Are two South-Western Atlantic wrasses involved in a case of social mimicry?

Journal of Ethology - We investigated whether two South-Western Atlantic wrasses [Halichoeres penrosei (models) and Thalassoma noronhanum (mimics)] were involved in social mimicry. In mixed shoals,...     

Are allozymes differing in substrate specificity involved in the evolution of Silene species?

Summary The concerted action of two flavone-skeleton modifying genes, P and Me, and the alleles of three independently segregating loci g, gl and fg involved in flavone-glycosylation lead to the 33 different flavones so far identified in Silene. The alleles of the different loci involved in flavone-glycosylation control enzymes which differ in substrate specificity, a phenomenon not often described in higher organisms. The alleles of the different loci are variously distributed over the different species. The possible evolutionary implications of these distributions are discussed.     

Are active oxygen species involved in induction of β-carotene in Dunaliella bardawil?

The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil.     

Historical stability of diversity patterns in African estrildid finches (Aves: Estrildidae)?

Studying shifts in species diversity through time and space is an essential component of many aspects of biogeography and ecology. In this study, we predict the potential distribution of 61 species of African estrildid finches in order to assess current and past diversity patterns. Models were projected onto two climatic scenarios (Community Climate System Model, CCSM, and Model for Interdisciplinary Research on Climate, MIROC) representing past climate conditions, as might be expected during the Last Glacial Maximum 21 000 years BP. Subsequent overlays of the resulting potential distributions were conducted under different dispersal assumptions and compared with expert maps. Our results suggest highly similar current distribution patterns obtained by both methods. Projections onto Pleistocene scenarios showed similar patterns, with only small differences under limited and unlimited dispersal assumptions. Looking separately at diversity patterns predicted for forest and savannah species, diversity hot spots of forest species under MIROC conditions were consistent with suggested forest refugia, but were inconsistent under CCSM conditions. According to our models, savannah species were more widely distributed during the cooler and drier conditions of the Pleistocene. By using ecological niche models we show that current diversity patterns of a whole species group may have changed only slightly since the Pleistocene, suggesting a pattern of general spatial stability. However, we emphasize the importance of using different climatic scenarios as well as including the supposed dispersal of organisms in the modelling, as these factors influence results on a broad scale. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 455–470.     

Are polyphosphoinositides involved in platelet activation?

In human platelets, the amounts of triphosphoinositides (TPI) and diphosphoinositides (DPI) increase after 30 sec and level off after 120 sec of thrombin stimulation. After 180 sec of thrombin challenge, TPI and DPI increase accounts for 66 and 80%, respectively. Polyphosphoinositide changes roughly parallel the release of N-acetyl-beta-D-glucosaminidase and appear as a later event compared to aggregation and serotonin secretion. It is concluded that an increased phosphorylation of polyphosphoinositides might participate in platelets to the process of stimulus-activation coupling and might be linked to thrombin receptor occupancy. A role of DPI in platelet activation is suggested by the observation that DPI promote platelet aggregation, the mechanism of which is discussed.     

Are caveolae involved in clathrin-independent endocytosis?

In addition to endocytosing molecules via clathrin-coated pits, cells also internalize membrane and fluid by a clathrin-independent endocytic mechanism. In this article we search for the equivalent of clathrin-coated pits in clathrin-independent endocytosis, and discuss some pitfalls in the interpretation of electron micrographs. We also discuss how the early steps in clathrin-independent endocytosis might be analysed morphologically, and we argue that caveolae are not involved in clathrin-independent endocytosis.     

Acoustic divergence in two cryptic Hipposideros species: a role for social selection?

