Reproductive Isolation

Abstract

The evolution of genetically based barriers to gene flow between populations or species, often referred to as ‘reproductive isolation’, characterizes the formation of new species. Reproductive isolation can vary quantitatively in magnitude, with stronger reproductive isolation characterizing speciation having proceeded further. There are many different forms of reproductive isolation, some of which act before zygote formation (i.e., prezygotic isolation) and some of which act after (i.e., postzygotic isolation). Some forms of reproductive isolation are ecological, and inherently involve natural selection such that their manifestation is dependent on the ecological setting. Other forms of reproductive isolation, such as intrinsic genetic dysfunctions in hybrid offspring, can manifest themselves independent of the ecological environment and can exist even in benign laboratory environments. Numerous different processes can cause the evolution of reproductive isolation, including divergent natural selection, the fixation of different, incompatible mutations in separate populations experiencing similar selective environments (i.e., uniform selection), and random genetic drift. The genetic basis and rate of evolution of reproductive isolation appear highly variable. Future work could use genomic tools to understand this variability, and to further examine how levels of gene flow vary across different regions of the genome.