Egg phenotype matching by cuckoos in relation to discrimination by hosts and climatic conditions

Although parasites and their hosts often coexist in a set of environmentally differentiated populations connected by gene flow, few empirical studies have considered a role of environmental variation in shaping correlations between traits of hosts and parasites. Here, we studied for the first time the association between the frequency of adaptive parasitic common cuckoo Cuculus canorus phenotypes in terms of egg matching and level of defences exhibited by its reed warbler Acrocephalus scirpaceus hosts across seven geographically distant populations in Europe. We also explored the influence of spring climatic conditions experienced by cuckoos and hosts on cuckoo-host egg matching. We found that between-population differences in host defences against cuckoos (i.e. rejection rate) covaried with between-population differences in degree of matching. Between-population differences in host egg phenotype were associated with between-population differences in parasitism rate and spring climatic conditions, but not with host level of defences. Between-population differences in cuckoo egg phenotype covaried with between-population differences in host defences and spring climatic conditions. However, differences in host defences still explained differences in mimicry once differences in climatic conditions were controlled, suggesting that selection exerted by host defences must be strong relative to selection imposed by climatic factors on egg phenotypes.     

Disappearance of eggs from nonparasitized nests of brood parasite hosts: the evolutionary equilibrium hypothesis revisited

The evolutionary equilibrium hypothesis was proposed to explain variation in egg rejection rates among individual hosts (intra‐ and interspecific) of avian brood parasites. Hosts may sometimes mistakenly reject own eggs when they are not parasitized (i.e. make recognition errors). Such errors would incur fitness costs and could counter the evolution of host defences driven by costs of parasitism (i.e. creating equilibrium between acceptors and rejecters within particular host populations). In the present study, we report the disappearance of host eggs from nonparasitized nests in populations of seven actual and potential hosts of the common cuckoo Cuculus canorus. Based on these data, we calculate the magnitude of the balancing parasitism rate provided that all eggs lost are a result of recognition errors. Importantly, because eggs are known to disappear from nests for reasons other than erroneous host rejection, our data represent the maximum estimates of such costs. Nonetheless, the disappearance of eggs was a rare event and therefore incurred low costs compared to the high costs of parasitism. Hence, costs as a result of recognition errors are probably of minor importance with respect to opposing selective pressure for the evolution of egg rejection in these hosts. We cannot exclude the possibility that low or intermediate egg rejection rates in some host populations may be caused by spatiotemporal variation in the occurrence of parasitism and gene flow, creating a variable influence of opposing costs as a result of recognition errors and the costs of parasitism.     

Leaf Litter Inhibits Growth of an Amphibian Fungal Pathogen

Past studies have found a heterogeneous distribution of the amphibian chytrid fungal pathogen, Batrachochytrium dendrobatidis (Bd). Recent studies have accounted for some of this heterogeneity through a positive association between canopy cover and Bd abundance, which is attributed to the cooling effect of canopy cover. We questioned whether leaf litter inputs that are also associated with canopy cover might also alter Bd growth. Leaf litter inputs exhibit tremendous interspecific chemical variation, and we hypothesized that Bd growth varies with leachate chemistry. We also hypothesized that Bd uses leaf litter as a growth substrate. To test these hypotheses, we conducted laboratory trials in which we exposed cultures of Bd to leachate of 12 temperate leaf litter species at varying dilutions. Using a subset of those 12 litter species, we also exposed Bd to pre-leached litter substrate. We found that exposure to litter leachate and substrate reduced Bd spore and sporangia densities, although there was substantial variation among treatments. In particular, Bd densities were inversely correlated with concentrations of phenolic acids. We conducted a field survey of phenolic concentrations in natural wetlands which verified that the leachate concentrations in our lab study are ecologically relevant. Our study reinforces prior indications that positive associations between canopy cover and Bd abundance are likely mediated by water temperature effects, but this phenomenon might be counteracted by changes in aquatic chemistry from leaf litter inputs.     

Human NCU-G1 can function as a transcription factor and as a nuclear receptor co-activator

Background  

Novel, uncharacterised proteins represent a challenge in biochemistry and molecular biology. In this report we present an initial functional characterization of human kidney predominant protein, NCU-G1.     

