Reproductive strategies of K/t-crossing Theria
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Mathematisch-Naturwissenschaftliche Fakultät I
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Abstract
Die Dissertation beschäftigt sich mit den möglichen Gründen für die divergente evolutionäre Entwicklung von Beuteltieren und plazentalen Säugetieren nach der Kreide/Tertiär-Grenze. Eine Erklärung könnten ihre unterschiedlichen Reproduktionsstrategien sein. Während die Beuteltiere sehr embryonale Jungtiere nach einer kurzen Tragzeit gebären, bringen Plazentalier deutlich weiter entwickelte Jungtiere nach einer relativ langen Tragzeit zur Welt. Die Aufrechterhaltung eines stabilen Metabolismus und thermoregulatorische Fähigkeiten der Jungtiere bieten einen großen Vorteil für die Anpassungsfähigkeit an ungünstige Umweltbedingungen, wie sie für die K/T-Grenze vermutet werden. Aus diesem Grund untersucht diese Studie den strukturelle Entwicklungsgrad der Lunge und die metabolischen Fähigkeiten von neonaten Marsupialia und Plazentalia. Histologische, ultrastrukturelle und kalorimetrische Untersuchungen erfolgten in einer integrativen Studie. Basierend auf den Ergebnissen wurde eine Grundplanrekonstruktionen der Neonaten von Marsupialia und Plazentalia durchgeführt. Als Vertreter für nesthockende Plazentalia wurde der Goldhamster (Mesocricetus auratus), die Moschusspitzmaus (Suncus murinus) und das Belangeri Spitzhörnchen (Tupaia belangeri) untersucht. Das Wildmeerschweinchen (Cavia aperea) und die Kurzohr-Elefantenspitzmaus (Macroscelides proboscideus) repräsentieren die nestflüchtenden Plazentalia. Als Marsupialia wurden die Hausspitzmaus-Beutelratte (Monodelphis domestica) und das Tammar-Wallaby (Macropus eugenii) untersucht. Die Ergebnisse bestätigen die starken Unterschiede im Entwicklungsgrad der Neonaten und in der postnatalen Entwicklung zwischen Marsupialia und Plazentalia. Die neonatalen Lungen von M. auratus und S. murinus befinden sich im späten “terminal air sac”-Stadium und weisen viele kleine Atemkammern von 50-80 µm Durchmesser auf. Die Alveolenbildung erfolgt bei M. auratus und S. murinus bereits im Alter von zwei beziehungsweise vier Tagen. Bei T. belangeri, C. aperea und M. proboscideus sind Alveolen bereits zum Zeitpunkt der Geburt vorhanden. Im Gegensatz dazu, befinden sich die Lungen der neonaten Beuteltiere M. domestica und M. eugenii im frühen “terminal air sac”-Stadium mit wenigen großen Atemkammern von 300-400 µm im Durchmesser. Die postnatale Lungenentwicklung erfolgt sehr langsam und die Alveolenbildung startet mit 28 Tagen bei M. domestica und mit 65 Tagen bei M. eugenii. Die Metabolismusmessungen ergaben, daß Marsupialia mit einer niedrigen Metabolismusrate geboren werden und den Adultmetabolismus erst spät in der postnatalen Entwicklung erreichen. Einhergehend mit der weit entwickelten Lungenstruktur weisen die Plazentalia hohe Metabolismusraten zur Geburt auf und erreichen den Adultmetabolismus innerhalb der ersten Lebenswoche. Die Ergebnisse zeigen, dass Jungtiere der Plazentalia, im Vergleich zu jungen Marsupialia, eine höhere Widerstandskraft gegen Umweltschwankungen haben, was als ein evolutiver Vorteil der Reproduktionsstrategie der Plazentalia unter ungünstigen Klimabedingungen interpretiert werden kann.
