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Lamprey metamorphosis

Author(s): Manzon RG, Youson JH, Holmes JA

Abstract

Among vertebrates, true metamorphosis is restricted to amphibians, two groups of bony fishes, and lampreys. This chapter provides a comprehensive review of the ecology, morphology, physiology, and molecular biology of lamprey metamorphosis. The lamprey life cycle includes an embryonic period, a larval period ending with metamorphosis, a parasitic or non-parasitic juvenile period, and an adult reproductive period. Lamprey metamorphosis is influenced by endogenous and exogenous factors, most significantly a rise in spring water temperature, the accumulation of sufficient lipid reserves for the non-trophic metamorphic phase, and thyroid hormones. In lampreys, thyroid hormones appear to have a dual role, whereby high levels promote larval growth and a subsequent sharp decline is important for development and metamorphosis. As with other true metamorphoses, dramatic biochemical, cellular, and morphological changes occur during lamprey metamorphosis. The external changes are striking and include the development of an oral (suctorial) disc and eyes, restructuring of the branchial region, and changes in the fins and body coloration. Internal changes include major modifications to the digestive system (new esophagus, remodeled intestine, and loss of hepatic biliary tree and gall bladder). The larval kidneys regress while the definitive juvenile kidney develops de novo. Numerous changes are also observed in the respiratory and skeletal systems in preparation for the juvenile and spawning periods.

KeywordsCondition factorHypothalamic-pituitaryLife historyLipidMetamorphosisTemperatureThyroid hormones

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