Download Guild coevolution

Coevolution
Fig wasps
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Every species of fig is pollinated exclusively by a single species of wasp
Phylogeny of wasp species matches the phylogeny of the fig species they
pollinate
– Speciation in parallel
Fig-fig wasp mutalism
Coevolution
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Reciprocal genetic change into interacting species owing to natural selection
imposed by each other
Three types
– Specific coevolution
– Guild coevolution
– Escape and radiate coevolution
Concordant phylogenies
Host switching
Evolution of enemies and victims
Predator-prey coevolution
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May have several results
– Evolutionary arms race
– Stable genetic equilibrium
– Continual cycles
– Extinction of one or both species
Arms race
• Unending arms race is unsustainable to due limited resources
Stable equilibrium
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May develop where costs equal benefits
Costs of secondary compounds in plants
– Wild parsnip and furanocoumarins
– Cucumber and cucubitacins
Irregular fluctuations
• Gene-for-gene interactions
– Host has several loci at which a dominant allele confers resistance (R) and
enemy has a corresponding recessive allele (v) which confers infectivity
– Frequency dependent selection – When R1 is high, v1 will rise, then R2 will
be selected for and v2 will rise, etc.
Quantitative traits
Examples of enemy victim coevolution
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Cuckoo and host
Examples of enemy-victim coevolution
Infectious disease
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Rabbits and myxoma virus
Over time, host evolved greater resistance and virus evolved a mid-level of
virulence
Mutualisms
Mutualisms
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Selection will favor protective mechanisms in one or both species to prevent
overexploitation
Mutualisms
• Selection will favor honest genotypes (i.e. those that do not cheat) if the
individuals genetic self-interest depends on the fitness of the host or partner
– Vertical transmission of endosymbionts
– Lifelong associations
– Restricted opportunities to switch partners
Yucca moths and yuccas
Yucca moths
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Why don’t moths cheat and lay more than a few eggs in each flower?
– The plant cannot mature all its flowers due to limited resources
– Preferentially aborts flowers with moths
• Strong selection against overexploitation
Not all mutualisms are stable
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Orchids cheat and provide no nectar
– Release a scent that mimics females sex hormones
Two lineages of yucca moths lay more eggs, after critical abortion period in
yucca
Competitive interactions
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Competition imposes selection for divergence in resource use
Major factor in divergence of species
Divergence
Divergence
Character displacement
Ecological release
• Differences greater when species exists alone
Community convergence
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Convergence of communities
Niche equilibrium
Parallel evolution of Anolis
Phylogeny of ecomorphs
Multispecies interactions
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Lodgepole pine, red squirrel and red crossbill
Selection mosaic
• Squirrels prefer narrow cones, lots of seeds and therefore impose selection for
wide cones, fewer seeds
• Crossbills cannot feed on larger wider cones with thick scales
• Crossbills have evolved longer deeper bills in squirrel free areas than in
squirrel areas
• Squirrels impede the coevolution of crossbills and pines
Mimicry rings