Biogeographische Muster der Meeresmuschel Cerastoderma edule entlang der europäischen Atlantikküste

The cockle Cerastoderma edule is a common bivalve that inhabits the marine soft-bottom intertidal along European shores. This invertebrate plays a key role in coastal food webs of the Northeast Atlantic coasts due of its high abundances. I studied cockles from 19 sites along the distribution range with the aim to describe the variation of geographic population structures on different analytical levels. Cockles from the Barents Sea to the African Atlantic coast were analysed with respect to their geographical differentiation in shell morphology, parasite load and population genetics. Morphological characteristics were analysed for a potential geographic pattern within the European cockle C. edule. Spatial differences of eight shell characteristics within samples from 18 sites were studied. However, biogeographic groups could not be discovered due to strong local variability in shell form parameters. Environmental conditions and/or co-existing species were suspected to shape the plasticity of cockle shells at each site. At sites where the sister species C. glaucum occurred together with C. edule, high variability of shell characters was found in both species. The lack of morphological character displacement in mixed populations confined reliable species identification to the DNA level. Since parasites often strongly influence host morphology and its life history traits, the biogeography of the trematode assemblage was studied for C. edule as first and second intermediate host. At ten European locations ranging from Norway to Portugal, 30 cockle specimens per site were sampled to detect trematode diversity and abundance. Cockles from the Scandinavian sites shared dominant trematode species (Himasthla elongata, Meiogymnophallus minutus and Renicola roscovita) with the south-western European populations. However, two geographical groups could be revealed, based on the occurrence of rare species and changes in the abundances of common trematodes. The geographic distribution of suitable hosts for closing parasite life cycles is most likely responsible for the separation of a southern and a northern community. Thus, the scatter of shell forms was not reflected in the parasite assemblages, but a similarity to warm and cold temperate biogeographic provinces could be found. The biogeographic groups in the parasite fauna raise the question whether the intermediate host may share the same pattern in terms of subpopulations. Hence, another hidden diversity was under survey comparing the common barcoding sequence (5’ part of mitochondrial cytochrome c oxidase (COI)) for intraspecific variation of C. edule populations. Analyses revealed significant biogeographic clustering of cockle populations along the European shores. Among the 383 C. edule individuals studied, the occurrence of 79 sequence variants divided the distribution range in two large-scale geographic groups. These geographic clusters are similar to marine biogeographic provinces. The south-western group includes all cockles from Morocco to the British Isles while one Scottish population showed particular differences. The northern group comprises the Wadden Sea, Shetland Islands as well as the Norwegian Sea. Within this northern group, Skagerrak/Kattegat populations showed both regional sequence characters indicating a secondary contact zone or a glacial refuge. The Arctic population near Murmansk deviates from all others but shows some genetic connection to Norwegian populations. In contrast to studies on other marine species, higher genetic diversity was found in populations at high latitudes than in the southern populations. Northern cockle populations displayed a complex network of genetic structure, and analyses indicate a surprisingly old demographic age. This study revealed that European cockle populations exhibit a well structured pattern along the East Atlantic shore on two different levels, bivalve population genetics and the associated trematode assemblage. Morphological plasticity was not constant throughout the range, but varied without a clear large-scale geographical pattern. With this thesis study, I contribute to the knowledge of the large scale patterns of marine organisms endowed with pelagic larvae and corroborate the upcoming hypothesis that against expection, coastal invertebrates are not panmictic on continental scale. The extraordinary genetic pattern with indication for a northern refuge may provide a basis for further studies to clarify the influence of Pleistocene ice ages on coastal marine fauna and flora. Studies on physiological characteristics of cockles may reveal an adaptation of warm and cold temperate populations. Co-speciation of host and parasite with the possible development of subspecies may be discovered by a phylogeographic approach. A shift of biogeographic patterns is expected with global warming whereas local extinctions may reduce plasticity and diversity of coastal biota

