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Hybridization and polyploidization are important evolutionary processes whose impacts range from the alteration of gene expression and phenotypic variation to the triggering of asexual reproduction. We investigated fishes of the Cobitis taenia-elongatoides hybrid complex, which allowed us to disentangle the direct effects of both processes, due to the co-occurrence of parental species with their diploid and triploid hybrids. Employing morphological, ecological, and RNAseq approaches, we investigated the molecular determinants of hybrid and polyploid forms. In contrast with other studies, hybridization and polyploidy induced relatively very little transgressivity. Instead, Cobitis hybrids appeared intermediate with a clear effect of genomic dosing when triploids expressed higher similarity to the parent contributing two genome sets. This dosage effect was symmetric in the germline (oocyte gene expression), interestingly though, we observed an overall bias toward C. taenia in somatic tissues and traits. At the level of individual genes, expression-level dominance vastly prevailed over additivity or transgressivity. Also, trans-regulation of gene expression was less efficient in diploid hybrids than in triploids, where the expression modulation of homoeologs derived from the “haploid” parent was stronger than those derived from the “diploid” parent. Our findings suggest that the apparent intermediacy of hybrid phenotypes results from the combination of individual genes with dominant expression rather than from simple additivity. The efficiency of cross-talk between trans-regulatory elements further appears dosage dependent. Important effects of polyploidization may thus stem from changes in relative concentrations of trans-regulatory elements and their binding sites between hybridizing genomes. Links between gene regulation and asexuality are discussed.

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Aim The long history of isolation of the Antarctic continent, coupled with the harsh ecological conditions of freezing temperatures, could affect the patterns of genetic diversity in the organisms living there. We aim (a) to test whether such pattern can be seen in a mitochondrial marker of bdelloid rotifers, a group of microscopic aquatic and limno‐terrestrial animals and (b) to speculate on the potential mechanisms driving the pattern. Location Focus on Antarctica. Taxon Rotifera Bdelloidea. Methods We analysed different metrics of genetic diversity, also spatially explicit ones, including number of haplotypes, accumulation curves, genetic distances, time to the most recent common ancestor, number of independently evolving units from DNA taxonomy, strength of the correlation between geographical and genetic distances, population genetics neutrality and differentiation indices, potential historical processes, obtained from an extensive sample of cytochrome oxidase subunit I (COI) sequences obtained from bdelloid rotifers. We included 2242 individuals from 23 species in a comparison between Antarctic and non‐Antarctic taxa, correcting for sample size directly in the analyses and then by confirming the results also using only a restricted dataset of nine well‐sampled species. Results Antarctic species had consistently lower genetic diversity and potential younger relative age than non‐Antarctic species, even if they were similar in sample size, geographical extent, neutrality and differentiation indices, and correlation between genetic and geographical distances. Main conclusions The extensive survey of genetic diversity in one mitochondrial marker in Antarctic bdelloids supports previous suggestions from other organisms that the origin and maintenance of terrestrial Antarctic fauna are different from those of other continents. Such differences could be speculated to be due, in the case of bdelloid rotifers, to the more recent origin of the species living there in comparison to non‐Antarctic species.