The role of an environmental gradient in driving population divergence in common gobies (Pomatoschistus microps) DISSERTATION der Mathematisch-Naturwissenschaftlichen Fakultät der Eberhard Karls Universität Tübingen zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) vorgelegt von ISABEL MAGDALENA MÜCK aus Bad Reichenhall TÜBINGEN 2016 Tag der mündlichen Qualifikation: 25. 05. 2016 Dekan: Prof. Dr. Wolfgang Rosenstiel 1. Berichterstatter: Dr. Katja Heubel 2. Berichterstatter: Prof. Dr. Katharina Foerster “There is no substitute for careful and intensive field work if one wants to find out what is happening in natural populations.” Endler, 1986 Table of Contents Zusammenfassung ................................................................................................................................... 7 Summary ................................................................................................................................................. 8 Introduction ......................................................................................................................................... 9 Environmental-dependent sexual selection .................................................................................... 9 Neutral versus adaptive evolution ................................................................................................ 10 Environmental gradients ............................................................................................................... 11 The Baltic Sea ................................................................................................................................ 12 The common goby (Pomatoschistus microps) .............................................................................. 14 Study goals ............................................................................................................................................ 16 (I) Ecological variation along the salinity gradient in the Baltic Sea and its consequences for mating success in common gobies .................................................................................................................... 16 (II) Population divergence in common gobies: neutral or adaptive evolution?.................................... 17 (III) Gonadal investment in common gobies along the salinity gradient in the Baltic Sea .................... 18 CHAPTER I .............................................................................................................................................. 19 Ecological Variation along the Salinity Gradient in the Baltic Sea and its Consequences for Mating Success in Common Gobies ................................................................................................................... 20 Abstract ............................................................................................................................................. 20 Introduction ....................................................................................................................................... 21 Methods ............................................................................................................................................ 24 Study species ................................................................................................................................. 24 Field study design .......................................................................................................................... 25 Habitat survey ............................................................................................................................... 25 Nesting resources .......................................................................................................................... 26 Population density and sex ratios ................................................................................................. 28 Body size ........................................................................................................................................ 29 Mating assay .................................................................................................................................. 29 Data analyses ................................................................................................................................. 30 Results ............................................................................................................................................... 32 Nesting resources .......................................................................................................................... 32 Population density ......................................................................................................................... 35 Operational sex ratio ..................................................................................................................... 35 Body size ........................................................................................................................................ 36 Male body size and size of Mya arenaria ...................................................................................... 37 Mating assay .................................................................................................................................. 38 Brood characteristics ..................................................................................................................... 40 Discussion .......................................................................................................................................... 42 Conclusion ......................................................................................................................................... 48 Acknowledgements ........................................................................................................................... 49 CHAPTER II............................................................................................................................................. 50 Population Divergence in Common Gobies: Neutral or Adaptive Evolution? ....................................... 51 Abstract ............................................................................................................................................. 51 Introduction ....................................................................................................................................... 52 Methods ............................................................................................................................................ 56 Study species ................................................................................................................................. 56 Fish collection and sampling sites ................................................................................................. 56 Genetic analyses ............................................................................................................................ 59 PST - FST comparison ........................................................................................................................ 62 Results ............................................................................................................................................... 64 Genetic analyses ............................................................................................................................ 64 PST- FST comparison ........................................................................................................................ 72 Discussion .......................................................................................................................................... 73 Genetic structure of common gobies on coarse and fine spatial scales ....................................... 73 Neutral versus adaptive evolutionary processes driving population divergence ......................... 75 Roles of natural selection versus genetic drift on phenotypic population divergence in Baltic common gobies: a PST – FST comparison ........................................................................................ 77 Conclusion ......................................................................................................................................... 79 Acknowledgements ........................................................................................................................... 80 Supplemental data ............................................................................................................................ 81 ........................................................................................................................................................... 83 CHAPTER III ........................................................................................................................................... 83 Gonadal Investment in Common Gobies along the Salinity Gradient in the Baltic Sea ........................ 84 Abstract ............................................................................................................................................. 84 Introduction ....................................................................................................................................... 85 Methods