). Archives of Natural History, 46, 240-252. Chapter 4 Egg shape in the Common Guillemot Uria aalge and 63 Brunnich’s Guillemot U. lomvia: not a rolling matter? Birkhead, T. R., Thompson, J. E. and Biggins, J. D. (2017). Journal of Ornithology, 158, 679-685. i Contents Chapter 5 The point of a Guillemot’s egg 75 Birkhead, T. R., Thompson, J. E., Jackson, D. and Biggins, J. D. (2017). Ibis, 159, 255-265. Chapter 6 Common guillemot (Uria aalge) eggs are not self-cleaning 91 Jackson, D., Thompson, J. E., Hemmings, N. and Birkhead, T. R. (2018). Journal of Experimental Biology, 221, jeb188466 (1-9). Chapter 7 The pyriform egg of the Common Murre (Uria aalge) is 105 more stable on sloping surfaces Birkhead, T. R., Thompson, J. E. and Montgomerie, R. (2018). The Auk, 135, 1020-1032. Chapter 8 The evolution of egg shape in birds: selection during the 123 incubation period Birkhead, T. R., Thompson, J. E., Biggins, J. D. and Montgomerie, R. (2019). Ibis, 161, 605-618. Chapter 9 General Discussion 143 Appendices Appendix 1 Avian egg collections: museum collection bias driven by 159 shape and size Thompson, J. E. and Birkhead, T. R. in prep. Appendix 2 Two-egg clutches in the Fulmar 185 Birkhead, T. R., Jensen, J-K., Thompson, J. E., Hammer, S., Thompson, P. and Montgomerie, R. (2020). British Birds, 113, 165-170. Appendix 3 New insights from old eggs – the shape and thickness of 197 Great Auk Pinguinus impennis eggs. Birkhead, T. R., Russell, D. G. D., Garbout, A., Attard, M. R. G., Thompson, J. E. and Jackson, D. (2020). Ibis, Early view, doi: 10.1111/ibi.12820 ii Summary Summary Birds demonstrate incredible intra- and interspecific diversity in various egg traits. In particular, there is considerable diversity in egg shape across bird species from nearly spherical to extremely pyriform (pointed) eggs. This variation in avian egg shape has long fascinated researchers and numerous efforts have been made to quantify egg shape traits and examine the possible evolutionary drivers and functions of the observed patterns of avian egg diversity. Previous studies have attempted to examine egg shape at various taxonomic scales and the evidence from these studies collectively suggest that avian egg shape diversity might be driven by two main sources: (i) indirect selection via anatomical constraints or life history trait changes, and/or (ii) direct adaptive selection during the incubation period. However, it is still unclear as to how important these drivers of egg shape diversity are and how their importance might alter at different taxonomic scales. Furthermore, current studies on avian egg shape lack a universally agreed method of accurately quantifying all egg shapes, which makes comparing studies and assimilating overall patterns of egg shape diversity challenging. This thesis presents published work that aims to contribute further to the understanding of avian egg shape diversity. Firstly, the thesis presents a paper highlighting a novel automated image analysis method that more accurately quantifies egg shape, compared to previous modelling methods, that could be used by all future studies. Second, the thesis presents several papers examining the adaptive function of the extremely pyriform egg of the Common Guillemot (Uria aalge). In these papers, evidence is presented that brings in to question the plausibility of the previously popular ‘rolling-in- an-arc’ adaptive explanation. Instead, three new alternative adaptive hypotheses for the Common Guillemot’s pyriform egg are presented: (i) mechanical damage prevention/limitation; (ii) faecal- debris contamination limitation, and (iii) increased stability. Based on current available evidence, it is concluded that the stability hypothesis is currently the strongest supported adaptive explanation for the Common Guillemot’s pyriform egg shape. Thirdly, the thesis presents a published paper that looked to examine potential drivers of egg shape patterns at a broader taxonomic scale. Here, the paper examined patterns of egg shape in alcids (Alcidae) and penguins (Spheniscidae), two taxa containing species with considerable variations in egg shape and incubation environments and behaviours. /Ŷ ƚŚĞ ƐƚƵĚLJ͕ evidence is presented that highlights the importance of incubation site characteristics as a driver of egg shape variation, something not evident in some other studies at broader taxonomic