Phylogeny and gene expression patterns of allopolyploid species of Pelvetiopsis (Phaeophyceae:Fucaceae)

Here we investigate the consequences of polyploidy for evolutionary rates and gene expression conservation in two recently identified allopolyploid species of brown algae in genus Pelvetiopsis (Phaeophyceae: Fucaceae), in the north-eastern Pacific ocean. Phylogenetic reconstruction using multiple nuclear loci dated their origin to the late Pleistocene. An overall increase in evolutionary rates, particularly in non-synonymous substitutions, was found even in the most modern species (ca. 0.2 MA), suggesting an immediate effect of relaxed selection following allopolyploidization. Gene expression in homoeologues and parental orthologues was found to follow patterns previously predicted for allopolyploid organisms across different kingdoms, where the majority of homoeologues exhibit conserved expression levels. Interestingly, high non-synonymous substitution rates were found in homoeologues with equal expression, suggesting that increased evolutionary rates can occur independent of pseudogenization. Gene expression was also found to be partially linked to gender of origin of homoeologues. Our results extend previous work on evolutionary rates and expression patterns in allopolyploid organisms, in an evolutionarily distinct marine lineage, the heterokont brown algae.