Frequency and inheritance of non‐male producing clones in Daphnia magna: evolution towards sex specialization in a cyclical parthenogen?

In Daphnia (Cladocera, Crustacea), parthenogenetic reproduction alternates with sexual reproduction. Individuals of both sexes that belong to the same parthenogenetic line are genetically identical, and their sex is determined by the environment. Previously, non-male producing (NMP) genotypes have been described in species of the Daphnia pulex group. Such genotypes can only persist through phases of sexual reproduction if they co-occur with normal (MP) genotypes that produce both males and females, and thus the breeding system polymorphism is similar to gynodioecy (coexistence of females with hermaphrodites), which is well known in plants. Here we show that the same breeding system polymorphism also occurs in Daphnia magna, a species that has diverged from D. pulex more than 100 MY ago. Depending on the population, between 0% and 40% of D. magna females do not produce males when experimentally exposed to a concentration of the putative sex hormone methyl farnesoate that normally leads to male-only clutches. Natural broods of these NMP females never contained males, contrasting with high proportions of male offspring in MP females from the same populations. The results from a series of crossing experiments suggest that NMP is determined by a dominant allele at a single nuclear locus (or a several closely linked loci): NMP × MP crosses always yielded 50% NMP and 50% MP offspring, whereas MP × MP crosses always yielded 100% MP offspring. Based on cytochrome c oxidase subunit I-sequences, we found that NMP genotypes from different populations belong to three highly divergent mitochondrial lineages, potentially representing three independent evolutionary origins of NMP in D. magna. Thus, the evolution of NMP genotypes in cyclical parthenogens may be more common than previously thought. Moreover, MP genotypes that coexist with NMP genotypes may have responded to the presence of the latter by partially specializing on male production. Hence, these populations of D. magna may be a model for an evolutionary transition from a purely environmental to a partially genetic sex determination system.     

Novel mitochondria-targeted compounds composed of natural constituents: Conjugates of plant alkaloids berberine and palmatine with plastoquinone

Novel mitochondria-targeted compounds composed entirely of natural constituents have been synthesized and tested in model lipid membranes, in isolated mitochondria, and in living human cells in culture. Berberine and palmatine, penetrating cations of plant origin, were conjugated by nonyloxycarbonylmethyl residue with the plant electron carrier and antioxidant plastoquinone. These conjugates (SkQBerb, SkQPalm) and their analogs lacking the plastoquinol moiety (C10Berb and C10Palm) penetrated across planar bilayer phospholipid membrane in their cationic forms and accumulated in isolated mitochondria or in mitochondria in living human cells in culture. Reduced forms of SkQBerb and SkQPalm inhibited lipid peroxidation in isolated mitochondria at nanomolar concentrations. In isolated mitochondria and in living cells, the berberine and palmatine moieties were not reduced, so antioxidant activity belonged exclusively to the plastoquinol moiety. In human fibroblasts, nanomolar SkQBerb and SkQPalm prevented fragmentation of mitochondria and apoptosis induced by exogenous hydrogen peroxide. At higher concentrations, conjugates of berberine and palmatine induced proton transport mediated by free fatty acids both in model and in mitochondrial membrane. In mitochondria this process was facilitated by the adenine nucleotide carrier. As an example of application of the novel mitochondria-targeted antioxidants SkQBerb and SkQPalm to studies of signal transduction, we discuss induction of cell cycle arrest, differentiation, and morphological normalization of some tumor cells. We suggest that production of oxygen radicals in mitochondria is necessary for growth factors-MAP-kinase signaling, which supports proliferation and transformed phenotype.     

Chromosomal localization and molecular organization of the human genomic fragment containing the TNF/LT locus in transgenic mice

The molecular organization, copy number, and chromosome location of the human TNF/LT transgenes were studied in the genomes of two transgenic mouse strains. One strain proved to carry two transgene copies arranged head-to-tail and detected on chromosome 8 by karyotyping. The other strain had one transgene copy observed on chromosome 5. The strains provide a model for studying the physiological functions of the tumor necrosis factor and lymphotoxin.     

