Keywords
Adaptation · Diversity · Evolution · Generalists · Secondary metabolites ·
Specialists · Specialization
1
Introduction
Herbivorous insects and vascular plants represent two of the most numerous groups
of multicellular organisms, driving major ecological processes in many terrestrial
habitats [1–3]. They owe their diversity largely to a long-shared history and to the
specificity of their interactions [4–6]. Various insect herbivores often show specific
responses to host plant defences, which reciprocally support diversification of plant
defensive strategies and in turn the diversity of plants and insects themselves [4, 5,
7, 8]. In this chapter, I summarize how the specificity of insect responses arises and
discuss the consequences for insect-plant coevolution. I focus on the role of insect
specialization and mode of feeding (i.e., a feeding guild) as two major factors
governing their response to host plant defences.
The first insects began utilizing plants as a food source in the Early Devonian period,
only several million years after vascular plants colonized terrestrial habitats [9, 10]. This
led to a progressive radiation in the diversity of herbivorous insects and their feeding
guilds. The pioneer insect herbivores were sap-suckers, stem-borers, and consumers of
spores [11]. Thalli, which evolved into leaves some time later, only started to be
consumed by chewing herbivores shortly after that in the Middle Devonian [10]. All
modern herbivore guilds, with the possible exception of leaf-miners, were present by the
Late Carboniferous, more than 300 million years ago [10].
The proliferation of herbivore lineages and guilds has increased and diversified
herbivory pressure on plants and led to an arms-race between plants and insects [4, 5]
(Box 1). This generally required plants to employ a broad suite of defences in order
to maintain efficient protection against diverse communities of herbivores [12, 13].
Box 1
In their seminal paper, Ehrlich and Raven [4] proposed the so-called escapeand-radiate scenario of insect-plant coevolution. According to the escapeand-radiate scenario, the genesis of novel defensive traits allows plants to
escape herbivory, leading to speciation of the respective plant lineage. However, after some evolutionary time, herbivores adapt to the novel defence and
overcome it. This allows herbivores to colonize that plant lineage, opening a
novel niche to them. The adapted herbivores speciate, and the process starts
over. This should, on the one hand, lead to diversification or escalation of host
plant defences over evolutionary time and on the other hand to co-diversification of the plant and insect lineages involved.
Recent studies suggest that clear cases of co-diversification are relatively
scarce [128, 129], with sequential radiation and phylogenetic tracking being
(continued)
78
M. Volf
Adaptation · Diversity · Evolution · Generalists · Secondary metabolites ·
Specialists · Specialization
1
Introduction
Herbivorous insects and vascular plants represent two of the most numerous groups
of multicellular organisms, driving major ecological processes in many terrestrial
habitats [1–3]. They owe their diversity largely to a long-shared history and to the
specificity of their interactions [4–6]. Various insect herbivores often show specific
responses to host plant defences, which reciprocally support diversification of plant
defensive strategies and in turn the diversity of plants and insects themselves [4, 5,
7, 8]. In this chapter, I summarize how the specificity of insect responses arises and
discuss the consequences for insect-plant coevolution. I focus on the role of insect
specialization and mode of feeding (i.e., a feeding guild) as two major factors
governing their response to host plant defences.
The first insects began utilizing plants as a food source in the Early Devonian period,
only several million years after vascular plants colonized terrestrial habitats [9, 10]. This
led to a progressive radiation in the diversity of herbivorous insects and their feeding
guilds. The pioneer insect herbivores were sap-suckers, stem-borers, and consumers of
spores [11]. Thalli, which evolved into leaves some time later, only started to be
consumed by chewing herbivores shortly after that in the Middle Devonian [10]. All
modern herbivore guilds, with the possible exception of leaf-miners, were present by the
Late Carboniferous, more than 300 million years ago [10].
The proliferation of herbivore lineages and guilds has increased and diversified
herbivory pressure on plants and led to an arms-race between plants and insects [4, 5]
(Box 1). This generally required plants to employ a broad suite of defences in order
to maintain efficient protection against diverse communities of herbivores [12, 13].
Box 1
In their seminal paper, Ehrlich and Raven [4] proposed the so-called escapeand-radiate scenario of insect-plant coevolution. According to the escapeand-radiate scenario, the genesis of novel defensive traits allows plants to
escape herbivory, leading to speciation of the respective plant lineage. However, after some evolutionary time, herbivores adapt to the novel defence and
overcome it. This allows herbivores to colonize that plant lineage, opening a
novel niche to them. The adapted herbivores speciate, and the process starts
over. This should, on the one hand, lead to diversification or escalation of host
plant defences over evolutionary time and on the other hand to co-diversification of the plant and insect lineages involved.
Recent studies suggest that clear cases of co-diversification are relatively
scarce [128, 129], with sequential radiation and phylogenetic tracking being
(continued)
78
M. Volf