On the role of food quality in grazing and development of life stages, and genetic change of body size during cultivation of pelagic copepods

Abstract

> 100 consecutive generations of Temora longicomis and 70 of Pseudocalanus elongatus (Copepoda: Calanoida) have been bred in the laboratory using a suitable mixture of three food organisms. The food value of the large heterotrophic flagellate Oxyrrhis marina is demonstrated by observations on grazing on this flagellate by the different life stages of T. longicornis. Weight-specific ingestion increased with age from 35% in NII and III to an optimum in CV of 115% (males)and 170% (females)of body C · day −1. Body size in the adult stage and rate of development were reduced when T. longicornis was raised using only the small Isochrysis galbana as food, compared to the intermediate Rhodomonas sp. or the mixture of flagellates. P. elongatus developed equally fast with the three types of food, however, body size was significantly reduced with I. galbana as the sole food whereas lipid content of females decreased with smaller sizes of the food particles. I. galbana and Rhodomonas sp. must be the main food of young nauplii in the cultures whereas O. marina becomes so in older copepodite stages. During prolonged cultivation of four copepod species, body size increased or decreased, depending on the species. In T. longicornis, body size decreased genetically. This appeared from interbreeding experiments of males freshly collected from the sea and females cultured in the laboratory in which the original size of the offspring was restored. Large seasonal changes of body size of male parents did not influence the adult size of their progeny when cultivated at constant conditions, indicating that genotypic variance does not contribute significantly to seasonal changes of body size. It is hypothesized that changes of body size in the cultures might be an adaptation to the food offered.