Bangor University MASTERS BY RESEARCH The Evolution of Defensive Strategies in Cobras Jones, Bryony Award date: 2017 Awarding institution: Bangor University Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 28. Sep. 2021 The Evolution of Defensive Strategies in Cobras Bryony Jones Supervisor: Dr Wolfgang Wüster Thesis submitted for the degree of Masters of Science by Research Biological Sciences The Evolution of Defensive Strategies in Cobras Abstract Species use multiple defensive strategies aimed at different sensory systems depending on the level of threat, type of predator and options for escape. The core cobra clade is a group of highly venomous Elapids that share defensive characteristics, containing true cobras of the genus Naja and related genera Aspidelaps, Hemachatus, Walterinnesia and Pseudohaje. Species combine the use of three visual and chemical strategies to prevent predation from a distance: spitting venom, hooding and aposematic patterns. Although the functional morphology and mechanisms behind spitting and hooding are understood, few studies have investigated the evolution and variation of hood size. The aim of this thesis is to reconstruct the evolutionary history of defensive strategies in cobras, investigate the reasons why different strategies are used and to identify trade-offs. Focusing on variation in hood size, X-ray radiography was used to visualize and measure ribs of cobra specimens. Hood morphology and occurrence of hood pattern, ventral bands and spitting were analysed in phylogenetic comparative analyses. A single origin of hooding behaviour in core cobras prompted the evolution of extended ribs multiple times in Hemachatus and Naja, trending towards a large hood. Reduction in extended ribs occurred multiple times due to specialization to aquatic, subterranean or arboreal habitats. No trade-offs between spitting and hood pattern were uncovered due to the variation in pattern within Asian spitting cobras. Wide hoods were only associated with a hood pattern when phylogenetic signal was not considered, suggesting that correlation may be due to shared ancestry. In different species, size or distinctiveness of aposematic signals may be more important, leading to smaller hoods with bold patterns or large hoods with faint patterns. This study highlights the diverse morphology within cobras and the need for further investigation into frequency, extent of use of displays and predators to determine the triggers for the evolution of spitting. Page 1 of 74 The Evolution of Defensive Strategies in Cobras Contents Abstract ........................................................................................................................................... 1 List of Figures .................................................................................................................................. 3 List of Tables ................................................................................................................................... 3 List of Supplementary Tables .......................................................................................................... 4 Acknowledgements ......................................................................................................................... 5 Declaration and Consent ................................................................................................................. 6 1.0 Introduction ............................................................................................................................... 9 1.1 Cobra defensive strategies .................................................................................................. 10 1.1.1 Hooding ......................................................................................................................... 11 1.1.2 Hood markings and ventral patterns .............................................................................. 12 1.1.3 Spitting .......................................................................................................................... 14 1.2 Variation and trade-offs between strategies ......................................................................... 16 1.3 Comparative evolutionary studies on cobras ........................................................................ 18 1.4 Aims and objectives ............................................................................................................. 19 2.0 Methods .................................................................................................................................. 19 2.1 Hood morphometrics ............................................................................................................ 19 2.1.1 Specimens .................................................................................................................... 19 2.1.3 Production of X-ray images ........................................................................................... 20 2.1.4 Collection of hood morphological data ........................................................................... 20 2.2 Colour and pattern ............................................................................................................... 22 2.2.1 Pattern definitions .......................................................................................................... 22 2.2.2 Pattern in the core cobra group ..................................................................................... 22 2.3 Comparative analysis and ancestral state reconstruction ..................................................... 23 2.3.1 Categorisation of discrete data for all species ................................................................ 23 2.3.2 Comparative analysis .................................................................................................... 26 2.3.3 Ancestral state reconstruction ....................................................................................... 27 3.0 Results .................................................................................................................................... 28 3.1 Markings .............................................................................................................................. 31 3.1.1 Subgenus Uraeus .......................................................................................................... 31 3.1.2 Subgenus Boulengerina ................................................................................................ 31 3.1.3 Pattern in subgenus Afronaja ........................................................................................ 33 3.1.4 Pattern in subgenus Naja .............................................................................................. 33 3.1.5 Pattern in Aspidelaps, Walterinnesia, Hemachatus and Pseudohaje ............................. 34 Page 2 of 74 3.2 Hood size ............................................................................................................................. 34 3.3 Comparative analysis ........................................................................................................... 37 3.4 Ancestral state reconstruction .............................................................................................. 40 4.0 Discussion ............................................................................................................................... 43 4.1 Hood size and hooding behaviour ........................................................................................ 43 4.2 Spitting evolution.................................................................................................................. 44 4.3 Evolution of patterns ............................................................................................................ 46 4.4 Further reasons for variation in defensive strategies ............................................................ 49 4.5 Conclusion ........................................................................................................................... 51 5.0 Bibliography............................................................................................................................. 52 6.0 Supplementary Information ...................................................................................................... 61 List of Figures Figure 1. Hood pattern examples .................................................................................................. 22 Figure 2. Maximum clade credibility tree from Bayesian analysis of 2 mitochondrial (cytb & ND4) and 5 nuclear (NT3, PRLR, UBN1, c-mos and RAG1) genes. ......................................................