We present evidence that a relatively widespread and common bat from South East Asia comprises two morphologically cryptic but acoustically divergent species. A population of the bicoloured leaf-nosed bat (Hipposideros bicolor) from Peninsular Malaysia exhibits a bimodal distribution of echolocation call frequencies, with peaks in the frequency of maximum energy at ca. 131 and 142 kHz. The two phonic types are genetically distinct, with a cytochrome b sequence divergence of just under 7%. We consider the mechanisms by which acoustic divergence in these species might arise. Differences in call frequency are not likely to effect resource partitioning by detectable prey size or functional range. However, ecological segregation may be achieved by differences in microhabitat use; the 131kHz H. bicolor is characterized by significantly longer forearms, lower wing loading, a lower aspect ratio and a more rounded wingtip, features that are associated with greater manoeuvrability in flight that may enable it to forage in more cluttered environments relative to the 142 kHz phonic type. We suggest that acoustic divergence in these species is a consequence of social selection for a clear communication channel, which is mediated by the close link between the acoustic signal and receptor systems imposed by the highly specialized nature of the hipposiderid and rhinolophid echolocation system.     

Are species of bacteria unclassifiable?

Summary Every one of eleven different strains randomly selected from 10 different randomly selected genera have shown the same high frequency of occurrence of colony mutants as did almost all strains ofAcetobacter (previously considered outstanding in this respect). Correlation of other properties with such mutant colony forms was not specifically studied, but in 4 strains correlation was noticed, suggesting its presence in the others, as was so often found inAcetobacter. It is suggested from this, that a similar study of strains of other genera might reveal a similarly high frequency of occurrence of mutants, most so-called pure cultures being thus probably mixtures of different cells with different properties. Also the proportion of each cell-type in the culture may vary from predominance to extinction according to the biochemical and other tests applied for the purpose of the ‘characterization’ of the species for taxonomic purposes. If the classification of such varying mixtures is considered of doubtful use, then it seems to follow that ‘species’ of bacteria are virtually unclassifiable, and that even the conception of a genus should be on a broader basis than is often the case at present.     

Are gonadal steroid hormones involved in disorders of brain aging?

Human aging is associated with a decrease of circulating gonadal steroid hormones. Since these hormones act as trophic factors for neurones and glia, it is possible that the decrease in sex steroid levels may contribute to the increased risk of neurodegenerative disorders with advanced age. Sex steroids are neuroprotective in several animal models of central and peripheral neurodegenerative diseases, and clinical data suggest that these hormones may reduce the risk of neural pathology in aged humans. Potential therapeutic approaches for aged-associated neural disorders may emerge from studies conducted to understand the mechanisms of action of sex steroids in the nervous system of aged animals. Alterations in the endogenous capacity of the aged brain to synthesize and metabolize sex steroids, as well as possible aged-associated modifications in the signalling of sex steroid receptors in the nervous system, are important areas for future investigation.     

Are free radicals involved in tumor promotion?

Previously it was shown that lipophilic analogs of a free-radical scavenger, 2(3)-tert-butyl-4-hydroxyanisole (BHA), inhibit ornithine decarboxylase (ODC) activity which is induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse epidermis. With regard to this antitumor-promoting effect, eight analogs of BHA (2- and 3-BHA, 2-t-butyl-1, 4-dimethoxybenzene methyl-BHA), t-butylhydroquinone (t-BHQ), p-hydroquinone (HQ), 4-hydroxyanisole, phenol and 2-t-butylphenol) are evaluated herein for their antioxidant capacities for scavenging superoxide anions (O-2), of inhibiting lipid peroxidation and of inhibiting chemiluminescence (CL) in TPA-activated polymorphonuclear leukocytes (PMNs), an event associated with oxy-radical production. None of the analogs reacted with O-2, while 2- and 3-BHA suppressed the formation of O-2 by TPA-activated PMNs. T-BHQ underwent autoxidation in aqueous solution, reducing molecular oxygen and increasing the levels of O-2 that were formed chemically, enzymatically and cellularly. However, all of the phenolic antioxidant analogs of BHA inhibited TPA-stimulated CL in PMNs and ascorbate-initiated lipid peroxidation, while methyl-BHA (a non-antioxidant analog) was inactive. The inhibitory activities of these analogs for lipid peroxidation were related to both their lipophilic and antioxidant properties and corresponded favorably with their inhibitory activities for TPA-induced ODC activities in mouse epidermis. On the other hand, inhibition of the CL response by these antioxidants was independent of their lipophilicity and compared less favorably with their capacities to antagonize phorbol ester-induced ODC activity. These results imply that lipophilic BHA analogs inhibit TPA-induced ODC activity by scavenging free radicals other than O-2. Furthermore, the fact that t-BHQ was the most potent inhibitor of CL, lipid peroxidation and ODC activity and simultaneously reduced molecular oxygen, suggests the possibility that O-2 may act as a precursor to the formation of free radicals which are reactive with t-BHQ and more directly involved in the process of tumor promotion.     

