Transformations in the evolution of Peracarida (Crustacea)

Peracarida is one of the most species-rich taxa within crustaceans. They inhabit virtually all ecosystems, ranging form terrestrial ecosystems (including deserts) to the deep sea, where they often play a central ecological role. Their best-known representatives are the pill bugs or woodlice (Isopoda), but also Amphipoda and opossum shrimps (Mysida) are widely distributed and species-rich. The females brood pouch or marsupium, where the larvae are reared, is the common characteristic of Peracarida. The phylogenetic relationships within Peracarida are contested, even the common origin (monophyly) of Peracarida itself has been questioned by some molecular phylogenetic studies. If true, this would suggest the marsupium evolved at least twice independently. To better understand the evolutionary transformations and evolutionary processes within Peracarida, a well-founded phylogenetic hypothesis is a prerequisite. One of the main goals of this project is to test the monophyly of Peracarida and to resolve the relationships among its main taxa via combined molecular and morphological analyses. The morphological studies will be perfumed at the University of Rostock by Prof. Dr. Stefan Richter and the genetic analyses at Natural History Museum in Vienna by Dr. Martin Schwentner. Another goal is to assess the impact of transformations in the evolution of Peracarida. One crucial transformation is represented by the evolution of the marsupium, which had direct consequences for the locomotion apparatus due to its location ventrally on the body. The marsupium also transformed the reproductive strategy of Peracarida. Rather than having hundreds or thousands of offspring per clutch like other related crustacean taxa, Peracarida only have a small number of offspring per clutch. Their offspring also closely resemble the adults when they emerge from the marsupium. This is an important difference to many other marine taxa, which have a highly mobile, free-swimming larval stage that allows long- range dispersal. This change in reproductive mode probably had long-term consequences for many microevolutionary process, like genetic drift. First results suggest that indeed the substitution rates is higher in Peracarida compared to other higher crustaceans (Malacostraca). This effect will be studied in more detail using the extensive genetic dataset that will be generated during the project. Habitat shifts (e.g. between terrestrial and marine habitats and especially the deep sea) may have had similar microevolutionary consequences, as these would also affect dispersal capabilities and population sizes. This will also be studied in the course of the project.

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