LECTURE 15 COEVOLUTION AND MUTUALISM
pg. 381-383; 385-386; 389-396
MAJOR CONCEPTS
1) Coevolution involves mutual evolutionary responses by interacting populations.
2) Diffuse coevolution may be more common than strict coevolution.
3) Constraints restrict evolution of strict mutualisms.
4) Coevolution in plant-pathogen systems reveals genotype-genotype interactions
and involves a gene-for-gene concept and an ‘evolutionary arms race’.
5) Evidence for coevolution can arise from inference, circumstantial evidence, or
experimentation.
6) Mutualists have complementary functions; they involve trophic, defensive, and
dispersive functions.
Types of pairwise interspecific interactions
Mutualism (+/+)
Predation (+/-)
Competition (-/-)
Commensalism (+/0)
Amensalism (-/0)
Fluidity in type of relationship
Symbioses
Intimate, often obligatory association of two species
Usually involving coevolution
May be parasitic or mutualistic
Coevolution
Interacting species evolve in response to each other
Each species acts as selective agent on other species
Traits of each species affect fitness of other species
Traits have genetic basis
May be mutualistic or antagonistic
Strict coevolution
Limited to pair of species
Specialized response
May be rare and limited to very strong interactions
Diffuse coevolution
Response to many other species
Generalized response
Gene-for-gene concept and evolutionary ‘arms race’
Occurs in plant-pathogen and host-parasite systems
Based on single gene conferring resistance to host or virulence to pathogen
Back and forth selection between genotype of host and genotype of pathogen
