Somatic tissues in mature copepods are determinate in growth, not undergoing mitosis; cell number remains constant throughout adult life. Here we report evidence of polyploidization for eight species of cyclopoid copepods. Using static Feulgen-DNA cytophotometry, we measured individual somatic nuclei in populations of Eucyclops ensifer from Brazil and of Eucyclops agilis from Ohio, U.S.A. Small but potentiality significant percentages of the adult somatic cells in these species, as well as in Bryocyclops caroli, Halicyclops tagea, Macrocyclops albidus, Mesocyclops edax, Mesocyclops thermocyclopoides, and Thermocyclops decipiens, contained at least twice (4C) the amount of DNA found in their diploid (2C) cells. These species have 2C DNA values that are representative of the range of genome sizes in cyclopoid copepods which, as a group, have much smaller genomes than calanoid copepods. Polyploidy may be a previously unrecognized mechanism whereby copepods alter the DNA content or nucleotype during specific stages in development. DNA reduplication preceding a cycle of endomitosis may result in a doubling of the functional genome, thus providing additional template for mRNA transcription related to specific functions.

The DNA content of blood cell nuclei of 15 species of cranes was determined by Feulgen-DNA cytophotometry. Genome sizes agree with values reported elsewhere for several crane species analyzed by flow cytometry. Males have more DNA per cell than females in several species. A karyotype where 2n = 80 is reported for a male greater sandhill crane.

Several cytochemical studies of the DNA content and ploidy status of neuronal cell nuclei in the central nervous system have reported the occurrence of hyperdiploid amounts of DNA in Purkinje cells and suggest the existence of some type of ‘extra’ DNA, the biological significance of which is, as yet, unknown. To explore this phenomenon further, the DNA content of glial and Purkinje cell nuclei was determined in several vertebrate species, using the DNA‐specific fluorochrome 4′,6‐diamidino‐2‐phenylindole (DAPI) to stain isolated cerebellar nuclei for analysis with a single parameter flow cytometer. The Feulgen reaction for DNA was used to stain liver and cerebellar tissue imprints for the measurement of individual nuclei with a Vickers M86 integrating microdensitometer. In both types of analyses, chicken erythrocyte nuclei served as an internal reference standard of 2.5 pg DNA per cell. The mean DNA content of Purkinje cells and glial or granule cells was essentially the same as that found for diploid (2C) non‐neuronal cells, such as hepatocytes, in rainbow trout, Amazon molly fish, salamander (Plethodon), mouse, rat, rabbit, cat, dog, monkey and human. Although Purkinje cell nuclei with 4C DNA levels were found in all of these species, except salamander and rabbit, the frequency of such cells was low (1–7%) and varied with the species. There was a low incidence of Purkinje cell nuclei with interclass DNA amounts in all species examined. Our data show that most neuronal cell nuclei in the cerebellum contain 2C levels of DNA.

The unique chromosome biology of the fungus fly Sciara coprophila has fascinated investigators for over 80 years. Male meiosis exhibits a monopolar spindle, nonrandom segregation of imprinted chromosomes and nondisjunction of the X chromosome. The unusual mechanism of sex determination requires selective elimination of X chromosomes in embryogenesis. Super-numerary (L) chromosomes are also eliminated from the soma during early cleavage divisions. Distinctive DNA puffs on the larval salivary gland chromosomes are sites of DNA amplification. As a foundation for future genome studies to explore these many unusual phenomena, we have used DNA-Feulgen cytophotometry to determine genome size from hemocyte nuclei of male (X0) and female (XX) larvae and adults. The DNA content of the X chromosome is ∼0.05 pg DNA and the autosomal complement is ∼0.45 pg DNA. Measurements of DNA levels for individual sperm from adults showed that the DNA contribution of the germ line-limited (L) chromosomes constitutes as much as 35% of the DNA of the male gamete. A parallel study using Sciara ocellaris, a related species lacking L chromosomes, confirmed the presence of two X chromosomes in the sperm of this species.

Although genome sizes (C-values) are now available for 115 arachnid species (Gregory and Shorthouse [2003] J Hered 94:285-290), the extent of genome amplification (endonuclear DNA replication or polyploidization) accompanying tissue differentiation in this diverse and abundant class of invertebrates remains unknown. To explore this aspect of arachnid development, samples of hemolymph and other tissues were taken from wild-caught specimens as air-dried smears, stained with the Feulgen reaction for DNA, and assayed using both scanning and image analysis densitometry. Cells from midgut diverticula and Malpighian tubules of Argiope and Lycosa (=Pardosa) often showed giant nuclei with 50-100 pg of DNA per nucleus, reflecting at least four cycles of endonuclear DNA replication when compared to the DNA content of hemocytes or sperm from the same specimen. Nuclei with markedly elevated DNA levels also appeared, but far less frequently, in tissue samples from several other arachnid species (Antrodiaetus, Hypochilus, Latrodectus, Liphistus and Loxosceles), but revealed no correlation with differences in somatic cell (2C) genome sizes. Our data show that several DNA classes of polysomatic nuclei regularly arise during tissue differentiation in some species of spiders and may provide an interesting model system for further study of patterns of tissue-specific variation in DNA endoreduplication during development.

Adult somatic nuclear DNA contents are reported for eleven cyclopoid species (Megacyclops latipes, Mesocyclops edax, M. longisetus, M. ruttneri, M. leuckarti, M. woutersi, Macrocyclops albidus, Cyclops strenuus, Acanthocyclops robustus, Diothona oculata, Thermocyclops crassus) and for the harpacticoid Tigriopus californicus and range from 0.50 to 4.1 pg DNA per nucleus. These diploid genome sizes are consistent with previously published values for four Cyclops species (0.28-1.8 pg DNA per nucleus), but are strikingly smaller than those reported for marine calanoids (4.32-24.92 pg DNA per nucleus). We discuss three explanations, none of them exclusive of another, to account for the smaller size and range of cyclopoid genome sizes relative to calanoid genome sizes: (1) higher prevalence of chromatin diminution in the Cyclopoida, (2) phylogenetic structure or older age of the Calanoida relative to Cyclopoida and (3) nucleotypic selection that may influence life history variation and fitness. Measurements of genome size were made on Feulgen stained, somatic cell nuclei, using scanning microdensitometry which is well suited to the sparse and heterogeneous populations of copepod nuclei. The importance of measuring large numbers of nuclei per specimen, possible sources of variation associated with cytophotometric measurements, and appropriate use of internal reference standards and stoichiometry of the Feulgen stained nuclei are discussed.

Genome sizes for 36 species of cyclopoid copepods were determined by DNA-Feulgen cytophotometry of nuclei from adults collected from diverse habitats and locales in North America, South America, Europe, and Asia. Genome sizes are small, show a 20-fold range (C = 0.10-2.02 pg DNA), and vary in a discontinuous fashion. The genomes of cyclopoid copepods are remarkably small and constant within each species, unlike the large and variable genomes of marine calanoid species. These differences may reflect the evolutionary antiquity of marine copepods in relation to marine, brackish, and freshwater copepods, as well as differences in mechanisms used to modulate genome size. The small genome sizes of contemporary cyclopoids provide substantive evidence of evolutionary constraint, possibly favouring small genomes, rapid replication rates and accelerated development as adaptive strategies for survival in often fragmented, stressful, and changing habitats.