Does habitat-specific variation in trematode infection risks influence habitat distribution of two closely related freshwater snails?

Parasitism may be an important factor determining the geographic distribution of closely related species. A habitat-specific risk of parasitism may lead to exclusion of susceptible host types from parasite-rich environments, and promote speciation if it leads to reproductive isolation between susceptible and resistant types. We surveyed populations of the freshwater snail Lymnaea peregra for differences in habitat distribution and trematode parasitism between its two distinct shell morphs, L. ovata and L. peregra. We surveyed 58 populations (43 L. ovata, 15 L. peregra). At each location we recorded an array of habitat characteristics that were summarized using a nonlinear principal components analysis. This yielded two orthogonal habitat score variables. Discriminant analysis with these habitat dimensions indicated that the snail morphs differed in their habitat distribution. L. ovata preferred larger, more permanent natural habitats surrounded by forests, while L. peregra was found more often at a higher altitude, in nonpermanent habitats, often surrounded by meadows. The snails were parasitized by four cercarial types of castrating trematodes. The morphs had a similar prevalence of infection by each of the parasite types, with one exception: monostomid cercariae were found at a higher prevalence in L. ovata than in L. peregra. However, monostomes were rare parasites, and the difference in prevalence of infection was not significant when only populations with monostomes were compared. Our results indicate that variation in the overall prevalence of infection seems to be independent of snail morph, and do not support the idea that a difference in the rate of parasitism might explain differences in the habitat distribution of these snail morphs. Received: 4 January 1999 / Accepted: 30 June 1999     

Does endocytosis occur in fungal hyphae?

The evidence and arguments for and against the occurrence of endocytosis in fungal hyphae are summarized. The balance of evidence is in favour of the existence of endocytosis. This is supported by an analysis of the recently sequenced Neurospora genome which strongly suggests that this fungus possesses the complex protein machinery required to conduct endocytosis.     

Does follicular dominance occur in ewes?

The process by which a single follicle is selected to ovulate while others regress is unknown in ewes. If the dominant follicle secretes substances that directly inhibit the growth of other follicles, the superovulatory response to the administration of exogenous gonadotrophins may be blunted. Administration of 1250 iu pregnant mares' serum gonadotrophin (PMSG) before or after the emergence of the dominant follicle in the follicular phase, or 1000 iu PMSG in the presence or absence of a large healthy or atretic follicle during the luteal phase did not affect the induced ovulatory response. Comparisons between the ovary with or without the dominant follicle did not reveal any differences in ovulatory response to PMSG. The in-vitro features (i.e. mitotic index, oestradiol and testosterone production) of follicles ipsilateral or contralateral to the dominant follicle during the early and late follicular phases were also similar. If the dominant follicle secretes substances detrimental to the other follicles, this could be mimicked in vitro. Co-culture of small follicles with the largest follicles in a closed system did not reduce their incorporation of 3H thymidine in granulosa cells, compared with small follicles cultured alone. These data suggest that dominance is probably not operative in sheep. The administration of 500 iu of PMSG during the midfollicular phase increased ovulation rate in Merino ewes, indicating that dominance is essentially passive in ewes and can easily be overcome by raising gonadotrophin concentration.     

Does protein synthesis occur in the nucleus?

Although it is universally accepted that protein synthesis occurs in the cytoplasm, the possibility that translation can also take place in the nucleus has been hotly debated. Reports have been published claiming to demonstrate nuclear translation, but alternative explanations for these results have not been excluded, and other experiments argue against it. Much of the appeal of nuclear translation is that functional proofreading of newly made mRNAs in the nucleus would provide an efficient way to monitor mRNAs for the presence of premature termination codons, thereby avoiding the synthesis of deleterious proteins. mRNAs that are still in the nucleus-associated fraction of cells are subject to translational proofreading resulting in nonsense-mediated mRNA decay and perhaps nonsense-associated alternate splicing. However, these mRNAs are likely to be in the perinuclear cytoplasm rather than within the nucleus. Therefore, in the absence of additional evidence, we conclude that nuclear translation is unlikely to occur.     

