Latitudinal insect body size clines revisited: a critical evaluation of the saw-tooth model

1.?Insect body size is predicted to increase with decreasing latitude because time available for growth increases. In insects with changing voltinism (i.e. number of generations per season), sharp decreases in development time and body size are expected at season lengths where new generations are added to the phenology of a species, giving rise to saw-tooth clines in these traits across latitudes. Growth rate variation may affect the magnitude of variation in body size or even reverse the saw-tooth cline. 2.?In this study, we analyse latitudinal body size clines in four geometrid moths with changing voltinism in a common laboratory environment. In addition to body size, we measured larval development time and growth rate and genetic correlations among the three traits. 3.?The patterns of clinal variation in body size were diverse, and the theory was not supported even when saw-tooth body size clines were found. Larval development time increased and growth rate decreased consistently with increasing season length, the clines in these traits being uniform. 4.?The consistencies of development time and growth rate clines suggest a common mechanism underlying the observations. Such a mechanism is discussed in relation to the complex interdependencies among the traits.     

Effects of herbivory on competition intensity in two arctic-alpine tundra communities with different productivity

The effects of long-term (11 yr) exclusion of vertebrate herbivores on competition intensity and plant community structure were studied using manipulative field experiments in two arctic-alpine plant communities with contrasting productivity: an unproductive snowbed and a considerably more productive tall herb meadow. In the snowbed, the exclusion of herbivorous mammals resulted in a significant increase in the biomasses of vascular plants and cryptogams, whereas no corresponding response was observed on the tall herb meadow. The intensity of competition, measured with a neighbour removal experiment, did not differ significantly between three of the four habitat×treatment combinations – snowbed exclosures, meadow exclosures and open meadow plots – but was significantly lower on open snowbed plots. Our results thus suggest that the low competition intensity in the unproductive snowbed is caused by herbivorous mammals, which tend to depress plant biomass in relatively unproductive habitats. When herbivorous mammals have been excluded for a sufficiently long time to allow the build-up of plant biomass even in unproductive habitats, between-habitat differences in competition intensity disappear.     

Cold acclimation was partially impaired in boron deficient Norway spruce seedlings

Susceptibility of trees to freezing injury has been suggested to increase in boron (B) deficiency but there is no experimental evidence to support this proposition. In this study, Norway spruce (Picea abies L. Karst.) seedlings were cultivated for two growing seasons in deficient, intermediate and ‘optimal’ B levels. Cold hardening of the seedlings was measured after the second growing season. Freezing tolerance in tips of shoots, needles, stems and roots was determined by controlled freezing tests and electrolyte leakage method, and that of buds, in addition, by differential thermal analysis (DTA). Electrical impedance was used to monitor changes in the apoplastic space during cold acclimation. Root dry weight and shoot height growth were lower in B deficiency. Cold acclimation of buds and stems was reduced by B deficiency. When hardened seedlings were subjected to subzero temperatures for 3 weeks, extracellular electrical resistance of stems became the highest at the lowest B supply which was probably due to decreased desiccation tolerance. As a conclusion, susceptibility to freezing damage may be increased by B deficiency in Norway spruce trees.     

Phenolic compounds in Norway spruce as affected by boron nutrition at the end of the growing season

The increase in concentrations of phenolic compounds in boron (B) deficiency has been demonstrated in many herbaceous plant species, but information on woody plants is scarce. It has been suggested that accumulation of phenolic compounds plays a role in the development of cold hardiness in herbaceous plants but also that B deficiency decreases winter hardiness. Here we study the effects of B nutrition on phenolic compounds in Norway spruce (Picea abies L.) in the course of cold acclimation. Phenolic compounds were analysed in Norway spruce seedlings from three different B-fertilisation treatments in two harvests: non-acclimated and cold-acclimated seedlings. Norway spruce phenolic compounds consisted mainly of condensed tannins. During B deficiency, condensed tannins and monocoumaroyl–astragalin der. 1 increased in non-acclimated seedlings. The increase in tannins was 21%, which was nearly significant. However, the effect of B on phenolic compounds was almost absent in cold-acclimated seedlings. The condensed tannin concentration increased much more with time in the simulated autumn than due to B deficiency, and we conclude that the B effect was probably not large enough to be important for the hardening of the seedlings. The total phenolic concentrations more than doubled during the course of cold hardening suggesting that phenolics have a role in the winter hardiness in Norway spruce.     

Opioid receptor pharmacological chaperones act by binding and stabilizing newly synthesized receptors in the endoplasmic reticulum

Accumulating evidence has indicated that membrane-permeable G protein-coupled receptor ligands can enhance cell surface targeting of their cognate wild-type and mutant receptors. This pharmacological chaperoning was thought to result from ligand-mediated stabilization of immature receptors in the endoplasmic reticulum (ER). In the present study, we directly tested this hypothesis using wild-type and mutant forms of the human delta-opioid receptor as models. ER-localized receptors were isolated by expressing the receptors in HEK293 cells under tightly controlled tetracycline induction and blocking their ER export with brefeldin A. The ER-retained delta-opioid receptor precursors were able to bind [(3)H]diprenorphine with high affinity, and treatment of cells with an opioid antagonist naltrexone led to a 2-fold increase in the number of binding sites. After removing the transport block, the antagonist-mediated increase in the number of receptors was detectable at the cell surface by flow cytometry and cell surface biotinylation assay. Importantly, opioid ligands, both antagonists and agonists, were found to stabilize the ER-retained receptor precursors in an in vitro heat inactivation assay and the treatment enhanced dissociation of receptor precursors from the molecular chaperone calnexin. Thus, we conclude that pharmacological chaperones facilitate plasma membrane targeting of delta-opioid receptors by binding and stabilizing receptor precursors, thereby promoting their release from the stringent ER quality control.     

