Rate of Accumulation of Reproductive Isolation by Chromosome Rearrangements

摘要

The role of chromosome rearrangements as agents for rapid speciation has recently gained considerable support among evolutionary biologists, especially for the stasipatric model in which effective isolation is accomplished by fixation of a few strongly underdominant rearrangements. This support is, however, by no means universal, with critics citing the low probability of fixation of strongly underdominant rearrangements as a major problem of the stasipatric model. Population genetic considerations of the substitution rate of underdominant rearrangements in a finite population were examined by Lande, but as an estimator of long term effective deme size, rather than as a speciation model. The rate of accumulation of postzygotic isolation is analyzed for three models of underdominant rearrangements: strict underdominance; underdominance with the rearrangement homozygote being at a selective advantage; and underdominance with meiotic drive. It will be shown that reproductive isolation accumulates most rapidly in very small populations, but that strong homozygote advantage or drive can allow for fairly rapid speciation under certain conditions in large populations. Contrary to the stasipatric model, isolation usually proceeds most rapidly by fixation of a large number of weakly underdominant rearrangements even when moderate amounts of drive or homozygote advantage are allowed. Stasipatric speciation requires either the frequent occurrence of meiotically driven rearrangements or very small population sizes to operate in reasonable times. (ERA citation 07:012069)