Abstract
The enigmatic life cycle and elongated body of the European eel (Anguilla anguilla L., 1758) have long motivated scientific enquiry. Recently, eel research has gained in urgency, as the population has dwindled to the point of critical endangerment. We have assembled a draft genome in order to facilitate advances in all provinces of eel biology. Here, we use the genome to investigate the eel's complement of the Hox developmental transcription factors. We show that unlike any other teleost fish, the eel retains fully populated, duplicate Hox clusters, which originated at the teleost-specific genome duplication. Using mRNA-sequencing and in situ hybridizations, we demonstrate that all copies are expressed in early embryos. Theories of vertebrate evolution predict that the retention of functional, duplicate Hox genes can give rise to additional developmental complexity, which is not immediately apparent in the adult. However, the key morphological innovation elsewhere in the eel's life history coincides with the evolutionary origin of its Hox repertoire.
Highlights
The life history of the European eel (Anguilla anguilla L., 1758) involves two distinct ocean-dwelling larval stages, a protracted juvenile phase in European continental freshwater, and sexual maturation coincident with migration to spawning grounds in the Atlantic Ocean, presumably the Sargasso Sea (Figure 1) [1]
Long life, serious habitat reduction, pollution, and overfishing may be amongst the causes of the catastrophic collapse of the European eel population observed over the past decades [7]
Genome assembly of the European eel We have sequenced and assembled the genome of a female juvenile A. anguilla specimen caught in the brackish Lake Veere, the Netherlands in December 2009
Summary
The life history of the European eel (Anguilla anguilla L., 1758) involves two distinct ocean-dwelling larval stages, a protracted juvenile phase in European continental freshwater, and sexual maturation coincident with migration to spawning grounds in the Atlantic Ocean, presumably the Sargasso Sea (Figure 1) [1]. The complexity and geographical range of this life cycle have long inspired evolutionary and physiological studies, especially on the structure of the eel’s single, randomly mating (panmictic) population [2], interspecific hybridization with the American eel (A. rostrata, which shares the same oceanic spawning grounds [3]), its hidden migrations [4,5,6], and the development of fertility [6]. In order to alleviate this shortcoming, we have sequenced and assembled its genome
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