A molecular phylogeny of the north-east Atlantic species of the genusIdotea(Isopoda) with focus on the Baltic Sea

Pollinators of the sea: A discovery of animal-mediated fertilization in seaweed

The long-held belief that animal-mediated pollination is absent in the sea has recently been contradicted in seagrasses, motivating investigations of other marine phyla. This is particularly relevant in red algae, in which female gametes are not liberated and male gametes are not flagellated. Using experiments with the isopod Idotea balthica and the red alga Gracilaria gracilis, we demonstrate that biotic interactions dramatically increase the fertilization success of the alga through animal transport of spermatia on their body. This discovery suggests that animal-mediated fertilization could have evolved independently in terrestrial and marine environments and raises the possibility of its emergence in the sea before plants moved ashore.

An environmental gradient dominates ecological and genetic differentiation of marine invertebrates between the North and Baltic Sea

Environmental gradients have emerged as important barriers to structuring populations and species distributions. We set out to test whether the strong salinity gradient from the marine North Sea to the brackish Baltic Sea in northern Europe represents an ecological and genetic break, and to identify life history traits that correlate with the strength of this break. We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data, and data on the distribution, salinity tolerance, and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta, and Gastrotricha. We included seven non‐native species covering a broad range of times since introduction, in order to gain insight into the pace of adaptation and differentiation. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times, and migration rates between North and Baltic Sea populations, and analyzed correlations between genetic and life history data. The majority of investigated species is either genetically differentiated and/or adapted to the lower salinity conditions of the Baltic Sea. Species exhibiting population structure have a range of patterns of genetic diversity in comparison with the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Two of the non‐native species showed signs of genetic differentiation, their times since introduction to the Baltic Sea being about 80 and >700 years, respectively. Our results indicate that the transition from North Sea to Baltic Sea represents a genetic and ecological break: The diversity of genetic patterns points toward independent trajectories in the Baltic compared with the North Sea, and ecological differences with regard to salinity tolerance are common. The North Sea–Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non‐native species.

Diet-dependent gene expression highlights the importance of Cytochrome P450 in detoxification of algal secondary metabolites in a marine isopod

Isopods of the genus Idotea have an unusual ability to feed on algae containing high amounts of chemical defense molecules, such as species of the genera Fucus and Ulva. In this study, we compared gene expression patterns of Idotea balthica individuals fed with Fucus vesiculosus to individuals fed with Ulva lactuca. We generated the first-ever transcriptome assembly for this species, and found 3,233 differentially expressed genes across feeding regimes. However, only a handful of biological functions were enriched with regard to differentially expressed genes, the most notable being "alkaloid metabolic process". Within this category, we found eight differentially expressed cytochrome P450 (CYP) unigenes, all of which had a higher expression in the U. lactuca diet treatment. A phylogenetic analysis showed that the differentially expressed CYP genes are closely related to a CYP gene described from the hepatopancreas of the spiny lobster Panulirus argus, and we hypothesize that these transcripts are involved in metabolite detoxification. This is a first step in the understanding of this algae-grazer interaction, and will form a basis for future work to characterize cytochrome P450 functioning in marine crustaceans.