Cytonuclear genetic signatures of hybridization phenomena: Rationale, utility, and empirical examples from fishes and other aquatic animals

By definition, organisms of hybrid ancestry carry amalgamations of divergen t genomes. Thus, exaggerated effects of genomic interactions might be antic ipated in hybrid populations, thereby magnifying the impact of natural sele ction and making this and other evolutionary forces easier to document. Mat ing biases and other gender-based asymmetries also frequently characterize hybrid populations. Thus, maternally inherited cytoplasmic polymorphisms as sayed jointly with those at biparentally inherited nuclear loci provide pow erful genetic markers to dissect ethological, ecological, and evolutionary processes in hybrid settings. Population-level topics that can be addressed using cytonuclear markers include the frequency of hybridization and intro gression in nature, behavioral and ecological factors (such as mating prefe rences and hybrid fitnesses) influencing the genetic architectures of hybri d zones, the degree of consistency in genetic outcomes across multiple hybr id contact regions, and environmental impacts (including the introduction o f alien species) on hybridization processes. Several empirical studies on f ish populations in hybrid settings illustrate the application of cytonuclea r appraisals in such contexts.