Chemical ecology in coupled human and natural systems: people, manioc, multitrophic interactions and global change

Abstract

Chemical ecology provides unique perspectives for managing plant/human interactions to achieve food security. Allelochemicals function as chemical defences of crop plants, enhancing yields. While ingested allelochemicals can confer health benefits to humans, at higher concentrations they are often toxic. The delicate balance between their positive and negative effects in crop plants is influenced by many factors. Some of these-how environment affects optimal levels of defence, how metabolic interactions with nutrients affect toxicity of ingested allelochemicals-are the province of chemical ecology. These biological factors, however, interact with social factors, and neither can be studied independently. Chemical ecologists must work together with social scientists to understand the overall system. Here, we illustrate such an integrative approach, analysing the interactions between people and the major tropical crop manioc, which contains cyanogenic glucosides. Polymorphism for cyanogen levels in manioc facilitates analysis of how costs and benefits of crop defences vary among social systems. We first show how people/ manioc interactions diversified in this crop's Amazonian homeland, then turn to the remarkable cultural adaptations of African farmers since manioc's introduction 400 years ago. Finally, we evaluate new coevolutionary challenges in parts of Africa where people are still unfamiliar with a potentially dangerous crop. Current environmental and social catastrophes have restricted farmers' options, resulting in acute problems in health of humans and ecosystems. We show that high cyanogen levels confer important agronomic advantages, but also impose costs and constraints that can only be understood when biology is coupled with analysis of social, cultural and economic factors. Detoxifying manioc technologically requires know-how, time, water and other resources. Detoxifying residual dietary cyanogens metabolically depends on being able to grow, or to buy, the nutrients required for detoxification, primarily sulphur-rich proteins. Solutions that appear adaptive today may not be in the future, as changing climate, rising atmospheric CO 2 levels and decreased access to fertilizers affect productivity of crops and the nutrient and allelochemical composition of the foods they are used to produce.

A Comparative Study of the Socio-ecological Concomitants of Cassava (Manihot esculenta Crantz) Diversity, Local Knowledge and Management in Eastern Indonesia

“…Thus, bitterness appears to be selected for where competition is toughest. Such positive factors must be offset against health costs and constraints imposed by high levels of toxicity, and the need for effective detoxification processes or dietary buffers (McKey et al 2010). Moreover, where local populations are under nutritional and economic stress, there are advantages in being able to harvest early-yielding varieties and in diversifying these, which tend to be sweet rather than bitter.…”

Molecular characterization of 'sweet' cassavas (Manihot esculenta) from a germplasm bank in Brazilian Eastern Amazonia

“…This division is based on cyanogenic glycosides content on the roots. 'Sweet' cassava has low cyanogenic glycoside content (below 100 ppm fresh weight), while 'bitter' cassava has higher amounts (above 100 ppm fresh weight) (McKey et al 2010). Roots of bitter cassava must be properly cooked or efficiently processed to detoxify it before consumption.…”

Back to the Origin: In Situ Studies Are Needed to Understand Selection during Crop Diversification

“…Domesticated lupines, Lupinus spp., set seed earlier, produce larger seeds than wild lupines (Berger et al, 2017). In Cassava, Manihot esculenta, levels of toxic cyanogenic glucosides are dependent upon local preferences and knowledge on processing (McKey et al, 2010).…”