No description available.

We have developed a method of calculating the average local absorbance (ALA) of a nucleus from the integrated nuclear absorbance and area. One can use the ALA, along with nuclear areas measured at different point absorbance thresholds, to determine whether a nucleus is stained too lightly or too darkly for accurate absorption measurements; this allows selection of an optimal light wavelength for the performance of these measurements. The ALA can also be used for automatic and instantaneous correction of integrated absorbance values from darkly stained cells. This allows the rapid measurement of the integrated absorbances of a large number of nuclei that are heterogeneous in stain intensity. Coefficients of variation of approximately 3% are obtained for the integrated absorbances of nuclei of nontransformed G0/G1 cells. This correction method can be applied with any image densitometer that generates both integrated absorbance and area values.

Variation in nuclear DNA content within some eukaryotic species is well documented, but causes and consequences of such variation remain unclear. Here we report genome size of an estuarine and salt-marsh calanoid copepod, Eurytemora affinis, which has recently invaded inland freshwater habitats independently and repeatedly in North America, Europe, and Asia. Adults and embryos of E. affinis from the St. Lawrence River drainage were examined for somatic cell DNA content and the presence or absence of embryonic chromatin diminution, using Feulgen-DNA cytophotometry to determine a diploid or 2C genome size of 0.6-0.7 pg DNA/cell. The majority of somatic cell nuclei, however, have twice this DNA content (1.3 pg/nucleus) in all of the adults examined and possibly represent a population of cells arrested at the G2 stage of the cell cycle or associated with some degree of endopolyploidy. Both suggestions contradict assumptions that DNA replication does not occur in adult tissues during the determinate growth characteristic of copepods. Absence of germ cell nuclei with markedly elevated DNA values, commonly found for species of cyclopoid copepods that show chromatin diminution, indicates that E. affinis lacks this trait. The small genome size and presumed absence of chromatin diminution increase the potential utility of E. affinis as a model for genomic studies on mechanisms of adaptation during freshwater invasions.

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.

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.

No description available.

In this thesis relationships and the occurrence of reticulate evolutionary events in the club moss genus Diphasiastrum are investigated. Diphasiastrum is initially established as a monophyletic group within Lycopodiaceae using non recombinant chloroplast sequence data. Support is obtained for eight distinct parental lineages in Diphasiastrum, and relationships among the putative parent taxa in the hypothesized hybrid complexes; D. alpinum, D. complanatum, D. digitatum, D. multispicatum, D. sitchense, D. tristachyum and D. veitchii are presented. Feulgen DNA image densitometry data and sequence data obtained from three nuclear regions, RPB2, LEAFY and LAMB4, were used to infer the origins of three different taxa confirmed to be allopolyploid; D. zanclophyllum from South Africa, D. wightianum from Malaysia and an undescribed taxon from China. The two Asian polyploids have originated from two different hybrid combinations, D. multispicatum x D. veitchii and D. tristachyum x D. veitchii. Diphasiastrum zanclophyllum originates from a cross between D. digitatum and an unidentified diploid taxon. The occurrence of three homoploid hybrid combinations commonly recognized in Europe, D. alpinum x D. complanatum, D. alpinum x D. tristachyum and D. complanatum x D. tristachyum, are verified using the same three nuclear regions. Two of the three hybrid combinations are also shown to have originated from reciprocal crosses. Admixture analyses performed on an extended, dataset similarly identified predominately F1 hybrids and backcrosses. The observations and common recognition of hybrid species in the included populations are hence most likely due to frequent observations of neohybrids in hybrid zones. Reticulate patterns are, however, prominent in the presented dataset. Hence future studies addressing evolutionary and ecological questions in Diphasiastrum should emphasize the impact of gene flow between parent lineages rather than speciation as the result of hybridization.