Are astroglial cells involved in morphine tolerance?

Morphine gives rise to a cascade of events in the nervous system affecting, among others, neurotransmitter metabolism. Tolerance develops for various effects shortly after administration of the drug. Also, physical dependence develops and can be demonstrated by precipitation of withdrawal reactions. Biochemical events in nervous tissue have been extensively studied during morphine treatment. This overview will focus upon brain protein metabolism since macromolecular events might be of importance for development of long-term effects, such as tolerance and physical dependence. Both dose-and time-dependent changes in brain protein synthesis and the syntheses of specific proteins have been demonstrated after morphine treatment, although methodological considerations are important. Different experimental models (animal and tissue culture models) are presented. It might be interesting to note that astroglial protein synthesis and the secretion of proteins to the extracellular medium are both changed after morphine treatment, these having been evaluated in astroglial enriched primary cultures and in brain tissue slices. The possibility is suggested that proteins released from astroglial cells participate in the communication with other cells, including via synaptic regions, and that such communication might be of significance in modifying the synaptic membranes during morphine intoxication.     

Surface receptors: Are they involved in transformation of spermatozoa of Ascaris?

Exposure of the spheroidal spermatozoa of Ascaris suum to an extract of the male accessory gland causes their transformation into ameboid cells. We have investigated the mechanism of this transformation, also termed activation, by labeling the proteins of accessory gland extracts with fluorescein isothiocyanate (FITC) or [125I], followed by qualitative localization of the sperm activating substances (SAS) and quantitative measurements of [125I]-SAS binding. Fluorescent patches of FITC-conjugated SAS were localized at the spermatozoan surface and were concentrated primarily at the posterior region. Few fluorescent patches were detectable in the region of the newly formed pseudopodia following transformation. Although spermatozoan transformation occurs within 2-5 min after exposure to SAS, the fluorescent patches became more distinct after a minimum of 8 min and reached maximum density at 15-30 min. Spermatozoa activated with [125I]-SAS became radioactively labeled in direct proportion to the amount of available [125I]-SAS until a saturation level was reached. SDS-polyacrylamide gel electrophoresis combined with autoradiography indicated that the cells bind two SAS components, of small (9,000 MW) and large (56,000 MW) sizes. These same two components were also detectable in a membrane fraction, obtained by differential centrifugation, of the spermatozoa after incubation with [125I]-SAS. binding of the two SAS components was not inhibited by preincubation of the spermatozoa with trypsin or Concanavalin A; however, the 56,000 MW component of SAS was not detectable in autoradiograms of spermatozoa incubated with periodic acid (1.6-10 mM) treated SAS. Such cells also failed to transform into ameboid spermatozoa. These results indicate that the two components of SAS that bind to the spermatozoan surface are possibly responsible for inducing the cell transformations associated with activation.     

Are prostaglandins involved in atrial natriuretic peptide mechanisms of cardiovascular control?

