Abstract
The essential amino acid composition (EAA) of females and eggs of Euterpina acutifrons and their food was analyzed on copepods fed with different microalgae and collected from the field. There were not significant differences in the EAA of females, but the EAA of eggs varied according to food source. As predicted by homeostasis theory, a higher reproductive success was observed as the EAA of females and food became more similar. This chemical homeostasis explains the selective retention of amino acids observed in copepods, tells why conversion efficiencies of ingested nitrogen may vary according to the food source, and shows the importance of food quality on reproductive success in copepods.