Coexistence of Competing Parasitoid Species on a Host with a Variable Life Cycle

Several special cases of a general model in which two parasitoid species attack different developmental stages of a single host species are presented. The inclusion of different mathematical forms of a maturation weighting function allows us to investigate the effect of several aspects of variation in immature stage durations on the outcome of competitition between the parasitoids. The two parasitoid species cannot coexist if the host developmental stages are fixed in duration. The outcome of competition depends in part on the relative duration of the two stages attacked by the parasitoid species. However, coexistence is possible if there is sufficient variation in the time that different host individuals remain in each stage. Distributed host developmental delays promote coexistence because they cause the host population to be composed of a mixture of host types with different relative egg versus larval stage durations. Each host type is thus largely available to only one of the parasitoid species.     

An evaluation of sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the identification of microsporidia

Microsporidian spore polypeptides separated with sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) can be used to identify isolates of microsporidia. The spore polypeptides separated with SDS/PAGE provided unique, reproducible electrophoretic profiles which were not influenced by host species or the temperature at which the host larvae were maintained for development. Furthermore, host proteins were not detected in electrophoretic profiles of the spore polypeptides. Spore mixtures of two microsporidian species can be detected when the spore polypeptides of either or both species have been previously separated with SDS/PAGE.     

The effect of essential-fatty-acid deficiency on the activity of liver phosphatidate phosphatase in rats

The activities of the soluble and microsomal phosphatidate phosphatases (EC 3.1.3.4) are greater in the livers of essential-fatty-acid-deficient rats than in rats fed diets containing linoleic acid.     

INTRACELLULAR PHYTOCHROME DISTRIBUTION AS A FUNCTION OF ITS MOLECULAR FORM AND OF ITS DESTRUCTION

The immunocytochemically observed intracellular redistribution of phytochrome as a function of its molecular form is described by utilizing color photomicrography. The reversible change from a diffuse to a discretely localized distribution following photoconversion of the red-absorbing Pr form to the far-red-absorbing Pfr form observed with etiolated oat (Avena sativa L., cv. Garry) coleoptile parenchyma cells is not seen with etiolated wheat (Triticum sativum L., cv. unknown), barley (Hordeum vulgare L., cv. Harrison), or rye (Secale cereale L., cv. Balbo). Whether redistribution in these latter cases does not occur or is below the limit of detection is not known. Upon continuous actinic irradiation, phytochrome, which is discretely localized as Pfr, rapidly disappears by both immunocytochemical and spectral assay. However, after about 90 min irradiation, a new association of phytochrome with nuclei is evident which is more pronounced after 4 or 8 h of irradiation. With longer irradiation times there is a total loss of antigenically detectable phytochrome at the resolution employed in these experiments.     

Further characterization of human erythrocyte superoxide dismutase.

1. A simplified procedure for the preparation of highly purified human superoxide dismutase from erythrocytes was developed which avoided extremes of pH and ionic strength and the use of organic solvents; the properties of human and bovine proteins, prepared by the method, were compared. 2. Using the two dimensional electrophoretic procedure of O'Farrell, the human superoxide dismutase was found to consist of a single type of polypeptide. 3. The human protein was found to have a total of eight half-cystine residues per mole of protein, compared to six such residues for the bovine protein. The human protein has two sulfhydryl groups which are reactive toward mercurials when dissolved in 1M guanidine-hydrochloride and approximately 3 reactive sulfhydrls when the protein is dissolved in 6 M guanidine hydrochloride. The distribution of the eight sulfur atoms appears to consist of four involved in disulfide linkages, two deeply buried within the molecule and unreactive except under strongly denaturing conditions, and two which are reactive under mildly denaturing conditions. No zero-valent sulfur was found. 4. The visible optical absorption, the visible circular dichroism, and the electron paramagnetic resonance spectra are essentially identical with those of the bovine protein. No unusual absorbance was found at 330 nm. The near ultraviolet spectrum is different from that of the bovine protein, and this appears to be due to differing amino acid compositions. 5. Two fractions of superoxide dismutase activity were observed during chromatography of partially purified solutions on diethylaminoethyl-cellulose. The minor, less mobile form, was found to revert to the less mobile species on aging; the reverse process was not observed to occur. The minor component was found to contain equimolar amounts of Zn and Cu and to have a specific dismutase activity somewhat higher than that of the purified major fraction.     

