Breeding success and the question of clutch size of Northwestern Crows Corvus caurinus

The breeding biology of two island populations of the Northwestern Crow was studied in British Columbia over a period of five years. Both populations laid an average of four eggs per clutch, of which approximately 75% hatched. More young survived to fledge on Mandate than on Mitlenatch Island. The young from nests close (< 100 m) to the beach on Mitlenatch had a higher survival rate than those from further inland. The number of eggs lost or failing to hatch was lowest in clutches of four eggs. There was a non-significant trend for chick survival to be inversely related to clutch size. The net result was that clutches of five eggs produced no more young than did clutches of four eggs. It is suggested that the major limiting factor on clutch size is food availability but the decreased hatching success of any remaining eggs once hatching has started is also a contributing factor.     

Osmotic responses of unicellular blue-green algae (cyanobacteria): changes in cell volume and intracellular solute levels in response to hyperosmotic treatment

Abstract Changes in cell volume and solute content upon hyperosmotic shock have been studied for six unicellular blue-green algae (cyanobacteria): Synechococcus PCC 6301, PCC 6311; Synechocystis PCC 6702, PCC 6714, PCC 6803 and PCC 7008. The extent of change in volume was shown to be dependent upon the solute used to establish the osmotic gradient, with cells in NaCl showing a reduced shrinkage when compared to cells in media containing added sorbitol and sucrose. Uptake of extracellular solutes during hyperosmotic shock was observed in Synechocystis PCC 6714, with maximum accumulation of external solutes in NaCl and minimum solute uptake in sucrose solutions. Conversely, solute loss from the cells (K⁺ and amino acids) was greatest in sucrose-containing media and least in NaCl. The results show that these blue-green algae do not behave as ‘ideal osmometers’ in media of high osmotic strength. It is proposed that short-term changes in plasmalemma permeability in these organisms may be due to transient membrane instability resulting from osmotic imbalance between the cell and its surrounding fluid at the onset of hyperosmotic shock.     

Indirect effects of fish predation on calcite supersaturation, precipitation and turbidity in a shallow prairie lake

SUMMARY.

• 1 We tracked calcite saturation and seston composition during 1987 and 1988 in a shallow, hardwater prairie lake, 1 year before and 1 year after a lake-wide fish removal. We also measured the contribution of calcite to turbidity during 1988.
• 2 In both years calcite saturation increased rapidly after all ice had thawed and peaked during mid-late summer with the mineral saturation index of calcite (SI) sometimes exceeding 30.
• 3 Removal of calcite from lake seston by gentle acidification of unfiltered water samples showed suspended calcite to be an important source of lurbidity in this lake.
• 4 The lake-wide fish removal produced detectable changes in the annual cycle of calcite saturation and precipitation. Increased grazing by Daphnia galeata and Daphnia pulex apparently reduced calcite saturation during early summer by suppressing the phytoplankton, and lowering the demand for CO₂.
• 5 Lower calcite precipitation, as well as direct removal of calcite by Daphnia grazing, probably contributed to the improvement in water transparency observed after the fish kill.

     

Comparative effects of Steinernema feltiae (Nematoda: Steinernematidae) and insecticides on yield and cropping of the mushroom Agaricus bisporus

In a mushroom crop (Agaricus bisporus) affected by a very low level of sciarid fly (Lycoriella auripila) infestation, the effects of an indigenous isolate of insect-parasitic nematode (Steinernema feltiae) and of two commonly used insecticides (diazinon and diflubenzuron) were studied. When compared with untreated plots, nematodes applied to the casing had no adverse effects on mushroom yields whereas insecticides decreased yields. At a rate of 3 × 10⁶ infective juveniles per tray (surface area = 0.56 m²), S. feltiae elicited increases of 28.5% and 19% in the mean total numbers and weights of mushrooms respectively. Treatment only with diflubenzuron resulted in 14.6% and 6% reductions in mean total numbers and weights of mushrooms, respectively; treatment with both diazinon and diflubenzuron caused 18.5% and 9.4% losses. Application of nematodes generally reduced the mean weight per mushroom whereas insecticides increased it; nematodes delayed the onset of mushroom production (first flush) whereas diflubenzuron delayed the third and fourth flushes. Nematode contamination of sporophores was minimal when S. feltiae was applied at casing. Although their numbers declined with time, the nematodes persisted, in the casing layer, throughout the cropping period of seven weeks. It is concluded that yield benefits associated with nematode application can result mainly from nematode effects on A. bisporus and not solely from suppression of a damaging pest population.     

A revision of the genus Centranthus DC. (Valerianaceae)

Centranthus DC. is a mediterranean genus comprising 17 taxa (including 9 species and 7 subspecies). Two new subspecies, namely C. longiflorus subsp. atlanticus and C. calcitrapae subsp. trichocarpus , are described. Affinities within the genus are discussed and four species are newly circumscribed; five new infraspecific combinations are made. Vicariance is demonstrated with the aid of two dot maps.     

High‐throughput species identification: from DNA isolation to bioinformatics

Ichthyoplankton collections provide a valuable means to study fish life histories. However, these collections are greatly underutilized, as larval fishes are frequently not identified to species due to their small size and limited morphological development. Currently, there is an effort underway to make species identification more readily available across a broad range of taxa through the sequencing of a standard gene. This effort requires the development of new methodologies to both rapidly produce and analyse large numbers of sequences. The methodology presented in this paper addresses these issues with a focus on the larvae of large pelagic fish species. All steps of the methodology are targeted towards high‐throughput identification using small amounts of tissue. To accomplish this, DNA isolation was automated on a liquid‐handling robot using magnetic bead technologies. Polymerase chain reaction and a unidirectional sequencing reaction followed standard protocols with all template cleanup and transferring also automated. Manual pipetting was thus reduced to a minimum. A character‐based bioinformatics program was developed to handle the large sequence output. This program incorporates base‐call quality scores in two types of sample to voucher sequence comparisons and provides suggested identifications and sequence information in an easily interpreted spreadsheet format. This technique when applied to tuna and billfish larvae collected in the Straits of Florida had an 89% success rate. A single species (Thunnus atlanticus) was found to dominate the catch of tuna larvae, while billfish larvae were more evenly divided between two species (Makaira nigricans and Istiophorus platypterus).     

Transport and settlement of organic matter in small streams

1. After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (‘flexible’ red alder leaves and three ‘stiff’ particle types – Douglas‐fir needles, red cedar fronds and Douglas‐fir branch pieces). 2. Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas‐fir needles and red cedar fronds, which all reached constant still‐water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3. We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ‘riffle’ than a slow, deep ‘pool’. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4. These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second‐order coastal stream. 5. When the experimental channel and in‐stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams.     

Preliminary laboratory tests with two species of entomophilic nematodes for control of Musca domestica in intensive animal units‡

Two species of entomophilic nematodes, Heterorhabditis heliothidis (NZ strain) and Steinernema feltiae (Agriotos strain) were tested in the laboratory against immature and adult stages of a strain (G) of Musca domestica with multiple insecticide-resistance. Both species of nematodes killed larval stages of M. domestica on inoculated filter papers. S. feltiae was the most virulent parasite, and killed >90% of all larval stages at the two highest doses of 25 000 and 50 000 nematodes per 0·5 ml tap water. No puparia were parasitised by either species. There was no parasitism of the larval stages after exposure to chicken manure treated with nematodes. All adult flies were parasitised after they were exposed to bait-pads previously inoculated with S. feltiae, 93.3% were parasitised by H. heliothidis.