Tina Kesselring
Analysis of the reproductive biology of harbour porpoises (Phocoena phocoena) from the North and Baltic Sea on a long-term basis
Der Schweinswal ist die einzige in der deutschen Nord- und Ostsee beheimatete Walart und trägt als eine von wenigen Topprädatoren in diesen Gewässern eine hohe Bedeutung für das Gleichgewicht des Ökosystems dieser Meere. Da Schweinswale zahlreichen anthropogenen Einflüssen ausgesetzt sind, ist die mögliche Zeitspanne der Reproduktionsfähigkeit eine sensible Phase für ein Individuum und somit auch für die Populationsstabilität.
In dieser Arbeit wurden die Gonaden von weiblichen und männlichen Schweinswalen der Nord- und Ostsee auf makroskopischer und mikroskopischer Ebene untersucht, um reproduktionsbezogene Parameter wie postnatale Entwicklung, saisonale Veränderungen und Alter der Geschlechtsreife dokumentieren und analysieren zu können.
Von den weiblichen Schweinswalen konnte anhand von 111 Ovarien aus den Jahren 1990 bis 2016 das Alter der Geschlechtsreife durch die morphologische Untersuchung von Funktionskörpern wie Follikeln und Gelbkörpern bestimmt werden.
Die Exemplare und Proben wurden aufgrund von Parametern ausgewählt, welche sich negativ auf die Qualität der Präparate auswirken könnte, wie zum Beispiel Verwesungsgrad der Gewebe oder Einfrieren der Proben vor Untersuchung.
Auf dieser Analyse der Ovarien basierend wurde erstmalig eine Modellierung für das Alter der Geschlechtsreife von Schweinswalen aus deutschen Gewässern durchgeführt. Diese Analyse wurde mit der Berechnung der demographischen Altersstruktur ergänzt, um dann den Anteil geschlechtsreifer Weibchen an der Gesamtpopulation in der Nord- und Ostsee schätzen zu können.
Für die Analyse der männlichen Gonaden wurden die Hoden von 127 Schweinwalen der deutschen Nord- und Ostsee aus dem Zeitraum 1998 bis 2016 makroskopisch
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und histologisch untersucht und ausgewertet. Um Veränderungen der Hodenmorphologie und –morphometrie im Jahresverlauf messen zu können, wurden für jeden Monat des Jahres Merkmale im histologischen Bild, wie zum Beispiel Keimzellassoziationen dokumentiert und die Durchmesser der Tubuli seminiferi contorti gemessen.
Die Ergebnisse der Analysen der weiblichen Gonaden zeigen, dass Weibchen in einem durchschnittlichen Alter von 4.95 (± 0.6) Zeichen vorheriger Ovulation wie Gelbkörper oder ältere Narben (Corpora albicantia oder Corpora atretica) auf dem Ovar zeigen. Es konnten keine Unterschiede zwischen Tieren der Nord- und Ostsee festgestellt werden. Das durchschnittliche Alter, in dem die Tiere gefunden wurden, unterschied sich jedoch signifikant: Die Schweinswale der Nordsee waren zum Zeitpunkt ihres Todes durchschnittlich 5.70 (± 0.27) Jahre alt, während Tiere aus der Ostsee im durchschnittlichen Alter von 3.67 (± 0.30) Jahren gestorben sind.
Die Analyse der männlichen Gonaden ergab, dass erste Anzeichen der Pubertät bereits ab einem Alter von drei Jahren erkennbar sind und Tiere ab einem Alter von vier Jahren Spermatogenesestadien, einen saisonalen Verlauf des Keimepithels und somit volle Geschlechtsreife zeigen. Die Hauptpaarungszeit findet in den Monaten Juni und Juli statt. Während dieser Zeit sind im histologischen Schnitt des Hodengewebes acht verschiedene Keimzellassoziationen gleichzeitig in einem Tubulus seminiferus contortus auffindbar. Dieses Phänomen, welches bisher nur beim Menschen und einigen Affenarten gefunden worden ist, wird „multi-stage-arrangement“ genannt. Es konnten acht verschiedene Stadien der Spermatogenese identifiziert werden. In den restlichen Monaten des Jahres konnten vereinzelte Keimzellpopulationen oder die völlige Abwesenheit von Spermatogenese in adulten Tieren dokumentiert und somit der Schluss gezogen werden, dass die Reproduktionsruhe von August bis Mai stattfindet. In den Monaten August und September konnten vermehrt fehlende Keimzellgenerationen in den Tubulusquerschnitten gefunden werden.
Die vorliegenden Studien liefern eine detaillierte Beschreibung und Analyse der funktionellen Anatomie und Histologie der weiblichen und männlichen Gonaden des heimischen Schweinswales und können als Grundlage für weitergehende Untersuchungen zu Effekten von äußeren Einflüssen auf das Reproduktionspotential
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der Schweinswalpopulationen herangezogen werden.
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Chapter 7: Acknowledgements
First of all, I thank Prof. Prof. Dr. Ursula Siebert and Prof. Dr. Ralph Brehm for giving me the opportunity to work on this unique topic that challenged me as a biologist and veterinarian. Thank you for your supervision, support, patience, time and for sharing your extensive knowledge with me.
I thank the Ministry of Energy, Agriculture, the Environment and Rural Areas Schleswig Holstein (MELUR) and the state centre for coastal protection, national park and ocean protection Schleswig - Holstein (LKN), who partly funded this work.
Furthermore, I thank the lab technicians of the Institute for Terrestrial and Aquatic Wildlife Research (ITAW) Kornelia Wolff-Schmidt and Miriam Hillmann for the help during necropsies, sampling and handling of the data, as well as the lab technicians of the Institute for Anatomy, Marion Langeheine and Doris Voigtländer, for friendly teaching me histological techniques and advising me in photo – sessions. This work would not have been possible without you!
I would like to thank Prof. Dr. Martin Bergmann and his lab team for their work and the interesting meetings in Giessen. These sessions gave me a lot of motivation.
Many thanks go to my co-authors of the scientific manuscripts for great inputs and critical annotations at any point of the work.
I am very thankful for sharing an intense and memorable time – Kathi, Abbo, Marco, Susanne, Bianca, Johannes, Miguel, Eva, Helena, Steph, Anja, Jan, Vailett, Krissi, Julia – thanks for being great colleagues and friends. Sacha, thank you for your work and friendship during all these years.
My particular thanks go to my colleague and friend Lucie Grimm for always inspiring and encouraging me.
Finally I thank my mother Dr. Petra Kesselring and my grandma Inge Kesselring for the love and support during my whole education and their never-ending encouragement and help in any part of life.