BIOL3711 Lecture Notes - Lecture 11: Phenology, Glucosinolate, Brassicales
26 Jun 2018
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Coevolution
Ehrlich & Raven 1964 – Butterflies and Plants Coevolution
Butterflies and their food plants as models of plant/herbivore coevolution
Different groups of butterflies feed on different sets of plants that:
oHave characteristic secondary chemistries
Secondary chemistry mediates the performance of a nutritional
symbiont associated with a tree-killing herbivore
Proposed a coevolutionary arms-race between butterflies and their food
plants in which:
o A plant taxon evolves a novel chemical compound that protects it from
herbivores
oFreed from the pressure of herbivory:
The plants speciates and radiates in this new “adaptive zone”
oButterfly group LATER evolves some means of cracking the plant’s
defense
They then speciate and radiate in their new adaptive zone
Free from the pressures of competition, on the plants with
new chemical compound
And so on…
Hypothesis:
oMore closely related species should have more similar chemistry
oNatural selection caused by herbivores may result in rapid trait
evolution such that closely related species have divergent defenses
Escape and Radiate Coevolution
Ehrlich and Raven saw in this “escape and radiate” model of coevolution, a
mechanism for generating the tremendous diversity of:
oSecondary compounds in angiosperms AND
Secondary compounds:
Evolution of unpalatable or toxic plant compounds that
protects the plant from herbivory
oSpecies of insect herbivores
Animal-plant coevolution thus seen as:
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oA source of much of the worlds biodiversity
Patterns found in the phylogenies of insects and plants
Tibor Jermy (1984, 1993)
oWhat selective pressures do insect herbivores exert on their food
plants?
Insect ranges often plant ranges
oSmall populations of insects may exter a strong selective pressure
And plants vary in 2nd chemistry often vary in rates of herbivory
(selection for domestic crops, fruits)
oJermy considered:
A sequential model of coevolution
With insect specification following the diversification of
plants
More likely than reciprocal model of escape and radiate
Phylogeny of Insect-Plant Associations
How might the long evolutionary associations between plants and their
herbivores be reflected in their phylogeny?
oPhylogenis would differ when based on either Ehrlich and Raven or
Jermy’s model
Becerra, Noge and Venable (2009) – Macroevolutionary chemical escalation in an
ancient plant-herbivore arms race
Herbivore-plant coevolution is thought to lead to an escalation in the diversity
of secondary chemicals in plants
Looked at the chemical defences in Bursera (flowering shrubs and trees)
oBursera produces resin in a network of canals in the leaves
oThe resin contains terpenes (volatile hydrocarbons) and other
defensive chemicals
oCompounds decrease the survival of certain beetles that feed on the
plants
Continuous trend in production of new secondary compounds through time
oPerhaps resulting from arms-race with herbivores
Positive trend for more diverse defenses through time – as predicted by
coevolutionary theory
Squirting Bursera sp. tend to:
oHave relatively simple chemical defenses
oPossibly the squirting defense allows plants to reduce investment in
metabolic costs associated with terpenoid synthesis
Kursar et al. (2009) – Evolution of antiherbivore defenses in the tropical tree genus
Inga
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Document Summary
Ehrlich & raven 1964 butterflies and plants coevolution. Butterflies and their food plants as models of plant/herbivore coevolution. Different groups of butterflies feed on different sets of plants that: have characteristic secondary chemistries. Secondary chemistry (cid:0) mediates the performance of a nutritional symbiont associated with a tree-killing herbivore. Proposed a coevolutionary arms-race between butterflies and their food plants in which: a plant taxon evolves a novel chemical compound that protects it from herbivores, freed from the pressure of herbivory: The plants speciates and radiates in this new adaptive zone : butterfly group later evolves some means of cracking the plant"s defense. They then speciate and radiate in their new adaptive zone. Free from the pressures of competition, on the plants with new chemical compound. Hypothesis: more closely related species should have more similar chemistry, natural selection caused by herbivores may result in rapid trait evolution such that closely related species have divergent defenses.
