Developmental and Oxygen Consumption Rate Differences between Lactate Dehydrogenase-B Genotypes of Fundulus heteroclitus and Their Effect on Hatching Time

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Abstract
Recently, we reported that genetic variation at the lactate dehydrogenase-B (LDHB) locus of Fundulus heteroclitus is highly correlated with hatching time. In the present study, we explore several mechanisms which may be responsible for this correlation. Since hypoxia-induced hatching occurs when oxygen diffusion limits the metabolic rate of embryos, we tested the hypothesis that LDH-B genotype specific hatching times are the result of metabolic rate differences. While the hypothesis was correct, each genotype appears to receive the hypoxic hatching cue at the same time because the genotype with the higher metabolic rate ( ) was able to bind oxygen at lower partial pressures than the genotype. These results suggested that the genotype simply develops faster. This hypothesis was confirmed by testing the hatching competency of eggs when exposed to hypoxic conditions. Since oxygen consumption rate is generally correlated with growth rate in fishes, our results suggest that individuals develop faster because the allelic isozyme or a closely linked locus acts to increase the metabolic rate of the embryo with respect to the genotype.