Signal reliability compromised by genotype-by-environment interaction and potential mechanisms for its preservation

Sexual selection based on signaling requires that signals used by females in mate choice are reliable indicators of a male's heritable total fitness. A signal and the preference for it are expected to be heritable, resulting in the maintenance of genetic covariance between these two traits. However, a recent article has proposed that signals may quickly become unreliable in the presence of both environmental variation and genotype-by-environment interaction (G x E) with crossing reaction norms, potentially compromising the mechanisms of sexual selection. Here we examine the heritability and plasticity of a male dominance advertisement in the bank vole, Clethrionomys glareolus, in stable and changing rearing environments from father to son. The bank vole is naturally exposed to considerable sources of spatial and temporal environmental variation and male reproductive success is determined by both intra- (male-male competition) and inter- (females prefer to mate with dominant males) sexual selection. Significant G x E for male dominance was found with crossing reaction norms. Plasma testosterone level (T), rather than condition, determined a male's dominance and T also showed a significant G x E. Dominance showed a considerable plasticity across environments, but was only heritable under stable conditions. We document a negative between-environments correlation of male dominance, suggesting that when the environment changes between father and son, the dominance signal is unreliable to females and sexual selection may be compromised. We discuss how G x E and environmental variation interacting with other mechanisms may preserve the reliability of signals and thus the mechanism of sexual selection itself.     

The cost of reproduction induced by body size at birth and breeding density

Body size at birth has implications for the quality of individuals throughout their life. Although large body size is generally considered an advantage, the relationship between body size at birth and long-term fitness is often complicated. Under spatial or temporal variation in environmental conditions, such as the seasonally changing densities of Fennoscandian vole populations, selection should favor variation in offspring phenotypes, as different qualities may be beneficial in different conditions. We performed an experiment in which a novel hormonal manipulation method was used to increase phenotypic variance in body size at birth in the bank vole (Myodes glareolus). The effects of body size on the future fitness of young males and females were then studied at varying population densities in outdoor enclosures. Our results show that small body size at birth and high breeding density increase the survival costs of reproduction. However, there was no interaction between the effects of body size and density on survival, which suggests that the fitness effects of body size were strong enough to persist under environmental variation. Moreover, litter size and the probability of breeding were more sensitive to variation in breeding density than offspring size. Therefore, it is unlikely that individual fitness could be optimized by adjusting offspring body size to the prevailing population density through adaptive maternal effects. Our results highlight the significance of the costs of reproduction in the evolution of life-history traits, and give strong experimental support for the long-term fitness effects of body size at birth.     

Persisting chronic gastritis and elevated Helicobacter pylori antibodies after successful eradication therapy

AIM: The persistence of chronic inflammation in gastric mucosa and elevated Helicobacter pylori antibodies after successful eradication therapy are common findings in clinical practice. We studied their possible association with each other and disappearance in long-term follow up, as well as their possible connection with gastric atrophy. PATIENTS AND METHODS: The study population consisted of 108 dyspeptic patients with successful eradication therapy median 6.4 years earlier. The patients underwent gastroscopy, and biopsies from antrum and corpus were evaluated by an experienced pathologist. Serum samples collected from 77 patients were studied for H. pylori antibodies, parietal cell antibodies, as well as for pepsinogen I, pepsinogen II, and gastrin-17 levels. RESULTS: The prevalence of chronic gastric inflammation and elevated H. pylori antibodies after successful eradication therapy decreased by time, but still after 5 years, 17 of 51 (33%) subjects had elevated H. pylori antibodies and 14 of 68 (21%) had a mild inactive chronic inflammation in gastric mucosa. In patients with and without chronic inflammation in gastric mucosa, elevated H. pylori antibodies were detected in three of 10 (30%) and 14 of 41 (34%), elevated parietal cell antibodies in one of 10 (10%) and six of 41 (15%), low pepsinogen I in one of 10 (10%) and none of 41, and elevated gastrin-17 in three of 10 (30%) and six of 41 (15%), respectively. CONCLUSION: More than 5 years after successful H. pylori eradication therapy, mild persistent chronic inflammation may occur in gastric mucosa in up to one-fifth and elevated H. pylori antibodies even in one-third of patients, although these two are independent phenomena.     

Herbivore Effects on Ecosystem Process Rates in a Low-Productive System

Ecosystems - Mammalian herbivores shape the structure and function of many nutrient-limited or low-productive terrestrial ecosystems through modification of plant communities and plant–soil...