consumers to each other resulted in the evolution of novel chemical defensive
mechanisms by plants and disarming mechanisms by herbivores. This process,
hence, would be responsible for the chemical diversity and toxicity of plants, and
feeding habits of herbivores. The coevolutionary model placed the plant-herbivore
interaction, or more precisely, its reciprocal evolutionary responses, as the ultimate
drivers of speciation and diversification [48, 89]. Although the phytochemical
coevolution has received some criticism [93, 161], a large body of experimental
evidence supports the view that secondary metabolites have diversified as a result of
natural selection [61, 65, 139, 186], suggesting that their occurrence reflects the
functional (adaptive) response to particular selective contexts mainly impose by
plant consumers.
2
History of Vascular Plants, Their Secondary Metabolism
and Interaction with Early Arthropods
Current ecological roles of secondary metabolites are diverse but mainly
associated to mediation of biotic interactions. Fossil-based evidence and biochemical and molecular analysis suggest that two major evolutionary events are implicated in the evolution of biosynthetic paths of secondary metabolites and their
early function: (1) the great oxygenation of the Earth and (2) plant vascularization
(Box 1). These events laid the foundations for the evolution of terrestrial ecosystems and preclude the emergence of arthropods (Fig. 1) and their interaction with
plants that came with it. The paleontological evidence from Paleozoic and Mesozoic eras has been crucial to trace the beginning of the association of plants and
arthropods and has contributed to the inference of the resulting evolutionary
patterns.
Box 1 Evolutionary Milestones of Photosynthetic Eukaryotes and Function of
Early Secondary Metabolites
Communities of cyanobacteria (i.e., photosynthetic prokaryotes able to produce oxygen) lived in freshwater and marine aggregates as early as one billion
years ago [207, 208]. Cyanobacterias are strongly implicated in the evolution
of photosynthetic eukaryotes (algae and plants) by endosymbiosis with plastids [201, 204] and are presumably responsible for converting the early
oxygen-poor, reducing atmosphere, into an oxidizing one, causing the “rusting
of the Earth” [206]. This photosynthetic activity would increase the metabolic
wastes or excretes. Early functions of secondary metabolites are thought to be
related to excretion mechanisms derived from the incomplete cycling of
primary compounds soluble in water [200, 201].
(continued)
3 Coevolution: Plant-Herbivore Interactions and Secondary Metabolites of Plants
49
mechanisms by plants and disarming mechanisms by herbivores. This process,
hence, would be responsible for the chemical diversity and toxicity of plants, and
feeding habits of herbivores. The coevolutionary model placed the plant-herbivore
interaction, or more precisely, its reciprocal evolutionary responses, as the ultimate
drivers of speciation and diversification [48, 89]. Although the phytochemical
coevolution has received some criticism [93, 161], a large body of experimental
evidence supports the view that secondary metabolites have diversified as a result of
natural selection [61, 65, 139, 186], suggesting that their occurrence reflects the
functional (adaptive) response to particular selective contexts mainly impose by
plant consumers.
2
History of Vascular Plants, Their Secondary Metabolism
and Interaction with Early Arthropods
Current ecological roles of secondary metabolites are diverse but mainly
associated to mediation of biotic interactions. Fossil-based evidence and biochemical and molecular analysis suggest that two major evolutionary events are implicated in the evolution of biosynthetic paths of secondary metabolites and their
early function: (1) the great oxygenation of the Earth and (2) plant vascularization
(Box 1). These events laid the foundations for the evolution of terrestrial ecosystems and preclude the emergence of arthropods (Fig. 1) and their interaction with
plants that came with it. The paleontological evidence from Paleozoic and Mesozoic eras has been crucial to trace the beginning of the association of plants and
arthropods and has contributed to the inference of the resulting evolutionary
patterns.
Box 1 Evolutionary Milestones of Photosynthetic Eukaryotes and Function of
Early Secondary Metabolites
Communities of cyanobacteria (i.e., photosynthetic prokaryotes able to produce oxygen) lived in freshwater and marine aggregates as early as one billion
years ago [207, 208]. Cyanobacterias are strongly implicated in the evolution
of photosynthetic eukaryotes (algae and plants) by endosymbiosis with plastids [201, 204] and are presumably responsible for converting the early
oxygen-poor, reducing atmosphere, into an oxidizing one, causing the “rusting
of the Earth” [206]. This photosynthetic activity would increase the metabolic
wastes or excretes. Early functions of secondary metabolites are thought to be
related to excretion mechanisms derived from the incomplete cycling of
primary compounds soluble in water [200, 201].
(continued)
3 Coevolution: Plant-Herbivore Interactions and Secondary Metabolites of Plants
49