Transformations in the evolution of Peracarida (Crustacea)

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Peracarida is a highly diverse and ecologically important group of malacostracan crustaceans. Morphologically, Peracarida is well characterized by a marsupium in which female’s hatch and rear embryonized larvae/juveniles. However, their monophyly was repeatedly questioned in molecular phylogenetic studies and no consensus has been reached regarding their internal relationships. The evolution of the intra-marsupial development had far reaching micro- and macroevolutionary consequences. In contrast to many other predominantly marine taxa, Peracarida lacks a dedicated dispersal stage, which increases population fragmentation, and Peracarida shifted from a reproductive r-strategy to a k-strategy. By altering the effective population size, this has long-term consequences for their rate of molecular evolution, as previously observed. The evolution of the marsupium also had consequences for the locomotion of peracarids, which is reflected in the morphology of the pleon. Shifts between habitats (like freshwater, terrestrial, or shallow-water marine and deep sea) might have similar long-term effects on the rate of molecular evlution. Hypotheses / research questions / objectives: Our key objectives are: Resolve the internal relationships within Peracarida and test their monophyly in a combined (morphological + molecular) approach. Understand the evolutionary transformation of the locomotory apparatus (thoracopods and pleon) in Peracarida as a result of the evolution of the marsupium. Identify long-term changes in the rate of molecular evolution in relation to the reproductive strategy or transitions between habitats in Isopoda. Approach / methods: We will combine modern morphological (μCT, cLSM and histology) and genomic (transcriptome sequencing and target capture) methods and will study up to 240 species (depending on the method). This will allow the most detailed reconstruction of the evolutionary history of Peracarida to date as well as tracing key morphological transitions and identifying long-term changes in the molecular substitution rate (including comparisons between protein-coding and non-coding loci and between synonymous and non-synonymous substitutions). The research will be conducted in Rostock (Germany) and Vienna (Austria). Level of originality / innovation: This will be the first project to combine morphological and phylogenomic analyses to resolve the relationships within Peracarida. A particular novelty is the usage of the vast genomic data sets to gain insights into genome evolutionary processes in addition to resolving the phylogenetic relationships. The latter will be of importance not only for Peracarida, but will help to better understand the long-term effects of life-history changes on rates of molecular evolution in general.