Polyploid incidence and evolution

Changes in ploidy occurred early in the diversification of some animal and plant lineages and represent an ongoing phenomenon in others. While the pre valence of polyploid lineages indicates that this phenomenon is a common an d successful evolutionary transition, whether polyploidization itself has a significant effect on patterns and rates of diversification remains an ope n question. Here we review evidence for the creative role of polyploidy in evolution. We present new estimates for the incidence of polyploidy in fern s and flowering plants based on a simple model describing transitions betwe en odd and even base chromosome numbers. These new estimates indicate that ploidy changes may represent from 2 to 4% of speciation events in flowering plants and 7% in ferns. Speciation via polyploidy is likely to be one of t he more predominant modes of sympatric speciation in plants, owing to its p otentially broad-scale effects on gene regulation and developmental process es, effects that can produce immediate shifts in morphology, breeding syste m, and ecological tolerances. Theoretical models support the potential for increased adaptability in polyploid lineages. The evidence suggests that po lyploidization can produce shifts in genetic systems and phenotypes that ha ve the potential to result in increased evolutionary diversification, yet c onclusive evidence that polyploidy has changed rates and patterns of divers ification remains elusive.