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Mei-chen Tseng – One of the best experts on this subject based on the ideXlab platform.
Evolution of microsatellite Loci of tropical and temperate Anguilla Eels.International journal of molecular sciences, 2012Co-Authors: Mei-chen TsengAbstract:
Anguilla Eels are divided into temperate and tropical Eels, based on their major distributions. The present study collected two temperate Eels, Anguilla japonica and Anguilla Anguilla, and two tropical Eels, Anguilla marmorata and Anguilla bicolor pacifica, to examine two questions: do temperate and tropical Anguilla Eels have different genetic polymorphic patterns?; and do temperate Anguilla japonica and Anguilla Anguilla have a closer relationship to each other than to tropical Eels? In total, 274 sequences were cloned and sequenced from six conserved microsatellite loci to examine polymorphic patterns of these four catadromous Eels. Different mutational events, including substitutions, and repeat-unit deletions and insertions, appeared in major regions, while different point mutations were observed in flanking regions. The results implied that parallel patterns of microsatellite sequences occurred within both tropical and temperate freshwater Eels. Consensus flanking sequences of six homologous loci from each of the four species were constructed. Genetic distances ranged from 0.044 (Anguilla bicolor pacifica vs. Anguilla marmorata) to 0.061 (Anguilla marmorata vs. Anguilla Anguilla). The tree topology suggests the hypothesis of Anguilla japonica and Anguilla Anguilla being a sister group must be rejected.
David K. Cone – One of the best experts on this subject based on the ideXlab platform.
What metazoan parasites tell us about the evolution of American and European EelsEvolution; international journal of organic evolution, 1993Co-Authors: David J. Marcogliese, David K. ConeAbstract:
Two hypotheses have been forwarded to explain the divergence of American (Anguilla rostrata) and European (Anguilla Anguilla) Eels from a common ancestor. The “oceanic” hypothesis proposes that Eels formerly inhabited either North America or Europe. Divergence occurred on the spawning grounds in the Sargasso Sea, with new oceanic currents arising during the Pleistocene carrying leptocephalid larvae to the new continent. The “vicariant” hypothesis proposes that an ancestral eel population inhabited the North Atlantic regions, including Greenland, Iceland, and Scandinavia. This population was forced southwards by the Pleistocene glaciation and separated into European and American components. Examination of the freshwater metazoan parasite fauna specific to Eels on both continents forces rejection of the “oceanic” hypothesis. Six parasites specific to Eels (Gyrodactylus Anguillae, Pseudodactylogyrus Anguillae, Bothriocephalus claviceps, Proteocephalus macrocephalus, Daniconema Anguillae, Paraquimperia tenerrima) infect Eels in freshwaters of both Europe and North America. This transcontinental distribution of freshwater parasites specific to Eels is incompatible with an oceanic separation of Eels on the spawning grounds, because adult Eels die after spawning and leptocephalid larvae cannot acquire these parasites at sea. The disjunct distribution of these parasites implies that at one time their ranges were continuous, thus supporting the “vicariant” speciation hypothesis. The American eel, Anguilla rostrata (LeSueur), and the European eel, Anguilla Anguilla (L.), are sister species inhabiting separate continents. They differ only in the number of vertebrae, the frequency of certain enzymatic alleles, and the frequency of several restriction endonucleases in the mtDNA genotype (Avise et al. 1986, 1990). Although it has been established that these Eels are distinct populations, some doubt exists as to whether they constitute distinct biological species (Williams and Koehn 1984). Although Anguillidae is an ancient family, the fossil record is virtually nonexistent (Cavender 1986). The earliest known Anguilla in North America dates from the late Pleistocene, while in Europe, to the Upper Miocene (Cavender 1986). These findings, together with the close relatedness of the sisterspecies Anguilla rostrata and Anguilla Anguilla, suggest that the two species were recently separated. Both species grow in coastal, estuarine, and freshwater habitats, and then undergo a spawning migration to the southwestern Sargasso Sea, where they spawn in a largely overlapping area (McCleave et al. 1987). Leptocephalid larvae migrate to the continent of parental origin, partially by passive dispersal in oceanic currents. The nature of their sympatric spawning grounds has created difficulty in determining the origin of the two species. Two contrasting hypotheses have been forwarded recently to explain the divergence of these two anguilliforms from a common ancestral stock and to account for their present distributions (Avise et al. 1990). The “oceanic” hypothesis states that Eels were native only to one side of the Atlantic, that is, Europe or North America (Avise et al. 1990). During the Pleistocene epoch, changes in ocean currents occurred that carried some eel larvae from the spawning grounds in the Sargasso Sea to the new continent. These Eels matured in the new habitat and returned to the spawning grounds. However, as they migrated from a new direction, that of the newly colonized continent,
Patrice Couture – One of the best experts on this subject based on the ideXlab platform.
Biotransformation, antioxidant and histopathological biomarker responses to contaminants in European and American yellow Eels from the Gironde and St. Lawrence estuariesChemosphere, 2017Co-Authors: Géraldine Patey, Catherine M. Couillard, Fabien Pierron, Magalie Baudrimont, Patrice CoutureAbstract:
Since the early 1980s, populations of American (Anguilla rostrata) and European Eels (Anguilla Anguilla) have suffered a sharp decline. The causes of their decline are likely multifactorial and include chemical pollution. A field study was conducted in eight sites varying in organic and metal contamination along the St. Lawrence (Eastern Canada) and Gironde (France) systems to investigate the relationships among contaminants, biological characteristics and biotransformation, antioxidant and histopathological biomarkers in Eels from both species. For A. rostrata, no major influences of persistent organic contaminants on biomarkers were identified. For A. Anguilla, Eels from the most contaminated site expressed higher surface of MelanoMacrophage Centers (MMCs) and Eels from another contaminated site expressed higher amount of spleen lipofuscin pigment. These two histopathological biomarkers were also associated with aging. Compared to Eels from the cleanest French site, higher hepatic catalase activity and density of MMC in Eels from contaminated sites was related to higher concentration of organic (DDT and metabolites, sum of PCBs, sum of PBDEs) and inorganic (Hg and Cd) contaminants. In both species, a higher deposition of spleen hemosiderin pigment was measured in Eels from the most brackish sites compared to Eels living in freshwater environments. Our results suggest an association between higher hemosiderin pigment and metal contamination (As for A. Anguilla and Pb for A. rostrata). Parasitism by A. crassus was observed in European Eels from freshwater sites but not in Eels from brackish habitats. Overall, contamination may pose a greater risk for the health of European compared to American Eels.