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Connectivity and Exploitation of Acanthurus Triostegus

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Connectivity and Exploitation of Acanthurus Triostegus Connectivity and exploitation of Acanthurus triostegus and Acanthurus leucosternon in the Indian Ocean: Application of genetics and single stock assessment to aid coral reef management A dissertation submitted by Levy Michael Otwoma to the Faculty 2 (Biology and Chemistry) University of Bremen, in partial fulfillment of the requirements for the degree of Doctor of Natural Sciences (Dr. rer. nat), September 2018, Bremen i This thesis was conducted between April 2015 and September 2018 at the Leibniz Centre for Tropical Marine Research (ZMT) in Bremen, Germany Examination committee 1. Reviewer: Prof. Dr. Martin Zimmer University of Bremen, Germany Leibniz Centre for Tropical Marine Research (ZMT), Bremen 2. Reviewer: PD. Dr. Hauke Reuter University of Bremen, Germany Leibniz Centre for Tropical Marine Research (ZMT), Bremen Additional examiners 1. Examiner: Prof. Dr. Wilhelm Hagen University of Bremen, Germany 2. Examiner: Dr. Achim Meyer Leibniz Centre for Tropical Marine Research (ZMT) Attending students 1. Rebecca Borges Ph.D. student at the Leibniz Centre for Tropical Marine Research University of Bremen, Germany 2. Anna Feuring Masters Student (Marine Biology), University of Bremen ii Abstract Extrinsic/abiotic and intrinsic/biotic factors can influence the connectivity and exploitation of reef fish. Coral reef fish from the genus Acanthurus have evolved different life history characteristics that can affect their connectivity and exploitation. The aim of this thesis is to explore the population genetic structure and growth parameters of Acanthurus triostegus and Acanthurus leucosternon in the Indian Ocean, to determine the influence of biotic and abiotic factors on the connectivity and exploitation of coral reef species. First, a 491bp fragment of cytochrome b and microsatellite loci was used to show that the long pelagic larval duration of acanthurids can confer widespread genetic connectivity to A. leucosternon in the Eastern Africa region. Although the global AMOVA (Analysis of Molecular Variance) involving all A. leucosternon Eastern African population is significant, the hierarchical AMOVA and STRUCTURE does not show any genetic breaks consistent with known Eastern African oceanographic and biogeographical barriers to dispersal. Second, a mitochondrial DNA fragment spanning the ATPase8 and ATPase6 gene regions is used to demonstrate that the genetic differentiation of A. triostegus is correlated with geographic distance throughout the Indo-Pacific. In addition, this study shows that populations of A. triostegus are significantly differentiated in the Indian Ocean (Western Indian Ocean and East Indian Ocean), but not in the Pacific Ocean (West, Central, and East Pacific). Third, using syntopic sampling of the spawning aggregating A. triostegus and monogamous pairing A. leucosternon this study determined the influence of mating behaviour on the connectivity of these two Acanthurus species. Contrary to expectations, DAPC (discriminant analysis of principal components), hierarchical AMOVA, and pairwise comparisons showed that the divergent mating behaviour does not lead to differences in the connectivity patterns of A. leucosternon and A. triostegus, but the two species experienced differences in their demographic history. A detailed analysis in BEAST (Bayesian Evolutionary analysis Sampling Trees) showed iii that A. leucosternon which is often restricted to coral reef habitats had a faster and more recent demographic expansion than the habitat generalist A. triostegus. Finally, the growth parameters and mortality of A. triostegus and A. leucosternon were estimated, to determine whether differences in mating behaviour can lead to differences in exploitation rate. Consistent with expectations, the length-based stock assessment showed that the A. triostegus, the species that often forms spawning aggregation has a higher exploitation rate than the monogamous pairing A. leucosternon, supporting previous studies indicating that spawning aggregation may increase the susceptibility of coral reef fish to fishing. iv Zusammenfassung Extrinsische/abiotische und intrinsische biotische Faktoren können die Konnektivität und Nutzung von Rifffischen beeinflussen. Die Konnektivität und Nutzung von Doktorfischen der Gattung Acanthurus wird durch verschiedene biologische Merkmale und ihren Lebenszyclus bestimmt. Ziel dieser Arbeit ist es die Populationsstruktur und Wachstumsparameter von Acanthurus triostegus und Acanthurus leucosternon im Indischen Ozean zu ermitteln, um den jeweiligen Einfluß der biotischen und abiotischen Faktoren auf Korallenriff Organismen festzustellen. Zunächst wurde mit einem 491bp großen Fragment der Cytochrome b Oxidase und genomischen Mikrosatelliten