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Secondary metabolites are important defensive compounds found in plants which deter pests and pathogens and play an important role in defending against herbivory and seed predation. The role of secondary metabolites in fruits is complex as plants must defend the costly fruits while also successfully attracting dispersers. Protein investment into fruits is costly for plants but can serve as a reward to dispersers. In this experiment, we examined the protein content of plant tissues and compared it with the secondary metabolite content. We extracted and measured protein content of leaf and fruit pulp tissues from 15 species of Psychotria (a genus of fruiting plants in the coffee family) and one closely related species in the genus Palicourea. All species sampled in the study are fruiting and animal-dispersed. The objectives were to determine the relationship between secondary metabolite (defensive chemicals) and protein concentrations in the sampled tissues. With a linear regression, we found that all tissue types exhibited a negative relationship between protein content and secondary metabolite content. Using an ANOVA, we found that there was an overall significant relationship between secondary metabolites and protein content from the sampled tissues. When tissue types were separated out, expanding leaves and mature fruits were significant and immature pulp was not significant. These results support the removal rate and relative risk models of the defense trade-off hypothesis; nutritionally rewarding fruits are removed quickly from the plant and do not require extensive chemical defenses.

Publication Date



Logan, UT


metabolite content, protein investment, Psychotria, tropical shrubs


Life Sciences

Relationship Between Protein and Secondary Metabolite Content in Congeneric Tropical Shrubs

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Life Sciences Commons