Moving at a Snail’s Pace: the effect of temperature and humidity cues on the behaviour of Littorina subrotundata by Karen J. C. Rickards A Thesis Presented to The University of Guelph In partial fulfilment of requirements For the degree of Master of Science in Integrative Biology Guelph, Ontario, Canada © Karen J.C. Rickards, 2012 ABSTRACT MOVING AT A SNAIL’S PACE: THE EFFECT OF TEMPERATURE AND HUMIDITY CUES ON THE BEHAVIOUR OF LITTORINA SUBROTUNDATA Karen J.C. Rickards Advisor: University of Guelph, 2012 Professor Elizabeth Grace Boulding Animals living in intertidal habitats are subjected to extreme variation in abiotic stressors such as high temperatures and low humidity during emersion at low tide. Rather than rely solely on physiological responses to these stressors, many intertidal animals use behaviour to respond to these environmental variables. I investigated three behaviours displayed by the northeastern Pacific intertidal snail Littorina subrotundata that are altered in response to temperature and/or humidity in other intertidal snail species. I found that under summer conditions, temperature and humidity did not appear to be primary environmental cues motivating altered microhabitat selection or aggregation propensity in L. subrotundata. Despite this, these stressors did appear to be important cues for altered activity level. This study demonstrates that behaviour typically assumed to be a response to temperature and humidity may be driven by alternate cues across different species and/or study systems. Acknowledgements First and foremost, for their invaluable advice, keen scientific insights, but perhaps most importantly for their bottomless wells of patience I owe endless thanks to my supervisor Elizabeth Boulding and my advisory committee of Claudia Wagner-Riddle and Beren Robinson. Many thanks are due to the whole team at the Bamfield Marine Sciences Centre; without your help the challenge of field logistics would have been insurmountable. Many thanks as well to the Huu-ay-aht first nation for access to and use of their beautiful traditional lands. I wish to extend thanks to Leslie-Ann Damphousse, Justine Ammendolia, Caitlin Yan, Mónica Ayala Díaz, Jean Richardson, Kathryn Anderson, Jason Van Rooyan, Amy McConnell, and AJ Chapelsky for their daring journeys to the intertidal; your bravery in the face of bears, inclement weather, long kayak journeys, and a cranky graduate student is nothing short of commendable. For their fearless forays into the depths of statistical theory I owe a deep debt to Jean Richardson, Michael Silvergieter, and Rob McLaughlin. For their tireless devotion to snail care and tolerance of their care-taker I thank Mathieu Brunette, Matt Cornish, and Bob Frank. I am very grateful to the Natural Sciences and Engineering Research Council of Canada, the University of Guelph, and the Western Canadian Universities Marine Sciences Society for their financial support. iii No man is an island, and no graduate student would complete her thesis without the invaluable help of those around her. Though I have mentioned only a small handful of people by name, over the last two years there have been countless others that have provided me with insights, support, stress relief, and most importantly perspective. Thank you to all who have been there for me; I really couldn’t have done it without you. So long...and thanks for all the fish. iv Table of Contents Acknowledgements ........................................................................................................................ iii Table of Contents ............................................................................................................................ v List of Tables ................................................................................................................................. vi List of Figures ............................................................................................................................... vii Chapter One: General Introduction ................................................................................................. 1 Chapter Two: Behavioural change in response to environmental cues ......................................... 9 Introduction ................................................................................................................................. 9 Methods..................................................................................................................................... 15 Results ....................................................................................................................................... 23 Discussion ................................................................................................................................. 26 Chapter Three: General Conclusions. ........................................................................................... 37 References ..................................................................................................................................... 40 Tables ............................................................................................................................................ 48 Figures........................................................................................................................................... 62 Appendices .................................................................................................................................... 73 Appendix 1: Habitat Selection on Artificial Substrate ............................................................. 73 Appendix 2: Comparison of Vapour Pressure Deficit Calculations ......................................... 81 Appendix 3: Data Set (attached electronic file) ........................................................................ 85 v List of Tables Table 1: Definitions of the five microhabitat categories used in this study Table 2: Definitions of the three activity categories used in this study Table 3: Descriptions of the nine multiple working hypotheses used for all QAICc analyses Table 4: Summary of the number of snails found at each site Table 5: QAICc values and ranks for nine models predicting a snail’s likelihood of being associated with a barnacle Table 6: Summary of the model that uses location and size of the snail to predict a snail’s likelihood of being associated with a barnacle Table 7: Summary of the average temperature found in each microhabitat classified by month and site Table 8: Summary of the average VPD found in each microhabitat classified by month and site Table 9: QAICc values and ranks for nine models predicting a snail’s microhabitat choice Table 10: Summary of the model that uses location and size of the snail to predict a snail’s microhabitat choice Table 11: QAICc values and ranks for nine models predicting a snail’s activity level Table 12: Summary of the model that uses temperature and VPD to predict a snail’s activity level Table 13: QAICc values and ranks for nine models predicting a snail’s likelihood of being aggregated Table 14: Summary of the model that uses location to predict a snail’s likelihood of being aggregated Appendix 1: Experimental microhabitat selection Table A1: values of the hierarchical terms for log-linear analysis (all snails) Table A2: values of the hierarchical terms for log-linear analysis (moving snails only) vi List of Figures Figure 1: Map of study sites (Prasiola Point and Nudibranch Point) and surrounding area Figure 2: Photographs of probes used to collect data on substrate temperature, relative humidity, and dewpoint Figure 3: Picture demonstrating four out of five of the microhabitat categories used Figure 4: Mean substrate temperature at each site, classified by month Figure 5: Mean VPD at each site, classified by month Figure 6: Percentage of snails found that were associated with barnacles Figure 7: Percentage of snails found in each of the five microhabitats Figure 8: Average substrate temperature found in each microhabitat, classified by month and site. Figure 9: Average VPD found in each microhabitat, classified by month and site Appendix 1: Experimental microhabitat selection Figure A1: Microhabitat plate used for selection experiment Figure A2: Proportion of snails in each treatment that selected each habitat Appendix 2: VPD calculation comparison Figure A3: Comparison of VPD calculated using back-calculated air temperature to VPD calculated using measured air temperature vii Chapter One: General Introduction Rocky Intertidal Habitat Rocky intertidal habitats are unique in that they display extreme environmental gradients along a very small spatial scale; this variation means that it is critical that organisms can respond to major abiotic fluctuations that occur on an hourly scale (Stephenson & Stephenson 1949; Newell 1979). These habitats are found between the high and low tide marks, and are characterized by tidal movements (driven by lunar cycles), hard continuous substrate, and strict zonation of the organisms that reside in them (Stephenson & Stephenson 1949). This habitat is covered and uncovered by tidal movements of the ocean one to two times per day, and the organisms that live there are subjected to an impressive array of both biotic and abiotic stressors (Newell 1979). In order to live in these habitats, organisms must be capable of surviving marked fluctuations of a variety of different abiotic stressors such as temperature (Tomanek & Helmuth 2002), humidity