Crawling to connectivity? The direct-developing journey of the spotted whelk (Cominella maculosa) Melanie Dohner A thesis submitted to Victoria University of Wellington in partial fulfilment of the requirements for the degree of Master of Science in Marine Biology Victoria University of Wellington 2016 Acknowledgements I am immensely grateful to my family and my parents for always encouraging me to go after what makes me happy. I couldn’t have taken the first steps of returning to school without my mom’s financial support. Thank you to my amazingly patient husband, David Milner, for talking out thesis concepts with me and accompanying me on whelk collecting excursions. I’d like to thank my supervisors for giving me the opportunity to work on such a fun project and for being such great people with which to work. Thank you to Nicole Phillips and Peter Ritchie for sharing your knowledge, being so easy to chat with, and buying me coffees during our meetings. I am so grateful to both of you that I was able to work on a project involving genetics. I am so appreciative of having found such good friends as Ali Duncan and Jana Wold during my time at VUW. You two awesome scientists have helped me collect whelks, conduct better experiments, interpret my data, and proof read my chapter drafts. All while keeping me sane and laughing with afternoon coffees and nights out. My field adventures in the remote Wairarapa are the best memories from my thesis. I would like to thank Glenburn, Glendu, and Pahaoa Stations for the use of their roads to access several field sites. I greatly appreciate everyone who sacrificed their time to collect whelks: Ali Duncan, Jana Wold, Gustav Kessel, Kerry Walton, Juliette Champagnat, Angela Fleming, and John van der Sman. I am so extremely grateful for everyone at VUCEL and in the genetics lab that made my time indoors entertaining. Huge thanks to Angela Fleming for teaching me DNA extraction and sequencing techniques and to Balam Jimenez Brito for ordering supplies and answering my myriad of questions in the genetics lab. A very large thank you goes to the VUCEL technicians for helping me build experiments and find equipment. Particular thanks to the senior students in the Phillips lab for helping me find supplies or statistics guides; Agnes Rouchon and Paul Wolf. I’d like to acknowledge Lisa Woods, the university stats consultant, for her huge help in analyzing my ecology data and coding R. Finally, I would like to thank Victoria University of Wellington for their support through the Master's by Thesis scholarship. ii Abstract The exchange of individuals between populations influences demographic connectivity on the ecological scale and genetic connectivity on the evolutionary scale. In some circumstances there are similarities between demographic and genetic connectivity, but in others there are differences. Whenever genetic differentiation is found between populations demographic uncoupling can also be inferred, but when gene flow is found there is uncertainty about whether populations are demographically connected or not. Marine invertebrates typically have large population sizes and many opportunities for dispersal. However, species that have limited planktonic dispersal power are often characterized by genetically and demographically discrete populations that exhibit an isolation- by-distance (IBD) pattern of gene distribution. Alternative methods of dispersal, such as rafting or drifting, produce departures from this expected pattern for species lacking planktonic larvae. Examining genetic patterns at fine geographic scales can identify key dispersal barriers and may give clues to alternative dispersal methods influencing large scale processes. The endemic, direct-developing spotted whelk, Cominella maculosa, is found in the intertidal rocky shores throughout most of New Zealand. This distribution makes it ideal for studying a species expected to exhibit low realized dispersal by crawling and is unlikely to experience dispersal by rafting. The first aim of this study was to investigate genetic patterns between two genetically distinct populations along the Wairarapa Coast of the North Island to determine if a barrier to dispersal was present or if the expected IBD pattern was observed. The second aim was to determine the likelihood of individual hatchlings undertaking long distance dispersal by drifting in the water column. The mitochondrial DNA COI gene was sequenced using 324 whelk samples collected at seven sites along 125 km of Wairarapa shoreline. No significant level of genetic isolation-by-distance or discontinuity in haplotype distribution was observed. Instead, two sites in the middle of the region form a contact area where the dominant northern and southern haplotypes coexist. To investigate dispersal by drifting in the water, three experimental trials were conducted with hatchlings obtained from field-collected egg capsules. When subjected to wave forces, or deposited directly in flow, hatchlings remained suspended and were carried a short distance. However, hatchlings circulated in currents and left for a longer period (12 hours) were rarely found drifting after this period. These trials indicate that wave dislodgement and local flow regime may result in small-scale displacement of hatchlings, but long- distance dispersal by drift is unlikely. Plankton sampling was also conducted at two sites with four nearshore traps. The rare capture of a related Cominella virgata hatchling supports the finding that hatchlings can be dislodged, but prolonged drift cannot be inferred. The findings from this study support the assumption that crawling is the dominant dispersal mechanism for C. maculosa. Crawling iii between sites best explains the blending of haplotypes in the middle of the Wairarapa and the genetic differentiation between populations. Crawling-mediated connectivity is unlikely to occur at the ecological scale; therefore populations are expected to be demographically isolated. The results of this research support the general findings in the literature that populations of direct developing species are often demographically isolated and have low levels of genetic connectivity. iv Table of Contents Acknowledgements .............................................................................................................. ii Abstract .............................................................................................................................. iii Table of Contents.................................................................................................................. v List of Figures .............................................................................................................................. vi List of Tables ...............................................................................................................................vii Chapter 1 Population Connectivity in the Marine Environment ............................................. 1 1.1 Introduction ...................................................................................................................... 1 1.2 Measuring Connectivity ..................................................................................................... 3 1.3 Patterns of Genetic Connectivity ........................................................................................ 5 1.4 Aim ................................................................................................................................... 8 Chapter 2 Genetic Connectivity in a Direct Developing species, Cominella maculosa ........... 10 2.1 Abstract ................................................................................................................................ 10 2.2 Introduction.......................................................................................................................... 11 2.3 Spotted Whelk Connectivity on the North Island .................................................................... 13 2.3.1 A Summary of the Current Situation ........................................................................................................ 13 2.3.2 Methods.................................................................................................................................................... 17 2.3.3 The Updated Situation: Results and Brief Discussion ............................................................................... 20 2.4 Fine Scale Connectivity along the Wairarapa Coast ................................................................ 27 2.4.1 Methods.................................................................................................................................................... 28 2.4.2 Results ...................................................................................................................................................... 29 2.4.3 Discussion ................................................................................................................................................. 36 Chapter 3 Dispersal Potential for Cominella maculosa Hatchlings by Drifting ...................... 41 3.1 Abstract ................................................................................................................................ 41 3.2 Introduction.......................................................................................................................... 42 3.3 Materials and Methods ........................................................................................................