Copepod development rates in relation to genome size and 18S rDNA copy number

It is known that body sizes and temperature-independent developmental durat ions within two genera of calanoid Copepoda (Crustacea) are positively rela ted to nuclear DNA contents of their somatic nuclei. Evidently because of t he constraint of similar cell numbers among the species, (nucleotypic) effe cts of nucleus size on cell size and on cell-level processes are expressed at the whole-organism level. Here, we show that developmental durations of eight species of five genera are also negatively related to their greatly d iffering numbers of 18S rRNA genes per unit DNA. We propose that levels of rDNA iteration among copepods have been controlled by natural selection to regulate ribosome concentrations, therefore protein production and developm ent rates, independently of the large variations in genome sizes, which are in turn adapted to regulating cell and therefore body sizes.