The evolution of postzygotic isolation: accumulating Dobzhansky-Muller incompatibilities

Area of Science:

• Evolutionary Biology
• Genetics
• Speciation

Background:

• Hybrid sterility and inviability arise from genetic incompatibilities between species.
• Dobzhansky-Muller incompatibilities accumulate with species divergence, previously theorized via a 'snowball effect'.

Purpose of the Study:

• To explicitly model the stochastic accumulation of Dobzhansky-Muller incompatibilities over time.
• To analyze the distributions of incompatibilities and waiting times to speciation by postzygotic isolation.
• To estimate the probability of genetic divergence contributing to hybrid dysfunction.

Main Methods:

• Approximation of the stochastic process for hybrid incompatibility accumulation between pairs of loci.
• Derivation of distributions for incompatibilities based on divergence time and waiting times to speciation.
• Analysis of empirical data from Drosophila and Bombina.

Main Results:

• The study explicitly models three levels of stochasticity in incompatibility accumulation: number of substitutions, number of incompatibilities, and their fitness effects.
• Derived distributions for the number of incompatibilities and waiting times to speciation.
• Estimated a very small probability (p ≈ 10^-6 or less) for individual genetic differences causing hybrid sterility or inviability.

Conclusions:

• The stochastic accumulation of Dobzhansky-Muller incompatibilities is a key factor in postzygotic isolation.
• The probability of specific genetic changes causing hybrid dysfunction is generally very low.
• This framework provides insights into the tempo and mode of speciation driven by genetic incompatibilities.