Does respiratory sinus arrhythmia occur in fishes?

The hypothesis that respiratory modulation of heart rate variability (HRV) or respiratory sinus arrhythmia (RSA) is restricted to mammals was tested on four Antarctic and four sub-Antarctic species of fish, that shared close genotypic or ecotypic similarities but, due to their different environmental temperatures, faced vastly different selection pressures related to oxygen supply. The intrinsic heart rate (fH) for all the fish species studied was approximately 25% greater than respiration rate (fV), but vagal activity successively delayed heart beats, producing a resting fH that was synchronized with fV in a progressive manner. Power spectral statistics showed that these episodes of relative bradycardia occurred in a cyclical manner every 2-4 heart beats in temperate species but at >4 heart beats in Antarctic species, indicating a more relaxed selection pressure for cardio-respiratory coupling. This evidence that vagally mediated control of fH operates around the ventilatory cycle in fish demonstrates that influences similar to those controlling RSA in mammals operate in non-mammalian vertebrates.     

Does macrovesicular endocytosis occur in fungal hyphae?

Like most eukaryotic organisms, fungi use endocytosis for nutrition, signal transduction, turnover of plasma membrane molecules, etc. It is generally accepted that in filamentous fungi, as in yeast, invaginations of the plasma membrane of a small size (up to about 100 nm) are formed in the early stages of endocytosis. These invaginations are surrounded by a rigid actin scaffold – an actin patch, and give rise to small primary endocytic vesicles after scission from the plasma membrane. However, in classical mycological studies, complex large-volume invaginations of the plasma membrane – lomasomes – were described in filamentous fungi. In our time, in a number of filamentous basidiomycetes when tracking endocytosis using styryl fluorescent labels, large invaginations of the plasma membrane have been found, presumably forming endocytic macrovesicles after scission. In this paper, for comparison, large-sized types of endocytosis in animal cells are briefly described. Information about tubular endocytic invaginations in fungi is presented. Three types of large invaginations of the plasma membrane, detected at the TEM level in basidiomycetes, are characterized. The main question this paper addresses is whether or not filamentous fungi do have an analogue of animal macropinocytosis – macrovesicular endocytosis. There are some indications that the answer to this question is yes, but further research is needed. The presence of macrovesicular endocytosis may change the well-established beliefs about the cellular organization of filamentous fungi and the physiology of their nutrition.     

Does glycolate decarboxylation occur in intact leaf peroxisomes?

Release of ¹⁴CO₂ during metabolism of [1-¹⁴C]glycolate was studied in purified, intact and Triton X-100-solublized peroxisomes isolated from leaves of Secale cereale. Decarboxylation, apparently resulting from H₂O₂ attack on glyoxylate, was stimulated in both intact and solubilized peroxisomal preparations by the catalase inhibitors aminotriazole and sodium azide. CO₂ evolution was also observed in solubilized peroxisomes in the absence of inhibitor when an amino donor was not provided for conversion of glyoxylate to glycine. Loss of CO₂ from labelled glycolate in the absence of amino donors was reduced by addition of exogenous catalase to the reaction medium.Intact peroxisomes showed no glycolate decarboxylation whether or not amino donors were supplied. It appears that the CO₂ release from glycolate observed in previous investigations may be an artifact of the peroxisomal preparations and the assay systems used, and not a significant factor in photorespiratory metabolism in vivo.     

Does autoregulation of megakaryocytopoiesis occur?

Although a major regulator of thrombocytopoiesis is the number of circulating platelets, several observations suggest that independent alternative regulatory mechanisms may exist. In some situations there is a curious association of megakaryocytopenia and megakarocytic macrocytosis in spite of normal platelet counts. If macrocytosis is considered as a sign of stimulation, this association suggests a cause and effect relationship between decreased numbers and increased size of megakaryocytes. This thesis was tested by examining the delayed effects of sublethal irradiation and the acute effects of hydroxyurea in mice. It was found that megakaryocytopenia and macromegakaryocytosis occurred together and that platelets counts were either normal or only slightly reduced. Therefore it was concluded that normal numbers of platelets could be produced by decreased numbers of megakaryocytes. Megakaryocytopenia appeared to be compensated, in part, by increased size of megakaryocytes, but the mechanism by which this occurred has not been elucidated. It is postulated that a reduction in the number of cells of the megakaryocytic system is sensed by a homeostatic mechanism that then acts to stimulate the cells that are present. This stimulation may then be manifested as macrocytosis of megakaryocytes.     