Evolutionary genetics of aging in Daphnia

Evolutionary theory of aging stipulates that aging is inevitable consequence of low effectiveness of natural selection acting on traits expressed late in the life span of the organisms. Two main hypotheses exist: the neutralist mutation-accumulation theory and selectionist antagonistic pleiotropy theory. Both theories predict the increase of genetic variance with age; the antagonistic pleiotropy theory also predicts negative genetic correlation between fitness related traits in the beginning and in the end of the life span. In order to test these predictions we measured life expectancy and age specific mortality in cohorts of 26 c lones of Daphnia magna extracted from a single cyclic parthenogen population. Simultaneously, fecundity and age to maturity were measured in representatives of the same clones. Log mortality increased linearly with age, with little evidence for leveling off, although some replicate cohorts did show a significant leveling off of mortality. Genetic variance of log mortality was significantly higher in the last quarter of the life span than in earlier time intervals. There was a significant positive genetic correlation between early fecundity and early mortality, but not between early fecundity and late mortality. This indicates that, although there is a trade-off between fecundity and survival, this trade-off is not based on pleiotropy across ages and therefore the data does not support the prediction of antagonistic pleiotropy theory.     

Chromosomal localization and molecular organization of human genomic fragment containing TNF/LT locus in transgenic mice

Molecular organization, copy number and chromosomal localization of human TNF/LT locus fragment were determined in genomes of two transgenic mouse lines. Genome of the first one contains two copies, organized in head-to-tail manner and determined on eighth chromosome by karyotyping; single transgene copy of the second line is observed on the fifth chromosome. These mice could serve as valuable model for studying both human tumor necrosis factor and lymphotoxin physiological functions.     

The first example of fluorescence of the solid individual compounds of Eu2+ ion: EuCl2, EuI2, EuBr2

Fluorescence (FL) from Eu²⁺ ion solid individual compounds was observed for the first time using the examples EuCl₂, EuI₂ and EuBr₂. Fluorescence was detected at excitation by ultraviolet (UV) light from powdered samples of Eu (II) halides at room temperature (RT) in an argon atmosphere. In air, FL of all Eu²⁺ compounds studied was stable, and intensity persisted for weeks. Depending on the nature of the halide anion and due to a nephelauxetic effect, the position of the maxima in the FL spectra underwent a red shift in the series: EuCl₂ (409 nm) < EuBr₂ (428 mm) < EuI₂ (432 nm). The lifetimes of the excited states of the Eu²⁺* ions for EuI₂, EuCl₂ and EuBr₂ were 355, 76 and 54 ns, respectively.     

Uncovering Cryptic Asexuality in Daphnia magna by RAD Sequencing

The breeding systems of many organisms are cryptic and difficult to investigate with observational data, yet they have profound effects on a species’ ecology, evolution, and genome organization. Genomic approaches offer a novel, indirect way to investigate breeding systems, specifically by studying the transmission of genetic information from parents to offspring. Here we exemplify this method through an assessment of self-fertilization vs. automictic parthenogenesis in Daphnia magna. Self-fertilization reduces heterozygosity by 50% compared to the parents, but under automixis, whereby two haploid products from a single meiosis fuse, the expected heterozygosity reduction depends on whether the two meiotic products are separated during meiosis I or II (i.e., central vs. terminal fusion). Reviewing the existing literature and incorporating recombination interference, we derive an interchromosomal and an intrachromosomal prediction of how to distinguish various forms of automixis from self-fertilization using offspring heterozygosity data. We then test these predictions using RAD-sequencing data on presumed automictic diapause offspring of so-called nonmale producing strains and compare them with “self-fertilized” offspring produced by within-clone mating. The results unequivocally show that these offspring were produced by automixis, mostly, but not exclusively, through terminal fusion. However, the results also show that this conclusion was only possible owing to genome-wide heterozygosity data, with phenotypic data as well as data from microsatellite markers yielding inconclusive or even misleading results. Our study thus demonstrates how to use the power of genomic approaches for elucidating breeding systems, and it provides the first demonstration of automictic parthenogenesis in Daphnia.     

Effect of selection on heterozygosity of farm animals

A stabilizing selection which is made in cattle according to phenotypic characters affects simultaneously a genetic character--the level of individual heterozygosity++. As a result animals with mean (modal) level of heterozygosity++ have the least probability of elimination. Similarly, the driving selection in pigs and horses leads to a change in both phenotypic characters and genetic character, the level of individual heterozygosity++. In this case the most heterozygous animals have the least probability of elimination.