Coevolution and Mutualisms Species interactions may be mutually beneficial In some cases, these interactions may lead to coevolution among participants

What is coevolution? Evolutionary change in one species causes evolutionary change in the other Species 1 Species 2

Five points about coevolution and specialization (Thompson The Coevolutionary Process) 1). Outcomes unlikely to be equal 2). Coevolution may occur in one population, but not another 3). Population-level variation in degree of specialization

Five points about coevolution and specialization (Thompson The Coevolutionary Process) 4). Variation in response leads to geographic mosaic of coevolution 5). Temporal variation in mosaic as well.

Coevolution difficult to document Many interactions are highly specialized but not coevolutionary Evolutionary response may be to generalized type of organism: diffuse coevolution. May also be specifically between 2 species- “narrow sense”

Example: rabbit control in Australia European rabbits introduced into Australia, spread rapidly Introduction of myxoma virus Coevolved relationship between resistance and virulence

Gene-for-gene mechanisms of coevolution 1. single-allele complementary system 2. elicitor-receptor model

Mutualisms Three basic types of mutualistic interactions May or may not involve coevolution Obligate versus facultative mutualism Cheaters

3 types of mutualisms 1. Trophic (obligatory) 2. Defensive (both facultative and obligatory) 3.Dispersive (some obligatory, most not)

Trophic mutualisms

Defensive Mutualisms Copyright: Hilton Pond Center

Dispersive Mutualisms

Pollination versus seed dispersal Pollination systems sometimes coevolved, seed dispersal systems are not Very great degree of specialization in some pollinator systems

Seed dispersal: mutualistic but not coevolved Why not coevolved? No specialization Sites suitable for seeds not predictable No “payment on delivery” (Wheelwright and Orians 1982) Advantages to non-specialization

Pollination: mutualistic, not always coevolved Target specificity Need for predictability

“How to be a fig” A stunning example of coevolution…

Two paths to pollination (and seed dispersal) Deception Reward Photo by Ken Gardiner Photo by Babs and Bert Wells

Trade-off in mutualisms How do you maximize your benefit for your cost? The plant perspective… The animal perspective…

Mutualisms: how do they work?? Theory poorly developed Apparent evolutionary instability Cheaters (Ferriere et al. 2002)

Specialization and phylogeny Specialization may already exist- “preadaptation” Phylogeny can often explain pread- aptations and intermediate steps Implications?....

Summary Mutualisms offer benefits to both participants Coevolution can occur in mutualisms but appears rare, hard to demonstrate Mutualisms have enormous impact on natural communities Mutualisms represent a cost-benefit balance between participants

Ungraded homework Assignment What are two ways plants can attract pollinators, and what is the cost or risk associated with each strategy?