The biogeography and ecology of myelin in marine copepods

Abstract

Calanoid copepods are ubiquitous in marine environments, where they are an abundant component of the plankton. Interestingly, this crustacean group is characterized by the co-existence of myelinate and amyelinate species. Myelin greatly enhances nervous system function, but requires the production and maintenance of large amounts of cell membranes. The role that myelin plays in the distribution and ecology of calanoids has not been investigated, yet should be significant given the costs and benefits of the adaptation. Surveying the available literature, habitats and ecological zones were identified, and calanoid species were categorized as either myelinate or amyelinate based on phylogeny. The diversity and abundance of the two types of calanoids were determined and compared to an expected ratio of 1:1. Myelinate taxa were predominant in oceanic epipelagic regions at all latitudes, while a majority of vertically migrating mesopelagic calanoids were amyelinate. Temperate and tropical estuaries were typically less diverse, with communities dominated by amyelinate calanoids. However, in many sub-tropical estuaries, myelinate species comprised >80 of the calanoid population. An enhanced escape response and savings in energy may promote the success of myelinate calanoids in habitats characterized by high predation risk and low standing stocks of phytoplankton. Environments with low food quality may favor amyelinate species, given the cost of producing large quantities of lipid-rich membranes. © 2012 The Author. Published by Oxford University Press. All rights reserved.