Nuclear Cytoplasmic Conflict in Hybrids of Roach <i>Rutilus rutilus</i> and Bream <i>Abramis brama</i> as a Consequence of the Divergence Species in Body and Genome Sizes

Abstract

Species divergence in body size is often associated with changes in genome size and the rate of evolution of mitochondrial DNA (mtDNA), which can lead to problems of nuclear-cytoplasmic compatibility and embryonic genome activation and reduce the fitness of hybrids. The bream Abramis brama (L.) is larger than the roach Rutilus rutilus (L.) in body and genome sizes. In the first generation of hybrids according to the ITS1 region of ribosomal DNA, a change in the donor genome of male to the level of the maternal species was previously established, which can affect the inheritance of traits from the male and, in particular, body size. Body length and height, a complex of diagnostic morphological characters, and genotyping (ITS1 rDNA and cyt b mtDNA) of underyearlings and mature individuals of bream, roach, F1 hybrids and underyearlings of backcrosses (Fb) were analyzed. Sexually mature hybrids of both directions of crossing are close in body length to R. rutilus, which indicates a violation of the paternal effect when inheriting the body length of a larger of species. Violation of the inheritance of bream body length in hybrids of cross R. rutilus × A. brama (♀ ♂, RA) is considered as a developmental deviation, which, obviously, can affect the adaptation of hybrids and determines the rarity of this variant in nature. At the same time, alloplasmic ARR backcrosses restore the body length of the bream even in the presence of the roach nuclear genome, which indicates the influence of mitochondrial genes on the development of this trait. The observed decrease in the fitness of first-generation hybrids with roach mtDNA may be associated with to an insufficient level of transcription of ribosomal genes due to a decrease in the number and variability of copies of the donor bream rDNA. Moreover, the high level of changes of mtDNA roach indicate a suboptimal mitochondrial-nuclear correspondence of respiratory a complexes in hybrids RA, which negatively affects key physiological processes, including growth and development of a large body size. Presumably, the development of large body size, as a complex trait with high aerobic fitness, is blocked in RA hybrids for energy reasons. The paper shows that differences families of repeated sequences rDNA and mtDNA in terms of the number and variability of copies in genome of R. rutilus and A. brama can lead to regulatory nuclear-cytoplasmic incompatibility of genomes and affect the fitness of hybrids already in the first generation.