The chemical composition and energy contents of copepods and cladocerans in relation to their size

The chemical composition and energy contents of four different species of cladocerans, one species of a calenoid copepod, and mixed samples of four species of cyclopoid copepods were quantitatively determined. The relative chemical composition, expressed as a percentage of the total organic matter (excluding chitin) of each of the different species analysed, were very similar. The mean relative composition for all species was 71·2% protein, 9·5% carbohydrates, 19·3% lipids, 16·5% total nitrogen and 2·1% total phosphate–phosphorus. A substantial amount of the total nitrogen was found to be non-protein nitrogen (mean of 23·3% of total nitrogen). The calorific value was calculated from the estimated amounts of proteins, carbohydrates and lipids using conversion factors. The relationship between the calculated organic matter and the chemical oxygen demand (COD) was found to be constant and did not vary much for the different species. The ratio of total organic matter to COD has a mean value of 0·51. Calorific values ranged from 5847 to 6353 cal/g total organic matter. The amounts of chemical substances or energy contents per individual Copepoda or Cladocera were calculated. Regression lines together with their correlation coefficients have been computed to describe the relationship between the amount of chemical constituents and energy contents per individual, and the length of the individual. The results are extensively compared with those given in the literature and differences are discussed.     

Character Displacement in Frogs

Additional evidence has accumulated over the past 20 years regardingthe significance of the anuran mating call and regarding reinforcementof this premating isolating mechanism when hybridization occursin zones of symnatry. No two sympatric species have the samecall. That the mating call is a home-specific mate attractanthas been demonstrated in five major anuran families. Discriminationagainst hybrid calls versus homospecific calls has been demonstratedin Bufo and Hyla. Principal examples of presumed reinforcementcontinue to be in Gastrophryne, Acris, and the Australian Hylaewingi group. Reinforcement may be the basis for striking differentiationof some populations of Scaphiopus bombifrons. Sympatric speciespairs of anurans show greater differentiation in call than doallopatric pairs in the same group. One hybridizing situationin Bufo appears to have changed over 30 years to discrete populationswithout intermediate calls. Effective call differences can evolvewithout sympatry, and there are sympatric situations in whichno reinforcement is evident.     

An Immobilization Antigen in Tetrahymena pyriformis Expressed Under Conditions of High Salt Stress*

SYNOPSIS. Cells of Tetrahymena pyriformis syngen 1 exposed to 200 mM NaC1 without previous exposure to a saline medium die within minutes. Lines that have been adapted to higher salt concentrations by growing in axenic peptone medium with 100 mM NaC1 are able to grow in previously intolerable concentrations. Acclimation to higher salt concentrations is accompanied by a transformation from the H serotype, expressed at room temperature in the standard peptone medium, to a new serotype, St. Complete transformation occurs at concentrations approaching the LD₅₀ for nonadapted cells, and the time required for the transformation is 3–4 days. The reverse transformation, St to H, involves a time interval during which the cells are refractory to both anti-St and anti-H. Among 12 of the 13 inbred families of T. pyriformis syngen 1, 2 different high salt serotypes are found. One of these, Sta, is found among families A, Al, A3, B, D, D1, E, and F. The other, Stc, occurs in families C, C1, C2, C3, and possibly B2.     

Ultrastructural Aspects of Fertilization in Spiralian Eggs

Normally, the eggs of Spisula are monospermic. How polyspermyis prevented in this organism is unclear, particularly whenthe cortex of the fertilized ovum is examined. Using conventionalmicroscopic procedures, little alteration of the surface ofthe egg is observed following insemination; the microvilli,vitelline layer and cortical granules are morphologically unchanged.Investigations employing freeze fracture replication of fertilizedand unfertilized Spisula eggs demonstrate that there is a dichotomywith respect to the distribution of intra membranous particleswithin the plasmalemma of Spisula eggs. There is a structuralreorganization of microvilli and a two-fold increase in particleson the A-face of the plasma membrane along their bases followinginsemination. These transformations in microvillar structureand intramembranous particle number may be involved in establishinga block to polyspermy, however, further evidence is necessaryto demonstrate a cause-effect relation.     

Localization of short-term memory in the brain of the bee, Apis mellifera

ABSTRACT. Fixed honey-bees were conditioned to a scent in a one-trial learning paradigm. In contrast to free-flying colour-conditioned bees, fixed scent-conditioned bees do not show a biphasic time dependence of the conditioned response. Small metal probes were used to cool localized areas of the antennal lobes, alpha-lobes, and calyces of the mushroom bodies of the brain at various times after conditioning. Localized cooling impaired the formation of memory in all three structures. The susceptibility to impairment after conditioning lasted approximately 3 min in the antennal lobes, 7 min in the alpha-lobes, and 10 min in the calyx area. It was possible to determine the influence of the contralateral hemisphere (relative to the learning antenna) by conditioning bees with only one antenna. No contralateral impairment was found in the antennal lobes; there were minor effects in the alphalobes; contralateral cooling led to reductions of the conditioned response only in the calyx area. The temperature dependence of memory impairment was different for the antennal lobes and the mushroom bodies (alpha-lobes and calyces). The latter were most sensitive to cooling at 5°C. No correlation between cooling duration and impairment of memory was found in the antennal lobes, but there was a linear relation between impairment and cooling duration in the alpha-lobes. Brief cooling (5 or 10 s) resulted in significant impairment of memory formation only in the calyx area. A series of control experiments proved that the impairment of memory is due to a reversible block of neural activity. It was possible to show that the impairment is specific for the three neural structures analysed, by cooling the lobula of the optic system at various times after conditioning. Lesions of the brain or application of KCl also resulted in time-dependent reductions of the conditioned response. Cooling the entire animal at various times after conditioning led to similar memory impairment to that resulting from localized cooling of the alphalobes.     

