Molecular Responses to Thermal and Osmotic Stress in Arctic Intertidal Mussels (Mytilus edulis): The Limits of Resilience

Increases in Arctic temperatures have accelerated melting of the Greenland icesheet, exposing intertidal organisms, such as the blue mussel Mytilus edulis, to high air temperatures and low salinities in summer. However, the interaction of these combined stressors is poorly described at the transcriptional level. Comparing expression profiles of M. edulis from experimentally warmed (30 °C and 33 °C) animals kept at control (23‰) and low salinities (15‰) revealed a significant lack of enrichment for Gene Ontology terms (GO), indicating that similar processes were active under all conditions. However, there was a progressive increase in the abundance of upregulated genes as each stressor was applied, with synergistic increases at 33 °C and 15‰, suggesting combined stressors push the animal towards their tolerance thresholds. Further analyses comparing the effects of salinity alone (23‰, 15‰ and 5‰) showed high expression of stress and osmoregulatory marker genes at the lowest salinity, implying that the cell is carrying out intracellular osmoregulation to maintain the cytosol as hyperosmotic. Identification of aquaporins and vacuolar-type ATPase transcripts suggested the cell may use fluid-filled cavities to excrete excess intracellular water, as previously identified in embryonic freshwater mussels. These results indicate that M. edulis has considerable resilience to heat stress and highly efficient mechanisms to acclimatise to lowered salinity in a changing world.

Of Lemmings and Mussels: Trophic Cascade Drives Population Dynamics of Long-Tailed Ducks Breeding in Siberia

Migratory animals experience very different environmental conditions at different times of the year, i.e., at the breeding grounds, during migration, and in winter. The long-tailed duck Clangula hyemalis breeds in the Arctic regions of the northern hemisphere and migrates to temperate climate zones, where it winters in marine environments. The breeding success of the long-tailed duck is affected by the abundances of predators (mainly Arctic fox Alopex lagopus) and their main prey species, lemmings Lemmus sibiricus and Dicrostonyx torquatus, whose population fluctuation is subject to climate change. In the winter quarters, long-tailed ducks mainly eat the blue mussel Mytilus edulis. We examined how North-west Siberian lemming dynamics affect long-tailed duck breeding success via predation pressure and how nutrient availability in the Baltic Sea influences long-tailed duck population size via mussel biomass and quality. The long-tailed duck population dynamics was predator-driven on the breeding grounds and resource-driven on the wintering grounds. Nutrients from fertilizer runoff from farmland stimulate mussel stocks and quality, supporting high long-tailed duck population sizes. The applied hierarchical analysis combining several trophic levels can be used for evaluating large-scale environmental factors that affect the population dynamics and abundance of migrants from one environment to another.

High genetic diversity of bivalve transmissible neoplasia in the blue mussel Mytilus trossulus Gould from the subarctic Sea of Okhotsk

There are increasing findings of the bivalve transmissible neoplasia derived from the Pacific mussel Mytilus trossulus (MtrBTN) in populations of different Mytilus species worldwide. The Subarctic is an area where this disease has not yet been sought despite the fact that Mytilus spp. are widespread there, and M. trossulus itself is a boreal species. We used cytological and histological techniques to diagnose disseminated neoplasia in a sample of M. trossulus from Magadan in the subarctic Sea of Okhotsk. Neoplasia was identified in 11 of 214 mussels studied. Using mtDNA COI sequencing, we revealed genotypes identical or nearly identical to known MtrBTN ones in the hemolymph of most of the diseased mussels. Both MtrBTN evolutionary lineages have been identified, the widespread MtrBTN2, and MtrBTN1, so far only known from M. trossulus in British Columbia on the other side of the Pacific from Magadan. In addition, MtrBTN2 was represented by two common diverged mtDNA haplolineages. These conclusions have been confirmed for selected cancerous mussels by molecular cloning of COI and additional nuclear and mtDNA genes. On the background of high genetic diversity, different cancers were similar in terms of ploidy (range 4.0 - 5.8n) and nuclear to cell ratio. Our study provides the first description of neoplasia and MtrBTN in mussels from the Sea of Okhotsk and from the Subarctic, of both MtrBTN1 and MtrBTN2 in the same mussel population, and the first direct comparison between these transmissible cancers.

The distribution and relative abundance of the invasive Northern blue mussel, M. galloprovincialis, in New Zealand: management implications

<p>Biological invasions are a growing problem on a global scale, are capable of causing moderate to severe damage, and are most often associated with human activity. This is particularly true in the marine environment, where there are many well documented cases of non-indigenous species (NIS) spreading via maritime traffic or undergoing a range expansion associated with ocean temperatures continuing to increase. The blue mussel Mytilus galloprovincialis, recognized a one of the most successful NIS globally, is one such species that is spreading in such ways. However, in the Southern hemisphere research over the past decade has shown that there are two lineages of M. galloprovincialis present, likely different species, one native to the Northern hemisphere and one native to the Southern hemisphere. In New Zealand, the Northern lineage of M. galloprovincialis (MgN) has successfully invaded and poses a unique threat to native biodiversity as there are higher rates of introgression with the native Southern lineage of M. galloprovincialis (MgS) than elsewhere in the Southern hemisphere. However, whether MgN is causing other ecological damage in New Zealand is still unknown. Therefore, the main objective of Chapter 2 is to provide a preliminary description of the distribution and relative abundance of MgN in New Zealand, and how abiotic factors may be influencing this invasion. Also, it was recently reported that M. galloprovincialis causes severe economic losses to the native greenshell mussel Perna canaliculus aquaculture industry. However, these reports did not differentiate between the native and invasive blue mussel lineages. The main objective of Chapter 3 then is to provide a description of the distribution and relative abundance of MgN in the Marlborough Sounds, the primary P. canaliculus aquaculture region in New Zealand. The results of Chapter 2 indicate that several abiotic factors significantly influence the relative abundance of MgN across New Zealand; and that intranational maritime traffic is a more important vector of spread than international maritime traffic. The results of Chapter 3 show that the relative abundance of MgN was approximately equal across aquaculture facility sites and adjacent shore sites, but that increased habitat space on the grow-lines of aquaculture facilities has resulted in significantly increased overall abundances of both MgN and MgS. This means that there is a much larger MgN population in this region than would be otherwise present due to the aquaculture facilities. Overall, these results indicate that human activity in New Zealand is significantly affecting the MgN invasion therein. These findings are important for both management purposes and for guiding future research.</p>

