Genetic evidence supports recolonisation by Mya arenaria of western Europe from North America

The softshell clam Mya arenaria (L.) is currently widespread on the east and west coasts of North America. This bivalve also occurs on western European shores, where the post-Pleistocene origin of the species, whether introduced or relict, has been debated. We collected 320 M. arenaria from 8 locations in Europe and North America. Clams (n = 84) from 7 of the locations were examined for mitochondrial DNA variation by sequencing a section of the cytochrome oxidase 1 (COX1) gene. These were analysed together with 212 sequences, sourced from GenBank, from the same gene from 12 additional locations, chiefly from eastern North America but also 1 site each from western North America and from western Europe. Ten microsatellite loci were also investigated in all 320 clams. Nuclear markers showed reduced levels of variation in certain European samples. The same common COX1 haplotypes and microsatellite alleles were present throughout the range of M. arenaria, although significant differences were identified in haplotypic and allelic composition between many samples, particularly those from the 2 continents (Europe and North America). These findings support the hypothesis of post-Pleistocene colonisation of European shores from eastern North America (and the recorded human transfer of clams from the east to the west coast of North America in the 19th century)

Other Disorders

6 pages, 6 figures.-- This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International LicenseNeoplasia are growth disturbances characterized by excessive, abnormal proliferation of cells, independent of normal-regulating mechanisms of the animal and persisting after termination of the stimulus that initiated growth. Over lasts years there has been an increase in research into tumors of invertebrates. In cephalopods, reports on the incidence of the tumors or neoplasia are scarce. They have been described as hard compact and homogeneous nodules of connective tissue located in the mantle or at the base of suckers. The aetiological origin of tumors observed in cephalopods is unknown, but it could be related to aquarium maintenance. Other injurious agents, including infectious (virus, bacteria, or parasites) and xenobiotics, may also have produced the lesions. In occasions inflammatory processes have been associated with tumors with severe oedema associated. Inflammation is part of the biological response to body tissues to harmful stimuli such as pathogens, damaged cells or effect of xenobiotics. The inflammatory focus is characterized by exudation with interstitial fluid changes and hemocytic migration. Some inflammatory lesions include fibrosis and necrotic cells in the affected area, with loss of histological features and even organ architecture. All this changes have been observed in cephalopods in inflammatory reactions originated by infection with different pathogens. The chapter covers a selection of the reported cases of disorders related to neoplasia and inflammationPeer reviewe

Bonamia ostreae in the Native Oyster Ostrea edulis

Ireland has a long history of producing and harvesting native flat oysters, Ostrea edulis. At the start of the nineteenth century, almost every bay and harbour, around the coast had abundant beds of native oysters. Intensive dredging to meet the demands of the markets in Dublin and England depleted the stocks, so that in 1845 the government passed legislation to permit the formation of private oyster beds to improve the ailing stocks. According to the book on “Shellfish & Shellfisheries of Ireland” (Wilkins, 2004) Irish stocks began to collapse between 1850 and 1860. By the second half of the twentieth century, only the beds of Tralee Bay, Galway Bay and Clew Bay were still yielding a good return for local fishermen. The arrival of the oyster parasite Bonamia ostreae in the mid 1980s was an additional blow to the Irish native oyster stocks. This report sets out to document the spread and the impact of the Bonamia ostreae parasite in Irish bays since the 1980s.Funder: Marine Institut

Susceptibility of a number of bivalve species to the protozoan parasite Bonamia ostreae and their ability to act as vectors for this parasite

8 pages, 1 figure, 7 tables.The protozoan parasite Bonamia ostreae (Pichot et al., 1980) is a serious pathogen of the native European flat oyster Ostrea edulis. Field and laboratory based experiments were carried out in Ireland and Spain to investigate the susceptibility to this protozoan of the Pacific oyster Crassostrea gigas, the mussels Mytilus edulis and Mytilus galloprovincialis, the European native clam Ruditapes decussatus and the Manila clam Ruditapes philippinarum. Their ability to act as vectors or intermediate hosts was also investigated. The study corroborated previous findings that demonstrated that flat oysters can be successfully infected both naturally in the field and experimentally in the laboratory, and the pathogen can be transmitted directly between flat oysters in the laboratory. However, the other bivalves tested could not be infected with the parasite either naturally or experimentally, and these bivalves did not appear to act as vectors or intermediate hosts for the parasite. These results have implications for movements of bivalves between areas within the European Union.This work was supported by European Union FAIR contract 94C 85/13.Peer reviewe

The Reproductive Biology of the Softshell Clam, Mya arenaria, in Ireland, and the Possible Impacts of Climate Variability

Little is known about the biology of the softshell clam in Europe, despite it being identified as a potential species to culture for food in the future. Monthly samples of the softshell clam, Mya arenaria, were collected intertidally from Co. Wexford, Ireland, over a period of sixteen months. The mean weight of sampled individuals was 74±4.9 g and mean length was 8.2±0.2 cm. Histological examination revealed a female-to-male ratio of 1 : 1.15. In 2010, M. arenaria at this site matured over the summer months, with both sexes either ripe or spawning by August. A single spawning event was recorded in 2010, completed by November. Two unusually cold winters, followed by a warmer-than-average spring, appear to have affected M. arenaria gametogenesis in this area, potentially affecting the time of spawning, fertilisation success, and recruitment of this species. No hermaphrodites were observed in the samples collected, nor were any pathogens observed. Timing of development and spawning is compared with the coasts of eastern North America and with other European coasts

Transcriptomic profile and targeted genotyping on OsHV-1 resistant and susceptible Crassostrea gigas

19th International Conference on Diseases of Fish and Shellfish, Porto,Portugal, 09 - 12 September, 2019Peer reviewe

Identification of molecular markers associated to OsHV-1 resistance in Crassostrea gigas

Póster.-- 113th Annual Meeting National Shellfisheries Association, Virtual Conference, March 22 – 25, 2021Significant mortalities have been regularly occurring in the Pacific oyster, Crassostrea gigas, associated with the incidence of OsHV-1 and impacting the aquaculture production at a global level. Long-term solutions such as the selection of resistant strains and the identification of molecular markers have been postulated as prioritizing strategies by the scientific community. In this context, the information gathered by novel sequencing methodologies offers new perspectives for the study of non-model species. RNA-seq data previously carried out for comparison of C. gigas spat with different susceptibility was further analysed for potential molecular markers examination. For that, read mappings corresponding to differently expressed transcripts were manually checked for variant localization. Validation of potential polymorphisms was carried out in oyster families produced by single pair matting of adult animals with different susceptibility to OsHV-1. Families were naturally exposed to OsHV-1 in a culturing raft and after a mortality outbreak; survivors were collected and compared to initial samples. A total of 461 animals were genotyped by sequencing using individual barcoding identification for multiplex amplification. Twelve transcripts containing 30 nucleotide variants were analysed. Among them, 18 variants were real single nucleotide polymorphisms (SNPs). The allele frequencies significantly varied in 10 loci on resistant families and 5 loci on susceptible families. Moreover, two linked SNPs were also significantly different attending to the disease susceptibility features of the broodstock. These results showed the identification of two linked molecular markers that can be used in selective breeding programmes.N