Аннотация
Postzygotic isolation between incipient species results from the accumulation of incompatibilities that arise as
a consequence of genetic divergence. When phenotypes are determined by regulatory interactions, hybrid incompatibility can evolve
even as a consequence of parallel adaptation in parental populations because interacting genes can produce the same phenotype
through incompatible allelic combinations. We explore the evolutionary conditions that promote and constrain hybrid incompatibility in
regulatory networks using a bioenergetic model (combining thermodynamics and kinetics) of transcriptional regulation, considering
the bioenergetic basis of molecular interactions between transcription factors (TFs) and their binding sites. The bioenergetic parameters
consider the free energy of formation of the bond between the TF and its binding site and the availability of TFs in the intracellular
environment. Together these determine fractional occupancy of the TF on the promoter site, the degree of subsequent gene
expression and in diploids, and the degree of dominance among allelic interactions. This results in a sigmoid genotype–phenotype map
and fitness landscape, with the details of the shape determining the degree of bioenergetic evolutionary constraint on hybrid in-
compatibility. Using individual-based simulations, we subjected two allopatric populations to parallel directional or stabilizing selection.
Misregulation of hybrid gene expression occurred under either type of selection, although it evolved faster under directional selection.
Under directional selection, the extent of hybrid incompatibility increased with the slope of the genotype–phenotype map near the
derived parental expression level. Under stabilizing selection, hybrid incompatibility arose from compensatory mutations and was
greater when the bioenergetic properties of the interaction caused the space of nearly neutral genotypes around the stable expression
level to be wide. F 2 ’s showed higher hybrid incompatibility than F 1 ’s to the extent that the bioenergetic properties favored dominant
regulatory interactions. The present model is a mechanistically explicit case of the Bateson–Dobzhansky–Muller model, connecting
environmental selective pressure to hybrid incompatibility through the molecular mechanism of regulatory divergence. The bioener-
getic parameters that determine expression represent measurable properties of transcriptional regulation, providing a predictive
framework for empirical studies of how phenotypic evolution results in epistatic incompatibility at the molecular level in hybrids.
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