Experimental studies on a lethal gene (1) in the Mexican axolotl, Ambystoma mexicanum.

1. Gene ? is a recessive lethal factor found in the white strain of axolotls. Animals heterozygous for the gene are phenotypically normal. When mated with each other they give offspring 25% of which exhibit the lethal effects of the gene. 2. The ?/? homozygotes develop normally to an advanced embryonic stage (Harrison stage 40) before the effects of the gene are first manifested. They then come to display a characteristic combination of abnormalities, including a disproportionately small head, small and poorly developed eyes, abnormal poorly developed gills, undifferentiated limb buds, and reduced overall growth rate. They may feed briefly, but soon stop and invariably die within a few weeks of the time of hatching. 3. The action of gene ? has been analyzed by parabiosing mutant and normal embryos, and by grafting various organ primordia reciprocally between mutant and normal embryos. Parabiosis to normal embryos fails to correct the abnormalities of the mutants, although their survival may be somewhat prolonged. Grafts of mutant organ primordia (eye, limb, gill, pronephros, gonad, head) also invariably fail to show improved development or to survive on normal hosts; normal organ primordia develop normally on mutant hosts so long as the mutant survives. These experiments indicate that gene ? is a recessive autonomous cell lethal affecting all of the organ systems during late embryonic and early larval development.     

Carry‐over Effects of Size at Metamorphosis in Red‐eyed Treefrogs: Higher Survival but Slower Growth of Larger Metamorphs

Most animals have complex life histories, composed of a series of ecologically distinct stages, and the transitions between stages are often plastic. Anurans are models for research on complex life cycles. Many species exhibit plastic timing of and size at metamorphosis, due to both environmental constraints on larval growth and development and adaptive plastic responses to environmental variation. Models predicting optimal timing of metamorphosis balance cost/benefit ratios across stages, assuming that size affects growth and mortality rates in each stage. Much research has documented such effects in the larval period, but we lack an equal understanding of juvenile growth and mortality. Here, we examine how variation in size at metamorphosis in the Neotropical red‐eyed treefrog, Agalychnis callidryas, affects post‐metamorphic growth, foraging, and behavior in the lab as well as growth and survival in the field. Surprisingly, many individuals lost mass for weeks after metamorphosis. In the lab, larger metamorphs lost more mass following metamorphosis, ate similar amounts, had lower food conversion efficiencies, and grew more slowly after mass loss ceased than did smaller ones. In field cages larger metamorphs were more likely to survive than smaller ones; just one froglet died in the lab. Our data suggest that size‐specific differences in physiology and behavior influence these trends. Comparing across species and studies, large size at metamorphosis generally confers higher survival; size effects on growth rates vary substantially among species, in both magnitude and direction, but may be stronger in the tropics.     

Immunochemistry of phytochrome

Purified oat and rye phytochrome were examined by analytical gel chromatography, polyacrylamide gel electrophoresis, N-terminal, and amino acid analysis. Purified oat phytochrome had a partition coefficient on Sephadex G-200 (σ₂₀₀) of 0.350 with an estimated molecular weight of 62,000; sodium dodecyl sulfate polyacrylamide electrophoresis gave an equivalent weight estimate. Purified rye phytochrome had a σ₂₀₀ value of 0.085 with an estimated molecular weight of 375,000; sodium dodecyl sulfate electrophoresis gave a weight estimate of 120,000, indicating a multimer structure for the nondenatured protein. Comparative sodium dodecyl sulfate electrophoresis with purified phycocyanin and allophycocyanin gave a molecular weight estimate of 15,000 for allophycocyanin, and two constituent classes of subunits for phycocyanin with molecular weights of 17,000 and 15,000. Amino acid analysis of oat phytochrome confirmed a previous report; amino acid analysis of rye phytochrome differs markedly from a previous report. Oat phytochome has four detectable N-terminal residues (glutamic acid, serine, lysine, and leucine, or isoleucine); rye phytochrome has two detectable groups (aspartic and glutamic acids). Model experiments subjecting purified rye phytochrome to proteinolysis generate a product with the characteristic spectral and weight properties of oat phytochrome, as it has been described in the literature. It is concluded that the structural characteristics of purified rye phytochrome are likely those of the native protein.