Cobitis, gynogenetic reproduction, asexual, clonality, hybridization, RNA sequencing

Hybridisation and polyploidy played crucial role in evolution and induce more or less dramatic changes in genetic architecture, gene expression and phenotypic variation of resulting forms. Nevertheless, a long-lasting debate is carried as to whether these effects, which are observed in many independent taxa, have some common background or are rather case-specific. Moreover, disentangling the direct effects of both phenomena is often difficult as many polyploids are of hybrid origin and might have accumulated many postformational changes. This study took the advantage of a model taxon (Cobitis, Cypriniformes) where cooccurrence of allodiploid and allopolyploid hybrids between species C. elongatoides and C. taenia allows such disentanglement. The recent origin of studied hybrids further allows direct comparisons with parental species offering a possibility to investigate the role of cis- versus trans- regulatory elements in gene regulation. For each biotype, we investigated its habitat preferences, morphological variability as well as gene expression profiles in gonadal (oocytes) and somatic tissues (livers) including the homeologue-specific expression. The data indicated that neither hybridization, nor polyploidy induces massive transgressivity but hybrids’/polyploids’ appeared rather intermediate between parental species. Surprisingly, however, such intermediacy has not been achieved by additive gene expression, since vast majority of genes showed patterns of expression-level dominance when individual genes in hybrids were not expressed at intermediate level, but matched either one or the other parent. Homeologue-specific expression demonstrated complex interplay between cis- and transregulation of hybrids’/polyploids’ gene expression. Especially, we noticed that efficiency of trans-regulatory elements are strongly dosage-dependent so that the same gene, which is under cis-regulation in diploid hybrids appears as trans-regulated in triploids.

Hybridisation and polyploidy played crucial role in evolution and induce more or less dramatic changes in genetic architecture, gene expression and phenotypic variation of resulting forms. Nevertheless, a long-lasting debate is carried as to whether these effects, which are observed in many independent taxa, have some common background or are rather case-specific. Moreover, disentangling the direct effects of both phenomena is often difficult as many polyploids are of hybrid origin and might have accumulated many postformational changes. This study took the advantage of a model taxon (Cobitis, Cypriniformes) where cooccurrence of allodiploid and allopolyploid hybrids between species C. elongatoides and C. taenia allows such disentanglement. The recent origin of studied hybrids further allows direct comparisons with parental species offering a possibility to investigate the role of cis- versus trans- regulatory elements in gene regulation. For each biotype, we investigated its habitat preferences, morphological variability as well as gene expression profiles in gonadal (oocytes) and somatic tissues (livers) including the homeologue-specific expression. The data indicated that neither hybridization, nor polyploidy induces massive transgressivity but hybrids’/polyploids’ appeared rather intermediate between parental species. Surprisingly, however, such intermediacy has not been achieved by additive gene expression, since vast majority of genes showed patterns of expression-level dominance when individual genes in hybrids were not expressed at intermediate level, but matched either one or the other parent. Homeologue-specific expression demonstrated complex interplay between cis- and transregulation of hybrids’/polyploids’ gene expression. Especially, we noticed that efficiency of trans-regulatory elements are strongly dosage-dependent so that the same gene, which is under cis-regulation in diploid hybrids appears as trans-regulated in triploids.