gezeigt, dass die lange pelagische Larvalphase A. leucosternon eine weitreichende genetische Konnektivität in der Ostafrikanischen Region verleiht. Obwohl die globale Analyse der molekularen Varianz (AMOVA) in der Ostafrikanischen Population von A. leucosternon signifikant ist, konnte mit der hierarchischen AMOVA und dem Programm STRUCTURE keine genetische Trennlinie gefunden werden, die mit bekannten ozeanographischen oder biogeographischen Verbreitungsgrenzen im Einklang steht. Zweitens zeigt das mitochondrielle Fragment der Gene ATPase8 und ATPase6, dass die genetische Differenzierung bei A. triostegus mit der geographischen Distanz im Indopazifik korreliert. Zusätzlich wird gezeigt dass A. triostegus im Indischen Ozean (westlichen und östlichen Indischen Ozean) signifikant differenziert ist, im Gegensatz zu der Population im Pazifischen Ozean (West-, Zentral- und Ost-Pazifik). Drittends wurde durch ein syntopes Sampeln des in Gruppen laichenden A. triostegus und des paarlaichenden A. leucosternon der Einfluß des unterschiedlichen Paarungsverhaltens auf die Konnektivität dieser beiden Acanthurus Arten untersucht. Entgegen der Erwartungen konnte weder die DAPC (discriminant analysis of principal components), hierarchische AMOVA oder v paarweise Vergleiche Unterschiede der genetischen Konnektivität bei A. triostegus und A. leucosternon aufzeigen, aber die beiden Arten weisen Unterschiede in ihrer demographischen Entwicklung auf. Eine genaue Analyse in BEAST (Bayesian Evolutionary Analysis Sampling Trees) zeigte, dass A. leucosternon, dessen Vorkommen auf Korallenriffe beschränkt ist, eine jüngere und schnellere demographische Expansion aufweist als der Generalist A. triostegus. Zum Abschluss wurden Wachstumsparameter und Mortalität von A. triostegus und A. leucosternon bestimmt um festzustellen, ob die Unterschiede im Paarungsverhalten zu Unterschieden in Nutzungsraten führen. In Übereinstimmung mit den Erwartungen zeigte A. triostegus bei der längenbasierten Bestandsabschätzung eine stärkere Befischung als der paarbildende A. leucosternon. Dieses Ergebnis steht im Einklang mit früheren Studien die darauf hindeuten, dass in Gruppen laichende Korallenfische einer stärkeren Nutzung ausgesetzt sind. vi Contents Abstract ......................................................................................................................................................... iii Zusammenfassung .......................................................................................................................................... v Table of figures .............................................................................................................................................. x List of tables .................................................................................................................................................. xi 1. CHAPTER - General introduction ........................................................................................................ 1 1.1. Connectivity of reef species ............................................................................................................... 1 1.2. Estimators of connectivity in reef species .......................................................................................... 2 1.3. Population genetics of reef species ..................................................................................................... 4 1.4. Factors affecting the genetic connectivity of reef species .................................................................. 6 1.4.1. Extrinsic factors ........................................................................................................................... 7 1.4.2. Intrinsic factors ............................................................................................................................ 8 1.5. Study genus: Acanthurus .................................................................................................................... 9 1.6. Exploitation status of Acanthurus .................................................................................................... 11 1.7. Study region background: Indian Ocean .......................................................................................... 11 1.8. Aims and thesis structure ................................................................................................................. 13 2. CHAPTER - Connectivity of Acanthurus leucosternon...................................................................... 16 2.1. Introduction ...................................................................................................................................... 18 2.2. Materials and methods .....................................................................................................................
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