An alternative approach to the traditional mixotrophic cultures of Haematococcus pluvialis Flotow (Chlorophyceae)

In traditional mixotrophic cultures of microalgae, all the inorganic nutrients and organic carbon sources are supplied in the medium before inoculation. In this study, however, an alternative approach was adopted in Haematococcus pluvialis Flotow, a microalga capable of growing mixotrophically on sodium acetate (Na-Ac). First, the cells were grown under 75 micromol photons m-2 s-1 phototrophically without Na-Ac until the stationary phase and then exposed to five different light regimes by the addition of Na-Ac, e.g., dark, 20, 40, 75 and 150 micromol photons m-2 s-1. Dry weight (DW), pigments and especially cell number in alternative mixotrophy (AM) were higher than traditional mixotrophy (TM). Cell number in AM almost doubled up from 21.7 to 42.9 x 104 cells mL-1 during 5 day exposure to Na-Ac, whereas the increase was only 1.2-fold in TM. Maximum cell density was reached in 75 micromol photons m-2 s-1 among the light intensities tested. We propose that Na-Ac in TM of H. pluvialis can not be utilized as efficient as in AM. With this respect, AM is of several advantages against TM such as a much higher cell density in a batch culture period and minimized risk of contamination due to the shorter exposure of cells to organic carbon sources. In consequence, this method may be used for other strains of the species, and even for the other microalgal species able to grow mixotrophically.     

Growth and the expression of alternative life cycles in the salamander Ambystoma talpoideum (Caudata: Ambystomatidae)

Complex life cycles (CLCs) contain larval and adult phases that are morphologically and ecologically distinct. Simple life cycles (SLCs) have evolved from CLCs repeatedly in a wide variety of lineages but the processes that may underlie the transition have rarely been identified or investigated experimentally. We examined the influence of larval growth rate on the facultative expression of alternative life cycles (metamorphosis or maturation as gill-bearing adults [= paedomorphosis]) in the salamander Ambystoma talpoideum. We manipulated growth rates by altering the amount of food individuals received throughout larval development. The expression of alternative life cycles in A. talpoideum is influenced by growth via food levels, but the same growth rates at different points in the larval period elicit different responses. Individuals were more likely to metamorphose (i.e. express a CLC) when food levels and growth rates were high later in development and more likely to mature without metamorphosing (SLC) when growth rates were comparatively low during the same point in development. Growth rates at particular points in development, rather than overall larval growth rate, may be an important proximate factor in salamander life-cycle evolution.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 639–646.     

An alternative to the glyoxylate shunt

A cycle remains a cycle only as long as the spokes of the wheel are not stolen. To keep the citric acid cycle going requires anaplerotic reactions such as the glyoxylate shunt to restore the cycle intermediates that are withdrawn for the biosynthesis of cell constituents, e.g. amino acids and haemin precursors. The article by Erb et al . in this issue of Molecular Microbiology documents an alternative path that replenishes four-carbon intermediates during growth on acetate in the absence of the glyoxylate shunt. The reaction sequence forms malate and succinyl-CoA from three acetyl-CoA, one CO₂ and one HCO₃ in a linear pathway. This new pathway was discovered in phototrophic anoxygenic bacteria and in few aerobic bacteria, but it is probably widespread among many metabolic groups of bacteria.     

Species trees for the tree swallows (Genus Tachycineta): An alternative phylogenetic hypothesis to the mitochondrial gene tree

The New World swallow genus Tachycineta comprises nine species that collectively have a wide geographic distribution and remarkable variation both within- and among-species in ecologically important traits. Existing phylogenetic hypotheses for Tachycineta are based on mitochondrial DNA sequences, thus they provide estimates of a single gene tree. In this study we sequenced multiple individuals from each species at 16 nuclear intron loci. We used gene concatenated approaches (Bayesian and maximum likelihood) as well as coalescent-based species tree inference to reconstruct phylogenetic relationships of the genus. We examined the concordance and conflict between the nuclear and mitochondrial trees and between concatenated and coalescent-based inferences. Our results provide an alternative phylogenetic hypothesis to the existing mitochondrial DNA estimate of phylogeny. This new hypothesis provides a more accurate framework in which to explore trait evolution and examine the evolution of the mitochondrial genome in this group.     