This project deals with the possible reasons for the evolutionary differentiation between marsupial and placental mammals after the K/T-event. One explanation could be their different reproductive patterns. Marsupialia bear virtually embryonic young after a brief gestation period. In contrast, many eutherians bear anatomically advanced, highly precocious young after a relatively long gestation period. A stable metabolism and thermoregulatory abilities of the young are considered to offer a large adaptive advantage in a changing environment, how it is presumed for the K/T-boundary. Therefore this study determines the developmental stage and the respiratory efficiency of the lungs of marsupial and placental young. Histological, ultrastructural and calorimetric investigations were carried out in an integrated study and from the results morphotype reconstructions of the marsupial and placental neonates were carried out. As representatives for altricial Placentalia, the Golden hamster (Mesocricetus auratus), the Musk shrew (Suncus murinus), and the Belanger’s tree shrew (Tupaia belangeri) were examined. Furthermore the Guinea pig (Cavia aperea) and Short-eared elephant shrew (Macroscelides proboscideus) as typical precocial Placentalia were included. The Marsupialia were represented by the Grey short-tailed opossum (Monodelphis domestica) and the Tammar wallaby (Macropus eugenii). The results confirm clear differences in the developmental degree of the neonates and the postnatal development between marsupial and placental mammals. The newborn lungs of the altricially born placentals M. auratus and S. murinus are at the late terminal air sac stage with numerous small air sacs of 50 - 80 µm in diameter. Alveoli are formed shortly after birth at the age of 2 days in M. auratus and at the age of 4 days in S. murinus. In T. belangeri and in the precocially born C. aperea alveoli are already present at birth. In contrast, the lungs of the newborn marsupials M. domestica and M. eugenii are at the early terminal air sac stage with few large air sacs of 300 – 400 µm in diameter. The postnatal lung development proceeds very slowly in marsupials and alveoli are not present before the age of 28 days in M. domestica and 65 days in M. eugenii. The metabolic investigations demonstrate that Marsupialia have a low metabolism at birth and achieve the adult metabolism late in the postnatal development. All examined Placentalia showed the same pattern of oxygen consumption. Corresponding to their advanced differentiation of the lungs they also exhibit high metabolic abilities at birth and reach the adult metabolism during the first week of life. During this critical period placental young have a higher resistance against certain environmental stresses than marsupial young and this could mean an evolutionary advantage of the placental “reproductive strategy” under suboptimal climatic conditions.
This project deals with the possible reasons for the evolutionary differentiation between marsupial and placental mammals after the K/T-event. One explanation could be their different reproductive patterns. Marsupialia bear virtually embryonic young after a brief gestation period. In contrast, many eutherians bear anatomically advanced, highly precocious young after a relatively long gestation period. A stable metabolism and thermoregulatory abilities of the young are considered to offer a large adaptive advantage in a changing environment, how it is presumed for the K/T-boundary. Therefore this study determines the developmental stage and the respiratory efficiency of the lungs of marsupial and placental young. Histological, ultrastructural and calorimetric investigations were carried out in an integrated study and from the results morphotype reconstructions of the marsupial and placental neonates were carried out. As representatives for altricial Placentalia, the Golden hamster (Mesocricetus auratus), the Musk shrew (Suncus murinus), and the Belanger’s tree shrew (Tupaia belangeri) were examined. Furthermore the Guinea pig (Cavia aperea) and Short-eared elephant shrew (Macroscelides proboscideus) as typical precocial Placentalia were included. The Marsupialia were represented by the Grey short-tailed opossum (Monodelphis domestica) and the Tammar wallaby (Macropus eugenii). The results confirm clear differences in the developmental degree of the neonates and the postnatal development between marsupial and placental mammals. The newborn lungs of the altricially born placentals M. auratus and S. murinus are at the late terminal air sac stage with numerous small air sacs of 50 - 80 µm in diameter. Alveoli are formed shortly after birth at the age of 2 days in M. auratus and at the age of 4 days in S. murinus. In T. belangeri and in the precocially born C. aperea alveoli are already present at birth. In contrast, the lungs of the newborn marsupials M. domestica and M. eugenii are at the early terminal air sac stage with few large air sacs of 300 – 400 µm in diameter. The postnatal lung development proceeds very slowly in marsupials and alveoli are not present before the age of 28 days in M. domestica and 65 days in M. eugenii. The metabolic investigations demonstrate that Marsupialia have a low metabolism at birth and achieve the adult metabolism late in the postnatal development. All examined Placentalia showed the same pattern of oxygen consumption. Corresponding to their advanced differentiation of the lungs they also exhibit high metabolic abilities at birth and reach the adult metabolism during the first week of life. During this critical period placental young have a higher resistance against certain environmental stresses than marsupial young and this could mean an evolutionary advantage of the placental “reproductive strategy” under suboptimal climatic conditions.
Description
Keywords
Metabolismus, Evolution, Reproduktionsstrategien, Marsupialia, Plazentalia, Lungenentwicklung, postnatale Entwicklung, evolution, reproductive strategies, Marsupialia, Placentalia, lung development, metabolism, postnatal development
Dewey Decimal Classification
570 Biologie
Citation
Szdzuy, Kirsten.(2006). Reproductive strategies of K/t-crossing Theria. 10.18452/15483