Dissertation The Emergence of the Isthmus of Panama – a biological perspective – Carina Marek August, 2015 Dean Prof. Dr. Volker Wissemann Supervisor Prof. Dr. Thomas Wilke Co-supervisor PD Dr. Christoph Schubart Carina Marek: The Emergence of the Isthmus of Panama – a biological perspective – Dissertation zur Erlangung des Doktorgrades der Naturwissenschaftlichen Fachbereiche der Justus-Liebig- Universität Gießen, 2015. Cover: Panama and the transisthmian sister species pair Sesarma curacaoense De Man, 1892 (western Atlantic) and Sesarma rhizophorae Rathbun, 1906 (eastern Pacific). If there is one thing the history of evolution has taught us it's that life will not be contained. Life breaks free, it expands to new territories, and crashes through barriers, painfully, maybe even dangerously, but, uh...well, there it is. Ian Malcolm (Jurassic Park) Table of Contents Part I – Synopsis 1 Summary ................................................................................................................................... 3 2 Zusammenfassung .................................................................................................................... 5 3 Motivation and Research Objectives ........................................................................................ 7 Part II – State of the Art 4 Geological Evolution and Biological Evidences – The Formation of the Isthmus ...................... of Panama and its Closure ...................................................................................................... 11 4.1 What is the Isthmus of Panama?.................................................................................... 11 4.2 Chronology of events – The Miocene model ................................................................. 12 4.3 Chronology of events – The Pliocene model .................................................................. 13 4.4 Discrepancies between the models ............................................................................... 16 4.4.1 Time of collision and Isthmus closure ................................................................... 16 4.4.2 Migration- and divergence times of species ......................................................... 17 4.5 Summary......................................................................................................................... 18 5 Ecological Consequences of the Isthmus Formation .............................................................. 23 5.1 Abiotic changes during the isthmian uplift and patterns today..................................... 23 5.2 Climate and temperature ............................................................................................... 24 5.3 Salinity ............................................................................................................................ 26 5.4 Hydrodynamic forcing .................................................................................................... 28 5.5 Nutrients and productivity ............................................................................................. 29 5.6 Summary......................................................................................................................... 30 5.7 Biotic differences of the two oceans .............................................................................. 31 5.8 Summary......................................................................................................................... 36 6 Transisthmian Sister Species .................................................................................................. 40 6.1 What are transisthmian sister species? ......................................................................... 40 6.2 The evolution of transisthmian sister species ................................................................ 41 6.3 The criteria to be a transisthmian sister species pair..................................................... 42 6.3.1 Geographic isolation drives speciation processes ................................................. 43 6.3.2 The barrier and the consequentially isolated taxa are of the same age ............... 44 6.3.3 TSS distribution ranges are close to the Isthmus .................................................. 45 6.3.4 Morphological similarity between TSS .................................................................. 48 6.3.5 Similar divergence ages between TSS pairs and -complexes ................................ 49 i Contents 6.4 Summary......................................................................................................................... 50 7 The Molecular Clock ............................................................................................................... 51 7.1 The molecular clock — The discovery of the constant ticking ....................................... 51 7.2 The molecular clock — A controversial debate.............................................................. 52 7.3 Calibrating the clock — A difficult endeavor .................................................................. 52 7.4 Biological factors ............................................................................................................ 53 7.5 Set the clock — Calibration points/bounds and external molecular clock rates ........... 54 7.6 Summary......................................................................................................................... 56 Part III — Case Studies – A Critical View at the Transisthmian Sister Species Concepts – 8 Toward an Unified Definition of Transisthmian Sister Species .............................................. 61 8.1 Terminological survey .................................................................................................... 61 8.2 Discussion ....................................................................................................................... 65 8.2.1 Terminology of transisthmian sister species ......................................................... 65 8.2.2 Two special cases focusing on confusing terms .................................................... 66 8.3 Summary......................................................................................................................... 67 9 Criteria of Transisthmian Sister Species Pairs and -Complexes .............................................. 70 9.1 The TSS pair and -complex evaluation ........................................................................... 70 9.1.1 Geographic isolation drives speciation processes ................................................. 70 9.1.2 The barrier and the consequentially isolated taxa are of the same age ............... 70 9.1.3 TSS distribution ranges are close to the Isthmus .................................................. 72 9.1.4 Morphological similarity between TSS .................................................................. 73 9.1.5 Similar divergence ages between TSS pairs and -complexes ................................ 73 9.2 Discussion ....................................................................................................................... 73 9.2.1 Geographic isolation drives speciation processes ................................................. 74 9.2.2 The barrier and the consequentially isolated taxa are of the same age ............... 74 9.2.3 TSS distribution ranges are close to the Isthmus .................................................. 75 9.2.4 Morphological similarity between TSS .................................................................. 75 9.2.5 Similar divergence ages between TSS pairs and -complexes ................................ 76 9.3 Summary......................................................................................................................... 77 9.4 Criteria revised ............................................................................................................... 78 – Divergence Time Estimations of Transisthmian Sister Species – 10 Divergence Time Estimations of Transisthmian Sister Species .............................................. 81 10.1 Studied species ............................................................................................................... 81 ii Contents 10.1.1 Sesarma Say, 1817 ................................................................................................. 81 10.1.2 Panopeus H. Milne Edwards, 1834 / Eurytium Stimpson, 1859 ............................ 83 10.1.3 Pachygrapsus Randall, 1840 .................................................................................. 85 10.2 Phylogenetic analyses and divergence time estimations............................................... 87 10.3 Results ............................................................................................................................ 89 10.3.1 Phylogenetic studies of the genus Sesarma .......................................................... 89 10.3.2 Phylogenetic studies of the family Panopeidae .................................................... 91 10.3.3 Phylogenetic studies of the genus Pachygrapsus .................................................. 97 10.4 Discussion ..................................................................................................................... 100 10.4.1 Problems of divergence time estimations of TSS ................................................ 100 10.4.2 Evidences for the time of Isthmus closure