Does random collisional cross-linking occur?

In fluid membranes, mobile molecules are thought to collide at high frequencies. Concern has been expressed as to whether these colliding molecules are cross-linked during the chemical cross-linking of membrane molecules, thereby creating problems in interpreting such experiments. Hemoglobin was used as a model to test this possibility. Oligomers larger than the tetramer could be cross-linked depending on factors such as hemoglobin concentration, duration of the cross-linking reaction and the type of reagent. Under certain conditions, however, such as a hemoglobin concentration less than 150 μM or a duration of cross-linking shorter than 15 min, larger oligomers were not detectable. Analysis of these data suggests that the probability of random collisional cross-links under normal conditions is insignificant.     

Does the family Meesiaceae (Musci) occur in Africa?

Meesia kenyae P. Varde, a species originally described in 1955 from the altimontane elevation on Mt. Kenya in tropical East Africa, is briefly assessed taxonomically and some details of the type material are illustrated. This species is considered to be conspecific with Ceratodon purpureus (Hedw.) Brid., a weedy, cosmopolitan and highly protean species. Because M. kenyae is the only representative of the Meesiaceae in Africa, this taxonomic conclusion results in the exclusion of this small family from the bryoflora of this continent. Accordingly, the Meesiaceae are represented in the tropics only by three species, namely Meesia triquetra (Jolycl.) Ångstr. in Papua New Guinea, M. longiseta Hedw. in Colombia and M. ulei Müll. Hal. in Brazil.     

Does egg competition occur in marine broadcast‐spawners?

When the availability of sperm limits female reproductive success, competition for sperm, may be an important broker of sexual selection. This is because sperm limitation can increase the variance in female reproductive success, resulting in strong selection on females to compete for limited fertilization opportunities. Sperm limitation is probably common in broadcast-spawning marine invertebrates, making these excellent candidates for investigating scramble competition between broods of eggs and its consequences for female reproductive success. Here, we report our findings from a series of experiments that investigate egg competition in the sessile, broadcast-spawning polychaete Galeolaria caespitosa. We initially tested whether the order in which eggs encounter sperm affects their fertilization success at two ecologically relevant current regimes. We used a split-clutch-split--ejaculate technique to compare the fertilization success of eggs from individual females that had either first access (competition-free treatment) or second access (egg competition treatment) to a batch of sperm. We found that fertilization success depended on the order in which eggs accessed sperm; eggs that were assigned to the competition-free treatment exhibited significantly higher fertilization rates than those assigned to the egg competition treatment at both current speeds. In subsequent experiments we found that prior exposure of sperm to eggs significantly reduced both the quantity and quality of sperm available to fertilize a second clutch of eggs, resulting in reductions in fertilization success at high and low sperm concentrations. These findings suggest that female traits that increase the likelihood of sperm-egg interactions (e.g. egg size) will respond to selection imposed by egg competition.     

Does developmental acclimatization reduce the susceptibility to predation in newt larvae?

Many organisms respond to the heterogeneity of abiotic environmental conditions by plastic modifications of their phenotypes (acclimation or acclimatization). Despite considerable research efforts in this area, the beneficial (adaptive) effect of acclimation or acclimatization is still debated. We examined whether the development of newt larvae (Ichthyosaura alpestris) under different natural light and thermal conditions subsequently altered their susceptibility to predation in sun‐exposed versus shaded tanks in nature. During predation trials in various light and temperature conditions, newt larvae that developed in sun‐exposed warmer tanks consistently suffered from higher predation by dragonfly nymphs (Aeshna cyanea) compared to larvae from shaded or colder tanks. We conclude that higher sun exposure during embryonic and larval development negatively affects antipredator performance even in sun‐exposed tanks: this result is inconsistent with the beneficial acclimation hypothesis. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

An elusive endosymbiont: Does Wolbachia occur naturally in Aedes aegypti?