Atrial natriuretic peptide (ANP) can excite cardiac nerve endings and invoke a decrease in arterial blood pressure and a reduction in renal sympathetic nerve activity. Our laboratory has previously demonstrated that this renal depressor reflex was invoked by systemic injection of ANP and not by the direct application of ANP to the epicardium, a major locus for vagal afferents. We now examine whether inhibition of prostaglandin synthesis impairs reflex responses that are normally associated with ANP injections. Renal sympathetic nerve activity, arterial blood pressure, and heart rate were recorded in anesthetized rats. Indomethacin was used to inhibit prostaglandin synthesis through the cyclooxygenase pathway. The ANP-mediated decrease in arterial blood pressure and renal sympathetic nerve activity, observed when prostaglandin synthesis was inhibited, did not differ significantly from the decreases observed in these parameters when prostaglandin synthesis was not inhibited. Heart rate remained unchanged. Our results suggest that the sympatho-inhibitory effects of ANP do not require prostaglandins as intermediary compounds.     

Phenotypic similarity in sympatric crow species: Evidence of social convergence?

Crows, rooks, and ravens (Corvus spp.) display marked morphological and voice similarities that have been hypothesized to stem from competitive interactions, as a case of nonaposematic mimicry. Here, I test predictions of the mimicry hypothesis at the macrovolutionary scale, examining whether species morphological and acoustic traits covary with those of coexisting congeners, and whether phenotypic similarity has facilitated the coexistence of related species after secondary contact. Body size and the temporal patterns of the commonest call display high levels of similarity among sympatric species, even after controlling for the effect of shared climate and habitat, and phylogenetic constraints in the production of variation. When sister species differed in these acoustic and morphological traits, their transition to secondary sympatry was delayed relative to those with more similar traits. No similarity was found in the sexual call of crows, suggesting that convergence occurs only when function does not favour maintenance of species‐specific traits. Crow similarities in morphological and acoustic features may therefore be associated with coevolving interactions with congeners, in line with a broad array of studies documenting convergence among species that interact aggressively or forage communally.     

Are accessory nuclei involved in the establishment of developmental gradients in hymenopteran oocytes?

Summary In the oocytes ofTenthredo olivacea, accessory nuclei (AN) are formed by budding from the nuclear envelope of the oocyte nucleus. Newly formed AN contain electron-dense material of nuclear origin and are surrounded by a double envelope devoid of pores. Such structures are subsequently transported to the peripheral ooplasm (periplasm), where they grow to reach a final diameter of 5 µm. In the envelopes of advanced AN nuclear pores arise. Through these pores nuage material is extruded into the surrounding periplasm. These findings are discussed with respect to a possible involvement of AN in the establishment of developmental gradients in hymenopteran oocytes.     

Are cyclic nucleotides involved in the initiation of mitogenic activation of human lymphocytes?

In order to obtain more insight into the possible role of cyclic AMP or cyclic GMP in modulating the initial cellular processes following activation of lymphocytes, we measured the effects of the T-cell mitogen concanavalin A and other substances including hormones on the cyclic nucleotide levels in human peripheral blood lymphocytes. The enzyme activities of the corresponding nucleotide cyclases, adenylate cyclase and guanylate cyclase were measured in both isolated plasma membranes or the cytosol of resting or concanavalin A stimulated rabbit thymocytes. Concanavalin A in a mitogenic concentration of about 5-10 micrograms/ml caused small, but consistent increases in cAMP but no changes in cGMP levels during the first hour of activation. Concomitantly, the specific activity of plasma membrane-bound adenylate cyclase was always increased at least 1.5-fold 30 min after stimulation of rabbit thymocytes with concanavalin A, but no effect could be detected on the specific activities of plasma membrane-bound or soluble guanylate cyclase. At high, supraoptimal concentrations of concanavalin A (more than 20 micrograms/ml) cAMP levels dramatically increased in human lymphocytes within minutes, but cGMP levels again were unaffected. Forskolin and beta-adrenergic hormones elevated cAMP in human lymphocytes, whereas cGMP levels were increased by the addition of sodium nitroprusside or alpha-adrenergic hormones. Sodium nitroprusside, in concentrations which elevated cGMP in human lymphocytes, had no influence on the incorporation of [3H]uridine into RNA of resting or concanavalin A stimulated human lymphocytes. Addition of forskolin resulted in an increase of cAMP levels and a dose-dependent decrease of [3H]uridine incorporation into RNA of concanavalin A-stimulated lymphocytes with no effect on resting lymphocytes. The data suggest that cGMP does not play a role in the initial phase of mitogenic activation of lymphocytes, whereas cAMP may be involved in the blast transformation process as an inhibitory signal.     