Neurotoxicological Examination of the Piglet Brain after Prenatal and Postnatal Exposure to Trichlorfon

Piglets were given 10 repeated doses of the orga-nophosphorus compound trichlorfon during the postnatal period in order to examine the effect on the brain development (Experiment 1). Following prenatal exposure to trichlorfon, the ability of a presumptive hypoplastic cerebellum and cerebrum at birth, to regenerate postnatally was investigated (Experiment 2). Administration of repeated doses of trichlorfon postnatally was accompanied by only small changes in brain weights, morphology and transmitter enzyme activity (choline acetyltransferase, glutamate decarboxylase, aromatic amino acid decarboxylase) in 35 days old piglets. Animals exposed prenatally, and sacrificed at the age of 35 days, showed a significant increase in brain weights and enzyme activities. The animals did, however, not reach control values in cerebral weight, cerebellar weight or total enzyme activities. Morphological changes still showed regional loss of Purkinje cells in the cerebellum. The study clearly indicated that the pig brain was less vulnerable to trichlorfon in the postnatal period of development than when exposed to the compound prenatally.     

The Acute Effect of Ammonium Acetate on Levels of Amino Acids in the Intact and Decorticated Rat Neostriatum

Unilateral frontal cortex ablations were performed in rats so that the glutamate terminals in the ipsilateral rostral neostriatum were removed. At 1 or 7 days later, intraperitoneal injections of ammonium acetate induced different changes in amino acid concentrations in the intact and deafferentated neostriatum. After 1 day, the level of glutamate decreased only in the intact side, whereas that of glutamine increased and that of aspartate decreased to the same extent on both sides following ammonia injection. After 7 days, the glutamate level decreased more in the intact than the decorticated side in both nonconvulsing and convulsing rats. The concentration of alanine increased most in the intact neostriatum, whereas glutamine levels increased and aspartate levels decreased to the same extent on both sides in nonconvulsing and convulsing rats. The results indicate that ammonia has a more pronounced effect on neuronal than glial glutamate pools.     

The genetic basis of altitudinal variation in the wood frog Rana sylvatica II. An experimental analysis of larval development

Summary The variation in larval developmental patterns in the wood frog, Rana sylvatica, along an elevation gradient of 1,000 m was experimentally studied. Larval populations at high elevation ponds had lower growth rates, developmental rates and were larger at all stages (including metamorphic climax) than larval populations developing in low elevation ponds. There was considerable variation among ponds within each elevation in both the length of the larval period and size at metamorphic climax. Reciprocal transplant experiments and controlled laboratory experiments revealed that most of the observed variation between high and low elevation populations could be explained by the effects of temperature induction during ontogeny. Significant genetic differences in growth rates and non-genetic maternal effects on developmental rates between larvae of mountain origin and lowland origin were also demonstrated. Selection in both environments has acted to minimize the prevailing environmental effect of pond temperature on developmental rates, but has accentuated the prevailing environmental effects on larval body size. As a consequence mountain larvae were capable of completing metamorphosis sooner and at a larger size in all environments than lowland larvae.     

Amino acid neurotransmission: Dynamics of vesicular uptake

Glutamate, GABA and glycine, the major neurotransmitters in CNS, are taken up and stored in synaptic vesicles by a Mg²⁺-ATP dependent process. The main driving force for vesicular glutamate uptake is the membrane potential, whereas both the membrane potential and the proton gradient contribute to the uptake of GABA and glycine. Glutamate is taken up by a specific transporter with no affinity for aspartate. Evans blue and related dyes are competitive inhibitors of the uptake of glutamate. GABA, β-alanine, and glycine are taken up by the same family of transporter molecules. Aspartate, taurine, and proline are not taken up by any synaptic vesicle preparations. It is suggested that vesicular uptake and release are characteristics that identify these amino acids as neurotransmitters. We also discuss that “quanta” in the brain are not necessarily related the content of neurotransmitter in the synaptic vesicles, but rather to postsynaptic events. Special issue dedicated to Dr. Herman Bachelard.     

The ontogeny of the uptake systems for glutamate,GABA, and glycine in synaptic vesicles isolated from rat brain

The ontogeny of the uptake of glutamate, GABA and glycine into synaptic vesicles isolated from rat brain has been investigated. The vesicular uptake of the three amino acids increased with developmental age in parallel with synaptogenesis, indicating a functional role of uptake of the amino acids by synaptic vesicles in the nerve terminals. Uptake of the amino acids by plasma membrane particles (synaptosomes) in brain homogenate showed a somewhat different developmental profile. The uptake of glutamate increased markedly with developmental time, while the uptake of GABA showed only a slight increase. Uptake of glycine by plasma membrane particles was very low and therefore not registered. The observed developmental increase in uptake of glycine by synaptic vesicles isolated from brain, supports previous reports indicating that glycine can be taken up by vesicles from non-glycine terminals.Special issue dedicated to Dr. Morris H. Aprison.