Betalain Color Morphs Exhibit Differential Growth, Defensive Ability, and Pollen Tube Growth Rates inMirabilis jalapa(Nyctaginaceae)

Abstract

Premise of research. Nonphotosynthetic pigments play significant roles in plant life history, including in pigmentation, pollinator attraction, antioxidants, and defense against pathogens and herbivores. However, little is known about the specific roles of the betalains, which are present in several families of the Caryophyllales. In this study, we took a phenotypic and experimental approach to investigate whether betalain pigments might play diverse roles in plant life history as their phylogenetic counterparts, the anthocyanins, do.Methodology. We measured floral and leaf betalain concentrations and several phenological and performance traits in four floral color morphs of horticultural lines of Mirabilis jalapa (Nyctaginaceae). We also performed herbivore assays and measured pollen tube length in situ to investigate the role of betalain concentration in defense and prezygotic barriers among the floral color morphs.Pivotal results. Our results show that betacyanin and betaxanthin concentrations in leaves are negatively associated with leaf damage by a generalist herbivore and that pollen performance is associated with betacyanin and betaxanthin levels in the donor or recipient flowers. We also suggest that the floral color morphs significantly differ with respect to phenotypic architecture, with the pink morphs being slightly larger but germinating later than the other color morphs.Conclusions. Our experiments using these horticultural lines suggest that betalains and resulting floral color morphs of M. jalapa are associated with several plant life-history traits, such as growth rate, germination, defense against herbivory, and pollination success. It is likely that these roles are subject to selection, and further studies should be conducted along these lines.