Hookworms in the Americas: An alternative to trans-Pacific contact

Recent New World archaeoparasitological discoveries of hookworm in pre-European contexts have revived a long-standing debate about the origin of hookworms in the Americas. Historically, the climatic conditions of Beringia encountered by migrating people have been considered too harsh for tropical hookworms to survive, suggesting that hookworms must have been introduced into South America by 'storm-tossed' fisherman or explorers from Asia. Here, John Hawdon and Susan Johnston review the history of hookworms in the Americas, and propose an alternative to their trans-Pacific introduction based on the unique natural history of one of the human hookworms.     

An alternative method to the osmotic stressing polymers: the osmomanometer

Although stressing polymers have been widely and successfully used to determine the osmotic properties of solutes in aqueous media, the osmotic stress method presents some limitations. To overcome these drawbacks, an alternative and more direct method, which has been named the osmomanometer, is described in this letter. The osmotic pressure accessible by this method ranges typically from 1 to 30 kPa using a simple hydrostatic effect and can be extended to higher pressures by using pressurized gas. This method needs neither a pressure sensor nor calibration.     

Conjugation in Hyalophysa chattoni Bradbury (Apostomatida): An adaptation to a symbiotic life cycle

Hyalophysa chattoni, borne as an encysted phoront on a crustacean's exoskeleton, metamorphoses to the trophont during the host's premolt. After the molt within 15 min to 2 h conjugants with food vacuoles appear in the exuvium, swimming along with the trophonts. Starvation in other ciliates usually precedes conjugation, but food vacuoles in conjugants do not preclude starvation. Only after ingestion and dehydration of vacuoles ceases, does digestion of exuvial fluid begin. Conjugants resorb their feeding apparatus as they fuse. A single imperforate membrane from each partner forms the junction membrane. In a reproductive cyst conjugants divide synchronously, but now the junction membrane is interrupted by pores and channels. After the last division the daughters undergo meiosis – two meiotic divisions and one mitotic division yielding two prokarya as they simultaneously differentiate into tomites. After fertilization, pairs separate and the synkaryon divides once into a macronuclear anlage and a micronucleus. Exconjugants leave the cyst and seek a host. The parental macronucleus remains active until the phoront stage when the anlage develops. Owing to random association of micronuclei during meiosis, Hyalophysa's exconjugants are more genetically diverse than exconjugants from conventional patterns of conjugation.     

Fitness consequences of alternative life histories in water striders,Aquarius remigis (Heteroptera: Gerridae)

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles.     

Calculation of protein volumes: An alternative to the Voronoi procedure

All the methods that have been applied to assessing local volume occupation or packing in proteins have particular defects. For example, the Voronoi method used by Richards (method A) and by Finney misallocates both non-bonded and covalent contacts in a geometrically rigorous, though chemically inconsistent, manner. Richards' method B, in which covalent and non-bonded contacts are partitioned in chemically sensible ways, is unfortunately not completely rigorous, in that every polyhedron vertex has associated with it a small vertex-error polyhedron, which is not allocated to any atom.We present here a generalization of the Voronoi method that is particularly suited to multicomponent assemblies such as proteins. This radical plane partitioning of volume is completely rigorous; it gives rise to no vertex error, and handles the more numerous non-bonded contacts realistically. Its application to RNAase-S is described and the results compared with both Voronoi's method and Richards' method B. A particular advantage of both the radical plane and Richards' methods is a relative insensitivity to the treatment of the surface, a problem that has plagued other approaches to describing packing in proteins. Although the radical plane is seen to misallocate volume chemically between covalently-bonded neighbours, this problem vanishes when groups of atoms in side-chain residues are considered.     

Independent life cycles: an alternative to the asynchronism hypothesis for antarctic Calanoid copepods

Previous analyses of the life cycles and distributions of large antarctic copepods have concluded that competitive exclusion is the most important causal factor. It has been suggested that these species have asynchronous life cycles, their reproduction differing in time as a result of their interspecific interaction. I have analyzed these ideas by studying zooplankton samples collected by six expeditions in the Atlantic sector of the Antarctic ocean between 1963 and 1985. The results show no evidence of asynchronism among the species analyzed. An alternative hypothesis (independent life cycles), in which no competitive interactions are considered, is presented.Contribution No. 94 of the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven.     

