The use of ultrasound scanning to study the relationship of vitellogenesis, mating, egg production and follicular atresia in captive ploughshare tortoises Geochelone yniphora

Reproductive organs of seven female ploughshare tortoises, Geochelone yniph ora, at the Durrell Wildlife Conservation Trust's tortoise breeding centre at Ampijoroa, Madagascar, were examined by ultrasound scanning. Structures which could be identified included vitellogenic ovarian follicles of variou s sizes (September and March/April), preovulatory follicles (March/April), atretic follicles (September and March/April), oviducal eggs (March/April) and in one case previtellogenic follicles in juvenile ovaries. Vitellogenes is was well under way during September, more than two months before the sta rt of the mating season. Mating and nesting data of the last eight breeding seasons suggest that ovulation and egg production only occurred when copul ations took place during the mating season and that the vitellogenic follic les of un-mated females became atretic and were re-absorbed.