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Kuchling, G. , Differences in the reproductive biology of the malagasy tortoises astrochelys radiata and astrochelys yniphora: Implications for captive breeding - abstract. Unpublished paper presented at Program and Abstracts of the Tenth Annual Symposium on the Conservation and Biology of Tortoises and Freshwater Turtles. 
Added by: Admin (06 Jan 2014 18:22:54 UTC)
Resource type: Conference Paper
BibTeX citation key: anon2012.14531
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Categories: General
Keywords: Astrochelys radiata, Astrochelys yniphora, Fortpflanzung - reproduction, Habitat - habitat, Madagaskar - Madagascar, Schildkröten - turtles + tortoises, Testudinidae
Creators: Kuchling
Collection: Program and Abstracts of the Tenth Annual Symposium on the Conservation and Biology of Tortoises and Freshwater Turtles
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Testudinidae Geochelone Egg production and nesting appears to occur year-round in Astrochelys radiata populations in arid southern Madagascar where seasonal temperature fluctuations are pronounced, but rainfall is unpredictable and low (310-460 mm annually). In contrast, Astrochelys yniphora only nests during the wet season in its native range in tropical subhumid northwestern Madagascar (annual precipitation 1231 mm). Astrochelys radiata breeds readily in captivity in various climatic zones and in both hemispheres, for example in the Ivoloina Forestry station on Madagascar's humid tropical east coast (3055.7 mm annual precipitation) where no egg laying could be observed in A. yniphora. Until today A. yniphora only breeds successful in captivity in the breeding centre of Ampijoroa, in tropical subhumid north-western Madagascar close to its native range. Ultrasound monitoring of seven females at Ampijoroa revealed that ovulation is obligatorily induced by mating and copulation prior to the nesting season: following copulations, females produced several clutches of eggs over a 5-7 month nesting period without any additional inseminations. Vitellogenesis continued throughout the breeding season in both females paired with males during the mating season and in females which were not paired, but no ovulations occurred in the latter and the preovulatory follicles were slowly absorbed through atresia. In contrast, A. radiata appears to ovulate spontaneously and independently of mating once follicles reach pre-ovulatory size. Although the reproductive trait of A. radiata to spread out egg production throughout the year to exploit any beneficial climatic events like unpredictable rains makes this species relatively easy to breed in captivity throughout the world, due to an apparently unique reproductive physiology, A. yniphora appears to be more difficult to breed outside its native tropical subhumid climate. Without copulations Astrochelys yniphora females show for many years cycles of vitellogenesis without ovulation, but concurrent atresia. This normal physiological mechanism in unmated A. yniphora females can lead to a misdiagnosis of follicular stasis, followed by ovariectomy and the termination of any possibility for future breeding. This happened in 1995 to the, until now, only proven breeding A. yniphora female in the USA which was acquired in 1971 and is still alive at Honolulu Zoo.
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