Comparative phylogeography of two sister (congeneric) species of cardiid bivalve: Strong influence of habitat, life history and post-glacial history

International audienceSister (congeneric) species may exhibit disparate patterns of biogeographic genetic structures due to different life histories and habitat preferences. The common cockle Cerastoderma edule and the lagoon cockle Cerastoderma glaucum probably diverged from their common ancestor in the present territory of Sahara around 5 million years ago. Although it is difficult to separate both species morphologically, various genetic markers, both mitochondrial and nuclear, clearly distinguish them. Furthermore, their lifestyles are different, as C. edule has a much less fragmented coastal habitat and a longer duration of pelagic larval stage than C. glaucum. A comparative genetic analysis was conducted on 17 populations of C. edule and 13 populations of C. glaucum using a 506 bp fragment of mitochondrial DNA (COI).We tested the hypothesis that differences in habitat types and life history are reflected in the genetic structure patterns of these two cockles. Indeed substantial differences in population genetic structures between them are revealed. Genetic diversity within C. glaucum populations decreases northwards as a consequence of post-glacial (re)colonization from southern refugia, while C. edule displays an opposite pattern indicating survival in glacial refuges in the northern Atlantic. Among populations within geographic groups, genetic differentiation is low in C. edule, probably as a result of larval dispersal with coastal currents, while it is extremely high in C. glaucum, best explained by the fragmented habitats. Interestingly, long distance divergence is less expressed in C. glaucum than in C. edule, which supports the speculation that migrating birds (frequently observed in lagoons) may occasionally transport the former more often or more efficiently than the latter. The approach applied in this study (e.g., rarefaction procedure, selection of samples of both species from the same regions) enabled a new and reliable comparative analysis of the existing raw datasets

An efficient method to find potentially universal population genetic markers, applied to metazoans

<p>Abstract</p> <p>Background</p> <p>Despite the impressive growth of sequence databases, the limited availability of nuclear markers that are sufficiently polymorphic for population genetics and phylogeography and applicable across various phyla restricts many potential studies, particularly in non-model organisms. Numerous introns have invariant positions among kingdoms, providing a potential source for such markers. Unfortunately, most of the few known EPIC (Exon Primed Intron Crossing) loci are restricted to vertebrates or belong to multigenic families.</p> <p>Results</p> <p>In order to develop markers with broad applicability, we designed a bioinformatic approach aimed at avoiding multigenic families while identifying intron positions conserved across metazoan phyla. We developed a program facilitating the identification of EPIC loci which allowed slight variation in intron position. From the <it>Homolens </it>databases we selected 29 gene families which contained 52 promising introns for which we designed 93 primer pairs. PCR tests were performed on several ascidians, echinoderms, bivalves and cnidarians. On average, 24 different introns per genus were amplified in bilaterians. Remarkably, five of the introns successfully amplified in all of the metazoan genera tested (a dozen genera, including cnidarians). The influence of several factors on amplification success was investigated. Success rate was not related to the phylogenetic relatedness of a taxon to the groups that most influenced primer design, showing that these EPIC markers are extremely conserved in animals.</p> <p>Conclusions</p> <p>Our new method now makes it possible to (i) rapidly isolate a set of EPIC markers for any phylum, even outside the animal kingdom, and thus, (ii) compare genetic diversity at potentially homologous polymorphic loci between divergent taxa.</p

Workshop Summary: Environmental protection of the High North – How to protect the Arctic from afar?

