BODY CONDITION THRESHOLD FOR BREEDING IN A VIVIPAROUS SNAKE

One major goal of physiological ecology is to seek links between life history traits. Identification of a body condition threshold for breed ing (e.g. critical level of body reserves) provides a link between the physiological process involved in storage of body reserves and the ab ility to reproduce. One hundred and twenty-nine free-ranging adult fem ale Vipera aspis, a viviparous snake, were marked with electronic iden tification tags and/or by scale clipping, weighed, and measured at the onset of vitellogenesis, and immediately released in the field in wes tern central France (47 degrees 03'N; 02 degrees 00'W). The 129 snakes were recaptured 2-6 months later between ovulation and parturition, a nd individual reproductive status was then determined. Eighty-four fem ales (65%) captured at the onset of vitellogenesis became vitellogenic , 45 did not. There was no difference in mean body length between repr oductive and non-reproductive females. Initial body condition influenc ed reproductive outcome: we found a precise threshold in body conditio n necessary for the induction of vitellogenesis. Almost all females (8 8%) with a body condition greater than the observed threshold became v itellogenic, 12% did not, and no female with a body condition under th e threshold became vitellogenic. Body reserves were estimated in the 1 29 living females using data gathered on 69 autopsied females. Females which became vitellogenic had large body reserves, but females which did not were not particularly emaciated (whilst postparturiant females had few body reserves remaining). This precise condition threshold fo r breeding is discussed in terms of the reproductive ecology of this s pecies.