Maintenance of transposable element copy number in natural populations of Drosophila melanogaster and D. simulans

To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes, which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra, Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2 × 10^-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations. The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements in this species could result from a low transposition rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crustacean plankton in Høylandet

Crustacean plankton was studied in 12 lakes in theHøylandet area in 1986–87. Basic lake characteristicsare elevation 134–415 m, surface area 9–530 ha, pH 5.9–7.1,conductivity (25 °C) 12–40 µS cm^-1 andSecchi depth 4–9 m. Number ofspecies present varied between 3 and 11. Populationnumbers between 4000 and 400 000 per m² andbiomasses were within the range 30 to1800 mg m^-2 dry weight. Cladocera dominated overCopepoda in lakes with allopatric brown trout (Salmo trutta L.), on the contrary to lakes also populatedby Arctic charr (Salvelinus alpinus (L.)). Thesevariations are caused by differences in elevation,lake morphometry, water quality, fish predation andthe general distribution of the species. The largestlakes at lowest elevation were richest in species. Theacid sensitive genus Daphnia was represented by 3species. The lakes Storgrønningen (530 ha) andRøyrtjønna (27 ha) were sampled monthly in theice-free seasons of 1986–89, and Storgrønningen moreintensively from June to November in 1987 and 1988. The same6 species of Cladocera and 5 of Copepoda were presentin both lakes. Their life cycles were traditional orknown from several other Scandinavian lakes. Meanseasonal biomasses were of the range600–750 mg m^-2. At the species level, there wereconsiderable variations between years inStorgrønningen and particularly in Røyrtjønna. Noeffects of human impacts on the crustacean planktonwere found. The Høylandet lakes are representative forScandinavian oligotrophic to almost ultra-oligotrophiclakes. Storgrønningen is well qualified as a referencesystem. The between year variations in Røyrtjønna areso extreme, that any human impact could only be traced at alevel causing the extinction of species.     

蓟属两种植物的染色体研究

本文对蓟属（Ｃｉｒｓｉｕｍ）的两个形态相似的近缘种大刺儿菜和小刺儿菜进行了染色体研究,其中后者为首次报道。观察结果表明：两个种的染色体数目均为２ｎ＝２ｘ＝３４：它们的核型是：大刺儿菜．２ｎ＝２ｘ＝３４＝２０ｍ＋１２ｓｍ＋２ｓｔ：小刺儿菜．２ｎ＝２ｘ＝３４＝２２ｍ＋１０ｋｍ（２ＳＡＴ）＋２ｓｔ。通过核型比较,认为它们是两个独立的种．而且后者比前者进化。     

活血莲的核型分析

对活血莲的染色体数目及核型进行了研究,结果表明,活血莲的染色体数目为２ｎ＝６０,其核型公式为２ｎ＝２ｘ＝６０＝４６ｓｍ＋１２ｓｔ＋２ｍ。没有观察到带随体的染色体。     

The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures

A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids.     

A reassessment of the binding of napthaleneacetic acid by membrane preparations from maize

Naphthalene-1-acetic acid (NAA) binding by membrane fractions derived from maize has been re-evaluated. Using a computer curve-fitting procedure only one major type of NAA binding, in terms of binding affinity, could be identified. Auxins, antiauxins and structurally related compounds have been tested for their competitive effect on NAA binding and the inhibitor constants for a number of these have been determined. Extracts from various plant species have been examined for their NAA binding ability, but all showed much less binding than maize leaf or coleoptile preparations. The possibility of the NAA binding by maize extracts being due to a true hormone receptor is discussed.Abbreviations BA benzoic acid - CPIB p-chlorophenoxyisobutyric acid - 2,4-D 2,4-dichlorophenoxyacetic acid - DCB 2,4-dichlorobenzoic acid - IAA indolyl-3-acetic acid - NAA napthalene-1-acetic acid - 2-NAA napthalene-2-acetic acid - NAOA napthalene-2-oxyacetic acid - PA phenylacetic acid - PU phenylurea - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid - TIBA 2,3,5-triiodobenzoic acid