Plants, microbes, some fungi, and an increasing number of
marine invertebrates have unique, but arbitrarily defined, dichotomous
metabolic pathways referred to as primary and secondary
metabolism. Myriad chemicals are lumped under the umbrella
"secondary metabolites" and yet some have major roles in the growth,
development, and/or reproduction of plants. We argue that the artificial
distinction made between primary and secondary metabolites obfuscates their
ecological and evolutionary roles. Based on data from a literature
survey, we show that terms such as venom, hormone, pheromone and toxin have
clear and consistent evolutionary and ecological connotations, and are rarely
obscured by the context of secondary metabolism. We show that attempts to create similar clarity in the
literature surrounding secondary metabolites, such as the adoption of the term
"plant-defense compound" have had limited success (ca. 1 article/month for the
past five years), whereas the production of articles containing the term
"secondary metabolite" is ca. 200/month for the past five years. Additionally,
we demonstrate that a large body of literature (ca.
20,000 articles) has been developed searching for the "cause" or cost of
single, or a few secondary metabolites rather than investigating the ecological
or evolutionary tradeoffs in producing the diverse array of chemicals with which
organisms can engage their continually changing environment. Fruit
chemistry, where the evolutionary and ecological fitness impacts are perhaps
clearer, offers an excellent case study on the importance of looking beyond the
false dichotomy of primary/secondary metabolism to understand the maintenance
of metabolic tradeoffs. Here we
use wild chilies (Capsicum chacoense)
and the production of capsaicinoids in the developing fruit as a case study.