Intra-inflorescence variation in reproductive traits of Conopholis alpina (Orobanchaceae): effect of flower maturation pattern and resource competition

Abstract

The ecological and evolutionary implications of intra-individual variation in plant traits have been acknowledged. Several studies have described the existence of intra-inflorescence variation in reproductive traits. Moreover, some of those studies have attempted to provide a plausible explanation to the gradient of intra-inflorescence variation observed. However, most of them fail to separate the effects of inflorescence architecture from those of resource allocation. The goal of this study was to determine the existence of intra-inflorescence variation in reproductive traits (attractive, reproductive organs, and reproductive success) of Conopholis alpina (Orobanchaceae), a holoparasite plant common in oak forests. Corolla length, number, viability, and diameter of pollen grains per flower, number of ovules per flower, pollen:ovule ratio, fruit size (length, width, and area), number of seeds per fruit, and seed set were measured in reproductive structures produced in three different regions within the inflorescence (i.e., bottom, middle, top). We found a significant effect of the region in which reproductive structures were produced on all traits, except pollen:ovule ratio. In all those traits in which significant differences among regions were found, reproductive traits had the highest values in the middle region of the inflorescence, which is also the first to reach maturity. Moreover, a trade-off between number of seeds and seed weight was detected on the bottom region of the inflorescence. Our results provide strong support towards the existence of differential resource availability among regions within the inflorescence as an explanation to the pattern of intra-inflorescence variation detected.