Food discrimination and induction of preference for artificial diets in the tobacco hornworm, Manduca sexta

ABSTRACT. Feeding discrimination of Manduca larvae reared on leaves and a variety of artificial media was tested against leaves, various media, solvent fractions of leaves and media, and media components, including pure chemicals. Field-collected animals showed the same preferences as did animals cultured in the laboratory for many generations. Rearing larvae on a leaf species, an artificial diet, or homogenized leaves added to artificial diet induced a preference for that food in subsequent choice tests. Extracts of these foods using organic solvents (particularly hexane) elicited feeding choices resembling those evoked by the foods themselves: water extracts were effective as stimulants or deterrents, but responses to them differed considerably from responses to the foods. Animals raised on a defined artificial diet showed an increased preference (or decreased deterrence) for the lipid component (linolenic acid) of that diet in behavioural tests. Thus induction of preference was shown to be influenced by a specific nutrient compound. Fifteen artificial diets were tested; three were successful, including a completely defined medium. Various components of the diets were tested for feeding preferences, both as omissions from the main diet and as pure compounds. Some were stimulatory, most were neutral or slightly deterrent; a few were strongly deterrent. With the exception of linolenic acid, preferences for pure compounds were not significantly correlated with the food on which the animals were reared. The data suggest that food discrimination depends on the perception of a complex chemical message comprised of both polar and non-polar compounds, with the latter being of somewhat greater importance. The results are consistent with the explanation of the induction of feeding preferences being due to a reduced responsiveness to deterrents, to an increased preference for feeding stimulants or to both.     

Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems

• 1 The genus Castor comprises two species: the Eurasian beaver Castor fiber, and the North American beaver Castor canadensis. Both species suffered from overexploitation, but have seen a revival since the 1920s due to increased protection and reintroduction programmes. Increases in the populations and distributions of species that are able to modify ecosystems have generated much scientific interest. Here we review the available literature concerning the possible ecological impact of beaver species in the Old and New World.
• 2 Beavers, being ecosystem engineers, are among the few species besides humans that can significantly change the geomorphology, and consequently the hydrological characteristics and biotic properties of the landscape. In so doing, beavers increase heterogeneity, and habitat and species diversity at the landscape scale. Beaver foraging also has a considerable impact on the course of ecological succession, species composition and structure of plant communities, making them a good example of ecologically dominant species (e.g. keystone species).
• 3 Nevertheless, the strength of beavers’ impact varies from site to site, depending on the geographical location, relief and the impounded habitat type. Consequently, they may not be significant controlling agents of the ecosystem in all parts of their distribution, but have strong interactions only under certain circumstances. We suggest that beavers can create important management opportunities in the Holarctic, and this review will help land managers determine the likely outcome of beaver activity.

     

Methane emission from Texas rice paddy soils. 1. Quantitative multi-year dependence of CH4 emission on soil, cultivar and grain yield

Methane emissions at different rice productivity levels were observed from Texas rice paddy soils during the years 1991–95. Analysis of field measurements showed that seasonal methane emission (E) was strongly dependent on soil, cultivar, and rice grain yield. The relationship can be quantitatively described by E (g m^–2) = 0.048 × SI × VI × GY. SI is a soil index to characterize the relative effect of soil texture on emission and is linked with soil sand percentage. VI is a variety index to identify the intervarietal difference in methane emission and is related to the amount of methane emission per unit grain yield. GY is grain yield (g m^–2). Constant 0.048 was derived from the measurements of 10 cultivars planted in 1993. Computed emission applying the relationship is well matched with measured data. The comparison of computed with measured seasonal methane emission over an 80-day period using a total of 32 data sets yields a correlation coefficient r ² of 0.800. In addition, the ratio of seasonal methane emission to net primary productivity was calculated on a carbon to carbon basis, which produces an average value of 2.8%, ranging from 1.2% to 5.4%. A further investigation indicated that the ratio is soil and variety dependent and can be quantitatively explained by C[CH₄]/C[NPP] (%) = 3.21 × SI × VI + 0.12 ( r ² = 0.738, n = 32). Under the condition of 30% soil sand, this ratio is ≈ 3% for the majority of cultivars.     

Ultrastructural and Morphometric Observations of Cortical Endoplasmic Reticulum in Arbacia,Spisula and Mouse Eggs*

Results of morphometric investigations indicate that Arbacia eggs possess a network of cortical endoplasmic reticulum equal in volume and surface area to that within the subcortex. The cortical endoplasmic reticulum surrounds individual cortical granules and forms associations with the plasma membrane reminiscent of junctions shared by the sarcolemma and sarcoplasmic reticulum. Mouse eggs, which also exhibit a cortical granule reaction, possess endoplasmic reticulum that is associated with cortical granules and the plasmalemma. The same relative volume of cortical endoplasmic reticulum is present in mouse eggs as in Arbacia. Significantly less cortical endoplasmic reticulum is present in Spisula eggs which do not undergo cortical granule discharge upon activation. These observations are discussed in light of the hypothesis that the cortical endoplasmic reticulum transduces the interaction of the gametes into an intracellular calcium release which initiates the cortical granule reaction and the activation of development.