INNATE AND ACQUIRED VARIATION OF NUCLEAR-DNA CONTENTS OF MARINE COPEPODS

Feulgen staining revealed significant geographical differences in mean DNA contents of somatic nuclei of adult female Calanus glacialis and Pseudocalanus acuspes from the Canadian arctic and Nova Scotia; the latter exhibited seasonal differences near Halifax in 1987 but not 1989-1990. Female P. elongatus reared for 96 generations in the laboratory had significantly less DNA per nucleus than did first-generation females from the same North Sea wild stock. Nuclei of C. glacialis reared from juvenile stages (copepodid III) in four food-temperature treatments had significantly more DNA at high food and low temperature. There were also significant treatment effects in P. elongatus and P. acuspes reared from egg to adult. There were always significant differences in DNA contents among females within samples and treatments. Increased variance among nuclei within individual C. glacialis may have resulted from suboptimal laboratory conditions. Body lengths in rearing experiments were positively correlated with nuclear DNA contents in C. glacialis and P. elongatus; there was no correlation of lengths with nucleus number in P. acuspes. Development rate of late-stage C. glacialis was negatively related to nuclear DNA contents. The slight, but significant, differences among females within and among samples and treatments suggest that their DNA contents are both inherent and subject to slight environmental effects. Results are also consistent with earlier indications that body sizes and development rates of copepods, because of restricted variation in cell number, are partly under nucleotypic control.