The distribution and relative abundance of the invasive Northern blue mussel, M. galloprovincialis, in New Zealand: management implications

<p>Biological invasions are a growing problem on a global scale, are capable of causing moderate to severe damage, and are most often associated with human activity. This is particularly true in the marine environment, where there are many well documented cases of non-indigenous species (NIS) spreading via maritime traffic or undergoing a range expansion associated with ocean temperatures continuing to increase. The blue mussel Mytilus galloprovincialis, recognized a one of the most successful NIS globally, is one such species that is spreading in such ways. However, in the Southern hemisphere research over the past decade has shown that there are two lineages of M. galloprovincialis present, likely different species, one native to the Northern hemisphere and one native to the Southern hemisphere. In New Zealand, the Northern lineage of M. galloprovincialis (MgN) has successfully invaded and poses a unique threat to native biodiversity as there are higher rates of introgression with the native Southern lineage of M. galloprovincialis (MgS) than elsewhere in the Southern hemisphere. However, whether MgN is causing other ecological damage in New Zealand is still unknown. Therefore, the main objective of Chapter 2 is to provide a preliminary description of the distribution and relative abundance of MgN in New Zealand, and how abiotic factors may be influencing this invasion. Also, it was recently reported that M. galloprovincialis causes severe economic losses to the native greenshell mussel Perna canaliculus aquaculture industry. However, these reports did not differentiate between the native and invasive blue mussel lineages. The main objective of Chapter 3 then is to provide a description of the distribution and relative abundance of MgN in the Marlborough Sounds, the primary P. canaliculus aquaculture region in New Zealand. The results of Chapter 2 indicate that several abiotic factors significantly influence the relative abundance of MgN across New Zealand; and that intranational maritime traffic is a more important vector of spread than international maritime traffic. The results of Chapter 3 show that the relative abundance of MgN was approximately equal across aquaculture facility sites and adjacent shore sites, but that increased habitat space on the grow-lines of aquaculture facilities has resulted in significantly increased overall abundances of both MgN and MgS. This means that there is a much larger MgN population in this region than would be otherwise present due to the aquaculture facilities. Overall, these results indicate that human activity in New Zealand is significantly affecting the MgN invasion therein. These findings are important for both management purposes and for guiding future research.</p>

Using neutral and outlier loci to uncover the genetic structure of 'Mytilus galloprovincialis' populations from the eastern Adriatic coast using population genetic and seascape genetic approaches

<p>The genetic variation of the Mediterranean blue mussel, Mytilus galloprovincialis from the eastern coastline of the Adriatic Sea was investigated using polymorphic microsatellite markers. In total, 843 individuals were sampled from 18 populations representing a variety of coastal environments in Croatia, Bosnia-Herzegovina, Montenegro and Albania. Neutral loci revealed low levels of genetic structure in this continuously distributed species, while one outlier locus, MGE7, which may be under selection, provided strong evidence of genetic structure. The distribution of one of the alleles of this locus, MGE7²⁴³, was significantly correlated with latitude. A genetic seascape analysis using 9 environmental and 3 geospatial variables revealed a strong association between MGE7²⁴³ and three highly correlated environmental variables, maximum sea surface temperature, minimum salinity and maximum chlorophyll-a. This association was maintained for homozygous genotypes for the MGE7²⁴³ allele, but not for heterozygotes, providing further evidence that the locus MGE7 may be under selection or closely linked to a gene under selection. These findings highlight how previously unrecognised genetic structure can be identified through the use of genetic seascape approaches.</p>

Using neutral and outlier loci to uncover the genetic structure of 'Mytilus galloprovincialis' populations from the eastern Adriatic coast using population genetic and seascape genetic approaches

<p>The genetic variation of the Mediterranean blue mussel, Mytilus galloprovincialis from the eastern coastline of the Adriatic Sea was investigated using polymorphic microsatellite markers. In total, 843 individuals were sampled from 18 populations representing a variety of coastal environments in Croatia, Bosnia-Herzegovina, Montenegro and Albania. Neutral loci revealed low levels of genetic structure in this continuously distributed species, while one outlier locus, MGE7, which may be under selection, provided strong evidence of genetic structure. The distribution of one of the alleles of this locus, MGE7²⁴³, was significantly correlated with latitude. A genetic seascape analysis using 9 environmental and 3 geospatial variables revealed a strong association between MGE7²⁴³ and three highly correlated environmental variables, maximum sea surface temperature, minimum salinity and maximum chlorophyll-a. This association was maintained for homozygous genotypes for the MGE7²⁴³ allele, but not for heterozygotes, providing further evidence that the locus MGE7 may be under selection or closely linked to a gene under selection. These findings highlight how previously unrecognised genetic structure can be identified through the use of genetic seascape approaches.</p>