THE IMPACT OF HEMOGLOBIN EXPRESSION ON CARDIOVASCULAR PHYSIOLOGY AND THERMAL TOLERANCE OF ANTARCTIC NOTOTHENIOID FISHES

THE IMPACT OF HEMOGLOBIN EXPRESSION ON CARDIOVASCULAR

PHYSIOLOGY AND THERMAL TOLERANCE OF ANTARCTIC NOTOTHENIOID FISHES

By Jody M. Beers

Thesis Advisor: Dr. Bruce D. Sidell

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Marine Biology)

August, 2010

            Antarctic fishes provide excellent opportunities to investigate evolutionary adaptations to chronically cold body temperature.  One family, the ‘icefishes’ or ‘white-blooded’ fishes, uniquely lacks hemoglobin (Hb), a protein used to transport oxygen in the blood.  These animals have compensated for absence of an oxygen carrier with a suite of cardiovascular modifications: large hearts with a lot of mitochondria, large blood volumes pumped through large diameter blood vessels, and high cardiac outputs.  This study examines a number of questions related to the cardiovascular physiology and biochemistry of icefishes, using a variety of methodologies at levels from experiments on the whole animal to those at the level of DNA.  

            I examined mechanisms driving formation of one of the unusual traits we see in icefishes today, a remarkably dense vasculature within their eyes compared to those of red-blooded Antarctic fishes.  Results indicate that vascular proliferation stimulated by the signaling molecule nitric oxide may have led to the remarkable pattern of blood vessels in eyes of Antarctic icefishes.  I also found that populations of mitochondria, the energy producing ‘power houses’ of the cell, within eyes of icefishes are particularly dense compared to those in red-blooded Antarctic fishes.  High numbers of mitochondria provide a lipid-rich membranous network that aids movement of oxygen in species having a reduced ability to transport oxygen because of the absence of Hb.  Organismal temperature sensitivities of Antarctic fishes reveal that the pattern of Hb expression in these animals influences the temperature limits at which they can survive.  Icefishes, in particular, are susceptible to acute elevations of temperature and my results support the hypothesis that oxygen may be the limiting factor in setting their maximum thermal limits. Thus, hemoglobinless icefishes may be sentinel species for climatic warming in the Antarctic region.  This research provides insights into several different physiological/biochemical processes that are fundamental to vertebrate animals and may have important applications to both biomedicine and problems associated with global climate change.