The effect of social context and reproductive status on the metabolic rates of dwarf seahorses (Hippocampus zosterae)

Although we are beginning to understand the conditions in which monogamy is favored over a more promiscuous lifestyle, little is known about the proximate effects of monogamous pair bonding, and subsequent reproduction, on general metabolism. I determined the effects of these factors on the metabolic rates of dwarf seahorses (Hippocampus zosterae), recognized for their monogamous lifestyle and unique male care of offspring, in a sealed brood pouch where embryos develop until birth. Resting routine oxygen consumption rates were measured in newly-paired and reproductive adults using a continuous flow respirometer, and then compared to metabolic rates of sexually-isolated fish. Sex differences were observed in the relationship between log(10)mass and log(10)oxygen consumption, with pair-bonded females exhibiting a significantly higher slope than either pair-bonded males, or sexually-isolated fish. Mass-specific metabolic rates in sexually-isolated fish were 15% higher than in pair-bonded fish, indicating that social conditions can strongly influence metabolic rate. Specific metabolic rates only differed by gender during male pregnancy, when male metabolic rate increased from 10 to 52% over pre-gravid levels. A male's developing brood only explained 4-31% of this increase, suggesting that increased metabolic demands on fathers accounts for most of the increase in metabolic rate during gestation. This study suggests that pair bonding can strongly affect the general metabolism of organisms, with potential differences between males and females that increase with age. (C) 2001 Elsevier Science Inc. All rights reserved.