Sexual Selection and Natural Selection on the Social Signals of Gliding Lizards
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THE EVOLUTION OF ORNAMENT DIVERSITY: Sexual selection and natural selection on the social signals of gliding lizards Danielle Alice Klomp A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Evolution and Ecology Research Centre School of Biological, Earth and Environmental Sciences University of New South Wales June, 2016 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: First name: Other name/s: Abbreviation for degree as given in the University calenDar: School: Faculty: Title: Diversity in animal colour and form can often be attributed to communication signals, which play an important role in species recognition and mate choice. Divergence of signals among populations is therefore thought to be a driver of speciation. This thesis examines signalling processes in the species rich agamid genus, Draco, to understand their influence on signal design, signal divergence and ultimately speciation. Draco lizards are known as ‘gliding lizards’, as they have retractable gliding membranes. They communicate with extendable throat-fans, called dewlaps, which are diverse in colour, shape and size among species. Chapter two assesses the importance of dewlap signal design for detection and recognition in Draco melanopogon, by presenting free-living lizards with robots displaying dewlaps of different designs. Dewlap design does not affect the latency of signal detection by conspecifics, but once the robot dewlap had been detected, males responded with greater intensity to dewlaps that best resembled the species’ typical design, suggesting pattern is important in species recognition. As signal components may evolve differently in populations exposed to different selection pressures, chapter three assess the relationships between the dewlap components (colour and size) and aspects of their environments. Males of different species employ colour contrast and dewlap size as alternative strategies for effective communication, and predation intensity may play a role in which strategy a species employs. Further, correlations between male dewlap components and sexual dimorphism suggest that sexual selection is also a major factor influencing dewlap design. Chapter four shows that the different gliding membrane colouration of two populations of Draco cornutus closely match the colours of freshly fallen leaves in their respective habitats as they appear to the visual system of predatory birds. This suggests the populations have diverged in colouration to mimic the colours of local falling leaves and thereby reduce predation by birds. Chapter five tests whether Draco sumatranus lizards use their position relative to the sun to enhance the transmission of light through the dewlap, and thus the apparent brightness of their dewlap during display. Lizards are significantly more likely to orientate themselves perpendicular to the sun when displaying, ensuring maximum sun exposure for the extended dewlap. This thesis confirms the centrality of sexual selection, species recognition and predation as major factors influencing signal design in Draco, and thereby furthers our understanding of the evolution of ornament diversity. Declaration relating to disposition of project thesis/Dissertation I hereby grant to the University of New South Wales or its agents the right to archive anD to make available my thesis or dissertation in whole or in part in the University libraries in all forms of meDia, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 worD abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). …………………………………………………………………… …………………………………………………………………… ……….…15/10/2016………………… Signature Witness Date The University recognises that there may be eXceptional circumstances requiring restrictions on copying or conDitions on use. Requests for restriction for a period of up to 2 years must be maDe in writing. Requests for a longer period of restriction may be consiDereD in eXceptional circumstances anD require the approval of the Dean of GraDuate Research. FOR OFFICE USE ONLY Date of completion of requirements for AwarD: ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed …………………………………………….............. Danielle Klomp (Candidate) Date …………………………………………….........15/10/2016 iii COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed ……………………………………………........................... Date ……………………………………………..........07/11/2016 ................. AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed ……………………………………………........................... Date ……………………………………………..........07/11/2016 ................. Introduction For my father, wlw provided the inspiration, and for Hugh, my audience of one. iv This thesis was made possible by an Australian Postgraduate Award from the Australian Research Council. The research presented here was funded in part by a postgraduate research award from the Ecology and Evolution Research Centre, a student research award from the Australasian Society for the Study of Animal Behaviour, and a grant to Devi Stuart-Fox from the National Geographic Society. My supervisors, Dr Terry Ord and Dr Devi Stuart-Fox, helped me in the field and at every stage of the analysis and writing. I genuinely appreciate their professionalism and personal support. I am also grateful for field support provided by Indraneil Das, Pui Yong Min, Adi Shabrani, Arvin Diesmos, Norhayati Ahmad, Adnan Moussalli, Elizabeth Cassidy and Audrey Stewart. Many others assisted at various stages of the field preparation, data analysis and writing, but in particular I’d like to thank John Morrongiello, Wayne Robinson, Heather Try, Nathan Adler, Nick Klomp and Hugh McKenzie-McHarg. On a personal note, I am eternally grateful to the members of the E&ERC at UNSW and Stuart-Fox lab at the University of Melbourne, who greatly enriched this experience for me, and to my wonderful and supportive family who have helped me through every stage of my thesis. v Diversity in animal colour and form can often be attributed to communication signals, which play an important role in species recognition and mate choice. Divergence of signals among populations is therefore thought to be a driver of speciation. This thesis examines signalling processes in the species rich agamid genus, Draco, to understand their influence on signal design, signal divergence and ultimately speciation. Draco lizards are known as ‘gliding lizards’, as they have retractable gliding membranes. They communicate with extendable throat-fans, called dewlaps, which are diverse in colour, shape and size among species. Chapter two assesses the importance of dewlap signal design for detection and recognition in Draco melanopogon, by presenting free-living lizards with robots displaying dewlaps of different designs. Dewlap design does not affect the latency of signal detection by conspecifics, but once the robot dewlap had been detected, males responded with greater intensity to dewlaps that best resembled the species’ typical design, suggesting pattern is important in species recognition. As signal components may evolve differently in populations exposed to different selection pressures, chapter three assesses the relationships between the dewlap components (colour and size) and aspects of their environments. Males of different species employ colour contrast and dewlap size as alternative strategies for effective communication, and predation intensity may play a role in which strategy