scales. iii Acknowledgements Acknowledgements To be able to work under the guidance of a world-renowned ornithologist like Professor Tim Birkhead is an incredible and exciting opportunity, and I have been very lucky to have had that opportunity for over a decade. It is never dull doing research with Tim, and I have learnt a great amount about what it takes to be a successful researcher through him. Tim has always been supportive, encouraging and constructively critical, and is the person who opened the door of opportunity that gave me the chance to write this PhD thesis. Thank you, Tim, for your unwavering support, for believing in my capabilities as a researcher, and for taking this Yorkshire lad to places I would likely not have ever had opportunities to see. I will always be forever grateful and remember those times together on the guano-covered guillemot ledges of Skomer Island with great fondness. I have also been incredibly lucky to have learnt under the guidance of Dr Nicola Hemmings. Your support and encouragement during my undergraduate and working days at The University of Sheffield has been pivotal in making me the researcher I am today. Thank you for this continued support and guidance, for being a great scientific role model, and for trusting me with providing assistance on some of your PhD work all those years ago! During my time as a research technician at The University of Sheffield, I have been incredibly lucky to work with many great people that have made various research projects fun and thought-provoking. Particularly, whilst researching all things eggs, both Dr Duncan Jackson and Dr Marie Attard have provided invaluable assistance and stimulating discussions that has helped shape my research. I am also incredibly grateful to have had the opportunities to work with some great collaborators from other departments and institutions, including Professor John Biggins (School of Mathematics and Statistics, The University of Sheffield) and Professor Bob Montgomerie (Queen’s University, Ontario). Thanks to all the collaborators for their vital contributions to the work presented in this thesis and for providing me with opportunities to learn a great deal from them. I would like to take the opportunity to thank all the museum curators who have allowed myself and Tim to measure and photograph eggs from their collections, including: Julian Carter and Jennifer Gallichan (The National Museum of Wales); Henry McGhie and Rachel Petts (Manchester Museum); iv Acknowledgements Professor Robert Barrett (Tromsø University Museum); Professor Jon Fjeldså (Natural History Museum of Denmark), and Dan Gordon (Tyne and Wear Archives and Museums). Special thanks, in particular, go out to Douglas Russell (Natural History Museum at Tring) who has continued to provide invaluable support and access to the Natural History Museum’s egg collections throughout the entirety of this research project – I am incredibly grateful for your tireless assistance and forever amazed by your stories about the collections. Thanks also goes out to The Wildlife Trust of South and West Wales, particularly Lizzie Wilberforce and previous Skomer Island wardens Birgitta Büche and Edward Stubbings, for supporting our research on Skomer Island. Natural Resources Wales provided their permission and necessary licencing for us to undertake research on Common Guillemot and Razorbill eggs on Skomer Island, for which I am grateful for. I would also like to thank Dr Julie Riordan, Dr Jodie Crane and Dr Elspeth Kenny who have all provided assistance with fieldwork at various times and, all of which, have made fieldwork that more enjoyable over the years. Whilst writing this thesis, I have received critical feedback from Tim, Nicola and Dr Kathryn Maher that has allowed me to dramatically improve my thinking, clarity and writing skills, for which I thank them all for. Thanks to ‘The Lunch Bunch’ for their amazing friendship and laughter they bring to every work day. Throughout my pursuits in scientific research, my family has always been my rock. Always supporting and encouraging me. Always interested to hear how I am getting on. Always there when I have the inevitable emotional wobble. I am forever grateful and thankful for everything you do for me, and inspired by you all. My love and thanks to you all, always. Finally, all my thanks and love must go to my partner Katy.