VARIANCE-INDUCED PEAK SHIFTS

The increase in phenotypic variance that occurs in some populations as a result of bottlenecks and founder events can cause a dramatic incre ase in the probability of a peak shift from one adaptive state to anot her. Periods of small population size allow drift in the amount of phe notypic variance. Increases in phenotypic variance, coupled with a con stant individual fitness function with multiple peaks, can cause the m ean fitness landscape to change from bimodal to unimodal, thereby allo wing the population's mean phenotype to change deterministically by se lection. As the amount of phenotypic variance is returned to an equili brium state, the multiple peaks reemerge, but the population has moved from one stable state to another. These variance-induced peak shifts allow punctuational evolution from one peak to another at a rate that can be much higher than that predicted by Wright's shifting-balance pr ocess alone.