The Arctic is home to unique habitats that are increasingly threatened by the effects of climate change and the release of pollutants. As the region warms up and becomes more accessible, also the planning and conduct of economic activities puts more stress on the region’s ecosystems. Due to the inevitable linkages between Arctic and non-Arc-tic regions, Arctic states and states that do not directly border Arctic regions are responsible to promote environmental protection of the region. The expert workshop aimed to enable exchange and discussion on how Arctic Council observers can engage strategically and practically in Arctic environmental protection. In an exchange with states that are active in the High North, indigenous communities, businesses, research, and civil society, potential solutions were developed for a sustainable development in the Arctic that allows reconciling a wide spectrum of interests in the region. Topics included in particular climate change and air pollution control, ship-ping, and tourism

Marine Strategy Framework Directive - Descriptor 2, Non-Indigenous Species, Delivering solid recommendations for setting threshold values for non-indigenous species pressure on European seas

Marine Non-Indigenous Species (NIS) are animals and plants introduced accidently or deliberately into the European seas, originating from other seas of the globe. About 800 marine non-indigenous species (NIS) currently occur in the European Union national marine waters, several of which have negative impacts on marine ecosystem services and biodiversity. Under the Marine Strategy Framework Directive (MSFD) Descriptor 2 (D2), EU Member States (MSs) need to consider NIS in their marine management strategies. The Descriptor D2 includes one primary criterion (D2C1: new NIS introductions), and two secondary criteria (D2C2 and D2C3). The D2 implementation is characterized by a number of issues and uncertainties which can be applicable to the Descriptor level (e.g. geographical unit of assessment, assessment period, phytoplanktonic, parasitic, oligohaline NIS, etc.), to the primary criterion D2C1 level (e.g. threshold values, cryptogenic, questionable species, etc), and to the secondary criteria D2C2 and D2C3. The current report tackles these issues and provides practical recommendations aiming at a smoother and more efficient implementation of D2 and its criteria at EU level. They constitute a solid operational output which can result in more comparable D2 assessments among MSs and MSFD regions/subregions. When it comes to the policy-side, the current report calls for a number of different categories of NIS to be reported in D2 assessments, pointing the need for the species to be labelled/categorised appropriately in the MSFD reporting by the MSs. These suggestions are proposed to be communicated to the MSFD Working Group of Good Environmental Status (GES) and subsequently to the Marine Strategy Coordination Group (MSCG) of MSFD. Moreover, they can serve as an input for revising the Art. 8 Guidelines

Molluscs in a coastal ecosystem: invaders infected by native parasites

MOLLUSCS IN A COASTAL ECOSYSTEM: INVADERS INFECTED BY NATIVE PARASITESM. KrakauAlfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt, Hafenstrasse 43, 25992 List, GermanyFollowing the Enemy Release Hypothesis, a lack of predators or pathogens let benefit introduced species leading to a competitive advantage over native species. In the European North Sea region, it has been assumed that introduced species of coastal ecosystems were not infested with metazoan parasites.Recent results show that only the introduced gastropod Crepidula fornicata was found to be free of trematodes. In contrast, native parasites, dominated by the trematode Renicola roscovita, infected the introduced bivalves Crassostrea gigas and Ensis americanus. However, when comparing these introduced species with native ones from the same locality, trematode intensity was always lower in the introduced bivalves.Implications for the coastal ecosystem will be presented concerning (1) the question whether introduced species do have an advantage over native species after invasion; (2) the influence of introduced bivalves affecting parasite populations, and (3) the natural infection pattern related to different susceptibility of the host organism. These results suggest that the Enemy Release Hypothesis may have to be modified in some cases

Diversity hot spots in the North? - Unexpected haplotype pattern for the marine bivalve Cerastoderma edule (L.)

We report on XMM-Newton observations of the “Black Widow pulsar”, PSR B1957+20. The pulsar's X-ray emission is non-thermal and best modeled with a single powerlaw spectrum of photon index $2.03^{+0.51}_{-0.36}$. No coherent X-ray pulsations at the pulsar's spin-period could be detected, though a strong binary-phase dependence of the X-ray flux is observed for the first time. The data suggest that the majority of the pulsar's X-radiation is emitted from a small part of the binary orbit only. We identified this part as being near to where the radio eclipse takes place. This could mean that the X-rays from PSR B1957+20 are mostly due to intra-shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star