DNA reassociation kinetics and diversity indices: richness is not rich enough

DNA reassociation kinetics, also known as Cot curves, were recently used by Gans and co-workers to estimate the number of bacterial species present in soil samples. By reanalysing the mathematical model we show that rather than the number of species, Simpson and Shannon diversity indices are encoded in the experimental data. Our main tool to establish this result are the so-called Rényi diversities, closely related to Hill numbers, illustrating the power of these concepts in interpreting ecological data. We argue that the huge diversity encountered in microbial ecology can be quantified more informatively by diversity indices than by number of species.     

Feeding History Affects the Response of the Predatory Mite Typhlodromus Kerkirae (Acari: Phytoseiidae) to Volatiles of Plants Infested with Spider Mites

The response of adult females of the predatory mite Typhlodromus kerkirae (Acari: Phytoseiidae) to volatiles emitted from bean leaves infested with Tetranychus urticae (Acari: Tetranychidae) or from leaves of Oxalis corniculata infested with Petrobia harti (Acari: Tetranychidae) was studied in the laboratory using a Y-tube olfactometer. Typhlodromus kerkirae females reared from larvae through to adults on T. urticae and pollen of Vicia faba responded to volatiles of bean leaves infested with T. urticae, either when they had a choice between infested and non-infested bean leaves or between bean leaves infested with T. urticae and O. corniculata leaves infested with P. harti. However, they did not respond when they had been reared only on the carotenoid-deficient pollen of V. faba. Female T. kerkirae that had been reared from larva to the tenth day of adult life on T. urticae and subsequently fed for 1 week on V. faba pollen did not respond to volatiles of bean leaves infested with T. urticae. In contrast, those that had been reared on V. faba pollen to the tenth day of adult life and subsequently fed for 1 week on T. urticae responded to volatiles of infested bean leaves.     

Control of Hydrogen Photoproduction by the Proton Gradient Generated by Cyclic Electron Flow in Chlamydomonas reinhardtii

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H₂ production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H₂ photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H₂ production.     

Chromosomal evolution within the family Estrildidae (Aves) III. The Estrildae (waxbill finches)

The C- and G-banded karyotypes of five species of waxbill finches belonging to the Estrildidae were examined. Extensive chromosomal variation including inversions and fissions was found to differentiate the species, showing the waxbills to be the most chromosomally diverse group of estrildid finches. None of the variation, however, matched that recorded in related species of Pytilia (Christidis, 1983). By comparing the G-banded karyotypes of species belonging to all three estrildid lineages it was possible to reconstruct the presumed ancestral karyotype for the Estrildidae as a whole. This was found to approximate the karyotype of the Australian peophilid species, Poephila guttata most closely. From it chromosomal relationships within the three estrildid lineages, Poephilae, Lonchurae, Estrildae, can be determined.     

Impaired spermatogenesis in the finch hybrid L. castaneothorax by L. punctulata: Transmission electron microscopy and genetic analysis

As part of a project to determine whether there is any correlation between the form of hybrid sterility and the genetic relatedness of the parental species, we studied a male intrageneric hybrid between two finch species (Lonchura custaneothorax × L. punctuluta), and compared the ultrastructural basis of hybrid sterility in this species with that reported by Swan [1985] for an intergeneric bird hybrid. In the latter study the sterility appeared to have an autoimmune basis, due to lack of Sertoli-Sertoli tight junctions. In the hybrid examined in the present study, lanthanum tracing showed that the junctions were tight. There was no testicular immune reaction; the parental species were almost identical in chromosomal constitution, having only a small inversion difference on chromosome 5, and only two structural protein differences could be detected through examination of the variation at 38 protein loci. Nevertheless, the hybrid appeared sterile and had the following ultrastructural testicular features. Intercellular bridges where present were usually abnormal in structure; centrioles in a centriole pair were arranged in parallel. Many spermatocytes and spermatids degenerated and were phagocytosed by Sertoli cells. Some spermatids progressed to mature testicular spermatozoa in sperm bundles, but commonly had multiple (2–4) axonemes or disrupted doublets and accessory fibers. The multiple axonemes present in most spermatids inserted separately into the base of the nucleus and the multiple centrioles were capable of organizing separate neck structures. We conclude that these cytological abnormalities were caused by genic effects and discuss why they appeared to be restricted to the germ line.     

An analytical approach to spatio-temporal dynamics of neutral community models

We propose a spatial version of the neutral community model on a network of interconnected patches. The dynamical equations for the abundances and higher order moments of the abundances are established. Due to the neutrality assumption these equations are autonomous, enabling an exact analysis of spatio-temporal dynamics. We compute local (i.e., inside a patch) and global (i.e., between patches) diversities, and illustrate our results with two examples: (1) a non-spatial community, for which we recover previous results, and (2) a model with a finite number of patches which are all connected to each other with equal migration intensity. We discuss the relevance of this model for experiments in microbial ecology.     

The Heterochromatic Rolled Gene of Drosophila Melanogaster Is Extensively Polytenized and Transcriptionally Active in the Salivary Gland Chromocenter

This paper reports a cytogenetic and molecular study of the structural and functional organization of the Drosophila melanogaster chromocenter. The relations between mitotic (constitutive) heterochromatin and α- and β-heterochromatin are not fully understood. In the present work, we have studied the polytenization of the rolled (rl) locus, a 100-kb genomic region that maps to the proximal heterochromatin of chromosome 2 and has been previously thought to contribute to α-heterochromatin. We show that rolled undergoes polytenization in salivary gland chromosomes to a degree comparable to that of euchromatic genes, despite its deep heterochromatic location. In contrast, both the Bari-1 sequences and the AAGAC satellite repeats, located respectively to the left and right of rl, are severely underrepresented and thus both appear to be α-heterochromatic. In addition, we found that rl is transcribed in polytene tissues. Together, the results reported here indicate that functional sequences located within the proximal constitutive heterochromatin can undergo polytenization, contributing to the formation of β-heterochromatin. The implications of this finding to chromocenter structure are discussed.     

Preliminary observations using HIV-specific transfer factor in AIDS

Twenty five HIV-1-infected patients, at various stages (CDC II, III and IV) were treated orally with HIV-1-specific transfer factor (TF) for periods varying from 60 to 1870 days. All patients were receiving antiviral treatments in association with TF. The number of lymphocytes, CD4 and CD8 subsets were followed and showed no statistically significant variations. In 11/25 patients the number of lymphocytes increased, whilst in 11/25 decreased; similarly an increase of the CD4 lymphocytes was observed in 11/25 patients and of the CD8 lymphocytes in 15/25. Clinical improvement or a stabilized clinical condition was noticed in 20/25 patients, whilst a deterioration was seen in 5/25. In 12/14 anergic patients, daily TF administration restored delayed type hypersensitivity to recall antigens within 60 days. These preliminary observations suggest that oral HIV-specific TF administration, in association with antiviral drugs, is well tolerated and seems beneficial to AIDS patients, thus warranting further investigation.