Are there latitudinal gradients in species turnover?

Aim To examine the effect on the observed relationship between spatial turnover and latitude of both the measure of beta diversity used and the method of analysis. Location The empirical analyses presented herein are for the New World. Methods We take the spatial distributions of the owls of the New World as an exemplar data set to investigate the patterns of beta diversity across latitudes revealed by different analytical methods. To illustrate the strengths and weaknesses of alternative measures of beta diversity and different analytical approaches, we also use a simple random distribution model, focusing in particular on the influence of richness gradients and landmass geometry. Results Our simple spatial model of turnover demonstrates that different combinations of analytical approach and measure of beta diversity can give rise to strikingly different relationships between turnover and latitude. The analyses of the bird data for the owls of the New World demonstrate that this observation extends to real data. Conclusions For the particular assemblage considered, we present strong evidence that species richness declines at higher latitudes, and there is also some evidence that species turnover is greater nearer the equator, despite conceptual and practical difficulties involved in analysing spatial patterns of species turnover. We suggest some ways of overcoming these difficulties.     

Are osmotic forces involved in influenza virus-cell fusion?

The kinetics of the fusion process of unsealed and resealed erthyrocyte ghosts with influenza virus (A/PR8/34, A/Chile 1/83), were measured under hypotonic, isotonic and hypertonic conditions using a recently developed fluorescence assay (Hoekstraet al. (1984)Biochemistry 23:5675–5681]. No correlation between the external osmotic pressure and kinetics and extent of fusion was observed. Influenza viruses fuse as effectively with unsealed ghosts as with resealed ghosts. It is concluded that osmotic forces as well as osmotic swelling of cells are not necessary for virus-cell membrane fusion.     

Are hyaluronan receptors involved in three-dimensional cell migration?

Hyaluronan (HA), an unbranched polysaccharide consisting of repeated glucuronic acid/N-acetylglucosamine disaccharide units, is ubiquitously present in the extracellular matrix of many tissues (for a more comprehensive review see: Fraser et al., 1997). Increased amounts of hyaluronan are produced by solid tumors and tumor-associated fibroblasts, and tumor-induced HA is correlated with poor prognosis. HA is well known to stimulate the migration of a large variety of cell types. Stimulation of cell migration by HA has been explained by different mechanisms. HA was shown to specifically bind to cell surface receptors, and inhibition of HA-receptor function was demonstrated to decrease cell migration and tumor growth. On the other hand, HA as a large hydrophilic molecule is also known to modulate the extracellular packing of collagen and fibrin, leading to increased fiber size and porosity of extracellular substrates. Hence a modified matrix architecture might similarly account for increased locomotion of cells. In this review, we attempted to summarize the available data on HA-induced cell migration, with particular emphasis on the role of HA receptors in three-dimensional cell migration. Although the HA receptor CD44 has been shown to mediate migration of cells over two-dimensional hyaluronan-coated surfaces in vitro, there is only little evidence that HA-binding to CD44 or other HA receptors has major impact on the locomotion of cells through three-dimensional matrices in vivo. We showed recently that the promigratory effect of HA in fibrin gels is largely due to HA-mediated modulation of fibrin polymerization. By increasing the porosity of fibrin gels, HA strongly accelerates cell migration. The porosity of matrices therefore appears as an important and probably underestimated determinant of cell migration and tumor spread.