Trade-off between sexual and vegetative reproduction of the weedy Heliotropium curassavicum

Abstract

Reproductive behaviour and trade-off between sexual and vegetative reproduction in Heliotropium curassavicum were investigated by monitoring the seedling regeneration and aerial shoot emergence. Life table and fecundity schedule were analysed based on sexual and vegetative reproduction in a naturally growing population in the deltaic Mediterranean coast of Egypt. The seedling and aerial shoot emergence were controlled by variation of site openness, soil moisture content and depth of buried seeds and adventitious root buds in soil. In open sites (< 10% plant cover), sexual reproduction provided the main input of colonizing individuals, while in closed sites (> 90% plant cover), recruitment from vegetative reproduction was frequent. The phalanx growth form dominated in closed sites, while guerrilla growth form was superior in the open sites. The overall seedling regeneration decreased with depth of the buried seeds, while the aerial shoots emergence showed an optimal response to variation of depth. The pattern of survival ( l x), mortality ( q x) and killing power ( k x) were similar in both sexual and vegetative reproduction. The sequence of age-specific stages in vegetative reproduction occurred over shorter time than in sexual reproduction. The expectation of future life ( e x) was stage specific and decreased with age. In both sexual and vegetative reproduction, the reproductive rate ( l x b x) increased and the reproductive value ( V x) decreased with age. The net reproductive rate ( R o) and intrinsic rate of increase ( r) were higher in sexual reproduction than in vegetative reproduction. In accordance with r- and k-selection, the species has a high degree of r-selection in vegetatively open sites, and acquires k -selection strategy in vegetatively closed sites.