Catadromous Eels of the North Atlantic: A Review of Molecular Genetic Findings Relevant to Natural History, Population Structure, Speciation, and Phylogeny

Abstract

The North Atlantic is home to two recognized species of “freshwatereels” (Fig. 1): Anguilla Rostrata of the Americas, and A. anguilla of Europe and North Africa. Like the approximately 13 other named Anguilla species of the western Indo-Pacific region (Ege 1939; Jellyman 1987; Nelson 1994), Atlanticeels have a catadromous life cycle, spending most of their lives in estuarine or inland waters, but, on reaching sexual maturity, migrating far out to sea for a once-in-a-lifetime (semelparous) spawn (Bertin 1957; Tesch 1977; but see also Tsukamoto et al. 1998). This peculiar life history has raised a number of interesting ecological and evolutionary questions. Does spawning byeels in the open sea occur at random with respect to the coastal localities from which the adults had emigrated? Does the dispersal of larvae back to North America and Europe occur in ways that genetically homogenize continental populations across vast geographic areas? How does speciation occur within the context of this diadromous life cycle? Do different morphological forms of Atlanticeels hybridize? How and when dideels colonize the Atlantic from their probable ancestral homeland in the Indo-Pacific? This review examines how molecular genetic data from polymorphic markers have contributed to a current understanding of the natural history and evolution of Atlanticeels.

As the young moved shoreward, there passed beneath them another host ofeels, another generation come to maturity and clothed in the black and silver splendor ofeels returning to their first home. They must have passed without recognition —these two generations ofeels— one on the threshold of a new life; the other about to lose itself in the darkness of the deep sea.

Rachel Carson, 1941.