Parasites in hybridizing communities: the Red Queen again?

Over the past two decades, infection levels in hybrids have frequently been compared with those in their progenitor species to find out whether parasites favour or penalize hybridization. Four static infection scenarios are possible, depending on whether hybrid resistance differs from that of one or both parental species. All four alternatives have been supported by some empirical data, but any potential dynamics might have been overlooked because of limited sampling or experimental designs. However, coevolutionary oscillations generated by frequency-dependent selection might provide a better explanation for the observed results than does a static genetic perspective of host resistance.     

Mate Choice and Reproductive Success in the American Kestrel: a Role for Blood Parasites?

Blood parasites of breeding American kestrels, Falco sparverius (40 males and 27 females), were investigated to determine their connections to male showiness, mating success and host fitness. The only haematozoan found in the blood films was Haemoproteus tinnunculi (overall prevalence of 74% for females and 53% for males). In adult (+ 1-year-old) males, the subterminal tail band (character apparently used in female mate choice) was wider in infected males than in non-infected males. This was consistent with the Hamilton—Zuk hypothesis of parasite-mediated sexual selection. Our results also suggest that reproductive effort may increase susceptibility to parasitism. In yearling males, the proportion of individuals infected with H. tinnunuli was higher among those tending a large than a small brood at the time of fledging. Hunting effort (proportion of time spent in flight-hunting and wind-hovering) was also higher for males tending large broods than for those tending small broods, and it was higher for yearling than adult males on a given brood size. Reproductive effort may result in greater exposure and/or decreased ability to control chronic latent infections. Parasitic infections, in turn, may have detrimental effects on host fitness.     

Parasites: proxies for host genealogy and ecology?

Genetic information is used extensively to reconstruct the evolutionary and demographic history of organisms. Recently, it has been suggested that genetic information from some parasites can complement genetic data from their hosts. This approach relies upon the hypothesis that such parasites share a common history with their host. In some cases, parasites provide an additional source of information because parasite data can better reconstruct the common history. Here, we discuss which parasite traits are important in determining their usefulness for analysing host history. The key is the matching of the traits of the parasite (e.g. effective population size, generation time, mutation rate and level of host specificity) with the timescales (phylogenetic, phylogeographic and demographic) that are relevant to the issues of concern in host history.     

Taranabant Cuts the Fat: New Hope for Cannabinoid-Based Obesity Therapies?

Endocannabinoid/cannabinoid receptor signaling acts centrally and peripherally to govern appetite and energy balance. While system stimulation promotes eating and energy storage, receptor blockade can reduce food intake and facilitate weight loss. In this issue of Cell Metabolism, Addy et al. (2008) test the therapeutic antiobesity potential of taranabant, a cannabinoid 1 receptor inverse agonist.     

Parasites in biodiversity conservation: friend or foe?

Parasites stabilise food webs and facilitate species coexistence but can also lead to population- or species-level extinctions. So, in biodiversity conservation, are parasites friends or foes? This question is misleading: it implies that parasites are not part of biodiversity. Greater integration of parasites into global biodiversity and ecosystem conservation efforts is required.     

What Capabilities for the Animal?

In this essay, I defend a bi-constructivist approach to ethology—a constructivist ethology assuming that each animal adopts constructivist strategies. I put it in opposition to what I call a realist-Cartesian approach, which is currently the dominant approach to ethology and comparative psychology. The starting point of the bi-constructivist approach can be formulated as a shift from the classical Aristotelian question “What is an animal?” to the Spinozean question, which is much less classical but which seems to me to be much stronger: “What are the capacities of the animal?”. Is it possible to conceptualize an ethology which insists on interpretation and therefore on invention, innovation and creativity, rather than on causality, the monotony of behavioural routines, and/or genetic or environmental determination? Such an ethology would be based not on the fiction of an absent observer but on fully recognizing the necessity of an observer, who is effectively present in order to get an observation. A pluralistic ethology does not dissociate itself from the marginal epistemologies of practitioners like animal trainers, hunters, stockbreeders etc., or, moreover, non-western experts. An ethology of this kind is not clamped within the boundaries of purely academic epistemology, obsessed by demarcation lines between the human and the animal. My work on the bi-constructivist approach represents a contribution towards the elaboration of an authentically biosemiotic ethology, one which is significantly different from the mechanical ethology of today.     

Autophagy in Apicomplexa: a life sustaining death mechanism?

Programmed cell death (PCD) pathways remain understudied in parasitic protozoa in spite of the fact that they provide potential targets for the development of new therapy. The best understood PCD pathway in higher eukaryotes is apoptosis although emerging evidence also points to autophagy as a mediator of death in certain physiological contexts. Bioinformatic analyses coupled with biochemical and cell biological studies suggest that parasitic protozoa possess the capacity for PCD including a primordial form of apoptosis. Recent work in Toxoplasma and emerging data from Plasmodium suggest that autophagy-related processes may serve as an additional death promoting pathway in Apicomplexa. Detailed mechanistic studies into the molecular basis for PCD in parasitic protozoa represent a fertile area for investigation and drug development.     

Parasites lost? An overlooked hypothesis for the evolution of alternative reproductive strategies in amphibians

Amphibians exhibit the greatest diversity of reproductive strategies of all tetrapod vertebrates. While authors have traditionally attributed the evolution of these strategies to factors such as complex topography, unpredictable larval environments, and predation on larvae and eggs, support for any of these hypotheses has been limited. Importantly, most authors have ignored parasites, including unicellular pathogens and multicellular parasites, as selective agents capable of influencing amphibian evolution. Insights in disease transmission, amphibian immunity, and their interaction with various life histories require that we consider parasites to be selective pressures in our exploration of the evolution of amphibian reproductive strategies. I review recent findings and describe how these principles converge to form a novel conceptual hypothesis for the evolution of alternative reproductive strategies in amphibians. I offer some specific predictions and recommend that parasites be considered with other selective pressures when constructing formal, falsifiable hypotheses during evaluative studies of amphibian reproductive behavior.     

