An evolutionary interpretation of the “motivation to oviposit”

The ovipositional behavior of parasitoids and other insects is often described by phrases such as “motivation to oviposit” or “ovipositional drive”. This paper shows how an evolutionary (i.e. functional) interpretation can be given to such phrases. A detailed model for the parasitisation of Sycamore aphids by M. pseudoplatani is developed, using experiments by Collins and Dixon (1986). Two models are developed: i) one in which egg complement is the only state variable and ii) one in which egg complement and information concerning host densities are state variables. Comparisons of the behaviour of simulated parasitoids, using the decisions associated with the models, and the experiments suggest that both egg complement and information are important for the parasitoid's decision making. Accepting previously parasitized hosts may be optimal, and not simply an error in parasitoid perception. A number of other detailed predictions are made, such as the relative fitness of first and second eggs in superparasitized hosts and the nature of the memory of the parasitoid.     

Various strategies for obtaining artificial hemoproteins: From “hemoabzymes” to “hemozymes”

The design of artificial hemoproteins that could lead to new biocatalysts for selective oxidation reactions of organic compounds presents a huge interest especially in pharmacology, both for a better understanding of the metabolic profile of drugs and for the synthesis of enantiomerically pure molecules that could be involved in the design of drugs.The present results show that the so-called “host-guest strategy” that involves the non-covalent incorporation of anionic water-soluble iron-porphyrins into xylanase A from Streptomyces lividans, a low cost protein, leads to such an artificial hemoprotein that is able to perform the stereoselective oxidation of sulfides.     

From “magic bullet” to “specially engineered shotgun loads”: the new genetics and the need for individualized pharmacotherapy

Steady progress in the identification of human pharmacogenetic variants and new discoveries of disease susceptibility genes makes the old notion of one disease/one drug untenable. Advances in the ability to rapidly identify these variants, when coupled with appropriate drug delivery systems, should revolutionize pharmacotherapy. BioEssays 20 :683–685, 1998.© 1998 John Wiley & Sons Inc.     

Mangrove crab uses victory display to “browbeat” losers from re‐initiating a new fight

Signalling behaviour is integral to animal contests. However, post‐contest signals, such as victory displays, have received relatively little attention. One hypothesised function of victory displays is to ensure a more lasting dominance by reducing the risk of losers re‐initiating a new contest with winners. Despite several theoretical studies using game theory that support this hypothesis, empirical support for the understanding of when and why victory displays are used with respect to browbeating is lacking. We use a common South‐East Asian mangrove crab, Perisesarma eumolpe, to examine whether the performance of victory displays by winners, among other factors, affects the time of fight re‐initiation by losers, if at all re‐initiated. Using mixed‐effects survival analysis models, we analysed 77 fights from 27 staged contest trials between randomly paired males. We found losers that experienced victory display performed by winners, presented a decreased instantaneous hazard rate of re‐initiating a new fight than losers that did not. These results corroborate previous game theoretical models indicating that victory displays may function to reduce the chances of losers re‐initiating another fight. In discouraging losers from restarting a fight, winners reduce the potential costs of a future contest.     

“Spheroplasts” Prepared from Euglena gracilis by Proteolysis*

SYNOPSIS. Protoplast-like, osmotically-sensitive bodies were prepared from Euglena gracilis by treatment with a crude preparation of proteolytic enzymes. These spheroplasts were free of pellicles to varying degree as viewed by phase-contrast microscopy and were more easily ruptured than were untreated controls. The spheroplasts retained D-lactate dehydrogenase and acid phosphatase activity, but with altered permeability characteristics.     

Purification of “colony-forming” cells from immature rat testis

Follicle stimulating hormone (FSH) enhances colony formation (as a result of reaggregation) by dissociated 10-day-old rat testis cells in primary culture. The purpose of this study was to examine various cytological characteristics of the FSH-responsive cells and develop techniques for their purification. The ability of testis cells to form colonies in response to FSH (5 μg/ml) was tested at various ages and was found to be maximal at 15 days of age. No colony formation occurred at ages greater than 20 days. Using colony formation as an assay for the FSH-responsive cells, techniques were developed for their purification. Colony cells were purified on a continuous bovine serum albumin (BSA) step gradient (1 ml/step). In fractions purified in this manner and subsequently cultured 24 h with FSH (5 μg/ml) 99.4% of attached cells were colony cells. Light and electron microscopy indicated that the colony cells (1) were one cell type; (2) were not germinal cells; (3) ultrastructurally resembled in situ Sertoli cell of the immature rat testis; and (4) contained a nucleolus with satellite karyosomes, structures which are characteristic of rat Sertoli cells. The mitotic index of the purified cells was 0.014% following 24 h in 10⁻⁵ M colchicine. Based on these data, it was concluded that the FSH responsive cells in culture are Sertoli cells.     

Low-Resolution Density Maps from Atomic Models: How Stepping “Back” Can Be a Step “Forward”

Atomic-resolution structures have had a tremendous impact on modern biological science. Much useful information also has been gleaned by merging and correlating atomic-resolution structural details with lower-resolution (15–40 Å), three-dimensional (3D) reconstructions computed from images recorded with cryo-transmission electron microscopy (cryoTEM) procedures. One way to merge these structures involves reducing the resolution of an atomic model to a level comparable to a cryoTEM reconstruction. A low-resolution density map can be derived from an atomic-resolution structure by retrieving a set of atomic coordinates editing the coordinate file, computing structure factors from the model coordinates, and computing the inverse Fourier transform of the structure factors. This method is a useful tool for structural studies primarily in combination with 3D cryoTEM reconstructions. It has been used to assess the quality of 3D reconstructions, to determine corrections for the phase-contrast transfer function of the transmission electron microscope, to calibrate the dimensions and handedness of 3D reconstructions, to produce difference maps, to model features in macromolecules or macromolecular complexes, and to generate models to initiate model-based determination of particle orientation and origin parameters for 3D reconstruction.