Introduction
Considering animals most people think about vertebrates and thereby especially mammals and birds. These are often considered the most sophisticated and evolutionary successful animals on Earth. However, this is not true taking into account evolutionary history, biodiversity, ecology or biomass. Invertebrates outshine vertebrates in all these categories. Moreover, invertebrates have evolved novel structures and inhabited habitats unoccupied by vertebrates. Hence, invertebrates have much to teach us about evolution in general and in particular. On the other hand, except for a few flagship species and groups, invertebrates are heavily understudied, especially considering marine invertebrates. The latter is especially important as all animals live depends on water and originated from the marine realm. Hence, understanding the evolution of marine invertebrates will help us to understand evolution at much more detailed and complete level.
The topic of this thesis will build upon the results of the ArtsDatabanken-project “Biodiversity in the marine algae belt”. The marine algae belt comprising kelp forests, seagrass meadows and rocky reefs with coralline red seaweeds is one of the most active primary producing environments in the sea. It also harbors a great diversity of animals including sea squirts, ribbon worms, nick worms, serpulid worms, spionid worms and skeleton shrimps. The species of these groups occupy important ecological functions as herbivores, predators and filter feeding organisms and can be sessile or agile as well as solitary or colonial. Globally these taxa comprise more than 7,000 species with around 250 species documented from Norwegian waters. This is why we conducted a field inventory and collected species of these taxa in Norway (from the Skagerrak up to Troms?). With morphological and molecular methods, we determined species and learned more about their distribution and their association with Norwegian nature types. These efforts resulted into the record of 624 collection samples with 944 specimens of 73 species from these animal groups and 43 localities in Viken, Tr?ndelag, Vestland, and Troms og Finnmark comprising 19 Norwegian nature types. Our results show that we have found 3 species and 1 subspecies, which are new to Norway, and at least 10, which are new to science, but there may be 7 additional ones. However, the first analyses concerning the new species also showed that much more detailed studies on these are necessary. This is where this Master project will work on.
The sea squirts (“Ascidiacea”, Tunicata) are sessile benthic organisms ranging in size from <1 mm to 60 cm. Species can be both solitary and colonial, with some colonies being several meters in size. Sea squirts were found in all three targeted habitats. Ascidian species are also among some of the most dangerous marine invasive species causing strong habitat transformation and economic loss in aquaculture.
We found 26 species across all habitats, of which we regard two as new species and further six as possible new species. Within the genus Ascidiella, there is properly a new species. It is morphological similar to A. aspersa and occurs at an algae habitat in the Bergen region. Our specimens are part of a group comprising 90 other specimens identified as A. aspersa. It is only 2.5% different to another group containing other A. aspersa specimens. In the tree, the two clades are sister to each other. Another new species is a possible Polyclinum species, which morphologically similar to P. aurantium. In the molecular tree, it is more closely related to Aplidium pallidum than to the clade of P. aurantium. Moreover, it is 10% different to A. turbinatum and has a similar genetic difference to P. aurantium. Within the subgroup Phlebobranchia, the morpho-species Ciona intestinalis, Corella parallelogramma, and Ascidia mentula could also be new species. In our molecular tree, each species forms a monophyletic group with only very shallow branch length indicating that each is only one species within Norway and these habitats. However, on broader scale it looks different. Our C. intestinalis clade is 5% different to the closest group comprising 26 C. intestinalis sequences. Additional groups with C. intestinalis sequences included are at least 17% different. Moreover, C. intestinalis is already known to be a species complex making it very likely that we found a new species. Our C. parallelogramma sequences do not match to any Corella species (including one sequence of Corella parallelogramma). The closest hits are different tunicates with at least 20% genetic difference. The closest hit in GenBank is against a Corella species (i.e., C. eumyota) with a genetic difference of 14%. Hence, while the morphology agrees with C. parallelogramma, the molecular data are inconclusive. Ascidia mentula might also be new species. Our sequences are grouped together with several other A. mentula specimens. Its nearest neighbor is another A. mentula group from which it is about 17% different. Finally, within Aplousobranchia, the three morpho-species Clavelina lepadiformis, Aplidium pallidum and Didemnum albidum could also be new species. Each species forms a group with only very shallow branch length in the tree indicating that each is only one species within Norway and these habitats. However, on broader scale it looks different. Our C. lepadiformis sequences are placed in a group, which includes 22 other C. lepadiformis sequences from across Europe and which is 4% different to another C. lepadiformis group comprising only one specimen. Hence, it is not certain of this truly represents two different species or if the one specimen was erroneously assigned. Our A. pallidum specimens are about 10% different to another A. pallidum from the Irish sea. Similarly, our two D. albidum specimens are in a group together with another specimen from the US. It is most closely related to a single D. albidum sequence and about 5% different. However, there are in total four groups with D. albidum sequences given molecular data, which are about 17% different to each other. This indicates the possible presence of a species complex. Therefore, a detailed taxonomic assessment of all these species is required to determine among others, which group includes the name bearer as well as additional molecular markers, especially nuclear ones.
In your thesis, you obtain additional molecular data for new markers and specimens, as well as conduct detailed morphological studies using different forms of microscopy. You will compare your data with the publicly available data and literature and conduct a taxonomic revision of these species in Norwegian waters.
What you will learn:
You will learn to conduct taxonomic identification, extensive literature research and distribution mapping. This will include among others molecular barcoding and microscopy. You will apply programs for phylogenetic reconstruction and conduct statistical analyses of your results.
What we offer:
First and foremost, we offer a friendly and kind mentoring environment. We offer a membership in ForBio (the research school in biosystematics) where you will be able to take courses in several places in Norway. You will potentially be able to attend international courses if they fit with the objectives. You will be able to participate in a national conference (ForBio meeting) and potentially in an international conference depending on funding. If you are interested, we will be able to discuss travel opportunities and a travelling period abroad.
What we expect from you:
Commitment and dedication
Outcomes:
One (or more) scientific publications, conference communication
Supervision and teaching:
You will be supervised by Torsten Struck, and Ana Teresa Capucho (both UiO) and Thomas Stach (Humboldt University Berlin).
For further inquiries, please contact Torsten Struck (t.h.struck@nhm.uio.no)