Insect pollination of sugar-beet (Beta vulgaris) seed crops

The flowers of sugar-beet crops grown to produce hybrid seed were visited by many species of insects which often carried much sugar-beet pollen on their bodies and could have contributed to pollination.     

Race non-specific resistance to Bremia lactucae

Three ways of measuring race non-specific resistance to Bremia lactucae in lettuce were studied to determine the most important components of this form of resistance. Tests were conducted on leaf discs from 4–6 wk-old plants that were quantitatively inoculated and incubated under controlled conditions. Observations were made of disease intensity, latent period and production of conidia. Inoculum concentration markedly influenced disease intensity and latent period. Cv. Iceberg exhibited race non-specific resistance and this was characterised by a longer latent period, a lower disease intensity and reduced production of conidia compared to the susceptible control cv. Cobham Green. On older, intact plants, the differences in latent period and disease intensity between cultivars were even greater. Production of conidia was a particularly good criterion for discriminating levels of resistance.     

Simple three‐pool model accurately describes patterns of long‐term litter decomposition in diverse climates

As atmospheric CO₂ increases, ecosystem carbon sequestration will largely depend on how global changes in climate will alter the balance between net primary production and decomposition. The response of primary production to climatic change has been examined using well‐validated mechanistic models, but the same is not true for decomposition, a primary source of atmospheric CO₂. We used the Long‐term Intersite Decomposition Experiment Team (LIDET) dataset and model‐selection techniques to choose and parameterize a model that describes global patterns of litter decomposition. Mass loss was best represented by a three‐pool negative exponential model, with a rapidly decomposing labile pool, an intermediate pool representing cellulose, and a recalcitrant pool. The initial litter lignin/nitrogen ratio defined the size of labile and intermediate pools. Lignin content determined the size of the recalcitrant pool. The decomposition rate of all pools was modified by climate, but the intermediate pool's decomposition rate was also controlled by relative amounts of litter cellulose and lignin (indicative of lignin‐encrusted cellulose). The effect of climate on decomposition was best represented by a composite variable that multiplied a water‐stress function by the Lloyd and Taylor variable Q₁₀ temperature function. Although our model explained nearly 70% of the variation in LIDET data, we observed systematic deviations from model predictions. Below‐ and aboveground material decomposed at notably different rates, depending on the decomposition stage. Decomposition in certain ecosystem‐specific environmental conditions was not well represented by our model; this included roots in very wet and cold soils, and aboveground litter in N‐rich and arid sites. Despite these limitations, our model may still be extremely useful for global modeling efforts, because it accurately (R²=0.6804) described general patterns of long‐term global decomposition for a wide array of litter types, using relatively minimal climatic and litter quality data.     

Parental role division predicts avian preen wax cycles

Previous studies have shown that preen wax composition in some sandpipers shifts from the usual monoesters to diesters during the breeding season, possibly to reduce the ability of mammalian predators to find nests using olfactory cues. To investigate further the relationship between incubation and wax secretion, we examined seven sandpiper species with different incubation patterns (species in which both sexes incubate, in which only males incubate and in which only females incubate). During the breeding period, diester preen wax was secreted almost exclusively by the incubating sex in species with uniparental incubation, and by both sexes in species with biparental incubation. These findings suggest that diester preen waxes have a function that is directly related to incubation. Unexpectedly, in female-incubating Curlew Sandpiper Calidris ferruginea and Buff-breasted Sandpiper Tryngites subruficollis , some males also secreted diester preen waxes during the breeding period. This suggests that some males may in fact incubate, that these waxes may be a remnant from their evolutionary past when both sexes incubated, or that males need to be olfactorally cryptic because they are involved in the making of nest scrapes. The seasonal pattern of preen wax composition was also studied in captive male, female and female-mimicking male ('faeder') Ruff Philomachus pugnax . Captive female Ruff changed preen wax composition from monoesters to diesters in the spring despite the fact that no incubation took place. This suggests that circannual rhythms rather than actual incubation behaviour may trigger the shift to diester waxes. All captive male Ruff, including the faeders, continued to secrete monoesters, supporting the hypothesis that only the incubating sex secretes diesters.     

Calcium Uptake by a Psychrophilic Achromobacter Strain

The permeability of a psychrophilic Achromobacter strain to calcium ions was examined with the radioisotope ⁴⁵Ca²⁺. The amount of radioactivity that remained associated with the cells after exposure to 5 to 200 mM solutions of radioactive calcium was determined. The concentration of ⁴⁵Ca²⁺ of the cells compared to that of the surrounding medium gave a ratio larger than one, and this ratio increased with decreasing ambient calcium concentration. The same results showed that the higher the external calcium concentration was, the more calcium remained with the cells. The radioactivity of the cells had the following characteristics: 1. It was rapidly lost when the cells were washed with ⁴⁰Ca-solution. 2. Most of it was retained after water washings. 3. It was not affected by the presence of 2,4-dinitrophenol. 4. It was only slightly affected by temperature. 5. It increased when the cells were treated with toluene or heat and reached a maximum of 2–3 times the value of untreated cells. The same treatment brought about a smaller increase of the uptake of ²²Na⁺. 6. Approximately 60% of the radioactivity of whole cells was associated with isolated cell envelopes.     