The plastid in Apicomplexa: what use is it?

An extrachromosomal genome of between 27 and 35 kb has been described in several apicomplexan parasites including Plasmodium falciparum and Toxoplasma gondii. Examination of sequence data proved the genomes to be a remnant plastid genome, from which all genes encoding photosynthetic functions had been lost. Localisation studies had shown that the genome was located within a multi-walled organelle, anterior to the nucleus. This organelle had been previously described in ultrastructural studies of several genera of apicomplexa, but no function had been attributed to it. This invited review describes the evolution of knowledge on the apicomplexan plastid, then discusses current research findings on the likely role of the plastid in the Apicomplexa. How the plastid may be used to effect better drug treatments for apicomplexan diseases, and its potential as a marker for investigating phylogenetic relationships among the Apicomplexa, are discussed.     

Hope for a broken heart?

Heart failure affects 23 million people worldwide and results from cardiac dysfunction characterized by decreased responsiveness to beta-adrenergic stimulation. A recent publication by W.J. Koch and colleagues highlights evidence for targeted beta-adrenergic receptor kinase (betaARK1) inhibition by gene transfer to improve contractile function and beta-adrenergic responsiveness in failing human myocardium. This proof-of-concept study has great importance for future heart failure therapy because it provides evidence for the therapeutic effectiveness of betaARK1 inhibition in failing human myocardium.     

What are the driving forces for water lifting in the xylem conduit?

After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal‐ and non‐invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high‐resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to ? 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel‐ and gas bubble‐supported interfacial gradients. The multiforce theory overcomes the problem of the Cohesion Theory that life on earth depends on water being in a highly metastable state.     

Hope for a broken heart?

Heated debate has surrounded the issue of whether adult stem cells can differentiate into cardiac myocytes and contribute to the function of the heart. In this issue of Cell, demonstrate stem cells in the adult rat heart that differentiate into cardiac myocytes in vitro and, when injected into the adult rat heart, can reconstitute the injured myocardium and improve function. These findings should weigh heavily in future debates about the existence of stem cells in the adult heart and their capacity for functional repair after injury.     

Parasites as probes for prehistoric human migrations?

Host-specific parasites of humans are used to track ancient migrations. Based on archaeoparasitology, it is clear that humans entered the New World at least twice in ancient times. The archaeoparasitology of some intestinal parasites in the New World points to migration routes other than the Bering Land Bridge. Helminths have been found in mummies and coprolites in North and South America. Hookworms (Necator and Ancylostoma), whipworms (Trichuris trichiura) and other helminths require specific conditions for life-cycle completion. They could not survive in the cold climate of the northern region of the Americas. Therefore, humans would have lost some intestinal parasites while crossing Beringia. Evidence is provided here from published data of pre-Columbian sites for the peopling of the Americas through trans-oceanic or costal migrations.     

What place for polyacrylamide in proteomics?

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) continues to deliver high quality protein resolution and dynamic range for the proteomics researcher. To remain as the preferred method for protein separation and characterization, several key steps need to be implemented to ensure quality sample preparation and speed of analysis. Here, we describe the progress made towards establishing 2D-PAGE as the optimal separation tool for proteomics research.     

Oxidative Stress in Phenylketonuria: What is the Evidence?

Phenylketonuria (PKU) is an inborn error of amino acid metabolism caused by severe deficiency of phenylalanine hydroxylase activity, leading to the accumulation of phenylalanine and its metabolites in blood and tissues of affected patients. Phenylketonuric patients present as the major clinical feature mental retardation, whose pathomechanisms are poorly understood. In recent years, mounting evidence has emerged indicating that oxidative stress is possibly involved in the pathology of PKU. This article addresses some of the recent developments obtained from animal studies and from phenylketonuric patients indicating that oxidative stress may represent an important element in the pathophysiology of PKU. Several studies have shown that enzymatic and non-enzymatic antioxidant defenses are decreased in plasma and erythrocytes of PKU patients, which may be due to an increased free radical generation or secondary to the deprivation of micronutrients which are essential for these defenses. Indeed, markers of lipid, protein, and DNA oxidative damage have been reported in PKU patients, implying that reactive species production is increased in this disorder. A considerable set of data from in vitro and in vivo animal studies have shown that phenylalanine and/or its metabolites elicit reactive species in brain rodent. These findings point to a disruption of pro-oxidant/antioxidant balance in PKU. Considering that the brain is particularly vulnerable to oxidative attack, it is presumed that the administration of appropriate antioxidants as adjuvant agents, in addition to the usual treatment based on restricted diets or supplementation of tetrahydrobiopterin, may represent another step in the prevention of the neurological damage in PKU.     

Creatine supplementation in health and disease: What is the evidence for long-term efficacy?

Creatine supplementation is an established ergogenic aid in sports and is now claimed to have therapeutical applications in a variety of diseases. The available literature mainly covers the short-term (one to several weeks) effects of creatine supplementation on skeletal muscle function in health and disease, which is of little help to evaluate the long-term (two or more months) potential of creatine as a drug in chronic disorders, such as neurodegenerative diseases or muscular dystrophies. Recent findings in healthy humans indicate that the beneficial effect on muscle function and muscle total creatine content may disappear when creatine is continuously ingested for more than two or three months. The mechanism for this habituation to chronic creatine exposure is poorly understood. The primary purpose of the present review article is to critically evaluate the available evidence for long-term efficacy of creatine administration and to hypothesize about ways to optimize creatine administration regimens.