How to study adaptation? Design – optimality theory Experiment –Track success of different phenotypes –Manipulate phenotype Comparative method –Test an adaptive hypothesis –Phylogenetically independent data A. B. vs.

How to study adaptation? –Periodic selection (Attwood, 1951) –Complications to simple fitness: Stable equilibrium Sexual selection Conflicting selection Group selection & cheating Selfish elements

Modes of selection Fitness disadvantage

Key terms of selection Absolute fitness (R i ) vs. relative fitness (W i ) –Rate of change depends upon relative fitness –We define W i relative to ancestor (W o = 1.0), thus W i = R i / R o Coefficient of selection (s i ) –We define s i relative to ancestor (s i = W i – 1) –“Hard” vs. “soft” selection Components of fitness –Performance during each “life stage” (lag, exponential, stationary) –Depends upon environment…

What can prevent fixation? Mutation/selection balance & gene flow Heterozygote advantage Antagonistic & varying selection? Frequency-dependent selection –Negative (fit when rare) Scale-eating cichlids

Alternate equilibria Positive frequency-dependence Heterozygote disadvantage Multi-peaked adaptive landscape –Can get ‘stuck’ on local peak (Elena & Sanjuán, 2003)

Looking forward… Assignment: Final plan from each group (< 2 pages) AS No class on Monday (President’s Day) Microbiology review sessions (in 3081): 2/15, 6 pm – Brock 1, 2, 5 (General micro & metabolism) 2/20, 6 pm – Brock 6, 9, 12, 13 (Microbial growth, basic virology, overview of bacterial & archaeal diversity) Special guest lecture (in 2062): 2/22, 6 pm – Daniel Segrè, “Origin of biological networks” *pizza & beer will be provided*