Pleiotropic Effects of a Temperature-Sensitive Mouthless Mutation in Tetrahymena thermophila on the Excretion of Extracellular Enzymes

The mode of enzyme excretion was investigated during balanced growth in wild type Tetrahymena thermophila and in a temperature-sensitive mutant that did not form a mouth and food vacuoles at the restrictive temperature. The mutant was used to determine which of the extracellular enzymes are normally excreted by defecation. During balanced growth at the permissive temperature the excretion of enzymes was constant, and maximal in complex medium. No protease activity against azocasein was detected. Changes in the growth temperature of the wild type cells only affected the release of 3′-nucleotidase. For the mutant, however, the excretion changed markedly with increasing temperature: (a) ribonuclease, deoxyribonuclease, α-glucosidase, and β-glucosidase were detected in 0–10% of normal amounts; (b) 3′- and 5′-nucleotidase, not measured previously in Tetrahymena, were found in 10- to 14-fold of normal amounts; (c) excretion of acid phosphatase was unaffected. We therefore conclude that the extracellular enzymes (a) are released by defecation, that 3′- and 5′-nucleotidase are secreted through the membrane system, and that acid phosphatase is released by lysosomes emptied through pinocytosis. It is proposed that the lysosomes used for the formation of digestive vacuoles are different from those used for the formation of pinocytotic vacuoles and for autophagic vacuoles.     

Multiple ice‐age refugia in Pacific cod,Gadus macrocephalus

Pleistocene ice‐ages greatly influenced the historical abundances of Pacific cod, Gadus macrocephalus, in the North Pacific and its marginal seas. We surveyed genetic variation at 11 microsatellite loci and mitochondrial (mt) DNA in samples from twelve locations from the Sea of Japan to Washington State. Both microsatellite (mean H = 0.868) and mtDNA haplotype (mean h = 0.958) diversities were large and did not show any geographical trends. Genetic differentiation between samples was significantly correlated with geographical distance between samples for both microsatellites (F_ST = 0.028, r² = 0.33) and mtDNA (F_ST = 0.027, r² = 0.18). Both marker classes showed a strong genetic discontinuity between northwestern and northeastern Pacific populations that likely represents groups previously isolated during glaciations that are now in secondary contact. Significant differences appeared between samples from the Sea of Japan and Okhotsk Sea that may reflect ice‐age isolations in the northwest Pacific. In the northeast Pacific, a microsatellite and mtDNA partition was detected between coastal and Georgia Basin populations. The presence of two major coastal mtDNA lineages on either side of the Pacific Ocean basin implies at least two ice‐age refugia and separate postglacial population expansions facilitated by different glacial histories. Northward expansions into the Gulf of Alaska were possible 14–15 kyr ago, but deglaciation and colonization of the Georgia Basin probably occurred somewhat later. Population expansions were evident in mtDNA mismatch distributions and in Bayesian skyline plots of the three major lineages, but the start of expansions appeared to pre‐date the last glacial maximum.     

Electrophysiological responses of the chemoreceptor neurones in the antennal taste sensilla to plant alkaloids and glucosides in a granivorous ground beetle

The electrophysiological response of chemoreceptor neurones from the antennal chaetoid taste sensilla of the omnivorous ground beetle Pterostichus oblongopunctatus to several plant alkaloids and glucosides is investigated. A quinine‐sensitive neurone responding to quinine and quinine hydrochloride is found, most probably related to the granivorous feeding habit of P. oblongopunctatus. The response to quinine hydrochloride is concentration‐dependent at 0.001–50 mm , with the response threshold at 0.01 mm and a maximum rate of firing of 67 spikes/s at 50 mm . The stimulatory effect of caffeine is very weak, where the firing rate increases by only 1.4 spikes/s at a concentration of 10 mm compared with that evoked by a control stimulus. In addition, both quinine and quinine hydrochloride strongly inhibit spike production by the salt‐ and pH‐sensitive neurones when presented in mixtures with 10 mm NaCl. Several tested plant secondary compounds (i.e. salicin, sinigrin, caffeine and nicotine), which have only little or no effect on the firing rate of the quinine‐sensitive neurone, greatly reduce the responses of the salt‐ and pH‐sensitive neurones. The results of the present study suggest that the antennal taste sensilla of P. oblongopunctatus may detect plant defensive compounds both through the activation of a quinine‐sensitive neurone and via peripheral inhibition of other chemoreceptor neurones of the taste sensillum.     

Twelve microsatellite markers developed in woundfin (Plagopterus argentissimus), an endangered warmwater fish of the lower Colorado River basin

Woundfin (Plagopterus argentissimus) is one of several endangered warmwater fishes once common to the lower Colorado River basin. Dexter National Fish Hatchery & Technology Center maintains a refugium stock founded in 1982, and augmented with c. 1000 young fish in 1989. Genetic characterization of the refugium stock and salvaged fish from the Virgin River is necessary to develop a strategy to incorporate salvaged fish into the hatchery stock. We developed an enriched microsatellite library and 12 species‐specific polymorphic loci. Alleles per locus ranged from 10 to 19, averaging 13. The average expected and observed heterozygosities were 0.884 and 0.895, respectively.     

Histone gene transposition in the phylogeny of the Drosophila obscura group

The chromosomal location of the histone genes was determined in seven species of the Drosophila obscura group by in situ hybridization. Histone genes occur on more than one site per genome and on non-homologous chromosome elements. In addition, the metaphase karyotypes and the banding pattern of the polytene chromosomes were compared. Based on chromosomal characters, the cladogenesis of the D. obscura group was established. From the distribution of histone sites in different species, analysed in this paper and in previous studies, the phylogenetic history of histone gene transposition was derived. The molecular mechanisms responsible for the generation of new histone sites are discussed.