Population genetic structure and identification of loci under selection in the invasive tunicate,Botryllus schlosseri,using newly developed EST-SSRs

Botryllus schlosseri, also known as golden star tunicate, is generally considered of European origin and has successfully invaded coastal waters of all continents except Antarctica. Owing to its significantly negative ecological impacts, it is crucial to understand its dispersal dynamics and mechanisms of invasion success. Here, we identified 1020 microsatellite-containing sequences from 98,626 expressed sequence tags (ESTs), and developed and characterized 17 polymorphic microsatellites (i.e. EST-SSRs) based on populations both from native (French coast) and invasive ranges (Canadian coast). The number of alleles, observed heterozygosity, and expected heterozygosity ranged from 2 to 12, 0.200 to 0.783, and 0.523 to 0.888 for the French population, and from 2 to 10, 0 to 0.524 and 0.043 to 0.827 for the Canadian population, respectively. We found significant population genetic differentiation between the native and invasive populations (pairwise F_ST = 0.1712). Moreover, principal coordinates analysis and Bayesian clustering test suggest long-distance dispersal between distant populations. When all loci were subjected for selection analyses, two loci (BS3244 and BS5339) were under selection based on the LOSITAN test. The results obtained in this study can help understand how ecological and evolutionary processes shape population genetic structure, and further how these processes contribute to invasion success.     

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.     

Regeneration of the epithelial lining of the stomach after autotomy of a disk in the brittle star Amphipholis kochii (Lütken) (Echinodermata: Ophiuroidea)

The regeneration of the epithelial lining of the stomach of the brittle star Amphipholis kochii after autotomy of the aboral part of the disk was studied. It was shown that a part of the stomach epithelium remained after autotomy. Its cells participated in regeneration of the epithelium during restoration of the lost digestive system. There was a partial dedifferentiation of the epithelium cells of stomach, their migration and proliferation; cells of the stomach retained some specialized cytoplasmic structures, secretory vacuoles, and pinocytic vesicles. Migration of ectodermal cells of the esophagus in the damaged area was also recorded.