Investigating How Movement Affects Prey Camouflage Using an Insect Predator
Total Page:16
File Type:pdf, Size:1020Kb
UNIVERSITA’ DELLA CALABRIA Dipartimento di Biologia, Ecologia e Scienze della Terra Dottorato di Ricerca in Scienze della Vita CICLO XXIX Investigating how movement affects prey camouflage using an insect predator Settore Scientifico Disciplinare BIO/05 Zoologia Coordinatore: Ch.mo Prof. Marcello Canonaco Firma _____________________________ Supervisori/Tutors: Ch.mo Prof. Pietro Brandmayr Firma______________________ Ch.ma Prof. Candy Rowe Firma______________________ Dottorando: Dott.ssa Diana Umeton Firma _____________________ i Thesis Abstract Patterns that help prey camouflage themselves whilst stationary prove to be ineffective once prey move. Given that motion breaks camouflage, can a moving prey ever be effectively concealed? Recent studies have found that certain patterns might help prey deceive their predators whilst moving, as in the case of ‘motion dazzle’. However, research with moving prey has been conducted using only humans or birds as predator models, and consequently, it is now known how other predator species might behave. In addition, it is important to know not just how motion affects camouflage, but also how the speed of motion can affect the efficacy of different defensive patterns. This thesis aims to address these current gaps in the field. First, I explore the visual acuity in a group of insect predators, the praying mantids, to explore if different species vary in their visual acuity, which could impact on what they can perceive and which selective pressure they could exert on prey defensive patterns. Second, using praying mantids tracking computer-generated stimuli, I empirically investigate how cryptic and conspicuous patterns might enhance the survival of moving prey. In particular, I specifically investigate if high contrast striped prey could reduce predation risk through the visual phenomenon known as “flicker fusion effect”. I found that when prey were slow moving, all patterns were equally detectable by the mantids. However, once prey moved at faster speed, a cryptic pattern was more likely to be tracked than a more conspicuous black-and-white striped pattern suggesting that the latter was successful in inducing flicker fusion effect in praying mantids’ eyes. This thesis starts to disentangle how pattern and speed could combine to help camouflage an animal when moving through its environment. The outcome of the study are discussed in the wider context of how animals coloration and behaviour evolved together to confer them survival advantages. ii Acknowledgments It was a privilege to be mentored by Professors Pietro Brandmayr and Candy Rowe: I am grateful to you both for guiding and encouraging me; I have learned so much from you in the past years. Also thank you for your patience and for dealing with all the bureaucracy needed to allow me to carry out my research at Newcastle University A big thank to Professors Jenny Read and Claire Rind, and to everyone in Rowe and Read lab. In particular, thank to Ghaith Tarawaneh for coding the visual stimuli and dealing with the infinite number of pilots and changes in the code.; thank to Eugenia Fezza for helping me to collect some of the pilots data. I would like to thank everyone in the Institute of Neuroscience for making me feel welcome since the very first day and for doing great in interpreting my English; well done! My journey in Newcastle wouldn't have been the same if not accompanied by the amazing people I met; thanks to my international-geordie family. In particular thank to Sarah and Simona, for different reasons and at different stages of this PhD journey: your company has kept me alive; thanks for all the nights out and the nights in (..the library!). A special thank to my friends widespread all over the word: Ester, Fanj, Fausta, Federica, Mara, Marilu’, Valeria and Patrizio: no matter how far we are, you are part of my everyday life. Thanks for being next to me, sharing every little conquest and fail. Thank to my family for always believing in me: if I am where I stand today, it is because of your continuous love and support. This thesis is dedicated to Nonna: without her love and strength, nothing of this work would ever have been possible. iii Table of contents Thesis Abstract ...................................................................................................................... ii Acknowledgments ................................................................................................................. iii Table of contents .................................................................................................................. iv Chapter 1: General introduction ............................................................................................ 1 1.1 Animal camouflage ...................................................................................................... 1 1.2 Camouflage whilst in motion ........................................................................................ 3 1.3 The importance of predators’ perception and cognition for the evolution of prey defences ............................................................................................................................ 5 1.4 Aims of the thesis ........................................................................................................ 7 Chapter 2: Unravelling the illusion of ..................................................................................... 8 flicker fusion effect ................................................................................................................ 8 2.1 Abstract ....................................................................................................................... 8 2.2 Introduction .................................................................................................................. 8 2.3 What is the mechanism underlying the flicker fusion effect? ...................................... 11 2.4 What defensive function might the flicker fusion effect have? .................................... 20 2.5 How is confusion arising through current terminology? .............................................. 23 2.6 Discussion ................................................................................................................. 25 Chapter 3: Introducing mantids as a predator model ........................................................... 27 3.1 Abstract ..................................................................................................................... 27 3.2 Introduction: why use insects as predator model? ..................................................... 28 3.3 How do insects differ from other well-studied predator models? ................................ 32 3.4 The visual hunter: praying mantis .............................................................................. 35 Chapter 4: Visual acuity variability across different species of praying mantids ................... 38 4.1 Abstract ..................................................................................................................... 38 4.2 Introduction ................................................................................................................ 38 4.3 Measures of eye morphology ..................................................................................... 42 4.4 Visual acuity using the optomotor response ............................................................... 45 4.4.1 Subjects .............................................................................................................. 46 4.4.2 Experimental set-up ............................................................................................ 46 4.4.3 Computer-generated visual stimuli ...................................................................... 48 4.4.4 Experimental procedure ...................................................................................... 49 iv 4.4.5 Data analysis ...................................................................................................... 51 4.4.6 Results ................................................................................................................ 52 4.5 Discussion ................................................................................................................. 56 Chapter 5: The flicker fusion effect can enhance ................................................................. 59 the concealment of moving prey ......................................................................................... 59 5.1 Abstract ..................................................................................................................... 59 5.2 Introduction ................................................................................................................ 59 5.3 Methods .................................................................................................................... 62 5.3.1 Subjects .............................................................................................................. 62 5.3.2 Experimental set-up ............................................................................................ 62 5.3.3 Computer-generated prey ................................................................................... 65 5.3.4 Experimental procedure ...................................................................................... 71 5.3.5 Data analysis .....................................................................................................