UNUSUAL GENETIC VARIATION IN BODY SIZE, DEVELOPMENT TIMES, OIL STORAGE, AND SURVIVORSHIP IN THE MARINE COPEPOD PSEUDOCALANUS

¹ Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada

Body size, development times of copepodid stages, and relative amounts of oil were measured among offspring of Pseudocalanus reared in excess food at 10° C in the laboratory. ANOVA of these traits among full-sib and half-sib families showed high proportions of variance contributed between sires (i.e., high heritabilities as normally interpreted), but negligible proportions between dams within sires. Although their parents (of a narrow size range) did not mate assortatively by size, as do those of a wider size range, it is concluded that the suppression of the contribution between dams, within sires, was due to assortative mating, using unknown phenotypic clues, by animals whose genetic differences in size, etc., were unmasked among offspring reared in controlled conditions. Although animals of wider size differences may be distinct species, no significant groupings of traits into two or more classes were found among the offspring treated by ANOVA. Development times of early stages, as well as survivorship (most deaths probably in early life), had high proportions of variance contributed between dams, within sires, and a negligible proportion between sires. These results suggest that underlying maternal and common-environment effects were expressed only early in life. Larger copepodid V stages from nature had relatively more oil and spent longer times developmentally suspended in this stage in the laboratory. Larger animals, whether their size is environmentally or genetically determined, may be more prone to enter such resting stages for overwintering, while smaller animals may benefit more from maturation and further generations. If the animals of the narrower size range near Halifax represent a single species, there are problems about maintenance of genetic variation of their demographically significant traits in nature. If they are a complex of cryptic species, then there are questions about their coexistence. Either situation poses problems for conventional systematics and nomenclature.