Short-term versus long-term effects of food intake on reproductive output in a viviparous snake, Vipera aspis

Feeding rates influence reproductive output in many kinds of animals, but w e need to understand the timescale of this influence before we can compare reproductive energy allocation to energy intake. A central issue is the ext ent to which reproduction is fuelled by long-term energy stores ("capital" breeding) versus recently-acquired resources ("income" breeding). Our data on free-living aspic vipers show that there is no simple answer to this que stion: reproductive frequency is determined by long-term energy stores, off spring size is influenced by maternal food intake immediately before ovulat ion, and litter size is influenced by both long-term stores and short-term energy acquisition. Thus, offspring size in free-living vipers reflects the mother's energy balance over the preceding year (via a trade-off between l itter size and offspring size) as well as her energy balance in the current breeding season. Hence, different components of a given reproductive outpu t (litter) are not only functionally linked, but also respond to different temporal scares of prey availability. A female's body size has little effec t on her reproductive output. Attempts to quantify reproductive energy allo cation must take into account the fact that different reproductive traits ( such as offspring size versus number) may respond to energy availability ov er different timespans. Thus, although the aspic viper is a typical "capita l breeder" in terms of its reliance on stored reserves for maternal "decisi ons" concerning reproductive frequency, it is to some degree a facultative "income breeder" with respect to the determination of offspring size and li tter size.