Khaitov, V. | Search bioRxiv

bioRxiv2023

Molecular diversity of bivalve transmissible neoplasia of blue mussels in the Kola Bay (Barents Sea) indicates a recent migration of the cancer lineages between the North Pacific and Northern Europe

Bivalve transmissible neoplasia (BTN) is a leukemia-like cancer "metastasizing" by transmission of living cancer cells between molluscs. Blue mussels harbor two evolutionary lineages of BTN, MtrBTN1 and MtrBTN2, both derived from Mytilus trossulus. While MtrBTN1 has been found only in M. trossulus in North Pacific, MtrBTN2 parasitizes different Mytilus species worldwide, particularly in Western Europe. No targeted studies of BTN in Northern European mussels (M. edulis, M. trossulus) have been made. We searched for BTN in mussels from the Kola Bay (Barents Sea) with the help of flow cytometry of the hemolymph, qPCR with primers specific to cancer-associated alleles and sequencing of mitochondrial and nuclear loci. The species of the mussel hosts was ascertained genetically. Both MtrBTN1 and MtrBTN2 were present in our material, though their prevalence was low ([~]0.4%). The only instance of MtrBTN2 was found in M. trossulus. MtrBTN1 occurred in M. trossulus and in a hybrid between M. trossulus and M. edulis. This finding indicates that MtrBTN1 may potentially infect the latter species. The mtDNA haplotypes found in both lineages were nearly identical to those known from the North Pacific, but not from elsewhere. Our results suggest that they arrived in the Kola Bay fairly recently, probably with the maritime transport along the Northern Sea Route, and that the invasion was independent of that in Western Europe. A relatively young evolutionary age of MtrBTN1 seems to suggest that it is an emerging disease in the process of niche expansion.

evolutionary biology↗

bioRxiv2022

Taxonomically mixed blue mussel Mytilus populations are spatially heterogeneous and temporally unstable in the subarctic Barents Sea

Subarctic populations of blue mussels represented by "cryptic" species Mytilus edulis (ME) and M. trossulus (MT) have been studied less intensively than Arctic and boreal populations. Ecological features of ME and MT in sympatry are poorly known everywhere. The knowledge about mussels at the northeasternmost boundary of the Atlantic littoral communities on Murman coast of the Barents Sea is based on data obtained 50-100 years ago. Our study provides the first insight into the long-term dynamics of the Barents Sea mussels, the habitat segregation of ME and MT, and the interannual dynamics of their mixed settlements. The Tyuva Inlet (Kola Bay), which is 3 km long, was used as the study site. Mussels were found everywhere in the littoral and the sublittoral down to a depth of 4 m. Their characteristic habitats were sandbanks, littoral rocks, sublittoral kelp forests and "the habitat of the mussel bed" in the freshened top of the inlet. The main spatial gradients explaining the variability of demographics of the settlements (abundance, age structure, size) were associated with the depth and the distance from the inlet top. ME and MT were partially segregated by depth: ME dominated in the sublittoral and MT, in the littoral. In addition, ME dominated both in the littoral and in the sublittoral parts of the mussel bed. The ratio of species in the mixed settlements varied over time: between 2004 and 2010 the proportions of MT decreased everywhere, by 22 % on average. Historical data indicate that the abundance of the Murman mussels declined sharply between the 1960s and the 1970s, which coincided with the cooling of the Arctic. It seems that the populations have not completely recovered in the abnormally warm recent decades. The habitat distribution of mussels apparently changed with time, too: unlike today, in the 20th century mussels were rarely observed in kelps. We suggest that the spatial and temporal dynamics of subarctic mussels can be partly explained by the competition between ME and MT combined with their differing sensitivity to environmental factors.

ecology↗