Live fast,die young: the life cycle of the brooding feather star Aporometra wilsoni (Echinodermata: Crinoidea)

We present here the first documentation of the entire life cycle of a crinoid. A population of the diminutive feather star Aporometra wilsoni, which broods larvae, was sampled near Adelaide, in the Gulf St Vincent, South Australia, every fortnight between February 2004 and February 2005. Body size, sex, and reproductive status were recorded for 30–50 individuals collected on each occasion. The population showed a sex ratio of 1:1, with unequivocal male and female specimens found in 10 of 13 months. The average size (arm length) of individuals increased until June, when it stabilized and females began to brood larvae. Females were found brooding larvae until November, when adults began senescing. By January, the majority of the population consisted of small recruits. The entire life cycle of this small ovoviviparous crinoid occurs over a single year, a life cycle that is unique among echinoderms.     

Self-sustained sequence replication (3SR): an alternative to PCR

 The amplification of target nucleic acids before hybridization is one of the most powerful approaches for the detection of low copy number RNA and DNA. The best known amplification reaction is PCR which has many applications. However, certain drawbacks of the PCR reaction provide a role for alternative amplification methods. One of these methods is the self-sustained sequence replication (3SR) reaction, which is an isothermal method for RNA amplification depending on the action of three enzymes. 3SR has been used in several in vitro applications and has also been modified for in situ use (IS-3SR). We have studied IS-3SR with the measles virus as a model and have found that it can significantly amplify the amount of intracellular RNA. Such a level of amplification could raise the amount of single copy RNA to the level of detection by conventional in situ hybridization. Although careful controls to insure its specificity must be carried out, IS-3SR has several advantages, including ease of use, preserved cell morphology, and specificity for RNA amplification, which make it an attractive alternative to the in situ PCR method. Accepted: 27 June 1997     

Sequential methods for comparing years of life saved in the two-sample censored data problem

This research develops nonparametric strategies for sequentially monitoring clinical trial data where detecting years of life saved is of interest. The recommended test statistic looks at integrated differences in survival estimates during the time frame of interest. In many practical situations, the test statistic presented has an independent increments covariance structure. Hence, with little additional work, we may apply these testing procedures using available methodology. In the case where an independent increments covariance structure is present, we suggest how clinical trial data might be monitored using these statistics in an information-based design. The resulting study design maintains the desired stochastic operating characteristics regardless of the shapes of the survival curves being compared. This offers an advantage over the popular log-rank-based design strategy since more restrictive assumptions relating to the behavior of the hazards are required to guarantee the planned power of the test. Recommendations for how to sequentially monitor clinical trial progress in the nonindependent increments case are also provided along with an example.     

Mathematical hazard models of mortality: an alternative to model life tables

A five-parameter competing hazard model of the age pattern of mortality is described, and methods of fitting it to survivorship, death rate, and age structure data are developed and presented. The methods are then applied to published life table and census data to construct life tables for a Late Woodland population, a Christian period Nubian population, and the Yanomama. The advantage of this approach over the use of model life tables is that the hazard model facilitates life-table construction without imposing a particular age pattern of mortality on the data. This development makes it possible to use anthropological data to extend the study of human variation in mortality patterns to small populations.     

1-Naphthol basic dye (1-NBD). An alternative to diaminobenzidine (DAB) in immunoperoxidase techniques

The usefulness of 1-naphthol as substrate for horseradish peroxidase (HRP) in immunohistochemistry was studied using the peroxidase-antiperoxidase (PAP) and avidin-biotin-complex (ABC) methods in the demonstration of glial fibrillary acidic protein (GFAP), vimentin, carbonic anhydrase C (CA.C), and factor VIII-related antigen (FVIII/RAg) in central nervous tissue and cerebral tumors. In the presence of ammonium carbonate, 1-naphthol is oxidized by HRP and hydrogen peroxide, producing a fine gray-violet precipitate. The oxidation product of 1-naphthol proved capable of binding a great number of basic dyes. For each stain the final reaction product had a characteristic color that was different from the spontaneous color of the dye and from the color displayed by nuclei. The final color obtained with this procedure was alcohol resistant and could be mounted in solvent-based mounting media. The results obtained with the 1-naphthol basic dye (1-NBD) method were compared with those obtained using the diaminobenzidine (DAB) reaction in the demonstration of GFAP-positive astrocytes. The DAB reaction produced a more intense staining but also a coarser precipitate than the 1-NBD reaction. The 1-NBD procedure showed more morphological detail of fine structures and did not obscure nuclei and mitosis. The very low toxicity of 1-naphthol compared with DAB (a suspected carcinogen) is an important advantage of the 1-NBD method, as is its high specificity and sensitivity.