Storage and the delayed costs of reproduction in the understorey perennial Lathyrus vernus

1. A trade-off between current and future reproduction, often referred to as the cost of reproduction, is a fundamental assumption in life history theory. In long-lived plants, large absolute differences in size between individuals, storage of resources between reproductive events and organ preformation may make such costs difficult to demonstrate, especially when only natural variation is considered. 2. The long-lived legume Lathyrus vernus shows large size differences compared with variation in carbon resource allocation, and is known to store resources in below-ground rhizomes. We therefore followed individual plants over a period of 4 consecutive years. We examined the cost of reproductive investment by comparing the performance of untreated plants that differed in size and herbivore damage. We also compared controls with plants where we experimentally reduced flowering in terms of fitness measured as: survival, growth, flower number, fruit:flower ratio and storage. 3. Natural patterns of flowering and fruiting provided no evidence of a negative relationship between current and future reproduction. Individuals that produced fruits did not experience a lower probability of surviving and producing fruits the following season compared with flowering individuals that failed to produce any fruits, even when differences in above-ground size and herbivore damage were taken into account. 4. Flower removal in a single season increased the allocation to the rhizome but the size of shoot buds for the next season was not increased. Experimental manipulation of reproductive effort by repeated removal of flowers during 3 consecutive years, however, resulted in a significant increase in vegetative size and the probability of flowering and setting fruit compared with control plants. 5. While long-term data on natural variation in fruit production and short-term experimental data provided no evidence of a cost of reproduction, such a cost is still present, although detectable only after repeated flower removal.