Schramm
Fakultäten » Mathematisch-naturwissenschaftliche Fakultät » Evolutionsbiologie und Umweltwissenschaften, Institut für » Evolutionary Biology » Prof. Dr. Vincent Ziswiler (ausgetreten) » Schramm
Completed research project
| Title / Titel | Steroid cycles in plasma and ultrasound scanning of reproductive structures in the Galapagos tortoise, Geochelone nigra | ||||||||
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| Abstract (PDF, 14 KB) | |||||||||
| Original title / Originaltitel | Steroid Zyklen im Plasma und Ultraschalluntersuchungen der Fortpflanzungsorgane der Galapagosschildkröte, Geochelone nigra | ||||||||
| Summary / Zusammenfassung | During a one year period (Nov. 1995 - Nov. 1996), blood samples were collected from male and female Galapagos tortoises (Geochelone nigra) living under seminatural conditions at the Charles Darwin Research Station (CDRS) on Santa Cruz Island, Galapagos. Plasma steroid hormones were measured by radioimmunoassays (RIAs). There were significant annual variations in plasma testosterone in both males and females. Plasma corticosterone was generally higher in males than in females, and varied throughout the year in both sexes. Plasma estradiol levels and progesterone concentrations showed significant elevations during vitellogenesis and around ovulation. Ultrasound investigations were performed at monthly intervals in 20 adult female Galapagos tortoises. During critical times, such as ovulation and nesting, the animals were investigated once a week. Vitellogenesis was monitored throughout the year with largest follicles ranging between 29 and 42 mm. Preovulatory sized follicles (40-42 mm) were seen in all animals from April to August coinciding with the end of the mating season (June) and the beginning of the nesting season (May). Atretic follicles were found in all months showing largest diameters between 8 and 62 mm and reaching largest sizes from February to June during the hot and rainy mating season. Females laid one to three clutches (5-14 eggs per clutch; mean = 7.5) during the dry season from May to October. Eggs remained in the oviduct between 8 and 74 days. The interclutch interval was between 30 and 89 days. | ||||||||
| Publications / Publikationen | Schramm, B.G.; Casares, M. & Lance, V.A. (1999): Steroid levels and reproductive cycle of the Galapagos tortoise, Geochelone nigra, living under seminatural conditions on Santa Cruz Island (Galapagos). Gen. Comp. Endocrinol. 114: 108-120.Schramm, B.G.; Casares, M. & Lance, V.A.: Ultrasound scanning of ovaries and eggs in Galapagos tortoises, Geochelone nigra, on Santa Cruz Island, Galapagos. Chelon. Conserv. Biol. (submitted)Schramm, B. & Lance, V.A.: Annual plasma calcium levels in the Galapagos tortoise (Geochelone nigra) on Santa Cruz Island (Galapagos), (in preparation)Weitere Informationen | ||||||||
| Keywords / Suchbegriffe | Reptilia, turtles, Testudines, Testudinidae, Geochelone nigra, Galapagos giant tortoise, reproduction, blood samples, plasma, steroids, estrogens, androgens, testosterone, estradiol, progesterone, corticosterone, ultrasonography, preovulatory follicles, atretic follicles, oviductal eggs, oviductal period, interclutch interval, retention, temperature, stress factors, seminatural conditions, Charles Darwin Research Station, CDRS, Santa Cruz Island, Galapagos | ||||||||
| Project leadership and contacts / Projektleitung und Kontakte |
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| Other links to external web pages | http://www.galapagos.org/ http://www.gct.org/ |
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| Funding source(s) / Unterstützt durch |
Universität Zürich (position pursuing an academic career), Others Charles Darwin Research Station (CDRS) - Galapagos Center f. Reproduction of Endangered Species (CRES) - San Diego USA University of California San Diego (UCSD) - USA |
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| In collaboration with / In Zusammenarbeit mit |
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| Duration of Project / Projektdauer | Mar 1995 to Aug 1999 |