Wolbachia are maternally inherited endosymbiotic bacteria found within many insect species. Aedes mosquitoes experimentally infected with Wolbachia are being released into the field for Aedes‐borne disease control. These Wolbachia infections induce cytoplasmic incompatibility which is used to suppress populations through incompatible matings or replace populations through the reproductive advantage provided by this mechanism. However, the presence of naturally occurring Wolbachia in target populations could interfere with both population replacement and suppression programs depending on the compatibility patterns between strains. Aedes aegypti were thought to not harbor Wolbachia naturally but several recent studies have detected Wolbachia in natural populations of this mosquito. We therefore review the evidence for natural Wolbachia infections in A. aegypti to date and discuss limitations of these studies. We draw on research from other mosquito species to outline the potential implications of natural Wolbachia infections in A. aegypti for disease control. To validate previous reports, we obtained a laboratory population of A. aegypti from New Mexico, USA, that harbors a natural Wolbachia infection, and we conducted field surveys in Kuala Lumpur, Malaysia, where a natural Wolbachia infection has also been reported. However, we were unable to detect Wolbachia in both the laboratory and field populations. Because the presence of naturally occurring Wolbachia in A. aegypti could have profound implications for Wolbachia‐based disease control programs, it is important to continue to accurately assess the Wolbachia status of target Aedes populations.     

Does SUNN-SYMRK Crosstalk occur in Medicago truncatula for regulating nodule organogenesis?

Recently we reported that overexpression of intracellular kinase domain of Symbiosis Receptor Kinase (SYMRK-kd) hyperactivated spontaneous nodulation in Medicago truncatula indicating the importance of SYMRK ectodomain in restricting nodule number. To clarify whether sunn and sickle pathways were overcome by SYMRK-kd for hyperactivation of nodule organogenesis, we overexpressed SYMRK-kd in these mutants and analyzed for spontaneous nodulation in absence of rhizobia. Spontaneous nodulation in skl/SYMRK-kd roots was 2-fold higher than A17/SYMRK-kd roots indicating nodule organogenesis induced by SYMRK-k_d to be ethylene sensitive. Intriguingly, sunn/SYMRK-kd roots failed to generate any spontaneous nodule which directly indicate the LRR-RLK SUNN to have a role in SYMRK-k_d mediated nodule development under non-symbiotic conditions. We hypothesize a crosstalk between SUNN and SYMRK receptors for activation as well as restriction of nodule development.     

Urine marking in male common voles: Does behavioural activity matter?

Rodent urine provides animals with a large amount of information, from the identity of the animal through its physical condition to social status. Many studies therefore focus on rodent urine-marking behaviour and use marking frequency as an indicator of social status or competitive ability. However, marking, like many other aspects of rodent behaviour, may be affected by individual behavioural activity, a factor that has not been examined so far. We therefore studied a relationship between male urine-marking in reaction to another male's marks (standard opponent) and individual personality profile, characterised by behavioural activity in an open field test (OFT). The marking appeared to be consistent and specific for particular individuals as there was a significant positive relationship between individual markings in two different phases of the experiment. The linkage between behavioural activity in the OFT and urine-marking frequency was non-linear (quadratic), which suggested that males with intermediate activity marked more intensively than males from the extremes of the behavioural spectra. The relationship between the opponent's and the tested males' markings was positive, however, we found no statistically significant evidence that the voles would attempt to overmark the opponent. Marking thus seems to have more of a self-advertising than a competitive function in the common vole. Further, as high marking activity is under strong intra- or intersexual selection, the result might suggest a stabilising selection of the personality trait described as behavioural activity in our study.     

Does Boutonneuse fever in France have equivalents outside the Mediterranean area?

In western of France, outside of mediterranean spotted fever area, several sera from autochthonous patients were positive for the presence of anti-R. conori antibodies by indirect immunofluorescence test. What is it all about: authentic rickettsiosis or paraspecific seroreactions with other microorganisms? We discuss these hypothesis.